Sponsored by UNESCO, IOC, MAB and CORILA
LAGOONS AND COASTAL WETLANDS in the Global Change Context: Impacts and Management Issues Proceedings of the International Conference Venice, 26-28 April 2004 Edited by: Pierre Lasserre, Pierluigi Viaroli and Pierpaolo Campostrini Publication: IOC Integrated Coastal Area Management (ICAM), Dossier N°3 ***** continued: Part 3 and Part 4 (papers 24 to 46)
© UNESCO 2005
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[34] BENTHIC COMMUNITY STUDIES ALONG THE DESE ESTUARY (LAGOON OF VENICE, ITALY) F. Maggiore, E. Keppel and S. Puppini
CNR-ISMAR Castello 1364, 30122 VENEZIA e-mail
[email protected]
Abstract: Mollusk and polychaete community distributions in the Dese estuary were analysed in spring and summer. The benthic macrofauna showed a zonation pattern affected by salinity and grain size in spring and by trophic status in summer. Key words: Benthos, Estuary, Lagoon of Venice.
Introduction. The Dese estuary is a distinctive habitat in the northern Venice lagoon basin of Venice characterized by wide tidal amplitudes and the Dese river flow. The estuary extends for 14 Km from the Dese outflow in the lagoon to the Lido inlet, forming a narrow, meandering channel (Canale di Burano) between salt marshes and mud flats. The Dese River is the main tributary into the lagoon (Zuliani et al., 2001) and the most important source of urban, agricultural and industrial pollution (Collavini et al., 2001). The area is characterized by marked variations of physical and chemical factors determining its real estuarine conditions (Ministero delle Infrastrutture e dei Trasporti-Magistrato alle Acque, 1999; 2002). Taking into account that the benthic macrofaunal community is often used to indicate environmental health, the aim of this work is to verify if there is a biological zonation pattern, and if there are any changes in the community structure related to environmental changes. The work is part of a more extensive study on biodiversity at the community level in the Venice lagoon and it concerns mollusk and polychaete distribution along Dese estuary in late spring and summer 2002.
Materials and methods Study area: The investigated area consists of nine stations located in the mud flats (Fig. 1). Physico-chemical parameters, measured in the water column, are reported in figure 2; the following aspects can be stressed:
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- a decreasing gradient of salinity and sediment grain size is established from the Lido inlet to “Palude di Cona”; salinity shows marked monthly fluctuations in the inner area (St 6, 7, 9); -temperature values are very low in January (from 0, 7 to 5, 4 C°) and increases until August; -concerning total nitrogen and phosphorous, a clear increasing gradient from Lido inlet to “Palude di Cona” is observed in winter and spring; in summer all values get closer, in autumn a general pattern cannot be recognized; Palude di Cona shows almost always higher values; -Chlorophill a shows low values in spring, winter and autumn and high values from late spring to summer.
Sample and data analysis Samplings were carried out in the mud flats during June and August 2002. At each station, three bottom samples were collected by means of an Ekman box corer, for a total sample surface of 0.06 m². Each sample was washed through a 1.0 mm mesh screen; the material retained was preserved in 10 % buffered formalin. All benthic organisms were sorted from the sediment and mollusks and polychaetes were identified, to the lowest possible taxonomic level, and enumerated. Data were analyzed through Correspondence Analysis (Benzecri, 1973) and Cluster Analysis (metodo k c-means) (Hartigan, 1975) to identify station groups characterized by the same assemblages of species.
Results and discussion Fig. 3 shows the outcome of Correspondence Analysis in spring (A) and summer (B); the observations are arranged in a parabolic outline (Guttman effect), implying that axis 2 is a quadratic function of axis 1; this situation occurs when systems with an underlying fundamentally unidimensional phenomenon are examined. The outcome of Cluster Analysis was plotted on the map of Dese estuary (fig. 4A and B). In spring (Fig. 3A), a succession of four communities, whose distribution is established by distance from the sea, is shown along the axis 1: - the first one, characteristic of stations close to the inlet (cluster 1) is made up of marine species linked to sandy-muddy and muddy sediments as Notomastus latericeus, Sternaspis scutata, Aphelochaeta multibranchiis, Paradoneis lyra; - the second one, characteristic of intermediated stations (cluster 3) is made up of “mixed species”* (sensu Guelorget & Perthuisot, 1992) linked to muddy-sandy and muddy sediments as Nepthys hombergi, Heteromastus filiformis, Hemilepton nitidum and brackish water species as Streblospio shrubsolii and Hediste diversicolor;
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- the third one, characteristic of inner stations (cluster 4) is made up of brackish species as H. diversicolor, S. shrubsolii, Abra segmentum, A. tenuis, Cerastoderma glaucum; - the fourth one (cluster 2) seems to be an inner community because of the dominance of brackish species S. shrubsolii. In summer (Fig. 3B), the correspondence analysis produced a difficult to read result because of noise caused by the concentration of Nassarius reticulatus and Glycera rouxii solely in station 1; indeed, station 1 and species linked to it are very far away from all the others, flattening them on the axis 1. Focusing the attention on the latest, a succession of four communities is shown along axis 1: - the first, characteristic of station 3 (cluster 1), and the second, characteristic of station 2 (cluster 2), are made up of marine species linked to muddy sediments and brackish species as S. shrubsolii. They differentiate in specific composition, the first being mainly composed by A. multibranchiis, Clymenura clypeata, Cossura soyeri, P. lyra and N. latericeus, the second by Microspio mecznikovianus, Capitella capitata, N. latericeus and H. nitidum. - the third (station 4) is mainly characterized by S. shrubsolii and by the first-order opportunistic species C. capitata; - the fourth, characteristic of remaining stations, is made up of brackish water species mainly by S. shrubsolii followed by H. diversicolor. In spring zoobenthos distribution follows a zonation pattern affected by salinity and grain size gradient; the zonation pattern fits to that proposed by Guelorget & Perthuisot (1992). In summer, when Chl a shows higher values, this pattern is modified; indeed, the inner community of spring (cluster 4) invades the space of the intermediate community (cluster 3) because of spreading of S. shrubsolii which becomes the dominant species in intermediate and inner areas; C. capitata present in cluster 2 becomes co-dominant with S. shrubsolii in cluster 3. The autoecology of the two species can explain this phenomenon: S. shrubsolii is a brackish water species whose abundance is strongly affected by availability of food of high nutritional value (Rossi & Lardicci, 2002); its population increases following disturbances such as anoxic crisis or H2S production; indeed, S. shrubsolii is considered an opportunist able to colonize enriched environments (Pearson & Rosenberg 1978; Sardà & Martin, 1993). In “Palude della Rosa” it dominated the early stages of recovery after anoxic crisis with C. capitata, Polydora ligni, H. diversicolor and oligochaeta (Tagliapietra et al. 1998). C. capitata is a marine species known as a first-order opportunistic species able to
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firstly colonize areas where gross organic enrichment caused elimination or reduction of fauna (Pearson & Rosemberg, 1978). Therefore the increasing and spreading of S. shrubsolii in “more” brackish areas and C. capitata in “more” marine areas could have been favoured by rising of trophic status.
Concluding remarks. In conclusion, the benthic macrofauna is distributed along an environmental gradient from the Lido inlet to the Dese river mouth, showing a zonation pattern according to the one proposed by Guelorget & Perthuisot (1992); this pattern can be affected by trophic status. Supposedly, the environmental gradient can be water dynamics as it is the leading environmental factor influencing salinity, grain size and trophic status; Solidoro et al. (2004) demonstrate the role of the tributary discharges and of the exchanges with the sea in determining the water quality and the dynamics of the ecosystem.
Acknowledgments. We gratefully acknowledge Dr. Taroni for helping us in statistical analysis. The work was supported by CO.RI.LA.
References Benzecri, J.P., 1973. L’ analyse des données. V.2. Dunod Paris, 619 pp. Collavini, F., Zonta, R., Bettiol, C., Fagarazzi, O.E., Zaggia, L., 2001. Drain project workshop; Venezia, Giugno 2001: 53-60. Guelorget, O., Perthuisot, J.P., 1992. Paralic ecosistems. Biological organization and functionning. Vie Milieu 42 (2):215-251. Hartigan, J., 1975. Clustering algorithms. Wiley & Sons, New York: 351 pp. Ministero delle Infrastrutture e dei Trasporti-Magistrato alle Acque on behalf of Consorzio Venezia Nuova. 1999. Mappatura dell’ inquinamento dei fondali lagunari. Ministero delle Infrastrutture e dei Trasporti-Magistrato alle Acque on behalf of Consorzio Venezia Nuova 2002. Monitoraggio Ecosistema Lagunare. Campagne di misura della qualità dell’acqua dalla XVII alla XIX del 2002. Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology. An Annual Revue 16: 229-311.
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Rossi, F., Lardicci, C. 2002. Role of the nutritive value of sediment in regulating population dynamics of the deposit-feeding polychaete Streblospio shrubsolii. Marine Biology 140: 1129-1138. Sarda’, R., Martin, D., 1993. Population of Streblospio (Polychaeta: Spionidae) in temperate zones: demography and production. Journal of Marine Biological Association of U.K. 73: 769-784. Solidoro, C., Cossarini G., Melaku Canu D., Bandelj, V., Pastres, R., 2004. Nutrient dynamic in coastal ecosystem: a quantitative analysis of space variability and time evolution of water quality parameters in the lagoon of Venice. In: Lagoons and Coastal Wetlands in the Global Change Context: Impacts and Management Issues. Unesco-Roste, Venice, pp 2425. Tagliapietra, D., Pavan, M., Wagner, C., 1998. Macrobenthic Community changes related to eutrophication in Palude della Rosa (Venetian lagoon, Italy). Estuarine coastal and Shelf Science 47: 217-226. Zuliani, A., Zonta, R., Zaggia, L., Fagarazzi, O., 2001. Drain project workshop. Venice, Giugno 2001: 31- 36.
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Figure 1. Map of Dese estuary showing the position of the sampling stations
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Figure 2: Monthly trend of total nitrogen, total phosphorous, chlorophyll a, temperature and salinity in the water column in five sampling areas and Shepard’s triangular diagram. Data were supplied by Ministero delle Infrastrutture e dei Trasporti-Magistrato alle Acque on behalf of Consorzio Venezia Nuova (1999; 2002).
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Figure 3 : stations and species arrangement in spring (A) and summer (B). The coloured areas show the station clusters. Variance: X=25.5%, Y=21.0 % (A); X=27,9 %, Y=22,4 % (B). Only most abundant species are quoted.
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Figure 4: stations groups in spring (A) and summer (B) obtained with cluster analysis, plotted on the Dese estuary map.
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