| SEASONAL AND SPATIAL CHANGES IN LARVAL FISH ASSEMBLAGES ALONG THE DUTCH COAST, SOUTHERN NORTH SEA |
| PÉREZ-DOMÍNGUEZ R. Institute of Estuarine and Coastal Studies (IECS), Department of Biological Sciences, University of Hull, Hull, HU6 7RX, United Kingdom; r.perez@hull.ac.uk |
| European environmental legislation has identified zooplankton as a sensitive biological quality element to evaluate the conservation status of coastal waters (EU Water Framework Directive). Disruptive pressure on spawning habitat, spawning stock biomass or direct effects on larval fish survival may impair normal demographic mechanisms resulting in altered larval assemblages that could be a sensitive measure of ecological impacts. The goal of this study is to assess a reference condition to scale possible impacts of human activities on larval fish survival and growth. This work (i) presents temporal and spatial dynamics of larval fish assemblages in the near shore (<30km) zone along the southern North Sea, and (ii) provides a predictive model of species associations using spatial (depth and latitude) and environmental variables (temperature (TEMP), salinity, chlorophyll a (Chlo) concentration, total suspended matter (TSM) and bottom silt percentage). Late fish larvae were collected in three separate cruises and included 100 stations sampled in April, July and October 2007 covering an area of 200 km x 30 km. A total of 28 larval fish species were encountered during the surveys with greater larval densities in April and a decreasing trend to the end of the survey period. Nineteen of these species were collected in April (11 unique species to April) grouped in 2 assemblages (cluster analyses & SIMPER), seventeen species in July (4 unique) and 4 assemblages, and finally nine species (1 unique) and 1 assemblage type in October. Herring (Clupea harengus), lesser sand-eel (Ammodytes marinus), and dab (Limanda limanda) dominated the catches in April; sand goby (Pomatoschistus minutus), dragonet (Callionymus lyra), and sprat (Sprattus sprattus) in July; and sand goby (Pomatoschistus minutus) in October. A statistically significant seasonal effect in assemblage composition was found (PERMANOVA p<0.0001) with well defined clusters for each month (nMDS analysis). Environmental gradients within each seasonal sample were comparatively small suggesting uniform conditions. Best explanatory seasonal models include TSM, latitude and TEMP (p<0.028) in April; TSM (p<0.001) in July; and latitude (p<0.05) in October. |
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