Diversity of the nematode communities in the Southern Bight of the North Sea

The nematode communities from 102 stations in the Southern Bight of the North Sea, sampled between 1972 and 1984, are examined. Overall, 456 species, belonging to 159 genera and 37 families were found. Sediment structure and chlorophyll a content were found to be determining environmental factors in the species composition of the nematode communities. Diversity is determined at different levels of the nematode community; i.e. species diversity of the whole community, species diversity of eight dominant families (Chromadoridae, Comesomatidae, Cyatholaimidae, Desmodoridae, Microlaimidae, Oncholaimidae, Thoracostomopsidae and Xyalidae), species diversity of the four feeding types, family diversity and trophic diversity within the whole community. The open sea stations are characterized by nematode communities which are comparable in terms of species diversity; the number of species S is about 30-35 per sample (sample size is about 100) with H' between 4.00-4.50 bits/ind. The communities in the coastal stations are less diverse (S=7-22); H'=1.4-3.5 bits/ind.). The stations along the Belgian east coast have communities with low diversity (S=7; H'=1.41 bits/ind.) and with a pronounced dominance of a few species (Simpson index=0.54); the diversity within the eight families is also very low. The relationship between environmental stability (or disturbance) and stability and diversity of the nematode communities can be explained by the following factors: habitat heterogeneity, food availability, productivity, density and population growth rates