Distribution, diversity and abundance of epibenthic fauna in the North Sea

The assemblages of attached and freeliving epibenthic species in the North Sea are described, based on analysis of samples collected with a small beam trawl. Clustering of survey sites based on the presence or absence of atta ched species indicated chat three regions had characteristic assemblages: t he northern North Sea, the central North Sea from 55 to 57 degrees N and th e southern North Sea. Clustering of sites based on counts of free-living ep ibenthic species also revealed that the sites formed three major groups but these corresponded to regions in the north-east North Sea, the northern an d western central North Sea and the southern and eastern central North Sea. Species which contributed most to the similarity within and dissimilarity between groups were identified. The environmental factors which best accoun ted for the grouping of sites were depth, winter temperature and the temper ature difference between winter and summer for attached species and depth a nd the temperature difference between winter and summer for free-living spe cies. The species richness of attached and free-living epibenthic species w as higher in the central and northern North Sea than in the south. The numb er of abundant (Hill's N-1) and very abundant (Hill's N-2) free-living spec ies also increased from south to north.