sandy beaches and coastal zone management

Université Mohammed V – Agdal 2011

INSTITUT SCIENTIFIQUE Rabat

SANDY BEACHES AND COASTAL ZONE MANAGEMENT

Travaux de l'Institut Scientifique, Série Générale, n°6

Proceedings of the Fifth International Symposium on Sandy Beaches 19 th-23 rd October 2009, Rabat, Morocco

Edited by Abdellatif BAYED

Travaux de l'Institut Scientifique Série Générale, n°6 2011

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Pour citer cet ouvrage : Bayed A. (Editeur), 2011. Sandy beaches and coastal zone management - Proceedings of the Fifth International Symposium on Sandy Beaches, 19th-23rd October 2009, Rabat, Morocco. Travaux de l'Institut Scientifique, Rabat, série générale, n°6, 148 p. Pour citer un article de cet ouvrage : Auteurs, 2011. Titre de l’article. In Bayed A. (Ed.) Sandy beaches and coastal zone management - Proceedings of the Fifth International Symposium on Sandy Beaches, 19th23rd October 2009, Rabat, Morocco. Travaux de l'Institut Scientifique, Rabat, série générale, n°6, n° page début – n° page fin de l’article.

Photographies de la couverture - Plage sableuse située au nord de la ville d'Asilah (Photo Abdellatif Bayed) - Les participants au 5 ème Symposium International sur les plages sableuses en visite à la mosquée Hassan II de Casablanca

ISSN : 1114-9256 ISBN : 978-9954-20-665-2 Dépôt légal : 2011 MO 1587

Université Mohammed V – Agdal



Proceedings of the Fifth International Symposium on Sandy Beaches 19th-23rd October 2009, Rabat, Morocco Edited by Abdellatif BAYED Unité de recherche OCEMAR [email protected]


Travaux de l'Institut Scientifique, Rabat, série générale, 2011, n°6.

A Brief Tribute to Three Sandy Beach Ecologists Susan McArdle, An de Ruyck and Alexandre Soares

Susan Bernadette McArdle 1960 - 2007

An Maria Cyriel de Ruyck 1959 - 2008

The past two years have, sadly, seen three young scientists who studied sandy beaches taken from us prematurely. I was fortunate to have hosted and worked with all of them in my research team in South Africa. Susan Bernadette McArdle (1960-2007) grew up in a large and close-knit Catholic family in Northern Ireland and studied at the University of Ulster, where she completed a PhD on estuarine oysters in 1987. She married Trevor Molloy before joining my research group at the University of Port Elizabeth as a postdoc in 1987. Susan was a warm and outgoing personality and, in the two years with us, she was the life and soul of the group. She developed of a technique to monitor swash action over the beach face and undertook a series of experiments to quantify the swash climate and how it changes with beach type. The two papers she produced on this provide simple techniques that ecologists can use to characterise swash climate and showed a clear change in this with beach type, a finding that has subsequently provided a basis for explaining many patterns in the benthic macrofauna. Susan passed away after a long battle with cancer, leaving her husband Trevor and four children, Joseph, Bridget, Michael and Elizabeth. An Maria Cyriel de Ruyck (1959-2008) was born in Belgium but migrated with her family to South Africa where she completed veterinary studies before joining my research group in 1988 to undertake a PhD. Entitled ‘Distribution and behaviour of three intertidal sand beach isopods’, it was completed in 1991. Thereafter she worked as a research officer studying human recreational impacts on beaches. She married Alexandre Soares and they moved to Belgium with their two daughters, Taiana and Camila. An was a free spirit who loved the outdoors and enjoyed field work greatly. The most useful aspects of An’s work were probably the

Alexandre Goulart Soares 1966 - 2008

demonstration that, whereas tidal and semilunar rhythms may predominate on macrotidal low energy beaches as studied in Europe, these are less clear and diurnal rhythms more pronounced on high energy microtidal beaches in South Africa. She also demonstrated clear patterns in recreational activity and impacts on sandy beaches. An lost her life, with her younger daughter, in a disastrous road accident. Alexandre Goulart Soares (1966-2008) was born in Rio de Janeiro and moved from Brazil to South Africa to join my research group in 1992 for doctoral studies. With an inquiring mind he was always questioning and he pursued studies on several aspects of beach ecology in addition to his doctoral research. His thesis was eventually completed in 2003 and entitled ‘Sand beach morphodynamics and macrobenthic communities in temperate, subtropical and tropical regions – a macroecological approach’. Alexandre’s main contributions to sandy beach ecology are his emphasis of the importance of phenotypic plasticity as an adaptation to these variable environments and his unpublished PhD which provides, arguably, the finest data set of intertidal macrobenthic surveys of sandy beaches anywhere. I hope other ecologists will make use of this valuable information for meta-analyses and other studies. Alexandre had separated from An but was still close to her and their daughters when he tragically took his life a month after An died. With so few scientists dedicated to studying beaches it is a great loss for these colleagues to be taken from us. Fortunately we have a written record of their research on sandy beaches so their contributions will be used and they will be remembered. The sandy beach research community extends our deepest sympathies to their families and friends. Anton McLachlan


Sandy Beach Publications of Susan, An and Alexandre Journal papers McARDLE, S.B. & A. McLACHLAN. 1991. Dynamics of the swash zone and effluent line on sandy beaches. Mar. Ecol. Prog. Ser. 76:91- 99. De RUYCK, A.M.C., A. McLACHLAN & T. E. DONN. 1991. Activity patterns of three intertidal sand beach isopods (Flabellifera: Cirolanidae). J. exp mar. Biol. Ecol. 146:163-180. De RUYCK, A.M.C., T.E. DONN & A. McLACHLAN. 1991. Life histories and breeding patterns of three intertidal sand beach isopods. Mar. Ecol. 12:105-121. McARDLE, S.B. & A. McLACHLAN. 1992. Sand beach ecology: swash features relevant to the macrofauna. J. cstl Res. 8:398-407. De RUYCK, A.M.C., T.E. DONN & A. McLACHLAN. 1992. Distribution of three intertidal cirolanid isopods (Flabellifera: Cirolanidae) on a South African sandy beach. Cah. Biol. Mar. 33:147-168. Van der MERWE, D., A. McLACHLAN & A.M.C. de RUYCK. 1994. Seasonal movements between habitats of whitefronted plovers Charadrius marginatus in a coastal dunefield. J. cstl Res. 10:747-751. McLACHLAN, A., E. JARAMILLO, O. DEFEO, J. DUGAN, A.M.C. de RUYCK & P. COETZEE. 1995. Adaptations of bivalves to different beach types. J. exp. mar. Biol. Ecol. 187:147-160. De RUYCK, A.M.C., A.G. SOARES & A. McLACHLAN. 1995. Factors influencing human beach choice on three South African beaches: a multivariate analysis. Geojournal 36:345-352. SOARES, A.G., A. McLACHLAN & T. SCHLACHER. 1996. Disturbance effects of stranded kelp on populations of the sandy beach bivalve Donax serra. J. Exp. Mar. Biol. Ecol. 205:165-186. McLACHLAN, A., A.M.C. de RUYCK & N. HACKING. 1996. Community structure on sandy beaches: patterns of richness and zonation in relation to tide range and latitude. Rev. Chilena Historia Natural 69:451-467. BRUCE, N.L. & A.G. SOARES. 1996. Taxonomy and ecology of the sandy beach isopods of the genus Eurydice (Cirolanidae) from the west coast of South Africa. Cah. Biol. Mar. 37:77-98. SOARES, A.G., T. SCHLACHER & A. McLACHLAN. 1997. Carbon and nitrogen exchange between sandy beach clams (Donax serra) and kelp beds in the Benguela coastal upwelling region. Mar. Biol. 127:657-664. De RUYCK, A.M.C., A.G. SOARES & A. McLACHLAN. 1997. Social carrying capacity as a management tool for sandy beaches. J. cstl Res. 13:822-830. De RUYCK, A.M.C. & A. McLACHLAN. 1997. Human recreation patterns on beaches with different levels of development. Trans. Roy. Soc. S. Afr. 52:257-276.

MOFFETT, M., A. McLACHLAN, WINTER, P.E.D. & A.M.C. de RUYCK. 1998. Impact of trampling on sandy beach macrofauna. J. cstl Cons. 4:87-90. SOARES, A.G., R.K. CALLAHAN & A.M.C. de RUYCK. 1998. Microevolution and phenotypic plasticity in Donax serra Roding (Bivalvia: Donacidae) on high energy sandy beaches. J. Moll. Stud. 64:407-421. SOARES, A.G., F. SCAPINI, A.C. BROWN & A. McLACHLAN. 1999. Phenotypic plasticity, genetic similarity and evolutionary inertia in changing environments. J. moll. Stud. 65:136-139. SCHOEMAN, D.S., R. NEL & A.G. SOARES. 2008. Measuring species richness on sandy beach transects: extrapolative estimators and their implications for sampling effort. Mar. Ecol. 29s1: 134-149.

Conference papers McLACHLAN, A., A.M.C. de RUYCK, P. du TOIT & A. COCKCROFT. 1992. Groundwater ecology at the dune/beach interface. In Proceedings of the first international conference on groundwater ecology, ed.J.A. Stanford & J.J Simons, Am. Water Res. Assn Tech. Pub. Ser. pp.209-216. De RUYCK, A.M.C., A. McLACHLAN & T. E. DONN. 1990. The ecology of three intertidal sand beach isopods. (Poster). 7th National Oceanographic Symposium: Natal, South Africa. McLACHLAN, A. & S.B. McARDLE. 1990. Swash dynamics and sandy beach macrofauna. Zoological Society of SA, Annual Symposium: Port Elizabeth, South Africa. De RUYCK, A.M.C., A. McLACHLAN & T.E. DONN. 1991. The activity of three intertidal sand beach isopods. Zoological Society of SA Annual Symposium: Stellenbosch, South Africa. McLACHLAN, A. & de RUYCK, A.M.C. 1993. Recreational activities and impacts on beach and dune systems in the Eastern Cape, South Africa. Fourth European Union for Coastal Conservation Congress: Marathon, Greece. De RUYCK, A.M.C. & A. McLACHLAN. 1993. Recreational use of beaches. (Poster). 8th SA Marine Science Symposium: Saldanha Bay, South Africa. McGWYNNE, L.E., A.M.C. de RUYCK, G.I.H. KERLEY & A. McLACHLAN. 1994. Dune conservation and beach recreation - is there a conflict? Dunes '94 Symposium: Port Elizabeth, South Africa. SOARES, A.G., A. McLACHLAN & A.M.C. de RUYCK. 1996. Ecology of Benguela sandy beaches: complex dynamics in simple environments. Benguela Dynamics Symposium: Cape Town, South Africa. SOARES, A.G. & N.L. BRUCE. 1996. Ecology, biogeography and taxonomy of new species of Eurydice (Crustacea: Isopoda: Cirolanidae) from Southern African sandy beaches. (Poster). ZSSA Symposium: Pretoria, South Africa.


SCHOEMAN, D.S., A.G. SOARES Sampling design, scale and macroinfaunal species richness Fourth International Symposium Vigo, Spain.

& the on on

R. NEL. 2006. estimation of sandy beaches. Sandy Beaches,

Reports De

RUYCK, A.M.C. & A. McLACHLAN. 1992. Macrofauna survey of sandy beaches at De Hoop. Report to Cape Provincial Nature Conservation, 15pp. De RUYCK, A.M.C. & A. McLACHLAN. 1993. Sandy beach conservation - perceptions and needs of beach managers. University of Port Elizabeth Institute for Coastal Research Report No. 34:33 pp.

McLACHLAN, A. & A.M.C. de RUYCK. 1993. Survey of sandy beaches in Diamond Area 1. Report to Consolidated Diamond Mines, Oranjemund, Namibia. 28pp. McGWYNNE, L.E., B.L. ROBERTSON, E.E. CAMPBELL, A.M.C. de RUYCK, W.K. ILLENBERGER, G.I.H. KERLEY & A. McLACHLAN. 1994. Biophysical and recreational assessment for the proposal to mine Skelmhoek and Hougham Park dune areas. UPE Institute for Coastal Research Contract Report No C23:113pp. McGWYNNE, L.E., A.M.C. de RUYCK, G.I.H. KERLEY & A. McLACHLAN. 1996. KwaZulu-Natal coastal dunes: ecological dynamics, human impacts and guidelines for planners. Town and Regional Planning Supplementary Report, Natal Town & Regional Planning Commission. 98pp.

Bayed A. (ed.). Sandy beaches and coastal zone management – Proceedings of the Fifth International Symposium on Sandy Beaches, 19th-23rd October 2009, Rabat, Morocco Travaux de l'Institut Scientifique, série générale, Rabat, 2011, n°6.

Contents / Sommaire Papers / Articles M. Achab - Les plages et les vasières des environs des embouchures des oueds Tahaddart et Gharifa (NW du Maroc) : dynamique morphosédimentaire et impact des aménagements sur leur évolution récente ......................................................................................................................................................................

1

A. Ayari, D. Bohli & K. Nasri-Ammar - Population dynamics and structure of talitrid amphipods from Bizerte sandy beach (North of Tunisia) ...........................................................................................................

13

M.F. Bouslama, F. Charfi-Cheikhrouha, M. El Gtari, K. Nasri-Ammar, A. Oueslati & F. Scapini Relationships between biological characteristics of the crustacean amphipod Talitrus saltator, including behavioural responses, and local environmental features. Case studies of Zouara and Korba (Tunisia) ...................................................................................................................................................................

17

I. Colombini, M. Brilli, M. Fallaci, E. Gagnarli & L. Chelazzi - Habitat partitioning and trophic levels of terrestrial macroinvertebrates of a Tyrrhenian coastal ecosystem (Grosseto, Italy) ..................................

25

K. El Khalidi, A. Minoubi, M. Chaibi, B. Zourarah, F. Leone & A. Aajjane - Caractérisation granulométrique de la plage sableuse de Sidi Moussa (côte atlantique marocaine) .................................................

37

S. Hammada, L. Linares & J. Cortes - Biodiversité floristique des dunes littorales de l’Oued El Maleh (Martil) et du Bas Tahaddart : résultats préliminaires ..............................................................................

45

Z. Idardare, A. Moukrim, J.F. Chiffoleau & A. Ait Alla - Trace metals in the clam Donax trunculus L. from the Bouadisse sandy beach, discharge zone of a plant sewage outfall in Agadir Bay (Morocco) ...............

51

A. Khattabi, A.T. Williams & A. Ergin - Assessment of quality and attraction of the sandy beaches of Nador province – Morocco ..................................................................................................................................

59

K.L.M. Martin, C.L. Moravek, A.D. Martin & R.D. Martin - Community based monitoring improves management of essential fish habitat for beach spawning California Grunion ........................................

65

M. Mouna, K. Bensusan, Ch. Perez & J. Cortes - A review of entomological research on sandy beaches in Morocco, with an emphasis on Coleoptera .............................................................................................

73

C. Rossano & F. Scapini - Endogenous locomotor activity rhythm of two sympatric species of Talitrids (Crustacea, Amphipoda) from a sandy beach of Tuscany, Italy ................................................................

81

F. Scapini & L. Fanini - The role of scientists in providing formal and informal information for the definition of guidelines, regulations or management plans for sandy beaches ........................................................

87

R. Zakhama-Sraieb, Y. Ramzi Sghaier & F. Charfi-Cheikhrouha - Sensibilisation sur l’importance des banquettes de Posidonia oceanica dans la protection des plages sableuses : Approche participative ...............

95

Extended abstracts / Résumés étendus M. Achab, J.M. Alveirinho Dias & O. Ferreira - Impact des opérations de rechargement en sables marins sur la dynamique des côtes sableuses du système lagunaire de Ria Formosa (Sud Portugal) ......................

99

A. Azirar & A. Bayed - Structuring conditions of the macroinfauna of sandy beaches in lagoon environment .............................................................................................................................................................

101

F. Barreiro, M. Gómez, R. De La Huz, M. Lastra & J. López - Wrack algae of exposed sandy beaches: effect on the nutrient supply to the coastal environment ...........................................................................

103

K. Bezuidenhout, T.H. Wooldridge & D.S. Schoeman - Macrobenthic trophodynamics of two South African pocket beaches: A not-so-simple perspective .............................................................................................

105

A. Chaouti & A. Bayed - Categories of importance as promising approach to valuate and conserve ecosystem integrity: case study of Asilah sandy beach (Morocco) ............................................................

107

O. Defeo - Sandy beach fisheries as complex social-ecological systems: emerging paradigms for research, management and governance ....................................................................................................................

111

H. L. S. Duong & P. G. Fairweather - What constitutes the wrack found on South Australian sandy beaches? ...................................................................................................................................................................

113

S. Fabiano, L. Fanini, A. Massolo & T. Mingozzi - Are the characteristic of nesting beaches influencing emergence rate and hatching success of loggerhead turtle Caretta caretta along the Ionian coast of Calabria (Italy)? ..........................................................................................................................................

115

M. Gómez, F. Barreiro, R. De La Huz, M. Lastra & J. López - Degradative processes in macroalgal wrack on sheltered beaches: ecological effects ........................................................................................................

117

D.M. Hubbard & J.E. Dugan - Beach grooming and the loss of coastal strand habitats in southern California ..................................................................................................................................................................

119

G.M. Janssen, L. Leewis & S. Marx - Mitigation of the ecological effects of nourishment on sandy shores, a case study ..................................................................................................................................................

121

A.R. Jones, T.A. Schlacher, D.S. Schoeman, J.E. Dugan, O. Defeo, F. Scapini, M. Lastra & A. Mclachlan - Sandy-beach ecosystems: Their health, resilience and management .............................................

125

M. Lastra, J. Mora, M.A. García Gallego & A. Sánchez Mata - Patterns of macrofaunal community in intertidal sedimentary shores in South Shetland Islands, Antarctica ....................................................................

127

L. Leewis, P.M. Van Bodegom, G.M. Janssen & J. Rozema - The influence of human activities and environmental factors on the presence of four dominant intertidal macro invertebrates on Dutch sandy beaches .....................................................................................................................................................................

129

J.P. Lozoya, J. Gómez & O. Defeo - Modelling large-scale occurrence and abundance of the sandy beach isopod Excirolana armata along the morphodynamic and salinity gradients of the Rio de la Plata Estuary, Uruguay .....................................................................................................................................................

131

J.P. Lozoya, R. Sardá & J.A. Jiménez - Beach multi-risk assessment considering ecosystem services and coastal hazards: a tool for ICZM .......................................................................................................................

133

T. Maria, A. Esteves, J. Vanaverbeke & A. Vanreusel - The effect of tides on the vertical distribution of nematodes on shore environments: a study case of De Panne’s beach (Belgium) ............................

135

K. Ortega, D.S. Schoeman, J. Laudien & A.J. Smit - The impact of a temporarily open/closed estuary on the community structure of a sandy beach macrobenthos in KwaZulu Natal, South Africa ...................

137

D.S. Schoeman, U.M. Scharler & A.J. Smit - An illustration of the importance of sandy beaches to coastal ecosystem services at the regional scale ......................................................................................................

139

J. Van Tomme, S. Degraer, W. Willems, J.C. Dauvin, L. Denis, R. De La Huz, G.M. Janssen, I. Menn, I.F. Rodil & M. Vincx - What is the structuring role of biotic interactions in explaining distribution and zonation patterns on West European sandy beaches? ....................................................................

141

J. Vanaverbeke, N. Lampadariou, M. Schratzberger, J. Kuhnert, M. Steyaert, H. Adão, N. Barnes, T. Campinas Bezerra, A. Drgas, V. Kalegeropoulou, R. Portugal, K. Sevastou, B. Urban-Malinga, L. Vandepitte, G. Veit-Köhler, P. Whomersley & T. Ferrero - The effect of increased rainfall on the sandy beach ecosystem: results from a pan-European experiment ....................................

143

Workshop reports / Rapports des ateliers All participants - Workshop 1: Sandy beach biological research – important questions for knowledge, understanding, policy and management ...................................................................................................................

145

All participants - Workshop 2: Monitoring of sandy beaches: theory and practice ...............................................

147

Bayed A. (ed.). Sandy beaches and coastal zone management – Proceedings of the Fifth International Symposium on Sandy Beaches, 19th-23rd October 2009, Rabat, Morocco Travaux de l'Institut Scientifique, Rabat, série générale, 2011, n°6, 1-12.

Les plages et les vasières des environs des embouchures des oueds Tahaddart et Gharifa (NW du Maroc) : dynamique morphosédimentaire et impact des aménagements sur leur évolution récente Mohamed ACHAB * Université Mohammed V – Agdal, Institut Scientifique, Département des Sciences de la Terre Av. Ibn Battota, B.P. 703, Agdal, 10090 Rabat, Maroc

Résumé. Le site de Tahaddart se trouve sur la façade occidentale de la péninsule de Tanger (nord-ouest du Maroc). L’objectif principal de ce travail est de reconnaître du point de vue sédimentologique, géomorphologique et hydrodynamique les environnements littoraux actuels entre Oued Tahaddart et Oued Gharifa et d’évaluer l'impact des aménagements sur leur évolution et leur équilibre. Les analyses granulométriques montrent des distributions unimodales, avec prédominance des sables fins modérément bien classés au niveau des plages et un faciès mixte de sable et de vase dans les vasières. L’analyse morphoscopique montre la prédominance de la fraction terrigène représentée principalement par des grains de quartz et des minéraux lourds dont la majorité est de type émoussé luisant. Ces résultats reflètent la dynamique du milieu caractérisée par l’interaction des agents de la morphogenèse littorale, notamment l’énergie mise en jeu pour le transport et la distribution du sable le long de la plage et les vasières (la houle et les courants de marée), ainsi que la nature granulométrique des particules sédimentaires transportées par les oueds. Les observations de terrain montrent que le vent est un agent déterminant dans la distribution et transport des sédiments et tout particulièrement au niveau de la dune. L’étude de l’évolution du trait de côte, à l'aide des techniques de photo-interprétation et de l’analyse cartographique, ont permis de quantifier la tendance évolutive du trait de côte entre 1958 et 2008. Elle fait ressortir que la tendance générale est un recul du trait de côte qui a été estimé à -1,7 m/an. Mots clés : site de Tahaddart, plages et vasières, dynamique côtière, impacts des aménagements, Maroc. Abstract. Beaches and mudflats surrounding the mouths of Tahaddart and Gharifa estuaries (NW of Morocco): morpho-sedimentary dynamics and impact of planning on their recent evolution. The site of Tahaddart belongs to the western coast of the peninsula of Tangier (NW of Morocco). The main objective of this work is to recognize the coastal environments between Tahaddart and Gharifa estuaries, from the sedimentological, geomorphological and hydrodynamics point of view. On the other hand, it is to evaluate and estimate the impact of various planning and development done in the study zone on the evolution and balance of this ecosystem. The grain-size analysis shows unimodale distributions with predominance of sand generally fine and moderately well sorted on beaches, and mixed facies of sand and mud on the intertidal zones. The morphoscopic analysis shows the dominance of the terrigenous fraction represented mainly by quartz grains and heavy minerals whose majority is of sub-rounded and bright type. These data reflect the environmental dynamics characterized by the interaction of the coastal morphogenesis factors, including the energy involved in transport and distribution of sand along the beach and intertidal zone (the waves and tidal currents), and the grains-size nature of sedimentary particles transported by estuaries. Field observations show that the wind is a determinant agent in the distribution and transport of sediment particularly at the dune. The study of the coastline evolution using photo-interpretation techniques and mapping analysis allowed us to quantify the evolutionary trend of the coastline from 1958 until 2008. It shows that the general trend is a decline of coastline estimated to -1.7 m/year. Key words: Tahaddart site, beaches & mudflats, coastal dynamics, impact of planning, Morocco.

INTRODUCTION Les rivages sableux sont des espaces fragiles et vulnérables où la pression humaine est devenue à la fois multiforme et profonde aggravant ainsi les risques que ces espaces peuvent encourir (Carter 1988, Paskoff 1998, Komar 1998, Pinot 1998, Legrain 2000, Doody 2001, Graham 2007). Au Maroc, les dégradations subies par ces espaces se sont accentuées, prenant des formes multiples (érosion, pollution, urbanisation, etc.). Une meilleure connaissance des atouts et des contraintes (naturelles et anthropiques) de ces milieux seraient appréciée et aiderait à définir les modes adéquats de gestion dans le but de garantir la durabilité des aménagements de ces espaces. D'autre part, ces zones côtières se présentent sous des *

aspects diversifiés (plages, falaises, dunes, zones humides, etc.) constituent une importante richesse en ressources naturelles (biologiques et minéralogiques), jouent un rôle de levier au niveau économique (industriel, touristique, halieutique, …) et sont des zones où se concentrent la population urbaine à l’échelle nationale (Snoussi & El Hafid Tabet 2000, Hannou 2003, Mansour 2003). Le Bas Tahaddart est un site classé par le gouvernement marocain comme site d’intérêt biologique et écologique ; il est classé également site RAMSAR (Projet WWF International, Dakki et al., 2003). Ce site conserve encore, en grande partie, ses caractéristiques naturelles originales, mais la pression des activités humaines et des usages sont à chaque fois plus intenses.

Adresse e-mail: [email protected]

1

M. Achab – Dynamique morpho-sédimentaire des plages sableuses et des vasières côtières

La zone d’étude a fait l’objet de plusieurs travaux multidisciplinaires (André & El Gharbaoui 1973, El Gharbaoui 1981, INRH 1991, Jaaidi et al. 1993, Guelorget et Lefevbre 1995, Orbi et al. 1997, Guerinech 1998, Hanssali 1998) et spécialisées (DRAPOR 2002, Massik et al. 2003, El Mrini 2004, Amharrak 2006, Nachite et al. 2008). Le présent travail se propose d’approfondir les connaissances sur le littoral de Tahaddart par l’étude des aspects morpho-sédimentaires des plages et des vasières des environs des embouchures des oueds (approches géomorphologique, sédimentologique et cartographique), d'une part, et d’analyser les facteurs régissant la distribution et le transport des sédiments (plages sableuses, estuaires et embouchures) et de caractériser la dynamique des phénomènes marins à la côte, d'autre part. Cette étude se penche également sur l'analyse de la stabilité des zones côtières en termes de recul et d'avancé du trait de côte. Enfin, une esquisse pour tenter d’estimer le niveau de l’impact des aménagements sur l’évolution et équilibre des systèmes côtiers. CARACTERISTIQUES DE LA ZONE D’ETUDE Contexte géographique et géomorphologique La zone d’étude se situe au nord-ouest du Maroc et occupe la partie septentrionale du littoral atlantique de la péninsule de Tanger entre 35° 30’ et 35° 40’ latitudes Nord et 5° 55’ et 6° 01' longitudes Ouest (Fig. 1). Elle s’étend sur une superficie de 100 Km2 ; sa limite nord est à quelque 15 km au sud de la ville de Tanger et sa limite sud se trouve à quelques kilomètres au nord d'Asilah. Le site de Tahaddart regroupe en fait deux bassins versants adjacents, séparés par la colline de "Haouta Ben Mediar", et dont les cours d'eau se rejoignent près de la côte pour former l'Oued Tahaddart. Il s'agit de l'Oued Mharhar, au Nord et de l'Oued El Hachef, au Sud. A ce système s’ajoute l'Oued Gharifa, localisé au Sud de l’Oued Tahaddart. L’arrièrepays de la région est constitué de collines basses et de plateaux peu élevés (collines Haouta Ben Médiar, colline

de Haouara, etc.) dont l’altitude varie de 50 à 228 m (Fig. 2). Le coté ouest correspond à une plaine alluviale basse et marécageuse caractérisée par l'étendue des dayas et des merjas qui occupent une grande partie de la zone littorale entre Tanger et Asilah. Les unités lithologiques affleurant le long du domaine littoral sont d’âges différents allant du secondaire au quaternaire, avec prédominance des formations récentes et peu consolidées qui caractérisent le trait côtier du paysage littoral. L’influence de la structure et de la tectonique récente sur le tracé de la côte est mise en évidence par l’orientation générale nord-sud des unités structurales et par les faciès des divers niveaux stratigraphiques, en particulier, la mise en place de baies et de plages dans les marnes et dégagement de côtes rocheuses dans les grés et les calcaires (André & El Gharbaoui 1973, El Gharbaoui 1981). De point de vue géomorphologique, l'estuaire de Tahaddart atteint l'Océan Atlantique en longeant un cordon dunaire, construit sur une flèche littorale d'orientation nord-sud déviant ainsi le tracé du fleuve vers le Sud et protégeant la zone marécageuse des intrusions marines (Jaaidi et al. 1993). Le lit de l’estuaire se caractérise par une asymétrie qui se traduit par la variabilité de la topographie de ses deux rives droite (ouest) et gauche (est) (Fig. 3). Les pentes sont fortes sur les berges concaves et faibles à modérées sur les berges convexes (Guelorget & Lefebvre 1995, Rapport INRH 1991). Au sud de Tahaddart, l’Oued Gharifa décrit à son tour des méandres libres dans une large vallée et son estuaire est occupé par un schorre aménagé en polders. La slikke présente deux rives aux formes dissymétriques. La berge sous le vent a un profil convexe tandis que la berge au vent, est modelée en une série de croissants dont la concavité est liée à l’amplitude des oscillations de la marée. Le cordon littoral ferme de larges plaines alluviales qui pénètrent profondément à l’intérieur des vallées.

Figure 1 : Carte de situation géographique et profils de plage effectués dans la zone d’étude

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Haoura Oued Mharhar Oued Tahaddart

Haouta Ben Mediar

Oued Hachef

Koudiet Dafa Oualad Sbaita

Figure 2 : Modèle en 3D du relief de la zone d’étude réalisée à l’aide du logiciel Surfer à partir de la carte topographique El Manzla au 1/50.000.

Climat et réseau hydrographique Le climat de la zone d’étude est sub-humide avec un hiver humide et doux et un été sec et chaud qui s'étend sur cinq mois, de mai à septembre. (Karrouk 1990). Les précipitations sont relativement fortes, avec une moyenne annuelle de 765 mm. la moyenne mensuelle est élevée en décembre (132 mm) et est faible en juillet et août (60%). Les hauteurs les plus fréquentes (40%) se situent entre 0,5 m et 1 m. Les hauteurs supérieures à 4 m restent peu fréquentes, représentant moins de 2%, et proviennent surtout du secteur ouest. La période de ces houles varie de 3 à 16 s et les plus fréquentes sont celles de 3 à 4 s (>90%) (Fig. 5). D’autre part, le littoral du site de Tahaddart est parcouru en direction du sud ouest par une dérive littorale dominante engendrée par des houles ouest-nord-ouest et dont la vitesse maximale ne dépasse pas 0,5 noeuds (El Gharbaoui 1981). Les houles du secteur ouest peuvent également engendrer une dérive littorale secondaire orientée du Sud vers le Nord. La turbulence du déferlement, très intense, alimente la dérive littorale en matériaux sableux qui sont redistribués dans l'estuaire par les courants de marée, et qui peuvent alimenter la courbure de la pointe de la flèche littorale (Orbi et al. 1997). La marée semi diurne est mésotidale ; le flot porte au Nord et le jusant au Sud. Le marnage moyen de 1m en mortes eaux et de 3 m en vives eaux (ONE 2002) semble être suffisant pour assurer le renouvellement des eaux de l’estuaire de Tahaddart favorisé par ses caractéristiques morphologiques (profondeur moyenne de 6 m) (Guelorget & Lefebvre 1995). 3


littorale, schorre, slikke, etc.), ainsi qu’au niveau de la plage de Kouass de part et d’autre de l’estuaire de l’Oued Gharifa. Dans le but d'individualiser les deux composantes du transport sédimentaire, longitudinale et transversale, 15 profils perpendiculaires au rivage (fleuve et mer) orientés est-ouest ont été effectués comme suit : neuf profils dans le secteur nord (E1, R1, R2, R3, R4 et F1, F2, F3, F4), quatre profils dans le secteur sud (R5, R6 et F5 , F6), et deux profils (P1 et P2) sur la rive droite de la plage de Kouass (Fig. 1). Chaque profil a fait l’objet de quatre prélèvements au moins dans des espaces littoraux différents (estran, miestran, pied de dune, et dune). L'échantillon sableux est prélevé en surface sur quelques millimètres. Le positionnement a été réalisé à l’aide d’un GPS de type 315 Magellan.

Figure 3 : Topographie de l’estuaire de Tahaddart en amont du pont Mohamed V (LPEE / CEH, 1997, modifié)

Figure 4 : Carte du réseau hydrographique du bassin versant de Tahaddart (source : Agence du Bassin Hydraulique du Loukkos).

L'étude de la composante longitudinale éait basée sur l’analyse de l’évolution de la moyenne obtenue pour les différents niveaux échantillonnés de chacun des profils. L'étude de la composante transversale tient compte de chacun des niveaux d’échantillonnage en analysant la moyenne obtenue pour chacun de ces niveaux sur l’ensemble des profils. Analyses granulométriques et morphoscopiques L'étude des caractéristiques granulométriques des sédiments permet d'accéder à des informations sur la dynamique de transport des sédiments des continents vers le milieu marin (Passega 1963, Degiovanni 1972). Des variations granulométriques au sein des apports sédimentaires peuvent refléter différents types de processus tels que le mélange de populations sédimentaires d'origines et de granulométries différentes ou des mécanismes sélectifs se produisant lors du transport ou du dépôt (Blanc & Froget 1979, Liu & Zarillo 1989, Suanez et al. 1996). Les échantillons prélevés ont fait l’objet d'une granulométrie sur une colonne de tamis à mailles carrées de norme AFNOR comprise entre 0,063 mm et 2 mm et d'une observation des refus de tamis à la loupe binoculaire et leur caractérisation sédimentaire. Les données granulométriques brutes, ont été traitées par le logiciel GRADIST (version 4.0) qui a permis de calculer les paramètres statiques les plus usuels (médiane, mode, moyenne graphique, écart type, asymétrie (skewness), etc.). Les paramètres granulométriques sont calculés selon la méthode de Folk et Ward (1957).

Figure 5 : Histogrammes des hauteurs et des périodes des houles pour l’année 2006 (Données de la Direction des côtes de l’Andalousie, Espagne.).

MATERIEL ET METHODES Echantillonnage et Profils de plage La caractérisation sédimentologique des plages et estuaires de la zone d'étude a été réalisée sur des échantillons prélevés à basse mer en 2007 et 2008. Un total de 75 prélèvements superficiels de sable a été effectué dans différentes parties de l’estuaire de Tahaddart (plage, flèche 4

L'analyse morphoscopique des sables de plage et les sédiments des vasières à été réalisée à l’aide d'une loupe binoculaire (x 40) et d'un microscope à faible grossissement. Elle permet la recherche de la nature de l’agent de transport en analysant la nature de l'usure des grains. Les principaux composants recherchés sont le quartz, les minéraux lourds, les fragments de roches, les foraminifères et les coquilles de mollusques. Analyse cartographique et photo-interprétation L’analyse cartographique et spatiale ainsi que la cinématique de l’évolution du trait de côte de l l’estuaire de Tahaddart ont été basées sur la photo-interprétation des


images satellite et de photographies aériennes verticales récentes et géoréférencées couvrant la zone d’étude (Crowell et al. 1993, Pajak & Leatherman 2002), et leur comparaison avec la carte topographique El Manzla (1/50000ème) de 1961 qui était basée sur des photographies aériennes de 1958. D’autre part, nous avons cartographié l’évolution de la position de trait de côte du site de Tahaddart depuis 1958 jusqu’ à 2008, afin de quantifier la tendance évolutive du trait côte et de calculer les taux d’érosion et de sédimentation produits à moyen terme (50 ans). Pour cela, nous avons utilisé le logiciel Arc View GIS de la société ESRI. Vue l’erreur liée à l'identification de la position du trait de côte qui est généralement influencée par les variations des marées, nous avons utilisé la localisation des pieds des dunes comme référence de positionnement (Boak & Turner 2005, Nachite et al. 2008). RESULTATS ET DISCUSSION 1. Caractéristiques morphologiques Plages sableuses du site de Tahaddart Les profils topographiques transversaux de ces plages montrent trois grandes unités géomorphologiques qui se caractérisent par leurs comportements dynamiques et sédimentaires (Achab et al. 2009) : i) La plage émergée s’étend du pied de dune à la limite supérieure de l’estran (Photo 1A). Elle est bien développée au niveau de la flèche littorale et réduite de part et d’autre de l’estuaire de Tahaddart. Cette zone est alimentée tantôt par les sables de la plage sous-marine, tantôt par les sables dunaires. ii) L’estran sableux présent de part est d’autre de l’Oued Tahaddart correspond à la zone de balancement de la marée. Il est large sauf au niveau de la flèche littorale (Photo 1B & 1C). Le bas estran se caractérise également par la présence des rides d’oscillations de marée et même des encroûtements calcaires qui tapissent l’estran sud de la rive droite de Tahaddart. L’estran sableux montre aussi des galets de tailles variables de part et d’autre des estuaires de Tahaddart et de Gharifa. iii) La plage sous-marine, ou immergée subit continuellement l’action des vagues (Degiovanni 1972, Chamley 1988, Weber 1989, Paskoff 1992) ce qui est à l’origine de la formation de petites barres sous-marines dans la zone de déferlement du côté de l’océan de la flèche littorale. Ce phénomène s’observe parfois au niveau de la plage de Kouass sur la rive droite de l’oued Gharifa) (Photo 1D). Les plages sont généralement dissipatives accusant des pentes faibles, mais dans certaines zones de la flèche littorale, en particulier le secteur sud, la pente de la plage est importante. Cette variation morphodynamique et topographique des côtes meubles a été signalée dans d’autres régions (Blanc 1976, Wright & Short 1984). Zone intertidale de l’estuaire de Tahaddart Au niveau de cette zone qui se situe juste derrière le pont Mohammed-V, trois unités morphologiques sont distinguées (Fig. 6) :

i) Le chenal correspond à la zone de l’oued toujours immergée même à basse mer. ii) La slikke. Elle se trouve inondée à chaque flot et se présente sous forme de bancs convexes vers le ciel, où la végétation est quasi absente. Elle est parcourue par les chenaux qui drainent les vasières durant le jusant. La slikke constitue aussi une zone de stockage des particules fines par suspension graduée et décantation. Sa limite supérieure est marquée par un petit abrupt de quelques décimètres et à pente douce qui correspond à l'érosion latérale due à la migration des chenaux. Cette attaque donne naissance à une microfalaise d'érosion (Guilcher 1979). iii) Le schorre. Il correspond à un vaste espace en amont du pont Mohamed V, en continuité directe avec le milieu franchement continental. Il n'est atteint et recouvert qu'au cours des marées à fort coefficient ou lors des tempêtes. Contrairement à la slikke, ce domaine d'anciennes vases consolidées poreuses est recouvert de végétation basse. La partie la plus interne n’est pratiquement jamais atteinte par la mer. 2. Caractéristiques granulométriques Dans ce travail, nous avons groupé nos résultats selon les deux composantes du transport sédimentaire: longitudinale et transversale. Nous avons travaillé sur les valeurs moyennes, de manière à faire ressortir l'évolution du comportement granulométrique des sédiments et leur dynamique de transport. 2.1. Site de Tahaddart Plages sableuses de l’Oued Tahaddart Les résultats relatifs à la granulométrie moyenne des échantillons de sable prélevés dans les différentes parties de la plage nord de la rive droite de l’Oued Tahaddart montrent une distribution granulométrique unimodale (Tabl. 1, Fig. 7). La classe modale apparaît à 2,5 phi (0,17 mm) et représente 60% de la totalité des fréquences. Le mode et la médiane (2,24 phi, 0,21 mm) indiquent la prédominance des sables fins, ces deux paramètres caractérisent les conditions moyennes de dépôt et de l’énergie de courant. L’écart type, la géométrie de l'histogramme des fréquences, ainsi que la pente de la courbe cumulative indiquent que les sables sont modérément classés. Les autres paramètres granulométriques montrent une distribution leptokurtique et une asymétrie vers les très grossiers. Ces résultats révèlent l'importance du classement réalisé au cours du transport par les agents de tri, essentiellement les courants de marée. Au niveau de la plage sud de la rive droite de l’Oued Tahaddart, les résultats des analyses granulométriques des sables ne montrent pas de grandes différences avec ceux du secteur nord. La distribution est unimodale et le mode (2,5 phi) représente 64% de l’ensemble des fréquences observées. Ce sont des sables généralement fins, modérément bien classés, avec une asymétrie vers les très grossiers. Le classement de ces sables pourrait être en 5


ces paramètres, montre que la taille des grains des sables diminue de l’estran (sables moyens modérément classés) vers la dune (sables fins bien classés).

relation avec l’effet de l’action des courants de marée et le vent dans le processus de tri et de distribution des particules sédimentaires. La distribution transversale de

Tableau I : Paramètres granulométriques des sables prélevés au niveau des plages de la zone d’étude Zone de prélèvement de sédiments Mode (phi) Médiane (phi) Asymétrie Ecart type (phi) Rive droite (Oued Tahaddart) 2.53 2.23 -0.31 0.77 Flèche littorale (Oued Tahaddart) 2.5 2.31 -0.18 0.62 Rive droite (Oued Gharifa) 2.5 2.38 -0.24 0.52

A

B

C

D

Kurtosis 1.1 1.05 5.2

Photo 1 : Unités géomorphologiques caractéristiques du littoral de Tahaddart. A : Plage émergée au niveau de l’estuaire de Tahaddart ; B &C : Estran sableux (estuaire de Tahaddart & flèche littorale) ; D : Plage sous marine adjacente à l’estuaire de Gharifa

Photo 2 : Sables de plage de l’Oued Gharifa vue à la loupe binoculaire (x40). Ils sont de nature variée, riches en quartz, en zircon et en grenat. Ils montrent la prédominance des grains EL sur les NU. La fraction bioclastique est représentée par des fragments de mollusque et quelques foraminifères. L’état des grains témoigne de la diversité des agents d’usures côtières.

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La répartition transversale des paramètres granulométriques montre que la taille des grains des sables augmente de l’estran (sables fin modérément classés) vers le pied de dune (sables moyens mal classés), puis diminue au niveau de la dune (sables fins modérément bien classés) (Fig. 8). L’évolution longitudinale de ces paramètres montre des résultats comparables à ceux observés pour la distribution transversale (Fig. 9). En effet le classement et la moyenne évoluent d’une manière inverse, le classement étant meilleur pour les sables fins et mauvais pour les sables moyens. Flèche littorale de Tahaddart La granulométrie moyenne des sables prélevés du secteur nord de la flèche de Tahaddart se caractérise par une distribution granulométrique unimodale (Tabl. I, Fig. 7). La classe modale apparaît à 2.5 phi et représente 65% de la totalité des fréquences. Ce sont des sables fins, modérément classés à bien classés, avec une asymétrie vers les très grossiers. Les sables de plage du secteur sud sont également semblables à ceux du secteur nord, avec prédominance des sables bien classés et une asymétrie vers les grossiers. Les distributions transversales et longitudinale des paramètres granulométriques des sables ne montrent pas de grandes variations, car les sables sont généralement de granulométrie fine et ont tendance à être bien classés (Fig. 10). Ces paramètres reflètent l’importance de l’action du vent et de la houle dans les différentes parties géomorphologiques de la flèche de Tahaddart. Dans ce secteur, le vent est un agent déterminant dans la distribution et le transport des sédiments et particulièrement au niveau de la dune. La dérive littorale joue un rôle très important dans le transport et la distribution des sables au niveau du bas estran. D’une manière générale, il est possible de confirmer que ces sables évoluent vers un état d’équilibre par rapport aux processus dynamiques qui contrôlent le transport des particules sédimentaire le long de la flèche de Tahaddart. Zone intertidale de l’estuaire de Tahaddart Cette zone est constituée de dépôts fins argileux plus ou moins riches en calcaire biogène. Ces vasières se situent dans la partie supérieure de l'étage littoral dont l'ensemble présente une succession des milieux à faciès très caractéristique (Chamley 1988). Les dépôts s'effectuent essentiellement lors du flot et au début du jusant. L’accumulation de sédiments fins se produit par décantation des particules en suspension lors des étales. Dans cette zone, la répartition et le transport des sédiments se trouvent contrôlés par la dynamique des courants de marée (El Mrini 2004, Nachite et al. 2008). L’analyse granulométrique des sédiments superficiels prélevés au niveau de la zone intertidale de l’estuaire de Tahaddart met en évidence des faciès sédimentaires à granulométrie variable. Au niveau du schorre, prédomine un faciès sableux, caractérisé par des teneurs en sables moyens supérieures à 70%, le complément étant constitué par des sables fins. Les sédiments de la slikke, sont dominés par un faciès mixte composé par un mélange de sable et de vase dont la teneur en sables fins est supérieure à 80%, alors que la fraction silto-argileuse ne dépasse pas

20% dans la majorité des cas. Le chenal, se caractérise par la dominance des sédiments fins de nature vaseuse et de couleur gris. La fraction sableuse y est également présente, avec des proportions inférieures à 20%.

Figure 6 : Coupe schématique montrant les trois unités morphologiques caractéristiques de l’estuaire de Tahaddart (juste en amont du pont Mohammed V). MH : marée haute, MB : marée basse.

Figure 7 : Courbes granulométriques moyennes des sables des plages de la zone d’étude. 2,5 2,0 1,5 1,0 0,5 0,0 Estran

Pied de dune

Dune

-0,5 Moyenne (Phi) Skewness

Ecart type (phi) Kurtosis

Figure 8 : Évolution Transversale des paramètres granulométriques des sables de la rive droite de l’Oued Tahaddart.

Figure 9 : Évolution longitudinale des paramètres granulométriques des sables le long de l’estran sableux de la rive droite de l’Oued Tahaddart.

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Figure 10 : Évolution longitudinale des paramètres granulométriques des sables le long de la flèche littorale de Tahaddart

2.2. Site de Gharifa Plage sableuse de l’Oued Gharifa Sur la rive droite de l’oued Gharifa, la distribution granulométrique est unimodale, le mode (2,5 phi) représente 74% des fréquences. Ce sont des sables fins, modérément classés à bien classés, avec une asymétrie vers les fractions grossières et différent peu de ceux de l’estuaire de Tahaddart ce qui témoigne d’une dynamique dont les caractéristiques (énergie, agents et sens de transport) sont comparables dans les deux estuaires. Les variations transversales des paramètres granulométriques sont peu significatives, car les sables sont homogènes de granulométrie fine et assez bien classés, notamment au niveau de la dune. Les caractéristiques granulométriques de ces sables reflètent en général l’action du régime hydrodynamique du milieu, notamment l’énergie mise en jeu pour le transport et la distribution du sable le long de la plage (houle et courants). 3. Analyse morphoscopique L'analyse morphoscopique de la fraction sableuse des échantillons des estuaires de Tahaddart et de Gharifa a montré la présence de deux types de constituants : (i) les terrigènes, représentent la fraction dominante dans la majorité des cas (80%) et sont composés principalement par des grains de quartz, des minéraux lourds et des fragments de roches ; et (ii) les constituants bioclastiques (20%) sont composés particulièrement de fragments de mollusques et foraminifères (Tabl. II). Cependant, les sables de ces deux sites se distinguent par la composition minéralogique de la fraction lourde. En effet, les sables de la plage de Tahaddart sont très riches en hématite et

magnétite, alors que ceux de Gharifa sont riches en zircon et en grenat (photo 2 & 3). Les grains de quartz sont dominés successivement par les grains émoussés luisants (EL), non usés (NU) et les ronds mats (RM). Des traces d’usure et de cassures ont été observées sur la majorité des grains émoussés luisants et sur certains grains anguleux. Au niveau des schorres et des slikkes, les bioblastes (différentes tailles) et les débris de végétaux sont relativement abondants. Il y a également des fragments de roches de tailles et de natures variables. Les grains de quartz sont aussi très abondants dont la majorité est de type EL. 4. Cinématique du trait de côte L’analyse des différents types de documents cartographiques relatifs à la frange littorale du site de Tahaddart, pour la période 1958-2008, fait ressortir des changements notables dans la configuration de ce littoral et montre que l’érosion des plages au niveau du site s’est produite à des vitesses variables. Le taux moyen global de recul des côtes sableuses a été estimé à plus de 85 m, soit de -1,7 m/an, alors que celui d’avancé est de l’ordre de 0,64 m/an. Les Plages de part et d'autre de l'estuaire de Tahaddart Pour la période 1958-2008, la tendance générale du trait de côte a été vers l’érosion, avec un taux moyen plus élevé pour les plages situées au nord de l’estuaire de Tahaddart (plage de Haouara) par rapport à celles du sud (plages de Briech et Kouass) (Fig. 11A & 11C). En effet, le taux moyen global de recul enregistré pour la plage de Houara est de 167 m, soit de -3,34 m/an, alors que pour les plages de Breich et de Kouass, le taux d’érosion annuel reste relativement faible; il est respectivement de -0,41 m/an et 0,86 m/an. Cependant, au niveau de la plage de Breich, et pendant la même période, il y a eu localement des indices d’une zone de faible sédimentation, estimée de 2 m, soit de +0,04 m/an. Des travaux antérieurs, réalisés dans la zone d’étude (Amharrak 2006, Nachite et al. 2008), montrent que la tendance générale de ces plages sableuses, pour la période 1958-1992 était vers l’érosion, soit de 2,14 m/an à Haoura et de -1,74 m/an à Breich. Durant cette période, le taux moyen annuel de recul linéaire dans les deux plages a été de -1,94 m/an correspondant à une perte de 68 m de largeur en 35 ans. Ces données, indiquent donc, une accélération du taux d’érosion des plages du nord par rapport à celles du sud durant la période 1992-2008.

Tableau II : Résultats de l’analyse morphoscopique des sédiments prélevés au niveau des estuaires de Tahaddart et de Gharifa (xxx : très abondant, xx : assez abondant, x : moins abondant). Zones de prélèvement Quartz Gharifa : rive droite Gharifa : rive gauche Tahaddart : embouchure Tahaddart : Rive droite Tahaddart : Le chenal Tahaddart : La slikke Tahaddart : Le schorre

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xxx xxx xx xxx xx xx xxx

Fractions terrigènes Fragments Minéraux de roche lourds x xx x xx x xxx x xx x x x x x xx

Fractions biogéniques Mollusques Foramminifères xx x xx x x x xx x xx x xxx x xx x

Etat d’usure du quartz Non Emoussés Ronds usés luisants mats xx xxx x xx xxx x x xxx xx xx xxx x xx xxx x xx xxx x xx xxx x


Photo 3 : Sables de plage d’oued Tahaddart vue à la loupe binoculaire (x40). Ils sont bien remaniés et riches en minéraux lourds, en particulier les hématites et les magnétites ; les grains terrigènes et bioclastiques témoignent de la variété des matériaux transportés par l’oued et de l’importance du transport effectué.

Flèche littorale et embouchure de Tahaddart L’évolution de la flèche littorale et de l’embouchure de Tahaddart se caractérise par une forte variabilité (Fig. 11B) et met en évidence une accrétion de la partie située au sud de la pointe de la flèche durant la période 1958-2008. Le taux moyen global de l’avancé de la flèche littorale (notamment la pointe de la flèche) est de 62 m, soit de +1,24 m/an). En revanche, sur la rive gauche, il y a un recul de l’ordre de 109 m, soit de -2,18 m/an. Cette évolution de la pointe de la flèche vers le Sud couplée avec un recul de la rive gauche de l’embouchure conduit au déplacement de l’embouchure vers le Sud par transit littoral et donc une diminution du taux de recul de la flèche en allant du Nord vers le Sud. Au niveau de l’estuaire de l’oued Gharifa, on observe également un déplacement de l’embouchure vers le sud de plus de 320 m durant les 50 dernières années, soit de 6,4m/an (Fig. 11D).

et de l’impact des actions anthropiques. Les plages étudiées évoluent de façon très différente les unes par rapport aux autres. Leur orientation, leur morphologie et leurs caractéristiques granulométriques respectives impliquent une réponse différente des agents de la morphogenèse. Leur évolution naturelle va dépendre de deux facteurs importants dont les effets peuvent s’ajouter ou se soustraire (Paskoff 1998, Pedreros 2003). (i) les oscillations relatives du niveau marin au niveau du rivage en favorisant les phénomènes d’érosion côtière et (ii) les paramètres hydrodynamiques, notamment l’énergie déployée par le vent, au niveau de la flèche littorale et par les houles atlantiques dont la turbulence intense due au déferlement érode les côtes sableuses et alimente la dérive littorale. De ce fait, l’ensemble du système sableux change de configuration et de morphologie en donnant des zones d’accrétion et des zones d’érosion.

Estuaire de Tahaddart Au niveau de l’estuaire de Tahaddart, la tendance évolutive diffère entre les rives droite et gauche (Fig. 11B). Des phénomènes d’érosion ont été observés au niveau de la rive droite où le taux moyen du recul est de 55 m, ce qui donne un retrait de -1.1m/an. Au niveau de la rive gauche, il y a un engraissement total de 43 m, soit +0,87 m/an. D’une manière générale, le principal enjeu des rives de l’estuaire de Tahaddart est leur mobilité dans le temps, suite au phénomène d’érosion-dépôt dans un système de méandres. C’est ainsi que la rive droite qui montre une topographie concave s’érode, à cause de la présence des courants marins à forte énergie ; alors que son homologue gauche, à profil convexe, s’engraisse en présence d’une dynamique marine de faible énergie.

L’évolution du littoral de Tahaddart est également liée à des facteurs anthropiques, notamment l’intensification des activités industrielles et l’urbanisation croissante et galopante qu’a connue la province de Tanger après l’indépendance. Ces activités socio-économiques ; ont conduit à la mise en place, ces dernières années, d’un certains nombre d’infrastructures et de travaux de construction et de nombreux ouvrages le long du littoral de Tahaddart, conduisant ainsi à des modifications dans la distribution des sédiments et à une dégradation de l’environnement naturel de ces zones (Amharrak 2006, Nachite et al. 2008). Dans la zone d’étude, certaines actions anthropiques peuvent avoir un lien direct avec ce déséquilibre et de là entraîner le recul du trait de côte. Parmi ces actions nous citons :

4.- Les causes de l’instabilité du littoral de Tahaddart La frange littorale de Tahaddart est un environnement côtier dont l'évolution et l’équilibre dynamique dépendent à la fois des facteurs naturels de la morphogenèse littorale

i) Le barrage Ibn Battouta (capacité de 45 millions m3) sur l’Oued Mharhar mis en service en 1977 pour l’alimentation en eau potable et l’irrigation (Agence du Bassin Hydraulique du Loukkos com. pers.). Ce réservoir 9


a réduit les débits liquide et solide, ce qui s’est traduit par un déficit dans le stock sédimentaire arrivant à la côte qui a été estimé à 0,55 millions de m3/an (Agence du Bassin Hydraulique du Loukkos com. pers.). Ce qui peut se traduire par un déficit moyen de quelques 17 millions de m3 de sédiments, pour le site de Tahaddart. ii) Le barrage du 9 Avril (capacité de 360 millions m3) sur l'Oued El Hachef, installé depuis 1995 (Agence du Bassin Hydraulique du Loukkos com. pers.), va accentuer l’effet dû au barrage Ibn Battouta sur les zones humides et la zone côtière. iii) Reboisement du cordon dunaire entre Haouara et Tahaddart (protection de la route principale RP2 des invasions sableuses). Cette intervention anthropique pourrait ralentir et parfois interrompre les échanges sédimentaires entre les dunes (réserves de sable) fixées et les autres unités de la plage. iv) L’extraction du sable des plages situées au nord du littoral de Tahaddart, notamment le site de Haouara (extraction abusive de plus de 5000 m3 de sable marin par jour) a favorisé le démaigrissement direct de la plage et une diminution du stock sédimentaire (LPEE/CRR/EE. 2001b). Ce déficit sédimentaire peut expliquer également l’accélération du taux d’érosion enregistré au niveau du secteur nord de ce littoral pendant la période 1958-2008. v) L’installation en 2004 de deux grandes infrastructures au niveau de l'estuaire de Tahaddart (centrale thermique en

aval et viaduc de l’autoroute en amont) qui avaient consommés de larges vasières de la zone humide. Les travaux d’endiguement de cours d’eau et de drainage des vasières, notamment à Briech et Haouara constituent également des aspects de dégradation des zones humides de Tahaddart. CONCLUSION 1- La dynamique du littoral de Tahaddart est soumise à une double influence marine et fluviale et les plages évoluent de façon très différente. Leur orientation, leur morphologie et leurs caractéristiques sédimentologiques impliquent une réponse différente des agents de la morphogenèse. Les agents de transport sédimentaire agissent différemment en fonction des unités géomorphologiques de la plage : le vent est un agent déterminant dans la distribution et le transport des sédiments en particulier au niveau de la dune. La dynamique des courants de la marée et celle de la dérive littorale joue un rôle très important dans le transport et la répartition des sables au niveau du bas estran. La morphoscopie des sables de plage montre des grains de nature variée et remaniée, et riches en quartz, minéraux lourds et fraction bioclastique. La nature et l’état des grains témoignent de la diversité des agents d’usures côtières et de la variété des matériaux transportés par les oueds.

Figure 11 : Evolution du trait de côte au niveau du site de Tahaddart entre 1958-2008. A : Plage de Haoura, B : Flèche littorale et embouchure de Tahaddart, C : Plage de Briech, D : plage de Kouass et embouchure de oued Gharifa.

10


2- L’étude qualitative et quantitative de l’évolution du trait de côte de la frange littorale comprise entre oued Tahaddart et oued Gharifa indique clairement que la tendance générale est vers l’érosion, avec un taux moyen annuel de -1,7 m/an. Cette évolution érosive de la côte s’est produite temporellement à des vitesses variables, mais également avec une variation spatiale qui se traduit par un taux moyen de recul plus élevé au niveau des plages situées au nord du site de Tahaddart qu’au sud. Ce qui peut expliquer la migration vers le sud de la pointe de la flèche littorale de Tahaddart, ainsi que le déplacement des embouchures des estuaires de Tahaddart et de Gharifa sous l’effet d’une dérive littorale principale qui porte du nord vers le sud. L’instabilité du littoral de Tahaddart dépend à la fois des facteurs naturels de la morphogenèse littorale et à l’impact des actions anthropiques notamment l’installation des barrages au niveau des oueds et de l’extraction abusive des sables destinés à la construction qui a accéléré le phénomène d’érosion côtière. Remerciements Ce travail a été financé par le projet WADI de la Commission Européenne Contrat n° INCO-CT-2005-015226-Wadi. Je remercie l’évaluateur anonyme pour ses remarques et commentaires qui ont contribué à l’amélioration du manuscrit. Je remercie également Mr. A. Bayed et Mme N. M’hammdi de l’Institut Scientifique (Rabat) et Mr. E.B. Jaaidi de la Faculté des Sciences (Rabat) pour leur aide et disponibilité.

Pramousquier, Var (France). The Mediterranean Sea, a natural sedimentation laboratory, 305-320. Doody J.P., 2001. Coastal Conservation and Management: an Ecological Perspective. Kluwer Academic Publishers, Boston, USA, 308 p. DRAPOR., 2002. Etude d’impact sur l’environnement des dragages des sables dans l’embouchure de l’Oued Tahaddart. Rapport de la Société de Dragage des Ports, 22194\M1\E\Rapport-AO, CID, 23 p. El Gharbaoui A., 1981. La terre et l'homme dans la péninsule tingitane : étude sur l'homme et le milieu naturel dans le Rif Occidental. Trav. Inst. Sci., série Géologie & Géographie Physique, 15, 1-439. El Mrini A., 2004. L’estuaire de Tahaddart (Province de Tanger – Maroc nord occidental) : Etudes préliminaires. Mém. DESA, Univ. Abdelmalik Essaadi, Fac. Sciences, Tétouan, 52 p. Folk R.L. & Ward W.C., 1957. Brazos River bar: a study in the significance of grain-size parameters. J. Sediment. Petrol., 27, 3-26. Guerinech A., 1998. Habitats naturels et valeurs écologiques du complexe de zones humides du bas Tahaddart (province de Tanger) : approche descriptive et cartographique. Mémoire Diplôme d'ingénieur des Eaux et Forêts, Ecole Nationale Forestière d'Ingénieurs, Salé, 84 p. Guelorget O. & Lefebvre A., 1995. L’estuaire de Tahaddart : Organisation et fonctionnement, 19 p. Guilcher A., 1979. Précis d’hydrologie marine et continentale. 2ème édition, Masson, Paris, p. 344.

Références

Graham E., 2007. Man’s Impact on the Coastline. J. Iberian Geology., 34(2), 167-190.

Amharak M., 2006. Evolution récente (occupation du sol et trait de côte) et impacts anthropiques au niveau de l’Estuaire de Tahaddart (Maroc Nord Occidental). Mémoire de DESA, Univ. Abdelmalek Essaadi, Faculté des Sciences Tétouan, 46 p.

Hannou E., 2003. Aménagement du territoire et développement du littoral : Cas de la partie septentrionale du Maroc. TS7 Coastal Zone Management; 2nd FIG Regional Conference, 2-5 décembre 2003, Marrakech (Maroc), 13 p.

André A. & El Gharbaoui A., 1973. Aspect de la morphologie littorale de la péninsule de Tanger, Rev. Géogr. Maroc, 23-24, 57-76. Blanc J.J., 1976. Evolution du profil des plages et phénomènes d’érosion littorale. Téthys, 7(2-3), 299-306.

Hansali H., 1998. Contribution à l'étude socio-économique et mode d'utilisation de la zone humide littorale de Tahaddart en vue de son aménagement (région nordouest marocaine). Mémoire Diplôme d'ingénieur des Eaux et Forêts, Ecole Nationale Forestière d'Ingénieurs, Salé, 117 p.

Blanc J.J. & Froget C., 1979. Présentation d’une méthode d’analyse sédimentaire dynamique appliquée aux plages. L’exemple du littoral de la Camargue. Bull. B.R.G.M., 2, 91-102. Boak E. & Turner I., 2005. Shoreline definition and detection: a review. J. Coastal Res., 21(4), 688-703. Crowell M., Leatherman S.P. & Buckley M., 1993. Shore-line change rate analysis: long term versus short term data. Shore and Beach, 61(2), 13-20. Carter R.W.G., 1988. Coastal environments. Academic Press (Ed.), New York, 617 p. Chamley H., 1988. Les milieux de sédimentation. BRGM éditions, 173 p. Dakki M., El Agbani M.A., Marraha M., Guerinech A. & Mouati N., 2003. Fiche descriptive du complexe du Bas Tahaddart. Projet d’Inscription de nouveaux sites marocains sur la liste Ramsar des Zones Humides d’Importance Internationale. WWF International – HCEFLCD – Inst. Sci., Rabat, Projet n°9E0702.01, 15 p. Degiovanni C., 1972. Essai d’interprétation hydrodynamique de la granulométrie des sédiments sableux, plage de

INRH, 1991. Structure hydrobiologique de l’estuaire de Tahaddart (Maroc). Rapport scientifique établi par l’Institut National de Recherche Halieutique (Casablanca) et le Laboratoire d’Hydrobiologie Marine (Montpellier). MERCI D’AJOUTER LE NOMBRE DE PAGES. Jaaidi E., Ahmamou M., Zougary R., Charte B., EL Moutchou, Malek F. & Naim K., 1993. Le littoral méditerranéen entre Tétouan et Ceuta et atlantique entre Tanger et Asilah (Maroc). Impact des aménagements portuaires sur la dynamique côtière : cas des ports de M’diq, RestingaSmir, Tanger et Asilah. In Berriane M. & A. Laouina (Eds) Aménagement littoral et évolution des côtes : Actes du Symposium de Tétouan-Tanger-Rabat, 21-33. Karrouk M.S., 1990. Aperçu sur les mécanismes climatiques rifains. Rev. Fac. Lettres, Tétouan, "le Rif, l’espace et l’homme", 4, 4ème année, 11-36. Komar P.D., 1998. Beach processes and sedimentation. PrenticeHall Englewood Cliffs, NJ, 544 p. Legrain D., 2000. Le conservatoire du littoral, Actes sud : Ed. locales de France (Conservatoire du littoral) , Paris , 109 p.

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Liu J.T. & Zarillo G.A., 1989. Distribution of grain sizes across a transgressive shoreface, Mar. Geol., 87, 121-136. LPEE/CEH., 1997. Plan bathymétrique de l’estuaire de Tahaddart au 1/1000ème. Rapport interne. LPEE/CRR/EE., 2001a. Régime des marées et influence des vents, Centrale thermique de Tahaddart. Rapport interne. LPEE/CRR/EE., 2001b. Etude des apports solides et diagnostique sédimentologique du site de la centrale thermique de Tahaddart. Rapport interne. Massik Z., Lakhdar I. & Zizah S., 2003. Impact d’une activité de dragage de sables sur la faune et la flore de l’estuaire de Tahaddart (Cas de l’estuaire de Tahaddart). Colloque International sur les sables et Environnement (Solution Alternatives). Casablanca, Maroc, 1-21 p Mansour M., 2003. Environnements littoraux et aménagement durable : Apport de l’information spatiale. TS7 Coastal Zone Management; 2nd FIG Regional Conference, Morocco. Marrakech (Maroc), 11 p. Nachite D., Bekkali R., Macias A. & Anfuso G., 2008. El estuario de Tahaddart: las bases para una gestión integrada de un espacio en plena transformación. Service de Publication de l’Université de Cadix (Espagne), 33 p. ONE. 2002. Rapport d’Etude d’Impact sur l’Environnement de la Centrale à Cycles Combinées de Tahaddart, volume II, Rapport Final, 186 p. Orbi A., Lakdar J.I. & Zidane H., 1997. Etude préliminaire de l’estuaire de l’Oued Tahaddart (Automne 1995-printemps et automne 1996). Travaux et Documents de l'Institut National de Recherche Halieutique.104, 1-82. Pajak M.J. & Leatherman S., 2002. The high water line as shoreline indicator. J. Coastal Res., 18(2), 329-337.

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Pedreros R., 2003. Impact du changement climatique sur les zones côtières. Rapport BRGM/RP-52803. Passega R., 1963. Analyses granulométriques, outil géologique pratique. Rev. Inst. français pétrole, XVIII (11), 14891499. Paskoff R., 1992. Côtes en danger. Pratique de la géographie, Masson, Paris, 250 p. Paskoff R., 1998. Les littoraux : impact des aménagements sur leur évolution. 3e édition, A. Colin, Paris, 257p. Pinot J.P., 1998. La gestion du littoral: 1. Littoraux tempérés: côtes rocheuses et sableuses. Collection Propos. Institut Océanographique, Paris, tomes 1 & 2, 760 p. Projet WWF International "Inscription de nouveaux sites marocains sur la liste Ramsar des zones humides d’importance internationale". HCEFLCD/Inst. Sci./WWF International/Bur. Ramsar, 15p. Snoussi M. & El Hafidi Tabet A., 2000. Integrated coastal zone management programme –Northwest African region case. Ocean and Coastal Management, 43-10. Suanez S., Arnoux-Chiavassa S., Bony P., Bruzzi C., Buffet R., Provansal M. & Fraunié P., 1996. Evaluation of coastal sediment transport. MEDDELT Final Report, Univ. AixMarseille I., 13p. Weber O., 1989. Les agents dynamiques et le transport sédimentaire dans la zone côtière. Bull. Inst. Géol. Bassin d’Aquitaine, Bordeaux., 45, 23-36. Wright L.D. & Short A.D., 1984. Morphodynamics variability of surf zones and beaches: a synthesis, Mar. Geol., 56, 93118.


Population dynamics and structure of talitrid amphipods from Bizerte sandy beach (North of Tunisia) Amel AYARI *, Dhouha BOHLI & Karima NASRI-AMMAR University of Tunis, Faculty of Science of Tunis, Research unit “Animal Biology and Evolutionary Systematics” El Manar II, 2092 Tunis, Tunisia

Abstract. This study was focused on some aspects of population dynamics of the amphipods populating of Bizerte sandy beach (North of Tunisia). Five species, belonging to the Talitridae family, were sampled: Talorchestia deshayesi, Talitrus saltator, Orchestia gammarellus, Orchestia montagui and Orchestia mediterranea. During study period, 6480 specimens were sampled with a dominance of T. deshayesi individuals (50%). Within this species the sex ratio was female biased, with a yearly mean of 0.25. The population of T. saltator also showed a sex ratio biased in favour of females throughout the study period, except for October 2007 and May 2008. This result might be correlated with autumn and spring recruitment periods respectively. In contrary to T. saltator, which has a continuous reproductive period, T. deshayesi population showed a seasonal reproduction with a sexual rest period from December to March. Key words: Sandy beach, Amphipods, Population dynamics, Talitrus saltator, Talorchestia deshayesi, Tunisia. Résumé. Structure et dynamique de populations d'amphipodes Talitridae de la plage sableuse de Bizerte (Nord Tunisie). La présente étude s'est focalisée sur certains aspects de la dynamique de population des amphipodes de la plage sableuse de Bizerte sur le littoral nord tunisien. Cinq espèces appartenant à la famille des Talitridae ont été échantillonnées : Talorchestia deshayesi, Talitrus saltator, Orchestia gammarellus, Orchestia montagui et Orchestia mediterranea. L'échantillonnage a permis de récolter 6480 individus avec la dominance de T. deshayesi (50% de l'abondance totale). Pour cette espèce la sex-ratio est défavorable aux femelles avec une moyenne annuelle de 0,25. La population de T. saltator montre aussi une sex-ratio défavorable aux femelles pour toute la période de l'étude sauf pour octobre 2007 et mai 2008. Ce résultat semble correspondre aux périodes de recrutements respectivement de l'automne et du printemps. Contrairement à T. saltator dont la période de reproduction est continue, la population de T. deshayesi a montré une reproduction saisonnière et une période de repos sexuel de décembre à mars. Mots clés : Plage sableuse, amphipodes, dynamique de populations, Talitrus saltator, Talorchestia deshayesi, Tunisie.

INTRODUCTION Talitrid amphipods occur in sandy beaches on a wide geographical scale (Dahl 1946) and are in some beaches the most dominant species (McLachlan et al. 1981). They play an important ecological role as decomposers and are considered potential bioindicators of the quality of sandy beaches (Griffiths et al. 1983, Ketmaier et al. 2003). Talitrid amphipods are thus suitable for studying the relationships between biological features and environmental changes (Scapini et al. 2002). In Tunisia, many studies were investigated on Amphipoda settlement. From one hand, the locomotor rhythm of some species was investigated in Bizerte, Barkoukech, Zouaraa, Kalaat Landalous, (Nasri-Ammar & Morgan 2006, Bohli et al. 2006, Ayari et al. 2008a, 2008b). On the other hand studies on the distribution, orientation, and biology have been carried out in Tunisia at Zouara and Korba (Charfi et al. 2000, Colombini et al. 2002, Scapini et al. 2002, Marques et al. 2003, Bouslama et al. 2007). In the present study, we aimed at characterizing the diversity of amphipods populating in Bizerte sandy beach

and at studying the population dynamics of three species: Talorchestia deshayesi, Talitrus saltator and Orchestia gammarellus, despite the fact that the last species is represented with low number. MATERIAL AND METHODS Amphipods were sampled in Bizerte sandy beach (37°19’N-9°51’E), situated in the North of Tunisia and characterised by the presence of a banquette of Posidonia oceanica and other macrophytes. This beach measures 15 m approximately in width. Field work was conducted each month, from June 2007 to May 2008, in the supralittoral zone. Individuals were collected by hand, during the morning with sampling effort varied between 1 to 2 hours. In the laboratory, the specimens collected were identified, measured, counted and sexed for different categories: non sexually differentiated juveniles, adult males, young females, non reproductive females with empty oostegites, reproductive females (with setae or with eggs/embrios). During the sampling, sand temperature and relative humidity were also recorded. Data were analysed using following indexes:

*

Corresponding author E-mail address: [email protected]

13

A. Ayari et al. – Population dynamics and structure of talitrid amphipods

RESULTS The highest relative humidity was recorded in January and February. Instead, two peaks of temperature were observed in June and July (Fig. 1). During this study, 6480 specimens were collected. Five species of Talitridae were identified: Talorchestia deshayesi, Talitrus saltator and Orchestia gammarellus, Orchestia montagui and Orchestia mediterranea. The frequency of occurrence showed that Talorchestia deshayesi, Talitrus saltator, Orchestia gammarellus were the most common species of the Bizerte sandy beach. The species richness showed two peaks in November and June indicating the presence of all species (Fig. 2). Furthermore, the Simpson index does not exceeded the value of 2. In April these two indexes are close, indicating that the talitrid community is more equilibrated in this month (Fig. 2). Shannon index, which takes into account rare species, varied between 0.1 and 1.1 (Fig. 3). Moreover, Pielou evenness index, which is insensitive to the richness, presented a minimum value in July (0.05), despite the presence of four species in this month. We analysed also the population dynamics of the most abundant species: Talorchestia deshayesi and Talitrus saltator. The sex-ratios biased in favour of females for T. deshayesi (Table I). For T. saltator, sex ratios biased in favour of males were observed in October and May. Moreover, O. gammarellus presented a sex ratio oscillating between 0 and 1, attended in August when the number of males was equal to females.

Air RH

Sand temp.

Air temp.

35 30 25

80 20 70 15 60 10 50

Temperature (°C)

90

Sand RH

5

40

0 June 07

J

A

S

O

N

D

Jan 08

Months

F

M

A

M

Figure 1: Variation of sand temperature (Sand temp.), air temperature (Air temp.), sand relative humidity (sand RH) and air relative humidity (air RH) at Bizerte sandy beach from June 2007 to May 2008. 6

S

2,0

Is

5 1,5 4 3

1,0

2 0,5

Simpson index (Is)

Pielou evenness index: J’= H’/Hmax Where Hmax = log2S

100

1 0

0,0 June 07

J

A

S

O

N

D

Jan 08

F

M

A

M

Months

Figure 2: Variation of species richness (S) and Simpson index (Is) at Bizerte sandy beach from June 2007 to May 2008. 1,20

H'

1,0

J'

1,00

0,8

0,80 0,6 0,60 0,4 0,40 0,2

0,20 0,00

Pielou evenness index (J')

Shannon-Weaver index: H’= -∑((Ni/N)*log2(Ni/N)) Where Ni is the individual number of species (i); N is the total individual number of settlement.

Relative humidity (%)

Simpson index: Is= 1/∑ (pi2) Where pi = number of individuals of the species (i) compared to the total number of individuals in the settlement.

Apparently T. deshayesi showed a seasonal reproduction with a sexual rest period extending from December to March. In contrast, T. saltator showed a continuous reproductive period with two rest period. Because of the limited number of females collected for O. gammarellus, we can not infer any reproductive cycle for this species (Table I).

Species richness (S)

Frequency of occurrence: F= (n/N)*100 Where n is the number of times the species appears in the sample; N is the total number of samples (N=12). A species is called common if 75% 4% are reported

56.7 ± 12.53

Variable

%

Water discharges

60.09

Mean grain size

18.91

Swash width

9.35

Seawater salinity

5.43

Intermediate nesting beaches Variable

%

Beach width

30.06

Beach slope

24.09

Swash width

20.07

Seawater salinity Probability to reach the sea ± SEM (odds ratio) 5.84 ± 1.14

beaches (N = 19)

Intermediate nesting beaches (N = 4)

Figure 5: Swash width (m)

2.24 ± 1.31

Straightness (D/L)

range

path from the sea to the nest

0.24 – 0.84

path from the nest to the sea

0.52 – 0.96

mean ± SD 0.62 ± 0.18 0.78 ± 0.12

Table 2: summaries of track straightness. N = 20 * p < 0.05; df = 38

Table 3: summaries of hatching success and probability to reach the sea. Mann-Withney test n.s.

18.58

No nesting beaches Variable

* Mean grain size

% 45.80

Swash width

14.64

Seawater salinity

19.07

Water discharges

9.07

CONCLUSIONS

The beaches under analysis resulted similar with respect to the supralittoral zone characteristics, independently on their coastline orientation and geomorphology. This may be rather related to the longshore sea currents, which have an effect on most of the variables found relevant to similarity among beaches. The track straightness indicated a research of the nesting site on the supralittoral zone, however no typical research patterns (e.g. loops, see Schöne, 1984) was found at overall level. This seems to confirm that the principal choice of the nesting site is taken by the female in water before the emersion, and the choice of the nesting beach is thus likely to depend upon features (e.g., imprinting, sea currents, etc) other than the supralittoral characteristics. Hatching success did not vary significantly among the different sites, and this could indicate that after the selection of a nesting site, the same hatching success is ensured. However, the relatively low power of the test due to low numbers claims for further studies. From these data, it is highlighted the importance of the consideration of littoral zone and longshore sea currents as a whole, to understand the critical phase of nesting of C. caretta and protect the species and the nesting beaches at the time.

ACKNOWLEDGEMENTS This study was carried out in the framewrok of TARTACare Calabria project ; we would like to acknowledge Arch. Leonardo Bertelli for supplying his expertise in track straightness estimation; we are also grateful to all thos people who helped us during fieldwork and to Prof. Felicita Scapini for her valuable suggestions.

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Degradative processes in macroalgal wrack on sheltered beaches: ecological effects Marina GÓMEZ * , Francisco BARREIRO, Rosario DE LA HUZ, Mariano LASTRA & Jesús LÓPEZ Universidad de Vigo, Facultad de Ciencias del Mar, Departamento de Ecología y Biología Animal Campus Lagoas-Marcosende, 36310 Vigo, Spain

INTRODUCTION Beach consumers are supported primarily by allochthonous inputs, mostly represented by macrophyte wrack including macroalgal and vascular plant material. Wrack deposits at the supralittoral zone undergo dehydration, aging and finally are usually covered by wind-blown sand. Phenolic compounds are secondary metabolites present in macroalgaes and seagrasses whose functions may include deterring being fed by herbivores. One of the main characteristic changes in chemical composition during the macroalgal decay is the loss of phenolic compounds. The goal of this study was to evaluate the loss of phenolic compounds during the decay of wrack and assess the possible effect on the associated herbivore macrofauna. MATERIAL AND METHODS The study was carried out on two sheltered beaches on the Northwest coast of Spain (Galicia): Mañóns (ungroomed) and Ladeira (groomed). Field sampling was carried out during spring low tides. Wrack samples were collected along two shore-parallel transects on two tidal levels: one located at the drift-line (Level 1) and the second located at the dune base (Level 2). The characteristics algaes of these zones were sampled on both levels by triplicate. Immediately after collection the samples were thoroughly washed with distilled water and their epiphytes were removed. The clean wrack material was chopped into fragments, weighted and kept at -30ºC for later analysis. Total soluble phenols were extracted with 80% methanol by homogenization with inert sand using cold mortar and pestle. Calculation was based on the calibration curve prepared with phloroglucinol using a modified (Van Alstyne 1995) Folin-Ciocalteu method (Folin & Ciocalteu 1927). Total phenolic compounds were expressed as percentage of phenolic compounds per dry weight. Macrofauna samples were collected with a 0.05 m-2 core to a depth of 15 cm on the two defined levels.

Samples were sieved through a 1mm mesh and stored in 4% formalin. The species composition and the number of individuals were determined for each sample. Total abundance for each beach was calculated. RESULTS The results showed that the most abundant stranded macrophyte wrack species were Ulva sp., Sargassum muticum, Cystoseira baccata, Laminaria sp., Fucus sp. and the seagrass Zostera marina. Phenolic analyses indicated that stranded wrack had lower values of phenolic compounds than fresh algae (Fig. 1). This decay of phenolic content is higher in algaes located on the upper level (Level 2) indicating an older degradative stage than that observed at the lower drift line level. This pattern of phenolic loss with the ageing is consistent in all the species analysed. Mean phenolic levels were higher in members of the Fucales (Fucus sp., Cystoseira baccata and Sargassum muticum) than in member of the Laminariales (Laminaria sp.). Likewise, the macrofauna presented differences in the total abundance between the two levels and the highest values were recorded in Level 1.Although in terms of the number of individuals both levels were dominated by amphipods Talitridae, the community composition at the two beaches differed. Ladeira was dominated by Talorchestia deshayesi and Mañons by Talitrus saltator (Table I). CONCLUSION There is a clear spatial zonation in the phenolic content of the stranded macrophyte wrack. This indicates different states of freshness of the algae according with tidal level of the deposits. The highest values of the phenolic content and the maximum total abundance of macrofauna were found on the same level. These results show that there are other variables that have more influence on the macrofauna distribution than the content of phenolic compounds, as for instance the tidal situation.

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Different macrophyte wrack may differ in physical structure (levels of branching, toughness), nutritional values and decomposition rates which could potentially influence wrack-associated macrofauna. Different physical structure of seaweeds may also modify microclimatic conditions, i.e. temperature and humidity of wrack deposits (Rodil et al. 2007).

Different beach grooming intensity could be the reason of different abundance and community composition between beaches. Human activities, such as beach grooming, strongly influence the structure of macrofauna. (Dugan et al. 2003).

Table I: Species and total individual abundance of macrofauna as sampling on the groomed (Ladeira) and ungroomed (Mañóns) beaches. Mañóns Level 2

564 227 15 70

2 52

Tylos europaeus Talitridae (juveniles) Talitrus saltator Talorchestia brito Talorchestia deshayesii Coleoptera Phaleria cadaverina Staphylinidae Tenebrionidae Diptera Tabanidae Diplopoda

2 1 3 3

Phenolic com punds (% DW )

15 4 2

Level 1

Level 2 1

5 101

34 2

1

4 3 1

10

2 1

References Dugan J., Hubbard D., McCrary M. & Pierson M., 2003. The response of macrofauna communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of southern California. Estuar. Coast. Shelf Sci., 58S, 25-40.

Fresh Level 1 Level 2

8

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Folin O. & Ciocalteu V., 1927. On tyrosine and tryptophane determinations in proteins. J. Biol. Chemistry, 73, 627-650.

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Figure 1: Phenolic contents in tissues of five macroalgaes and one seagrass characteristics of two beaches. Error bars represent standard errors.

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Ladeira

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Rodil I.F., Olavarria C., Lastra M. & López J., 2007. Differential effects of native and invasive algal crack on macrofaunal assemblages inhabiting exposed sandy beaches. J. Exp. Mar. Biol. Ecol., 358, 1-13. Van Alstyne K.L., McCarthy J.J, Hustead C.L., Duggins D.O., 1999. Geographic variation in poly-phenolic levels of Northeastern Pacific kelps and rockweeds. Mar. Biol., 133, 371-379.


Beach grooming and the loss of coastal strand habitats in southern California D. M. HUBBARD * & J. E. DUGAN University of California, Marine Science Institute, Santa Barbara, California 93106, USA

BACKGROUND Located on the boundary between a rising ocean and a growing populace, coastal strand ecosystems are losing ground to widespread activities, such as beach grooming, seaside development and reductions in sediment supply. The ecosystem services and functions provided by these dynamic coastal ecotones have no analogs, yet are profoundly threatened by the combination of sea level rise and ongoing losses to human activities. In California, coastal strand vegetation can act as an important ecosystem engineer by trapping windblown sand trapping and initiating dune formation. We used field surveys and experiments to investigate the role of beach grooming in the loss of these threatened coastal ecosystems. RESULTS & DISCUSSION Surveys of 29 southern California beaches in late summer indicated strong effects of grooming on beach zones, wrack and coastal strand vegetation. Unvegetated supralittoral zones were four times wider on groomed beaches (n=12) than on ungroomed beaches (n=17). The abundance (cover) of macrophyte wrack was nearly an order of magnitude lower on groomed beaches compared to ungroomed beaches. Native plant abundance and richness were 15 and >3 times higher, respectively, on ungroomed beaches than on groomed beaches. To investigate grooming effects on the performance of native coastal strand plants, we seeded four replicate experimental plots in seasonally groomed (May to September) and un-groomed sections of San Buenaventura State Beach, Ventura, California, USA in January 2002. Seedlings of three species of native plants (Atriplex leucophylla, Abronia maritima and Ambrosia chamissonis) recruited in experimental plots in three annual cohorts during the rain seasons of 2002-

03, 2003-04 and 2004-05 (Fig. 1). A small proportion of seedlings in each cohort in the ungroomed section reproduced and survived to the start of the next rain season. No plants reproduced and no plants survived beyond April in the seasonally groomed area (where grooming begins in May each year) in any of the years of our study (2002, 2003, and 2004) (Fig. 1). Experimental comparisons of native plant performance were consistent with beach survey results for vegetation. Although initial germination rates were similar, seed bank, survival and reproduction of native plants were significantly lower in groomed compared to ungroomed plots. Introduction of coastal strand plants via seeds was sufficient to establish native vegetation in the ungroomed area, but not in the groomed area. Physical processes also varied between our experimental plots in the groomed and ungroomed areas. Aeolian sand transport rates in seeded plots were ten to 1,000 times higher in groomed than ungroomed sections in short term field trials using sediment traps. Further, both native coastal strand plants and piles of fresh kelp wrack greatly reduced sand transport rates on short time scales (0.5 to 1 hour), causing a > 90% reduction of ambient rates in the center and immediately downwind of plants or wrack deposits. Our results suggest beach grooming impacts result in widespread conversion of coastal strand and dunes to unvegetated unstable sand sheets and the loss of protective dune formation. Conservation of these threatened coastal ecosystems could help retain sediment and maintain biodiversity, wildlife and human use in the face of rising sea levels. More details on this study are available in J.E. Dugan and D.M. Hubbard, 2010. Loss of coastal strand habitat in southern California: the role of beach grooming. Estuaries and Coasts 33(1): 66-77.

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1000 900 800 700 600 500 400 300 200 100 0 0

60

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180 2002

240

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360

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480

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540 2003

600

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720

780

840

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2004

Figure 1: Mean number of live native plants (3 species combined) present in 19.6 m2 experimental plots at San Buenaventura State Beach, Ventura County, California, USA between Jan 2002 and April 2004. Solid circles = ungroomed area, open circles = groomed area.

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Mitigation of the ecological effects of nourishment on sandy shores, a case study G.M. JANSSEN 1 2

*1,2

, L. LEEWIS 1 & S. MARX 2

Vrije Universiteit. Department of Systems Ecology, 1081 HV Amsterdam, The Netherlands. RWS Centre for Water Management, The Netherlands.

GENERAL INTRODUCTION

NATURE CONSERVATION

Nourishment is the principal option for shore protection in countries like the Netherlands and the United States and is increasingly employed in other countries (Nordstrom 2005). Since only a few years, nourishment projects are not just designed to fill eroded coastal areas, but also to meet wishes from recreation and nature conservation.

Large parts of the sea, the beach and the dunes have been designated as protected areas of natural beauty. All areas that are protected under the Birds and Habitats Directives form an ecological network known as Natura 2000. The main purpose of this network is to maintain or restore the habitats and species at a favorable conservation status in their natural range. Several nourishment activities are sometimes performed in so called Special Protection Area’s (SPA’s) and Special Areas of Conservation (SAC’s). SPA’s are high level protected sites classified in agreement with the Birds Directive. The species which are involved are listed in in Annex I of the Birds Directive and additional regularly occurring migratory species. SAC’s are protected sites assigned under the Habitats Directive. The habitat types and species concerned are listed in the Annexes I and II of the Habitats Directive. The list concerns habitat types and species that are considered to be most in need of conservation at the European level.

In literature more attention is paid on physical aspects of fill material placed on beach and foreshore than on the ecological aspects. However, studies on the ecological effects of borrow and fill activities are increasing in numbers and scope (Nordstrom 2005). Site specific knowledge on the functioning of the sandy shore ecosystem, and on the cumulative and long-term effects of nourishment and other human activities is still very poor. Nevertheless, based on environmental impact assessments recently nourishment practises are mitigated to minimize ecological effects. The Dutch coastline along the southeast part of the North Sea is about 350 km long. The coast consists of straight sandy beaches and various large-scale tidal inlet coasts. Large stretches of the coast have dunes that prevent the low lying hinterland (which at many places is below sea level) from being regularly flooded. Where dunes are lacking, sea dikes have been constructed as a flood protection measure. In the Netherlands, as in many other European countries there is an ongoing loss of habitat due to a combination of flood risk management and sea level rise. Coastal erosion is a common feature along the Dutch sandy shorelines. In order to stop any further structural recession of the coastline, in 1990 the Dutch Government adopted the national policy of Dynamic Preservation. The strategic objective of this policy is: a sustainable safety level and sustainable preservation of values and functions in the coastal area. This objective was translated into the tactical objective to maintain the coast line at its 1990 position.

Birds under special protection are for example breeding birds on the dry beaches, like the Kentish Plover (Charadrius alexandrinus) and that need the beach or fore shore for resting and foraging, like the Sanderling (Calidris alba) and the Common Scoter (Melanitta nigra). For all the protected birds, habitats and other relevant species favourable reference conditions, actual status and objectives are described. This is done both in quantitative parameters, like number of breeding birds on the beach or the range of mudflats and sand flats in km², and in quality parameters which are characteristic for the abiotic and biotic structure of the habitat type concerned. For instance the quality of the protected habitat ‘Sandbanks which are slightly covered by sea water all the time (the fore shore and surf zone)’ is characterised by the presence of benthic species like bivalves, and the presence of epibenthic like Common Whelk (Buccinum undatum) and fish species like the Thornback Ray (Raya clavata) and Small Sandeel

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(Ammodytes Thobianus). For the protected habitat ‘Mudflats and sandflats not covered by seawater at low tide (the intertidal beach) however, no quality parameters have yet been set. Although there is a legal basis for the protection of parts of the sandy shore ecosystem, the actual transmutation into conservation measurements for the beach and surf zone ecosystem is still very poor, mainly due to lack of ecological knowledge. Favourable reference conditions, actual status and objectives are still poorly described. Any flood protecting management plan or other project likely to cause a significant effect on a European site must be considered against requirements of the Bird and Habitat Directive and a appropriate Environmental Impact Assessment must be made. Where flood management works like nourishments are to be permitted in spite of a negative assessment of the implications for a European site, any compensatory measures necessary to protect the overall coherence of Natura 2000 must be secured before undertaking works. ECOLOGICAL EFFECTS First of all, it must be stated that nourishment over the last decades has stopped the coastline from further retreating, erosion and nourishment seems to be in balance. One can expect that some terrestrial coastal habitats, like Embryonic Dunes benefit from this. There is also a positive effect on the habitat Grey Dunes. In the past two decades large amounts of sand were sprayed by the wind from the nourished beaches into the dunes. The amount of this aeolian transport is comparable to 25% of the total amount of sand that was nourished in that period (Arens & Janssen 2009). This freshly transported sand is beneficial to coastal dune succession. On a large temporal and spatial scale nourishments contribute to the conditions of the formation of coastal habitats. It could therefore be seen as mitigation measurement for the loss of terrestrial coastal habitat as a consequence of the policy of fixing the position of the coastline against the background of sea level rise. Repeated sand nourishment with aberrant sediment composition compared to the originally sand present, may alter environmental condition over time. No information on this phenomenon, however, is available yet for the Dutch coast. Several authors have described ecological effects of nourishments on a smaller temporal and spatial scale which can be valued as undesirable. These are mainly effects on the scale of individuals (e.g. disturbing breeding birds), of populations and less on communities (e.g. burying benthic communities). A good overview is given by Speybroek et al (2006). 122

MITIGATION / COMPENSATION The Commission of the European Communities defined ‘mitigation’ as measures envisaged in order to avoid, reduce and, if possible, remedy significant adverse effects. The European EIA Directive has mitigation of project impacts as one of its main aims (Wood 2002), and it is required that Environmental Impact Statements (EISs) include details of proposed mitigation measures. There are many different types of mitigation measures, which may be classified in terms of levels of mitigation, the project phase at which mitigation occurs, or as part of a hierarchy (DETR 1997). The concept of ‘levels of mitigation’ refers to decisions made during project design to mitigate impacts, and includes alternative locations (such as foreshore, beach or dune nourishment) or processes, physical design methods (such as rain bowing or dumping), and management measures. If a significant adverse effect remains after mitigation, or if no mitigation is possible, one should look for alternatives. When no reasonable alternatives can be found and the project is of great importance (which is almost always the case when coastal erosion is concerned), the project can only take place when the damaged nature is compensated in advance. A new comparable nature area must be developed. Compensation usually takes place at a different location, where as mitigation is usually done at the same time and place. Until today, no compensation for nourishment projects has been carried out in the Netherlands since no EIA has stated that significant effects will occur from nourishment projects. Only recently mitigation measures are taken with respect to the effects of nourishments in the Netherlands (ANCLN 2010). The adverse effects are described, followed by the mitigation measure: Disturbing nesting birds on the beach. Monitoring on nesting sites before the nourishment project starts. If there are sites of coastal breeding birds (e.g. Kentish Plover, Ringed Plover, The Little Tern Sternula albifrons) activities concerning nourishment are not allowed within a radius of 250 m. As alternative, nourishment may be started before the breeding season. Destroying embryonic dunes by covering it with sand. Dragging pipelines and driving with heavy vehicles should be done with care of the embryonic dunes. Embryonic dunes are normally not expected at erosive beach sites where nourishment is carried out. However, a lot of beach activities accompany the nourishment activity in the areas on either side. These embryonic dunes are also very vulnerable to mechanical beach cleaning and other recreation related activities.

G.M. Janssen et al. – Mitigation of the ecological effects of nourishment on sandy shores

Disturbing resting seals. Ships carrying the nourishment sand to the dumping site should stay away at a clear distance from the resting areas (van Duin et al. 2007). Disturbing Red-throated Loon (Gavia stellata) and Common Scoter (Melanitta nigra). Ships are not allowed to disturb large populations of these foraging or resting birds. Shipping and dumping should not be done within a 1500 m. range of large populations of Common Scoter. Covering benthic populations. Carrying out large nourishment in two time steps and two locations gives the possibility to partial survival of the population and gives opportunity of remigration from the unaffected areas to the nourished sites next year. Covering population of the benthic polychaete Scolelepis squamata on the tidal beach will influence also the foraging potential of the Sanderling (Calidris alba). Alternatively, the foraging period of the Sanderling (December – February) and the period in which the main prey species Scolelepis squamata has its larval settlement (September – October) could be avoided. Covering dense populations of bivalves (e.g. Cut Trough Shell Spisula subtruncata or the Atlantic Jackknife Clam Ensis Americanus), which are important food source for the Common Scoter and Eider Duck (Somateria mollissima). Monitoring the proposed nourishment site on the presence of these shells. If important populations of these bivalves are present, these sites should be avoided. Covering benthic populations in the trough between the sandbars within the surf zone. Nourishment of the trough is to be avoided. Nourishment in the foreshore should take place at the seaward side of the outer breaker bar. The trough between the two breaker bars is a potential area of high biodiversity. The high abundance of the Sand Mason (Lanice conchilega) creates a habitat for other (epi)benthic and demersal organisms and is therefore an important area within the surf zone (Janssen et al. 2008). Deviating sediment composition and beach slope. This aspect of mitigation is still in development. Sediment composition of the nourishment sand should be more or less similar to the composition on the dumping site. Since the composition of the sediment from the extraction site is never completely comparable to the dumping site the question is raised to what extent a

deviation is acceptable. The same holds for the beach slope. Slope of the (inter tidal) beach is changed due to nourishment, with consequences for the surface of the intertidal area. The relation between the beach index BI (McLachlan & Dorvlo 2005) and marine species richness may be used to set the limits of deviation from the before situation in slope and sediment composition. To avoid a significant effect on the species richness, a deviation of less than 5% of the original species richness could be said to be acceptable. The deviation from the original BI and its components can than be calculated. Many problems are still to be solved: the change in sediment composition and slope will be temporally, some or total recovery will take place in time. This should be taken into consideration in setting the standard. This may lead to some standard of deviation over time from the original situation. References ANCLN, 2010. Authorization Nature Conservation Law Natura2000 Ameland. Deen, R.J. Provincie Fryslân 00871365, 1-39. Arens B & Janssen G.M., 2009. Kustverdediging, suppleties en natuur. Vakblad Natuur, Bos en Landschap 6(2009)5, 18-19. DETR,

1997. Mitigation measures in environmental statements. Department of Environment, Transport and the Regions, London, 64 p.

Duin C.F. van Gotjé W., Jaspers C.J. & Kreft M., 2007. MER Winning suppletiezand Noordzee 2008 t/m 2012. Grontmij 13/99080995/cd, revisie D1. Janssen G.M., Kleef H., Mulder S. & Tydeman P., 2008. A Pilot assessment of the depth related distribution of macrofauna in the surf zone along the Dutch coast and its implications for coastal management. Mar. Ecol., 29(suppl. 1), 186-194. McLachlan A. & Dorvlo A., 2005. Global patterns in sandy beach macrofauna communities. J. Coast. Res., 21, 674-687. Nordstrom, 2005. Beach nourishment and coastal habitats: research needs to improve compatibility. Restoration Ecology, 13(1), 215-222. Speybroeck J., Bonte D., Courtens W., Gheskiere T., Grootaert P., Maelfait J.P., Mathys M., Provoost S. Sabbe K., Stienen E.W.M., Van Lancker V., Vincx M. & Degraer S., 2006. Beach nourishment: An ecologically sound coastal defence alternative? A review. Aquatic Conservation: Marine and Freshwater Ecosystems, 16, 419-435. Wood C.M., 2002. Environmental Impact Assessment: a Comparative Review. Prentice Hall, Harlow (405 p.) (Second, completely revised, edition.

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Sandy-beach ecosystems: Their health, resilience and management A.R. JONES *1, T.A. SCHLACHER 2, D.S. SCHOEMAN 3, J.E. DUGAN 4, O. DEFEO 5, F. SCAPINI 6, M. LASTRA 7 & A. MCLACHLAN 8 1

Australian Museum, Sydney, Australia University of the Sunshine Coast, Maroochydore, Australia 3 University of Ulster, Coleraine, Northern Ireland 4 University of Santa Barbara, Santa Barbara, USA 5 Unidad de Ciencias del Mar, Facultad de Ciencias, Montevideo, Uruguay 6 Universita di Firenze, Firenze, Italy 7 Universidad de Vigo, Vigo, Spain 8 Sultan Qaboos University, Oman (currently at the University of Sydney, Australia). 2

Lining most of the world’s exposed shores, beach ecosystems are subject to numerous, increasing pressures imposed by burgeoning coastal development and climate change. Consequently, beach ecosystems are vulnerable and their ecological health and resilience are in question. This paper identifies the major threats to beaches, explores some of the ecological consequences, and discusses concepts of ecological health and resilience as applied to sandy shores. We also suggest some goals and strategies for coastal management and pose questions for which robust answers are currently lacking. Major threats to beach ecosystems include climate-change factors, erosion, nourishment and/or hard engineering to combat erosion, off-road vehicles, beach cleaning, pollution, fisheries, sandmining and, possibly, introduced species. These factors may act singly or interact in novel ways. Probable consequences include changes to habitat structure and environmental conditions. In particular, climate change will increase the sea level, temperature and acidity and generate more intense storms causing greater habitat instability. In turn, these physico-chemical changes may affect the biological structure and function of beach assemblages. For example, temperature change would affect the distribution and physiology of many species and acidification would challenge calcifying species such as molluscs and crustaceans. Human responses to sea-level rise are also important eg, if hard engineering, especially seawalls, is used to protect societal assets, the adjacent intertidal beach will be lost entirely. Ultimately, sandyshore systems may provide fewer ecosystem goods and services to society with severe social and economic consequences quite apart from the impairment of ecosystem health. Although the term ‘ecosystem health’ (EH) is increasingly used in both a management and a scientific context, it is difficult to define precisely. Different definitions emphasise stability, sustainability, resilience, unimpeded trajectory to climax state, vitality, flourishing/good

condition or similarity to pristine condition. Consequently, the concept of EH raises many questions. For example, if health refers to ‘condition’, does it mean optimum, natural, normal, productive, variable, stable or aesthetic condition? Does it mean a fit to a model (eg, Abundance Biomass Comparison) or the ability to resist or recover from disturbance, or any of these depending on context? It is also unclear whether an ecosystem in its natural state should necessarily be considered healthy given that natural variability can be large. How are alternative stable states interpreted in this context? Arguably, in practice, EH depends on what humans think ecosystems should be like according to a normative ideal. A pragmatic definition of EH is ‘an ecosystem is healthy if it sustainably produces the outcomes desired by human society’. Some outcomes (eg, recreation, production) are driven by anthropocentric ethics, others (eg, conservation) by ecocentric ethics. Of particular interest for beaches is the relationship between health and disturbance. A key premise is that beach biota are adapted to disturbance since they have experienced storms through evolutionary history. Secondly, disturbance may be necessary to maintain diversity/health (eg, intermediate disturbance hypothesis?). Moreover, disturbance type (ie, pulse, press or ramp) is important, particularly since some new threats (eg, increasing temperature and acidity) constitute press disturbances. Consequent questions arise. Will the biota adapt or acclimate to these press disturbances? Are there thresholds in frequency and intensity of storms that exceed tolerances? Will larger storms affect deep burrowers by reducing the depth of sand? Are biota adapted to new disturbances (eg, vehicles, beach cleaning and nourishment)? Will larger storms, vehicles and lower pH interact to affect biota? Will the effects of lower pH invalidate existing findings regarding vehicles? Will beach ecosystems recover after nourishment? Some premises of EH are that ecosystems generally have not evolved into an optimum state, that natural ecosystems

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vary greatly (are all natural states equally healthy?), and that it is easier to recognise a lack of health (ecosystem distress) rather than the healthy state since no single optimum state exists. Ecosystem distress is characterised by a shift to smaller organisms, reduced species richness, loss of sensitive species, dominance by weedy and exotic species, shortened food chains, altered energy flows and nutrient cycling and likely reduced stability. However, apart from reduced species richness and abundance/biomass, these diagnostic tools have been little tested for beaches. Both large spatial scale diagnostics and comparisons over time (time series/ prior-post comparisons) are needed. Nor have alternative diagnostic approaches which are employed in other systems (e.g. ABC, River Invertebrate Prediction and Classification System) or biotic indices been developed for beaches, but there is some progress in testing the utility of indicator species such as ghost crabs.

managers should seek to reconcile ecological, social and economic demands in beach conservation, making holistic resilience an important management concept.

Closely related to EH is resilience, a complex, ambiguous concept with two broad meanings. First, ‘ecological resilience’ has long been part of a semantically-confusing debate about ecological stability. In this ecological context, two main ideas are frequently presented: 1.) a system’s ability to stay unchanged (resistance to stress/constancy/inertia), and 2.) the type and speed of change after impact (recovery/elasticity). The second meaning of resilience occurs where social and ecological systems (SESs) are integrated into ‘holistic resilience’. This integration has arisen because of two false assumptions in natural resource policy. The first assumption is that ecosystem responses to human use are linear, predictable and controllable. The second is that human and natural systems can be treated independently. The increasing coastal population growth makes the latter assumption even less true for beach ecosystems.

Many key management questions for beaches arise. For example, will systems resist human-development and climate-change pressures, and if not, are the impacts in time and space acceptable? Will systems recover or adapt? Will systems slowly degrade or collapse to an unacceptable alternative state? What is unacceptable? These questions involve both scientific answers (eg, the first) and societal answers (eg, the last).

Holistic resilience is both inclusive and complex. It is inclusive because it links economic, social and ecological systems and also accommodates panarchy, the cross-scale, dynamic interactions between human and natural systems. It is complex because it takes an holistic, dynamic systems view, considers spatial and temporal scales, and the synergisms of multiple pressures. Importantly, it recognises the possibility of non-linear, discontinuous ecological responses that create alternative states when thresholds have been exceeded. Although the SES approach is in its infancy, beaches may offer a particularly pertinent system for the application of SES-based management. Beaches are of immense social importance for recreation and coastal development (the social dimension of resilience) and they provide several critical ecosystem services dependent on intact ecosystems (the ecological dimension of resilience). Consequently, coastal

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The purpose of management is to apply strategies that will achieve stated goals. For example, an overarching goal may be ‘to sustain society (wellbeing and economy) and ecosystems (structure, function, processes, goods and services)’. For sandy shores, the goal might be ‘to maintain beaches in a near-pristine state supporting fully diverse, functioning ecosystems and sustainable human uses’. The latter is consistent with ecologically sustainable development since a core objective is to protect biological diversity and maintain essential processes and life-support systems. Moreover, it is consistent with both ecocentric and anthropocentric ethics since the value of beaches to humans derives largely from their natural state.

Although the available answers are rarely satisfactory, achieving societal goals will be served by enhancing resilience in terms of both ultimate (underlying) and proximate (direct) measures. The former include mitigating climate change, accepting limits to growth and the primacy of ecosystem protection, acknowledging beaches as ecosystems, increasing and disseminating knowledge, adopting human values/behaviours consistent with resilience, and applying ecosystem-based management principles (active adaptive management, the precautionary principle, risk analysis, cumulative effects, synergisms/multiple stresses, linkages and scale). Proximate measures include habitat/ environment maintenance, protecting dunes/sand budget, providing setbacks, applying best-practice engineering, minimising pollution, maintaining genetic diversity/population size, providing refuges as sources of colonists, and carefully managing potentially damaging activities (eg, mining, vehicles, camping etc). As the World Resources Institute said in 2000 ‘The challenge for the 21st century, then, is to understand the vulnerabilities and resilience of ecosystems so that we can find ways to reconcile the demands of human development with the tolerances of nature.’ This challenge applies to all ecosystems, not least beaches.


Patterns of macrofaunal community in intertidal sedimentary shores in South Shetland Islands, Antarctica M. LASTRA *1, J. MORA 2, M.A. GARCÍA GALLEGO 1 & A. SÁNCHEZ MATA 2 1 2

University de Vigo, Faculty of Science, Department of Ecology and Animal Biology, Pontevedra, Spain. University of Santiago de Compostela, Department of Animal Biology, A Coruña, Spain

INTRODUCTION Sandy beaches occupy extensive coastal areas in temperate and tropical latitudes. However, in Antarctic regions, the scarce sedimentary river inputs and the presence of thick layers of ice above most of the coast line determines the poor presence of sedimentary shores in general and the scarcity of sandy beaches in particular. In the areas were ice cup disappear during summer period, most of the coastal sedimentary landscape is occupy by boulder and cobbles beaches, with sand or gravel fraction underneath. Thus, macrofaunal community that inhabits such an environment is a combination of boulder and sandy beach species.

and the swash zone. Lithorinid prosobranchs and Polychaetes are also relevant taxonomic groups of the low intertidal. The results obtained will supply biological data to elaborate a temporal long term series to provide a monitoring tool for the evaluation change in biotic environment and climate change effect on Antarctic beaches.

MATERIAL AND METHODS The intertidal benthic macroinvertebrate communities in two intertidal environments: South Bay, in Livingston Island, and Foster Bay, in Deception Island were studied during years 2004 and 2005. Species richness and abundance of the species, demographic parameters (size frequency plots, cohort analyses, etc) of the dominant macrofauna, as well as sedimentary characteristics were analysed at five sandy/boulder beaches at each island.

Figure 1: Mean number of macrofauanal species at Livingston and Deception islands beaches.

RESULTS AND CONCLUSION Data indicates that both islands show clear differences in community composition in the studied beaches. Deception Island, with volcanic origin, shows lower values in species richness and abundances than that obtained in Livingston beaches (Fig. 1, 2). Species zonation concentrates most of the abundances and diversity in the lower tidal level as well as the swash. Singularity of Antarctic communities consist in the almost lack of intertidal species in the truly intertidal zone, inhabited only by Oligochaetes; Low temperature during winter period and ice scouring are hypothetical reasons for the biotic depletion of the mean and upper tidal levels. High diversity and abundance of amphipods is the main biotic characteristics of the lower intertidal

Figure 2: Mean number of macrofauanal abundances at Livingston and Deception inlands beaches.

*

Corresponding author E-mail address: mlastra.uvigo.es

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The influence of human activities and environmental factors on the presence of four dominant intertidal macro invertebrates on Dutch sandy beaches L. LEEWIS *1, P.M. VAN BODEGOM 1, G.M. JANSSEN 1,2 & J. ROZEMA 1 1 2

Vrije Universiteit Amsterdam, Dept. Systems Ecology, Amsterdam, The Netherlands Centre for Water management, Lelystad, The Netherlands

The Dutch coast is one of the most densely populated in the world, resulting in high pressures of human activities. On the beach this results in recreational activities like sunbathing and all kinds of water related activities (i.e. wind- and kite surfing). Moreover, due to coastal squeeze, many parts of the Dutch coast are subject to erosion. Because of that, since 1990, beach and foreshore nourishments have been taking place to counteract the erosional effects. Basic ecological research on Dutch sandy beaches up to now has focussed on zonation patterns of macro invertebrates and differences in abundance and species richness between beaches have been related to abiotic factors. However, how macro invertebrate fauna on different beaches are influenced beach nourishments and other human pressures, additional to their abiotic and physical environment has not yet been investigated on Dutch sandy beaches. There have been several investigations on the effects of single beach nourishments on macro invertebrate fauna, usually based on BACI like designs. Results were variable and in some cases no complete recovery of the fauna was reached at the end of the research period. To try to get some idea of the recovery of macro invertebrate fauna after beach nourishment, a different approach was adopted. Beaches along the entire Dutch coast were sampled in a chronosequential manner. Thirteen beaches were nourished at different points in time and had different intensities of recreation. Also 4 control beaches were sampled where no nourishment had ever taken place and with low recreation intensities. For calculation purposes, the date of the control beaches was set on 1990: this year is, also in management, used as the baseline for the Dutch coast. The beaches and nourishment years were evenly respectively randomly distributed over the three main coastal areas: the Wadden Sea Islands, the Dutch main coast and the Delta area. We looked at four dominant intertidal species on Dutch beaches: Scolelepis squamata (adults

and juveniles), Eurydice pulchra, Haustorius arenarius and Bathyporeia sarsi. Twenty samples per beach (20 cm diameter, 20 cm deep) were taken in a stratified random design, located between Mean High Water and Mean Tidal Level, according to the zonation of the sampled species. Several abiotic and physical variables were also measured, next to variables related to the mentioned human influences. To assess the effects of beach nourishments on the fauna, single and multiple regression was used. To relate the species to their environment redundancy analysis (RDA) was used. Single regression analysis on the years of nourishment and each of the individual species all gave nonsignificant results with regression coefficients approaching zero. Exploration of the data showed a latitudinal effect for S. squamata. To account for this effect, a multiple regression was done with year and latitude and each of the species (Table I). The results of the total model were highly significant for S. squamata with high regression coefficients. The partial regressions for both factors were significant or showed a very strong trend (year for the adults). The positive Beta coefficients show that S. squamata is positively affected by the beach nourishments. S. squamata profits from this disturbance and this is an indication that the species may be an opportunistic species. The model was not significant for the other species. Latitude seems to play some role for B. sarsi since it was close to significant. The RDA showed that the total species variance explained by the environmental variables is 94%. A forward selection procedure with Monte Carlo permutation tests revealed that latitude, wave period, moisture and grain size contributed (almost) significantly to the variation in the total species data (pvalues respectively: 0.002, 0.010, 0.044, 0.054). However, there are also species specific differences (Fig. 1), where the reactions to the environment of S. squamata versus the three crustacean species are almost independent of each other.

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S. squamata is mainly affected by latitude and wave characteristics (breaker height and wave period), while the amphipods H. arenarius and B. sarsi are, next to waves, are also affected by beach characteristics (moisture and slope resp. sand sorting). H. arenarius is also affected by spring tidal range. For E. pulchra beach characteristics (grain size, slope, moisture) are most important, while recreation negatively affects both E. pulchra and B. sarsi.

nourishments on the investigated species. S. squamata even profits from the nourishments. Recreation negatively affects two of the species. Latitude is important for S. squamata, there might be some underlying factor that drives this, but this is not clear yet. The environment that affects the species mainly are physical factors that are linked to beach morphology, as is shown by many other researchers. The true abiotic factors seem to be less important.

The overall results showed that from this investigation, there seem to be no negative effects of beach

Table I: Results of multiple regression analysis with year and latitude per individual species. Significant results are indicated in bold, nearly significant results are underlined.

Species

Total model R2 p

Year Beta coeff.

0,059

Latitude Beta coeff. p 0,878

S. squamata (adults)

0,730

S. squamata (juveniles)

0,584

0,002

0,397

0,043

0,759

0,001

H. arenarius

0,159

0,298

-0,255

0,330

-0,376

0,160

E. pulchra

0,048

0,707

-0,114

0,677

0,161

0,559

B. sarsi

0,197

0,215

-0,077

0,761

-0,457

0,086

0,000

0,295

p

0,000

Figure 1: RDA ordination triplot with axes 1 and 2 (a) and axes 1 and 3 (b). Shown are species arrows (five in total, thin lines, text in italic), environmental arrows (fifteen, thicker arrows, text in bold) and samples (seventeen, after investigated beaches, dots with beach name codes, not mentioned in text). Species codes: Scol ad: S. squamata adults, Scol juv: S. squamata juveniles, Haust: H. arenarius, Eur: E. pulchra, Bsarsi: B. sarsi. Axes 1 to 4 (axis 4 not shown) explain respectively 39%, 24%, 18% and 11% in the total of 94% explained species variation.

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Modelling large-scale occurrence and abundance of the sandy beach isopod Excirolana armata along the morphodynamic and salinity gradients of the Rio de la Plata Estuary, Uruguay Juan Pablo LOZOYA *1,2, Julio GÓMEZ 2 & Omar DEFEO 2 1

Centre d’Estudis Avançats de Blanes (CEAB-CSIC), Carretera d’Accés a la cala St. Francesc 14, 17300 Blanes, Girona, Spain 2 Facultad de Ciencias, UNDECIMAR, Iguá 4225, PO Box 10773. 11400 Montevideo, Uruguay

Understanding the relationships between beach morphodynamics and macrofauna assemblages has been critical in theoretical evolution of sandy beach ecology (Defeo & McLachlan 2005). However, these relationships have been mainly analyzed in oceanic sandy beaches, being exceptional macroscale studies considering the concurrent effects of large-scale estuarine and morphodynamic gradients (Lercari & Defeo 2006, Celentano et al. 2010).

(Lercari & Defeo, 2006). This work evaluates macroscale concurrent effects of estuarine and beach morphodynamic gradients on the spatial distribution and abundance of E. armata. We developed a large-scale (400 km) and bi-annual study considering 16 sandy beaches with contrasting physical characteristics, along the full estuarine gradient of the RdlP estuary (Uruguay) (Table I, Fig. 1). A conditional two-step procedure was performed to model the spatial distribution of E. armata in relation to several environmental variables simultaneously. Considering that in both cases these relationships were likely to be nonlinear, a Generalized Additive Model (GAM) was used.

Excirolana armata constitutes one of the most widespread cirolanid isopod species in Atlantic sandy beaches of South America. In Uruguay, it is particularly abundant in exposed oceanic beaches (Defeo et al. 1997) and also occurs in beaches of the Rio de la Plata (RdlP) estuary

Table I: Environmental characterization based on variables registered in the 16 beaches along the Rio de la Plata estuary and the oceanic Uruguayan coast.

Environmental variables Salinity Water temperature (ºC) Swash width (m) Beach width (m) Breaker height (m) Beach slope (%) Mean grain size (mm) Sand compaction (kg·cm-2) Sand moisture (%) Wave period (s) Organic matter (%) Composite indices Dean’s parameter BDI

Median

Min.

Range Max. Percentile 25

25.1 18.5 8.0 48.0 0.5 4.8 0.3 3.2 8.9 11.5 0.22

0.1 7.4 0.0 16.0 0.0 0.7 0.1 1.0 2.4 0.0 0.05

34.3 32.0 20.0 120.0 2.5 13.9 0.9 5.0 23.9 25.0 0.89

13.3 13.4 4.0 38.0 0.2 3.4 0.2 2.6 6.5 9.0 0.15

30.5 21.7 10.0 57.0 1.0 6.9 0.4 4.3 15.3 14.0 0.32

2.7 63.2

0.4 10.4

10.2 1037.5

1.9 36.3

3.9 154.6

Percentile 75

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Main results were as follows: 1) the first-step GAM explained 65.3% of the deviance in isopod occurrence distribution and retained 6 physical descriptors in the model (decreasing order: mean grain size, sediment organic matter content, water salinity, beach width, sediment water content and water temperature); and 2) the second-step GAM explained 66.4% of the deviance in abundance and shows that mean grain size, water salinity, sediment water content, beach width, penetrability and sediment organic matter were the most important explanatory variables (decreasing order). Beach morphodynamic and salinity gradients affected large scale distribution and abundance patterns of E. armata. However, mean grain size was the principal predictor in both GAMs, suggesting an important substrate specificity of this isopod. A global scale (PanAmerican) review confirms that E. armata is more abundant in fine sands, supporting GAMs results and reinforcing its characterization as a high substratespecific species. Salinity was also a key factor; confirming that E. armata is a marine species with relatively high tolerance to estuarine conditions. The analysis of other population aspects (e.g. reproduction, mortality) will give additional evidences into the differential effect of these gradients in sandy beach populations

Acknowledgements We wish to express our gratitude to the ‘Benthic Ecology Group’ of UNDECIMAR for field and laboratory assistance. Financial support from CONICYT (project n°1018 and 4034), PDT (project S/C/OP/07/49) and DINARA (UTF/URU/025/ URU) is also acknowledged. JPL specially thanks AECID for the financial support (MUTIS PhD Grant). References Celentano E., Gutiérrez N. & Defeo O., 2010. Effects of morphodynamic and estuarine gradients on a sandy beach mole crab demography and distribution: implications for sourceesink habitat dynamics. Mar. Ecol. Progr. Series, 398, 193-205. Defeo O. & McLachlan A., 2005. Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis. Mar. Ecol. Progr. Series, 295, 1-20. Defeo O., Brazeiro A., de Alava A. & Riestra G., 1997. Is sandy beach macrofauna only physically controlled? Role of substrate and competition in isopods. Estuar. Coastal Shelf Sci., 45, 453-462. Lercari D. & Defeo O., 2006. Large-scale diversity and abundance trends in sandy beach macrofauna along full gradients of salinity and morphodynamics. Estuar. Coastal Shelf Sci., 68, 27-35.

Figure 1: Box-and-whisker plots (median, 25 and 75 percentiles, minimum and maximum) for the 16 sandy beaches with respect to salinity, mean grain size, organic matter and Dean´s parameter along the Rio de la Plata estuary and the oceanic Uruguayan coast.

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Beach multi-risk assessment considering ecosystem services and coastal hazards: a tool for ICZM Juan Pablo LOZOYA *1, Rafael SARDÁ 1 & José A. JIMÉNEZ 2 1

Centre d’Estudis Avançats de Blanes (CEAB-CSIC), Carretera d’Accés a la cala St. Francesc 14, Blanes 17300, Spain 2 Universitat Politècnica de Catalunya, Laboratori d’Enginyeria Marítima, ETSECCPB, Jordi Girona 1-3, Campus Nord Ed.D1, Barcelona 08034, Spain

Natural hazards are recurrent events which can produce economic damages and the loss of human lives becoming natural disasters (Pérez-Maqueo et al. 2007). Caused by natural factors or induced by anthropogenic activities, they are the outcome of development process whereby societies have generated vulnerabilities and risks (World Economic Forum 2009). On the coastal zones, damages have been strong mainly because of massive human concentration and their associated infrastructures (Costanza & Farley 2007). In a near future, global warming processes will increase severity and frequency of such coastal damages (Raschky 2008). Beach management has traditionally concentrated on geomorphic hazards and the recreational human-use of beaches, overlooking their ecological and broader environmental values (Ariza et al. 2008). As coastal management, risk reduction requires a systemic vision considering interactions between natural and socioeconomics variables (Ecosystem Approach). Coastal risk programs tend to be reactive and risk assessment still focuses on tangible damages to assets, overlooking other intangible damages associated to the ecosystem functions, which normally lead that risk management only manages a part of the total risk (Meyer et al. 2009). In order to improve coastal zone management we have developed a beach multi-risk assessment approach, which integrates the beach ecosystem services and coastal hazards. The proposed methodology stars (Vulnerability profile) with the identification and characterization of ecosystem services (receptors) provided by the beach and the stressors (hazards). The potential exposure is defined through a conceptual model (DPSIR), prioritizing both ecosystem services and hazards. The regulatory responsibilities, related to the hazards identified and the ecosystem services provided by the beach, were also analyzed in this step. An overview of

these key administrative aspects could be particularly useful in order to identify the appropriate jurisdictions which may be affected in a risk assessment. In the next step (Risk Assessment) the economic valuation of ecosystem services and the hazards quantification was done, in order to obtain a risk characterization. Considering subsequent interactions with risk managers, this framework allows risk estimation per ecosystem service, per hazard and for the entire beach. Risk Analysis is internationally recognized as an approach to assist decision making. This analysis provides managers with an objective, repeatable and documented assessment of the risks posed by a particular course of action, which can also be included into widely used environmental management systems applied today for planning and decision making (e.g. ISO 14001). In our case, a risk-based approach helps managers to prioritize ecosystem functions and services, and focus efforts when regulating hazards which are considered to have the greatest potential impact, improving and supporting an integrated coastal zone management process. Acknowledgements JPL specially thanks AECID for financial support (MUTIS PhD Grant). Financial support from VuCoMA project (CTM2008-05597/MAR) http://lim050.upc.es/vucoma/index.html and KNOWSEAS project (Framework Programme 7- EU) http://www.knowseas.com/. References Ariza E., Jiménez J.A. & Sarda R., 2008. A critical assessment of beach management on the Catalan coast. Ocean & Coastal Management, 51, 141160. Costanza R. & Farley J., 2007. Ecological economics of coastal disasters: Introduction to the special issue. Ecol. Econ., 63, 249-253.

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Meyer V., Scheuer S. & Haase D., 2009. A multicriteria approach for flood risk mapping exemplified at the Mulde river, Germany. Nat. Hazards, 48, 1739. Pérez-Maqueo O., Intralawan A. & Martínez, M.L., 2007. Coastal disasters from the perspective of ecological economics. Ecol. Econ., 63, 273-284.

Raschky P.A., 2008. Institutions and the losses from natural disasters. Nat. Hazards Earth System Sci., 8, 627634. World Economic Forum, 2009. Global Risks 2009: A Global Risk Network Report. World Economic Forum, Geneva, 36 p.

Diagram of the beach multi-risk assessment, presenting the main steps of the proposed methodology

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The effect of tides on the vertical distribution of nematodes on shore environments: a study case of De Panne’s beach (Belgium) T. MARIA 1 2

*1,2

, A. ESTEVES 2, J. VANAVERBEKE 1 & A. VANREUSEL 1

Ghent University, Biology Department, Marine Biology Section, Krijgslaan 281 S8, 9000 Ghent, Belgium Universidade Federal de Pernambuco, Departamento de Zoologia Av. Prof. Moraes Rêgo, S/N, , Cidade Universitária, Recife - Pernambuco, 50670-901, Brazil

INTRODUCTION It is widely accepted that the horizontal distribution of intertidal beach organisms is structured by factors related to the tidal regime. In addition, the vertical distribution of small (meiofaunal) organisms might be influenced because these organisms live in intimate contact with the interstitial environment which is heavily influenced by the tidal regime as well. Intertidal benthic organisms are known to ascend in the sediment during the high tide and a descendent migration is expected when the tide goes down (McLachlan et al. 1977), but they may also migrate deeper in the sediment, as an adaptive strategy used against desiccation, during the low tide or to avoid the harsh wave impact during the high tide (Fegley 1987). Therefore we investigated the effect of the tidal regime on the vertical distribution and community structure in the upper 5cm of a macrotidal ultra-dissipative beach. MATERIAL & METHODS De Panne is located in front of the nature reserve "Westhoek reservaat" (51°05’30’’N, 02°34’01’’E), Belgium. A transect of 25m parallel to the coast line was established in the middle shore of the beach and replicates were randomly taken during five periods of a tidal cycle: at low, flooding, high, draining, and a second low tide. All cores were sliced into sections of 1cm to the depth of 5cm. Three replicates were destined to meiofauna analysis and fixed in neutral 4% formaldehyde tap water solution. Three replicates for interstitial sea water and chlorophyll pigment equivalent (CPE) were also collected and kept cool till to arrive in the lab. They were storage in a freezer at -4°C for further analysis. Sediment temperature was measured in a specific core using a soil mercury thermometer in order to minimize disturbance since the thermometer was supposed to be introduced in the core until the depth of 5cm. Meiofauna extraction procedures followed a combination of decanting (through 1000 and 38 µm

sieves with tap water 10 times), flotation (in diluted Ludox-TM 50 at a specific gravity of 1.18 BE) and centrifugation (three times at 3000 rpm for 15 min each) of the organisms retained on 38µm sieve. Major meiofaunal taxa were identified and enumerated under a dissecting microscope. A subsample of 50 nematodes were transferred to a series of solution of glycerine, alcohol and formalin (De Grisse solutions) and mounted onto slides for further identification to species level. Interstitial sea water was calculated as the difference between wet and dry weight sediment after drying the sediment in an oven at 100° C for an overnight period; CPE was extracted in 90% acetone and measured with a Turner fluorometer according to Holm-Hansen et al. (1965). RESULTS AND DISCUSSION The tidal regime indeed influenced the vertical distribution and community structure of the nematodes in the upper 5 cm of sediment. In general, nematode densities were higher during the period of submersion and nematodes mostly occurred in the upper 2cm of sediment in this tidal stage (Fig. 1). Multivariate analyses of nematode community structure revealed a shift in the vertical distribution during the tidal cycle, mainly as a consequence of species-specific vertical migrations since none of the measured environmental variables seemed to be responsible for the difference in the community structure. Most species showed an upward migration in periods of inundation but other species migrated upwards during emersion periods. For example, upward movements of a predator, Sigmophoranema rufum, and some smaller deposit feeding nematodes during submersion were observed while the predator Enoplolaimus litoralis migrated upward during emersion. Our results partially corroborate the results of a previous investigated tidal flat (Steyaert et al. 2001) where nematodes did not migrate deeper as a consequence of tide increase.

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T. Maria et al. – Effect of tides on distribution of nematodes

0-1cm

1-2cm LT FD 2-3cm

HT DR LT2

3-4cm

4-5cm

0

100

200

300

400

500

600

700

800

900

1000

-2

ind.10cm

Figure 1: Vertical nematode density (ind.10cm-2) during the five tidal stages studied. (LT: first low tide, FD: flooding period, HT: high tide, DR: draining period, LT2: second low tide).

References Fegley S. R., 1987. Experimental variation of near-bottom current speeds and its effects on the depth distribution of sand-living meiofauna. Mar. Biol., 95, 183-191. Holm-Hansen O., Lorenzen C.J., Holmes R.W. & Strickland J.D.H., 1965. Fluorometric determination of chlorophyll. J. Conseil Permanent Intern. Explor. Mer, 30(1), 3-15.

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McLachlan A., Winter P.E.D. & Botha L., 1977. Vertical and horizontal distribution of sub-littoral meiofauna in Algoa Bay, South Africa. Mar. Biol., 40, 355-364. Steyaert M., Herman P.M.J., Moens T., Widdows J. & Vincx M., 2001. Tidal migration of nematodes on an estuarine tidal flat (the Molenplaat, Schelde Estuary, SW Netherlands). Mar. Ecol. Progr. Series, 224, 299-304.


The impact of a temporarily open/closed estuary on the community structure of a sandy beach macrobenthos in KwaZulu Natal, South Africa K. ORTEGA *1, D.S. SCHOEMAN 2, J. LAUDIEN 3 & A.J. SMIT 4 1

University of Bremen, International Studies in Aquatic Tropical Ecology (ISATEC), Germany University of Ulster, School of Environmental Science, Cromore Rd, Coleraine, Northern Ireland 3 Alfred Wegener Institute for Polar and Marine Research, D-27568 Bremerhaven, Germany 4 University of KwaZulu-Natal, School of Biological and Conservation Sciences, Durban, South Africa 2

The South African coast has nearly 250 estuaries, and approximately 70% of these have been classified as temporarily open/closed systems. These estuaries are highly dynamic and are strongly influenced by seasonal rain cycles. For instance, estuarine phytoplankton decreases in individual size and total productivity during dry winter periods (Froneman 2006), while microphytobenthic biomass increases during summer rain periods (Skinner et al. 2006). When estuary mouths are open; these released huge amounts of estuarine water carrying organisms and nutrients into the ocean. These changes in the basic trophic levels of the food web affect via trophic cascading invertebrate and vertebrate assemblages. Based on the strong interactions between estuaries and adjacent environments, it is likely that changes in estuarine flow impact adjacent coastal systems, including sandy beaches. In this context, the aim of the study was to determine the influence of the temporarily open/closed Umlalazi estuary on the sandy beach macrofauna of Mtunzini beach, South Africa. This study surveyed a series of eight intertidal transects arranged along a symmetrical gradient to the north and south of the mouth of the temporary open/closed Umlalazi River. Biological samples and environmental data were collected during the end of the dry phase, commence of the wet phase and the end of the wet phase. Standard multivariate approaches were used to evaluate the influence of the estuary on the benthic communities inhabiting the beach. The results revealed that (1) environmental parameters showed a clear temporal pattern, nMDS ordinations clustered separately measurements of the dry phase from the rainy phase, (2) total macrofauna and filter-feeders abundance significantly increased in the beach at the north of the estuary mouth through time (Fig. 1). Multivariate analysis also showed clear differences in the macrofauna community structure between dry phase and rainy phase. Beside, food availability (in terms of nanoplankton Chl a and microplankton phaeopigments), salinity, beach width and mean grain size were chosen

as the set of environmental parameters that best describe the community, (3) macrofauna isotope ratios showed significant differences between beach sides through time, indicating the use of different food sources by sandy beach macrobenthos at each beach side. Hierarchical agglomerative cluster analysis of macrofauna isotopes ratios also grouped separately signatures of the dry phase from the rainy phase. Twosource mixing model showed an increase in the contribution of estuarine food sources to the bivalve Donax madagascariensis δ 13C signatures through time. It highlights the importance of estuarine sources in the energy requirements of sandy beach benthic species. Our results provide clear insights on the importance of precipitation and estuarine flow as factors structuring spatio-temporal patterns in sandy beach communities. (Lercari & Defeo 2003 and references therein). In conclusion, this study demonstrates the importance of food availability, related to increase in precipitation and freshwater inflow, as main variable shaping the community structure/ along-shore distribution patterns of this sandy beach macrofauna community. Likewise, this also remarks the importance of the biological control structuring sandy beach macrofauna, even in these harsh and fluctuating environments.

References Froneman P.W., 2006. The importance of phytoplankton size in mediating trophic interactions within the plankton of a southern African estuary. Estuar. Coastal Shelf Sci., 70, 693-700. Lercari D. & Defeo O., 2003. Variation of a sandy beach macrobenthic community along a human-induced environmental gradient. Estuar. Coastal Shelf Sci., 58, 17–24. Skinner T., Adams J.B. & Gama P.T., 2006. The effect of mouth opening on the biomass and community structure of microphytobenthos in a small oligotrophic estuary. Estuar. Coastal Shelf Sci., 70, 161-168.

* Corresponding author E-mail address: [email protected]

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Oct-08

80000

Dec-08 70000

Feb-09

IST(ind.m-1)

60000 50000 40000 30000 20000 10000 0 South

North

Locations

Figure 1: Individuals per strip transect (ind.m-1) at Mtunzini beach per location in October, December 2008 and February 2009.

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An illustration of the importance of sandy beaches to coastal ecosystem services at the regional scale D.S. SCHOEMAN *1, U.M. SCHARLER 2 & A.J. SMIT 2 1 2

University of Ulster, School of Environmental Science, Coleraine, BT52 1SA, Northern Ireland University of KwaZulu-Natal, School of Biological and Conservation Sciences, Durban, South Africa

Sandy beaches are the dominant feature of most of the world’s ice-free coastlines, they are increasingly threatened by coastal squeeze and they are relatively poorly understood. Management intervention is often required for the persistence of functional beaches, especially in tourist centres. Here, engineering solutions are used either to maintain artificial beaches or to replace them with seawalls of various types. Both engineering interventions disrupt coastal processes. The pertinent questions for beach ecologists revolve around the degree of disruption to beach ecology and the resulting consequences. Where charismatic species, like turtles, seabirds and rare or commercially-important fish species use beaches for spawning or nesting, the degree of impact will depend on whether managed beaches can mimic natural conditions sufficiently well in terms of the physical parameters that determine the nesting or spawning success of the individual species. It is not clear that the resident biotic communities on beaches contribute much in this respect. However, providing breeding grounds for a limited number of conspicuous species is not the only ecosystem service that beaches provide. Here, we use a case study conducted in KwaZulu-Natal, South Africa, to investigate a broadscale index of ecosystem functioning for beaches that contextualises their importance to ecological processes in the coastal zone at regional scales. First, we argue that the trend towards quantifying ecosystem services is anthropocentric because the focus is on benefiting humanity. Where human benefits are concerned, short-term economic prerogatives are often prioritised under the guise of “sustainable development”, where sustainability is defined in financial terms rather than those of persistent ecosystem functioning. We prefer the idea that certain ecosystem processes can be used as a common currency to evaluate the relative importance of the contribution of different systems to overall ecological integrity (and therefore sustainability) at regional scales. Specifically, we advocate measures of carbon turnover in this regard, because they are ecocentric, univariate, processoriented, comparable across systems, and relevant to

ecosystem services (although not exclusively from a human perspective). The geographical context of our study is the KwaZuluNatal (KZN) shore. Stretching approximately 560 km southwards from South Africa’s northern border with Mozambique, this coastline is bathed in warm, oligotrophic subtropical waters. There is little macrophyte wrack, although organic inputs from wastewater outfalls and estuaries can be significant. Roughly two-thirds of this coastline is sandy, and onethird rocky and it is punctuated by more than 70 estuaries, some of which contain mangrove systems. We compiled estimates of biomass, primary productivity, community respiration rates and trophodynamic relationships based on the known structure of macro-, meio- and micro-biotic communities in KZN, supplemented with published values from comparable systems where data were scarce or absent. These formed the basis of a simple mass-balance model that we used to assess the total rate of carbon turnover through four coastal habitats: sandy beaches; rocky shores; estuaries; and mangroves. Preliminary results indicate that on a per-unit-area basis, sandy beaches turn carbon over an order of magnitude more slowly than do the other systems, especially when primary production (PP) is included in the estimates (PP on beaches is negligible, so when it is excluded beaches cycle carbon as fast per unit area as mangroves). However, when expressed on a per habitat rather than per unit area basis, beaches cycle an order of magnitude more carbon per unit time than rocky shores (irrespective of whether PP is considered or not) and mangroves (if PP is ignored). While estuaries cycle two orders of magnitude more carbon than beaches, much of this could be attributed to internal recycling because the majority of KZN estuaries are cut off from the sea by sand bars for much of the year; during this time, estuaries likely contribute less to overall coastal processes than their rates of carbon cycling would suggest. Moreover, because there is negligible PP on

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D. S. Schoeman. – The importance of sandy beaches to coastal ecosystem services

beaches, much of the carbon cycled by beaches is of allochthonous origin on the first trophic level (as detritus). This suggests that beaches provide significant services to the other coastal ecosystems in terms of processing their exported carbon (most probably in the form of particulate and dissolved organic carbon) and making this available to the macroscopic coastal food web in the form of trophically available biomass. In other words, beaches in KZN seem to be fulfilling their intuitively attributed function of acting as large biological filters for coastal systems. In many senses, this ecocentric ecosystem service provided by sandy beaches at regional scales is similar

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to that which might otherwise be provided in the pelagic ecosystem by the “slimes and jellies” that are thought to be replacing the conventional phytoplanktonzooplankton-fish assemblages in degraded marine ecosystems. While the importance of beaches at regional scales emerges here only because of the prevalence of beaches along the KZN coast, this proportion of beach to rock holds globally, so similar results are likely to emerge elsewhere, emphasising the importance of beaches at the global scale. These results suggest that coherent and integrated conservation strategies are needed for entire coastlines and that beaches should be treated as important ecological components within conservation plans.


What is the structuring role of biotic interactions in explaining distribution and zonation patterns on West European sandy beaches? J. VAN TOMME *1, S. DEGRAER 2, W. WILLEMS 1, J.C. DAUVIN 3, L. DENIS 3 R. DE LA HUZ 4, G.M. JANSSEN 5, I. MENN 6, I.F. RODIL 4 & M. VINCX 1 1

Ghent University, Biology Department, Marine Biology Section, Krijgslaan 281, Building S8, 9000 Gent, Belgium Royal Belgian Institute of Natural Sciences, Management Unit of the Mathematical Model of the North Sea, Marine Ecosystem Management Section, Gulledelle 100, 1200 Brussels, Belgium 3 Université de Lille1 Sciences et Technologies, Laboratoire d'Océanologie et de Géosciences, UMR CNRS 8187 LOG, Station Marine de Wimereux, avenue Foch 28, 62930 Wimereux, France 4 Universidad de Vigo, Departamento Ecología y Biología Animal, As Lagoas-Marcosende 36310, Vigo, Spain 5 VU University Amsterdam, Faculty of Earth and Life Sciences, Systems Ecology, De Boelelaan 1085-1087, 1081 HV Amsterdam, The Netherlands 6 Greenpeace e.V., Große Elbstr. 39, 22767 Hamburg, Germany 2

INTRODUCTION Biological communities on sandy beaches are generally considered physically controlled. Physical processes such as the movement of waves and tides, habitat characteristics en the swash climate are considered to be the strongest ecological factors structuring the communities on sandy beaches. Until recently, biotic interactions are regarded to be of minimal importance, although biotic interactions are known to play important roles in other intertidal habitats as rocky shores and intertidal flats. Some recent studies however, suggest that biotic interactions might play a role in structuring communities on sandy beaches as well, especially on a small scale and on dissipative beaches. As West European beaches are generally quiet dissipative, it was expected to find indications of biotic interactions on these beaches. The main objective of this research was to examine the role of abiotic and biotic factors in clarifying the distribution and zonation patterns of sandy beach macrobenthos in Western Europe.

MATERIAL & METHODS Data were collected of several West European beaches in Belgium, The Netherlands, Germany, France and Spain. Both macrobenthos data and environmental data were available for these beaches. The seven most important macrobenthos species were selected based on their prominent abundance on the West European sandy beaches. These selected species were the amphipods Bathyporeia pilosa and B. sarsi,

the isopods Eurydice pulchra and E. affinis and the polychaetes Scolelepis squamata, Nepthys cirrosa and Eteone longa. These species show a distinct zonation pattern on the beach, every species is occurring in its own specific zone. As information on the trophic position of these species is known, it was hypothesized that biotic interactions as competition and predation could play an important role in clarifying the distribution and zonation patterns. Recently, modeling techniques have been used for analyzing analogous ecological questions. In this study, a regression model was developed for each of the selected species, including possible abiotic and biotic factors influencing their distribution. The most appropriate models with significant abiotic and biotic factors were then selected by the AIC method (Akaike’s Information Criterion; Akaike 1974). The variance explained by the total model was divided in a part explained by the abiotic factors and a part explained by the biotic factors. RESULTS & DISCUSSION Results suggest that the two abiotic variables, generally considered as most important structuring factors on sandy beaches (mean sediment and emersion time), do not exclusively explain the variance in species distribution. Other variables such as food supply may play an important role on the beach and species-specific explanations might also be significant. Some species like Bathyporeia sarsi and Eteone longa inhabit a broad zone on the beach. The response of these species to abiotic variables is not that specific, so these variables were not selected in the regression models or their contribution was low. On the other hand, biotic

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J. Van Tomme et al. – Biotic interactions and zonation patterns on West European sandy beaches

interactions are suggested to explain up to one third of the variance in species distribution explained by the model. For more than half of the species models, other species were indicated as significant biotic variables, suggesting biotic interactions to be important. Both predator-prey interactions and competition were indicated for specific species associations. As on rocky shores, it could be stated that the lower distribution limits of several species were determined by the presence and interactions with other present macrobenthos. Furthermore, the presence of epibenthos and hyperbenthos on the beach during high tide might also influence the zonation pattern of the macrobenthos. The modelling approach does however not give sound proof for the presence of interactions. Only experiments

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can elucidate true interactions and the specific processes behind these interactions but this study gives strong indications for biotic interactions on sandy beaches. It is in our knowledge the first study that explicitly addresses the consequences of incorporating both abiotic variables and biotic interactions in modelling distribution and zonation patterns of sandy beach macrobenthos. It showed that the ecology of organisms inhabiting these apparently simple intertidal landscapes might be more complex than generally assumed. References Akaike H., 1974. New look at statistical model identification. Ieee Transactions on Automatic Control, AC19, 716-723.


The effect of increased rainfall on the sandy beach ecosystem: results from a pan-European experiment Jan VANAVERBEKE *1, Nikolaos LAMPADARIOU 2, Michaela SCHRATZBERGER 3, Jutta KUHNERT 4, Maaike STEYAERT 1, Helena ADÃO 5, Nathalie BARNES 6, Tania CAMPINAS BEZERRA 1, Alexander DRGAS 7, Vicky KALEGEROPOULOU 2, Rute PORTUGAL 5, Katerina SEVASTOU 2, Basia URBAN-MALINGA 7, Leen VANDEPITTE 8, Gritta VEIT-KÖHLER 4, Paul WHOMERSLEY 3 & Tim FERRERO 6 1

Ghent University, Marine Biology Section, Belgium Hellenic Centre for Marine Research, Crete 3 CEFAS, UK 4 DZMB, Germany 5 University of Evora, Portugal 6 National History Museum, UK 7 Fisheries Institute, Poland 8 VLIZ, Belgium 2

Sandy beaches represent a dynamic interface between the marine, terrestrial and groundwater systems which may be rapidly influenced by rainfall events. The meiofauna of beach sediments are responsive to changes in salinity, drying and periods of emergence and may be ideal organisms for modelling the direct effects of climate change. Recent research suggests that patterns of rainfall over Europe will change in quantity, frequency and intensity. Here we present the results from the largest fully standardised and replicated field experiment ever undertaken in meiofaunal ecology carried out in the framework of the European NoE MarBEF MANUELA subproject. Sandy beaches from four European locations (Poland - Baltic Sea, Belgium - North Sea, Portugal - NE Atlantic Ocean and Crete - Mediterranean Sea) representing different kinds of beaches in different climatic areas were subjected to artificially increased rainfall during a period of 2 weeks in order to investigate the response of meiofaunal nematodes in terms of densities, diversity and community composition to predicted climate change. Artificial rainfall was applied in such a way that it mimicked increased intensity and frequency. Changes in the benthic environment were assessed by analysing the vertical distribution of the concentration of chloride ions, as a proxy for interstitial salinity. Multivariate patterns in nematode community composition were investigated using Permanova. Homogeneity of multivariate dispersion was checked by the PERMDISP procedure. Univariate indices (densities

and diversity) were analysed using repeated measures ANOVA after testing for assumptions. Our results show that climate change indeed affects the sandy beach ecosystem of Europe. The application of artificial rain caused changes in the sedimentary environment, as salinity profiles (upper 15cm) changed drastically. After 4 days of artificial heavy rainfall, salinity levels were generally depressed. Only at the Baltic Sea station, concentrations of chloride ions were below detection limit in both treatment and control samples. However, the effect of increased rainfall on the biological communities depends on the geographical location. Nematodes from less dynamical beaches (e.g. the microtidal Mediterranean beach) were more drastically affected in terms of nematode density, diversity and community composition compared to nematodes inhabiting more dynamical beaches (macrotidal beaches from NE Atlantic or North Sea coasts). Nematode densities decreased significantly after 4 days of artificial rain in the North Sea (Fig. 1) and Mediterranean beaches. At the very dynamic Atlantic beach, nematode community composition was marginally affected (p=0.05) while the rain application did not affect nematode densities. Nematode communities inhabiting the low salinity Baltic coast appear to be more resistant. Therefore, we hypothesise that the decrease in nematode abundances and shifts in community composition that were observed were caused by changes in the interstitial salinity levels causing osmotic stress for the nematodes. The absence of large seasonal differences in e.g. temperature and rainfall in the Mediterranean locations probably

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J. Vanaverbeke – The effect of rainfall on the sandy beach ecosystem

increase the vulnerability of the sandy beach ecosystem to increased rainfall as the receiving communities are less adapted to such fluctuations. In addition, our results

suggest that many sandy beach ecosystems are indeed vulnerable to consequences of climate change.

Nematode densities 1200

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Figure 1: Evolution of nematode densities in treatment plots (R) and control plots (C) at the beach of De Panne (Belgium)

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Bayed A. (ed.). Sandy beaches and coastal zone management – Proceedings of the Fifth International Symposium on Sandy Beaches, 19th-23rd October 2009, Rabat, Morocco Bulletin de l'Institut Scientifique, Rabat, série générale, 2011, n°6, 145-148.

Sandy Beaches Workshop Reports Two workshops were held at the Fifth International Symposium on Sandy Beaches - Rabat, Morocco, 19th - 23rd October 2009. The first workshop identified high-priority questions concerning sandy beach biological research; the second addressed the issue of monitoring in theory and practice. All the conference participants contributed to the document below.

Workshop 1 - Sandy beach biological research: important questions for knowledge, understanding, policy and management

Most ecosystems are under numerous and rapidlygrowing human pressures. Consequently, there is a compelling need for scientifically-credible management if these systems are to sustain their ecological structures, functions and services to humans. This is especially true of sandy-beach ecosystems since they are both poorly studied and particularly vulnerable to the coastal squeeze of burgeoning coastal populations and the multiple pressures of climate change. Thus it is important to focus limited research resources on priority questions. In seeking to identify priority questions, this workshop followed previous exercises that proposed an ecological research agenda to promote a sustainable biosphere (Lubchenco et al. 1991 Ecology 72:371-412) or proposed priority ecological research areas relating to policy (Sutherland et al. 2006 J. Applied Ecology 43:617-627), conservation (Sutherland et al. 2009 Conservation Biology 23: 557-567), ecosystem services (Nicholson et al. 2009 J. Applied Ecology 46:1139-1157) and even business (Armsworth et al. 2010 J. Applied Ecology 47:235243). In the Rabat symposium, criteria used for the selection of questions included the filling of important gaps, developing new areas and methods of enquiry, the testing of important hypotheses, and, importantly, human utility in management for conservation, goods and services. As well, questions should be sufficiently specific and bounded to fit within reasonable spatial and temporal scales and they should be susceptible to realistic research designs.

The present workshop addressed four categories of questions: • Basic research that underpin applied questions • Human pressures, especially climate change • Conservation/protected areas • Ecosystem management, resilience and societal interactions Some of the suggestions below are framed as questions, others nominate areas of research.

Basic Research Biodiversity • What are the patterns of biodiversity at different spatial and temporal scales and their explanations? • Do biogeographic provinces exist? • What is the regional variation in the level of knowledge? Ecosystem structure and function • What are the important ecosystem functions in different kinds of beaches and at different spatial and temporal scales? • What are the functional roles of the interstitial and microbial communities? • Food web support provided by beach ecosystems. • What are the patterns of energy flow and linkages between beach ecosystems and dunes, ocean, watershed and estuaries? • Is there a relationship between ecosystem function and biodiversity? • Does the metapopulation concept of connected sub-populations apply to beaches? 145

All the conference participants. – Workshops report

• Will loss of beach biota affect nearshore fish nurseries? Stability and resilience of beach communities • What are the main factors/disturbances that affect stability? • What are the refuges that promote recovery following disturbance? • How important are metapopulations in enabling dispersal, recruitment, recolonization and recovery? • What are the natural ranges of temporal variation? • How fast is post-impact recovery? • What is the potential role of ecological restoration? • What are the life histories of key species? Timing of recruitment? Specific adaptations? Human Pressures • What are the responses of beach ecosystems to human pressures (eg, climate change, vehicles, fishing, pollution, urbanisation etc)? • Will pressures act individually or synergistically? For example, will larger storms, vehicles and lower pH interact to affect fauna? • Are impacts likely to accumulate over time? • How do you determine/assess impacts/recovery, especially in the absence of before-impact data? • Are urbanized/artificial beaches substantially different from pristine beaches? • Can we define and estimate resilience of sandybeach ecosystems? Resilience incorporates resistance to pressures; recovery following pulse disturbances (eg, pollution) and biotic adaptation to press disturbances (eg, lower pH). • Do regime shifts occur on beaches? What indices would we use to measure these? • Can we address some large-scale and long-term issues by developing large networks of scientists working with standardized methods? • How do we integrate other disciplines into beach ecology in order to better manage socialecological systems? • Are invasive species an issue and what are their direct and indirect effects? • Will larger storms produce more beach wrack? • Is more wrack good or bad for beach health? • What are the effects of large-scale, repeated nourishment? • Can calcifying species adapt/acclimate to decreasing pH?

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Conservation Conservation strategies should focus on systems rather than endangered species. The systems approach incorporates the beach habitat, its species, processes and people. • What are appropriate levels of protection for different contexts including indigenous interests? • What are the threats and pressures? The level of protection depends on these. • What are the appropriate scales for conservation? These depend upon the objectives of conservation and the tensions that arise eg, people versus system priorities or between local, regional and national priorities. • What are the ecological quality objectives? These correspond with conservation targets. • What level of protection is appropriate for beaches? How can it be incorporated in legislation? • At what point does conservation become effective? For example, should a threatening process be entirely excluded (including cultural/historical uses) or is there a tipping point/threshold below which effects are acceptable? • What are the relevant units that could fit into a systematic conservation plan? These include spatial units (eg, surf zones, dunes etc), patterns, processes, threats and targets. • What is an optimal reserve design to protect biodiversity? • How do we develop conservation targets? What are the conservation targets for sandy beaches in terms of biodiversity, services and processes? • What are appropriate setback lines (determined scientifically with participatory input from all stakeholders)? • What incentives would facilitate conservation? • How do we balance local objectives versus regional objectives, and who decides? • How do we sell beach conservation to the public/decision-makers? What can be used as flagship/key/focal/charismatic species? • What is the conservation status/vulnerability of beach species, particularly key species and rare or declining species? Which species are endemic to sandy beaches? • What is the ecological status of those systems that are nourished and maintained only for tourism (European beaches in general)? • Which conservation strategies are available – at which point do you adopt the strategies?


Beach Management • How do we raise awareness that sandy beaches are not just sand but valuable, diverse, dynamic ecosystems? • How do we generate adequate support for research and management? • Who are the stakeholders and users? • What is a healthy beach? • How are human management practices affecting biodiversity? • How do we manage anthropogenic disturbance? • How do we increase resilience of the dunebeach-nearshore system?

• What are the limits of acceptable change? • How do we increase the resilience of beaches as social-ecological systems? • What are the appropriate scales (spatial and temporal) of management? What are the boundaries of beaches in terms of ecological processes? • What are sustainable strategies for stabilizing or restoring eroding beaches? • What is the appropriate role of scientists – witness, advocate or both?

Workshop 2 - Monitoring of sandy beaches: theory and practice

The processes threatening sandy beaches are of deep concern. In particular, erosion caused by sea-level rise and increased storminess threatens the very existence of some beaches. In consequence, beach biologists are being asked to propose ecological monitoring programmes to inform management. But, apart from a vague commitment to sampling through time, what does monitoring mean? A key general requirement is that monitoring must be approached as a scientific exercise aimed at testing explicit hypotheses arising from clear aims and ecological models. Four general aims were identified by Downes et al. 2002 (Monitoring Ecological Impacts. Concepts and practice in flowing waters. Cambridge University Press): • Assess the ecological state of ecosystems; • Compliance with stated standards/performance criteria; • Detect and assess impacts/recovery/adaptive management; and • Assess responses to restoration Other general issues include the question of funding, ecological effect size, rapid assessment and communication with stakeholders. Funding is rarely adequate for ecological studies, especially in the long term. How do we raise the ecological profile such that monitoring is incorporated into legal mandates and adequately funded? Concerning effect size, if the purpose of monitoring is to detect change, then the magnitude of change that is unacceptable needs to be determined in order to design sampling with sufficient statistical power. This determination should

be a societal process with scientific input. Rapid assessment (via optimal surrogate indicators) is an important issue where funding is limited and there is a demand for quick results. This issue has not been investigated for sandy beaches. Finally, communication with managers, proponents and other stakeholders is often neglected. The workshop addressed monitoring under three headings • Long-Term Change (including baseline, health and state of the environment reporting) • Specific Pressures – Beach Nourishment • Specific Pressures – Coastal Armouring Various questions and strategies were identified under each heading. Long-term change In terms of monitoring for long-term change, there are more questions than answers. Among the more pressing questions to be answered before monitoring is initiated are the following: • What is the optimum definition of a beach environment (littoral-active zone, intertidal and supra-littoral zone, intertidal and surf zone?) and can any subset of these be used as a proxy for a beach? • How many beaches should be monitored in a long-term programme, and what would the basis 147


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be for their selection (biodiversity, vulnerability, uniqueness)? What ecosystem services characterise a fullyfunctional beach relative to a degraded beach? Are there process-oriented proxies for ecosystem functioning that could easily be measured (nutrient cycling, community respiration, etc.)? These might more completely capture the function of the beach as a whole by integrating macrofaunal, meiofaunal, and microbial food webs. Is it possible to make predictions on the basis of our ecological understanding of beaches, and to use long-term monitoring programmes to test these? Given the dynamic nature of beaches, is the establishment of ecological baselines a useful approach? Might a better approach be to compare observed ecological patterns against those modeled on the basis of observed changes in the physical environment? How can societal prerogatives best be incorporated into long-term monitoring programmes? How can the priorities of managers be reconciled with those of beach ecologists? How can networks of beach ecologists best be harnessed to maximise utility of data collected? How can political will and funding be generated for long-term ecological monitoring of systems that are as dynamic as beaches?

Specific pressures – Beach nourishment • What are the purposes of nourishment e.g., coastal defence, nature conservation, recreation? • Accommodate differences in engineering practice. For example, engineering methods vary as does the location of spoil deposition on the beach. • What is the optimum monitoring protocol? • Ecology • Economy • What is the best sampling design to assess impact and recovery: o BACI- type where reasonable control sites are available o Predictive modelling where there are no suitable controls.

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• What ecological indicators are appropriate to the engineering context or the resources available? Candidates include: Macrofauna Meiofauna Shorebirds Hyperbenthos Nearshore fish Habitat approach including vegetation and geomorphology o Ecological processes (predation etc) • Address the issue of cumulative nourishments. o o o o o o

• Monitor sediment composition after nourishment.

Specific pressures – Coastal armouring • Monitor the decision making process o Coastal management decisions can benefit from good technical input and processes that serve to clarify goals, benefits and impacts of armouring. • Identify management goals and targets o Coastal armouring is typically used to protect infrastructure in areas inland of soft-sediment shorelines. Even if goals are met, there may be physical and ecological impacts to intertidal and subtidal areas o Some armouring is intended to maintain recreational beaches o Determine if the armouring structure meets the main management goals (i.e. protection of infrastructure). If these goals are met, then monitor unintended impacts of the structure. • Determine costs and benefits of the armouring structures. Costs include loss or alteration of native habitats, development of non native habitats, impacts on donor habitats and carbon costs. • The presence of multiple interacting threats and factors is a major challenge to the understanding of causation. • Determine proper scales (spatial and temporal) of assessment and monitoring • Use the best, cost-effective techniques available.

Université Mohammed V – Agdal 2011



Travaux de l'Institut Scientifique, Série Générale, n°6

Proceedings of the Fifth International Symposium on Sandy Beaches 19 th-23 rd October 2009, Rabat, Morocco

Edited by Abdellatif BAYED
