Diversity, abundance and community structure of benthic ichthyofauna and crustaceans in the North Sea (Belgian continental shelf)
Oyugi, D.O. (1999). Diversity, abundance and community structure of benthic ichthyofauna and crustaceans in the North Sea (Belgian continental shelf). MSc Thesis. RUG: Gent. 95 pp.
Epibenthos data from 75 hauls taken by beam trawl (2.7 m wide) from Belgian continental shelf sandbanks, were analysed for species diversity (Hill's numbers), density and biomass. Samples for abiotic factors were also taken for each corresponding trawl. Two Way Indicator Species Analysis (TWINSPAN), Cluster Analysis and Canonical Correspondence Analysis of (CANOCO) assessed community assemblages. A total of 37 species of fish and 35 species of invertebrates were recorded belonging to 20 and 17 families respectively. Whereas the species number of species decreased seawards, species diversity showed a reverse trend with the lesser weever Echiichthys vipera dominating most of the offshore sandbanks. However, there was no significant difference in species diversity (Hill's N1) (P > 0.05) throughout the continental shelf. The brown shrimp Crangon crangon and sand goby Pomatoschistus minutus dominated most of the inshore sandbanks. Species density and biomass also followed the inshore-offshore gradient, with the density decreasing from 980.9 individuals/1000 m² ± 1.6 S.E in Oostende bank to only 15.0 individuals/1000 m² ± 1.2 S.E in Noordhinder bank. The epibenthos of the Belgian continental shelf was primarily grouped into offshore (Hinder banks) and inshore (Flemish sandbanks ) communities with the transition zone of the Zeeland banks in between. Temperature and depth were the major descriptors of the community boundaries, with the former dividing the Flemish banks into winter and autumn groups. Median grain size also showed some influence on the community assemblages. The general level of species diversity in the continental shelf, was relatively low compared to what is reported for the entire North Sea. It is important to emphasize that the community pattern in the continental shelf would be better assessed from a more elaborate amount of data preferably by considering diurnal effects on the efficiency of the beam trawl. A complementary study on the trophodynamics of the benthic community of the continental shelf would certainly allow a better community mapping.
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