Thalassas, 29(2) · June 2013: 45-58 An International Journal of Marine Sciences
Spatial-distribution of soft-bottom polychaetes in seagrass beds of the Ensenada de O Grove (NW Spain) Patricia Quintas(1), Eva Cacabelos(2) & Jesús S. Troncoso(1) (1) Departamento de Ecoloxía e Bioloxía Animal, Facultade de Ciencias, Campus Lagoas-Marcosende s/n, Universidade de Vigo, E-36210 Vigo, Spain. (2) Centro Tecnológico del Mar-Fundación CETMAR, C/ Eduardo Cabello s/n, E-36208 Vigo, Spain. Corresponding author:
[email protected]
ABSTRACT Distribution and composition of polychaete assemblages inhabiting seagrass beds were studied in the Ensenada de O Grove (NW Spain) by means of quantitative sampling. The studied muddy bottoms were colonized by Zostera marina L., Zostera noltei Hornemann or a combination of both seagrass species. A total of 36131 polychaetes belonging to 91 taxa were collected. Polychaetes were a diverse and abundant group mainly represented by the families Syllidae, Capitellidae, Spionidae, Sabellidae and Maldanidae. The species richness was high in the studied seagrass beds and some taxa (> 50%) were very common, common or constant with an overlapping faunal distribution. Three distinct faunal assemblages were detected though multivariate analyses: Group A included two subgroups: outer sites in muddy sands colonized exclusively by Z. marina with high diversity and species richness values and intertidal sites colonized by Z. noltei or both seagrass species in muddy sands or sandy muds. Group B only comprised a site characterized by low values of diversity and species richness. In a farther position, low diverse bottoms of site 37 located close to the mouth of the river, were colonized by Z. noltei. Significant differences between sites based on faunal composition were recorded using the ANOSIM test. The faunal distribution of polychaetes in the inlet was mainly conditioned by the salinity of bottom water, sort coefficient and depth, which were the most important abiotic variables selected through the CCA and BIOENV analyses. Key words: polychaetes, seagrass, Zostera marina, Zostera noltei, multivariate analysis, diversity, Ensenada de O Grove, Spain.
RESUMEN En el presente trabajo se estudia la distribución y la composición de las comunidades de poliquetos asociados a las praderas de fanerógamas de la Ensenada de O Grove (NW España) por medio de un muestreo cuantitativo. Los fondos fangosos estudiados están colonizados por Zostera marina L., Zostera noltei Hornemann o por una combinación de ambas fanerógamas. Se recogieron un total de 36131 poliquetos pertenecientes a 91 taxones. Los poliquetos constituyen un grupo diverso y abundante principalmente representado por las familias Syllidae, Capitellidae, Spionidae, Sabellidae y Maldanidae. En la pradera estudiada, los valores de riqueza en especies fueron elevados y varios taxones (> 50%) fueron muy comunes, comunes o constantes presentando la distribución de la fauna cierto solapamiento. Se detectaron tres asociaciones faunísticas a través de los análisis multivariante: Grupo A, formado por dos subgrupos: estaciones exteriores en arenas fangosas colonizadas exclusivamente por Z. marina con elevados valores de diversidad y de riqueza en especies y estaciones intermareales colonizadas por Z. noltei ó por ambas especies de fanerógamas en arenas fangosas o fangos arenosos. El grupo B únicamente compuesto por una estación caracterizado por bajos valores de diversidad y riqueza en especies. En una posición más lejana, se localizan los fondos con baja diversidad de la estación 37 situada cerca de la desembocadura del río y colonizados por Z. noltei. Se registraron diferencias significativas entre estaciones en base a la composición fanística usando el test ANOSIM. La distribución de la fauna en la Ensenada está principalmente condicionada por la salinidad del agua de fondo, el coeficiente de selección y la profundidad, que constituyen las variables abióticas más importantes seleccionadas a través de los análisis CCA y BIOENV. Palabras clave: poliquetos, praderas de fanerógamas, Zostera marina, Zostera noltei, análisis multivariante, diversidad, Ensenada de O Grove. España. Thalassas, 29(2) · June 2013
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Figures
Patricia Quintas, Eva Cacabelos & Jesús S.Troncoso
Figure 1: Map of the Ensenada de O Grove (Galicia, Spain) with the location of the sampling sites in the seagrass meadow.
Figure 1. Map of the Ensenada de O Grove (Galicia, Spain) with the location of the sampling INTRODUCTION
sites in the seagrass meadow.
Seagrass meadows are globally distributed in coastal and estuarine ecosystems of temperate and tropical latitudes (Hemminga & Duarte, 2000). They add structural complexity to shallow soft-bottoms and provide food and habitat for a variety of organisms. Seagrass structure (rhizomes, leaves and roots) provide refuge for many organisms (Orth, 1980; Heck & Thoman, 1981; Webster et al., 1998) and they constitute reproductive and nursery grounds for many species, including juveniles of important commercial fishes and shellfishes. Seagrass beds are also important in dampening wave energy and their extensive rhizome network traps fine particles stabilizing 46
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the sediments and contributing to avoid coastal erosion (Davison & Hughes, 1998; Terrados & Duarte, 2000). Seagrasses leaves support diverse sessile invertebrates consumed by many organisms (Duffy & Harvilicz, 2001). And moreover, the decomposition and degradation of the plant also increase the food availability for many species 23 by producing organic matter and detritus (Kitting et al., 1984). Therefore, seagrass meadows are some of the most valuable components of estuarine and coastal ecosystems, showing both important economic and ecological values (Costanza et al., 1997; Laborda et al., 1997; Hemminga & Duarte, 2000; Williams & Heck, 2001) and greatly influencing for maintenance of biodiversity and productivity of coastal waters (Orth et al., 1984).
Spatial-distribution of soft-bottom polychaetes in seagrass beds of the Ensenada de O Grove (NW Spain)
Seagrass meadows have been protected in Europe through “Habitat” directive 92/43/CEE. In these eastern Atlantic coasts, Zostera marina L. and Zostera noltei Hornemann are the major seagrass species, forming extensive meadows in intertidal and shallow subtidal areas (Laborda et al., 1997) of marine and estuarine waters. Benthic macrofauna are considered good indicators of marine bottom conditions (Grall & Glémarec, 1997), and therefore a detailed description of their composition and distribution would be useful to improve the control and management along protected areas. Polychaetes are important components of benthic marine fauna, both with regard to species richness and abundance. They have been the subject of many studies along the world, also in seagrass meadows, where the polychaetes can be a diverse and numerically dominant group (Bostrom & Bonsdorff, 1997), and along the rias, the particular estuarine systems of Galician coasts (Parapar et al., 1993; Moreira et al., 2006; Cacabelos et al., 2008; Lourido et al., 2008). Nevertheless, studies on the associated macrofaunal assemblages of seagrasses along the Galician coasts, despite their great economic and social importance, have been scarce (Currás & Mora, 1990; Currás et al., 1993; Junoy, 1996; Cacabelos et al., 2008; Esquete et al., 2010), and the findings achieved in this paper would be the first contribution to the knowledge of polychaete fauna in the inlet and the baseline for further comparative studies. Therefore, the main objectives of this paper are to characterize the composition, abundance and spatial distribution of the polychaetes in the seagrass beds of the Ensenada de O Grove (Galicia, NW Spain) as well as to study the influence of the environmental variables on the observed distribution and richness variability. MATERIAL AND METHODS Study area The Ensenada de O Grove is located in the inner part of the Ría de Arousa (Galicia, NW Spain) between 42º 41’- 42º28’N and 9º01’-8º44’W (Fig. 1). This sheltered area of approximately 15 km 2 is protected from open ocean by the presence of Peninsula de O Grove. Large freshwater inputs occur in the mouth of the inlet and in the innermost part. Soft-bottoms are mostly intertidal or shallow subtidal (< 20 m) and sediments are colonized in large areas by the seagrasses Zostera marina and Z. noltei. The high socio-economic value of the Ensenada de O Grove is derived from anthropogenic activities (such as mussel culture on rafts, bivalve collection, fishing, etc), that
have been sustainably exploited for years. Current legislation protect the inlet due to the presence of Zostera beds (Habitat Directive, Directive 92/43/CEE), and its ecological value for birds (ZEPAS, 1979, and RAMSAR Convention, 1990). In addition, the Ensenada de O Grove has been included in a natural space of importance for the European Community and listed in the “European Nature Net 2000”. Sampling The present study focuses in the macrofauna inhabiting soft bottoms of the inner part of the Ensenada de O Grove colonized by Zostera marina and Z. noltei, and it is included in a broader cartography of the benthic fauna associated to the soft bottoms of the whole inlet. Material was collected in 10 sites during October and November 1996 with a Van-Veen grab in order to compare our results with the remaining samples of the Ensenada de O Grove. Five replicate samples were collected from each site accounting for a total area of 0.28 m 2. Samples were sieved through a 0.5 mm mesh and retained material was fixed in 10% buffered formalin. Simultaneously, samples of surface and bottom water were taken at each site to measure salinity and temperature. An additional sample of sediment was collected from each site to analyze particle-size composition and the content in carbonate and organic matter. Laboratory analyses The fauna previously stained with Rose Bengal was sorted from sediment, identified (to species level when possible) and counted. Grain size analyses were determined according to Guitián & Carballas (1976). Median grain size (Q50) and sort coefficient (So) (Trask, 1932) were determined for each sample. Sedimentary types were characterized according to Rodrigues & Quintinho (1985). Carbonate content (%) was estimated by treating the sample with hydrochloric acid, and total organic matter (%) was estimated from the weigh loss on combustion for 4 h at 450ºC. Data analyses The structure of the polychaete assemblages was determined using the PRIMER v 6.0 software package (Clarke & Warwick, 1994). The DIVERSE routine was used to calculate several univariate measures for each site: total abundance (N), species richness (S), ShannonWiener diversity index (H’, log2) and Pielou`s evenness (J). Polychaete assemblages were determined through nonparametric multivariate techniques as described by Field et al. (1982). A matrix of similarities among sampling sites was constructed using the Bray-Curtis similarity Thalassas, 29(2) · June 2013
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Patricia Quintas, Eva Cacabelos & Jesús S.Troncoso
Figure 2:
2. Dendrogram produced using Bray-Curtis/Group Averagedata: Clustering techniques Dendrogram producedFigure using Bray-Curtis/Group Average Clustering techniques on fourth root transformed Three main polychaeteson assemblages were determined in the Ensenada de O Grove.
fourth root transformed data: Three main polychaetes assemblages were determined in the coefficient. Abundance datadewere previously fourth root Ensenada O Grove. transformed to down-weight the contribution of the dominant species. Once obtained this similarity matrix, a CLUSTER Analysis (UPGMA) tested by Simprof test and the multidimensional scaling (MDS) routine were performed to obtain the classification and ordination of sampling sites, respectively. To compare possible differences in faunistic composition between sites, the 1-way ANOSIM permutation test was used. The SIMPER procedure was also applied in order to evaluate the contribution of each species to the similarity/dissimilarity between assemblages. Species presented in each group of sites were classified according to the Constancy and Fidelity indexes. Species which occurred with more than 4% of the total specimens in a site or group of sites were termed “dominant” (Junoy, 1996). The Frequency X Dominance product was calculated in order to know the numerical importance of species.
measures were also analysed through the non-parametric Spearman’s rank test to detect significant relationships among variables (SPSS 15 software package).
Relationships between the polychaete distribution and the environmental variables were researched using the BIO-ENV procedure (PRIMER) and the canonical correspondence analysis (CCA) using the CANOCO v 4.02 (Canonical Community Ordination) package (Ter Braak, 1994). The forward selection was employed in the latter to detect which variables explained the most variance in the species data. The following variables were considered in these analyses: organic matter, carbonate content, pH and temperature of surface and bottom water, pH and temperature of sediment, granulometric fractions, median grain size, sort coefficient, and depth. Variables expressed in percentages were previously log (x+1) transformed. These variables and the aforementioned univariate
A total of 36131 individuals represented by 91taxa belonging to 29 families were collected. The Syllidae, Capitellidae, Spionidae, Sabellidae and Maldanidae were 24 the most abundant families. The numerically dominant species were the capitelid Capitella capitata (particularly in site 37), the syllids Parapionosyllis elegans, Exogone naidina, Exogone hebes, Sphaerosyllis campoyi, the spionids Microspio mezcnikowianus and Pseudopolydora sp., the nereid Platynereis dumerilii, the sabellid Fabricia stellaris stellaris (mainly in site 40), the maldanid Euclymene oerstedii and the spirorbid Janua pagenstecheri.
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RESULTS Sediments Sampling sites colonized by seagrasses were muddy bottoms, with moderate to high content of silt/clay (6-62%). Sand content was generally greater in subtidal sites and the sedimentary types ranged from muddy sand to mud (Table 1). Carbonate content ranged from 5 to 10%, while content in organic matter ranged from low values in subtidal sites (1.3-3.9%) to higher ones (10.715.5%) in intertidal inner areas (Table 1). Abundance, species richness and diversity
The lowest abundance was registered in sites 34 and 26 while the highest abundance were found in the sites
Spatial-distribution of soft-bottom polychaetes in seagrass beds of the Ensenada de O Grove (NW Spain)
Figure 3: Non-metric multidimensional scaling (MDS) ordination plot based on Bray-Curtis similarity coefficient showing the polychaetes assemblages in the study site.
Figure 3. Non-metric multidimensional scaling (MDS) ordination plot based on Bray-Curtis
influence to the similarity among sites of subgroup A1 35, 27, 24 and 40 (Table 2). Species richness ranged similarity coefficient showing the polychaetes assemblages in the study site. were members of the families Capitellidae (C. capitata, from 64 (site 27) to 23-15 (sites 34 and 37 respectively). Notomastus latericeus), Syllidae (E. naidina, E. hebes, Diversity (H’) was high in general (reaching values P. elegans, P. minuta, S. campoyi), Spirorbidae (J. of 3.72), except for the minimums found in sites 37 pagenstecheri), Maldanidae (E. oerstedii), Spionidae and 34 (1.23-2.11 respectively). Evenness (J) registered (Pseudopolydora sp., M. mecznikowianus), Nereidiade medium values (ranging from 0.58 to 0.70), although (Nereis caudata (Delle Chiaje, 1828)) and Cirratulidae a very low value was found in site 37 (0.31) due to the (Aphelochaeta marioni). small species richness and the high dominance of C. capitata. Diversity showed a positive correlation through In the subgroup A2, the main species responsible for non-parametric Spearman’s correlation coefficient the similarities between sites belonged to the families with carbonate content (p
