Epibenthic diversity in the North Sea

In 1999 the epibenthic fauna of the North Sea was investigated using the 3rd quarter 'InternationalBottom Trawl Survey' of five European countries. Altogether 241 stations were sampled covering 143 ICES rectangles.The objectives of the project were (i) to analyse epibenthic diversity patterns in the North Sea,(ii) to identify the spatial distribution of faunal communities and (iii) to relate environmentalfactors as well as fishing effort to species diversity.Epibenthic fauna was clearly divided between the southern North Sea and the centralnorthernNorth Sea, roughly along the 50 m depth Iine. The separation was based on an overallhigher number of species in the central and northern North Sea anda change in the speciescomposition from north to south.Sessile fauna including erect, branching species like bryozoans and hydrozoans were particularlydiverse along a corridor in the central-northern North Sea between 56 ~ and 58~ coincidingwith the area between the 50 m and 100 m depth line. Cluster analysis, based on the structure ofthe community, confirmed the north-south gradient found for species diversity. Separation ofclusters was driven to a great extent by species occurring predominantly or exclusively north ofthe 50 m contour line. Few species were exclusive to the south, but a number of scavengingspecies were found here more frequently and in higher numbers.Depth was positively correlated with the diversity of free-living fauna, whereas the type ofsediment showed no significant relationship with variations in numbers of species. Beam-trawlingeffort was negatively correlated with the diversity of sessile fauna