No abstract

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

ZOHLKE, R. & BLOME, D. & VAN BERNEM, K. H. & DITTMANN, S. (1998): Effects of the tube building polychaete Lanice conchilega (PALLAS) on benthic macrofauna and nematodes in an intertidal sandflat. -Senckenbergiana marit., 29 (1/6): 131-138, 4 figs., 2 tabs.; Frankfurt a. M.] Biogenic habitat structures playa major role for distribution pattems of benthic fauna. Tube-dwelling polychaetes provide one of the main features in the otherwise re[atively low structured sandy intertidal. The airn ofthis study was to investigate the effect of the tube-dwel[ing sand-mason Lanfce conchilega on macrofauna and nematodes in an intertidal sandflat in the Wadden Sea area offthe German coast. Field smdies and experiments were carried out on the associated macrobenthic fauna of natural L. concbilega aggregates and of artificial tubes. Furthermore, the distribution of nematode species at increasing distances along transects arising from individual L. conchilega mbes, was investigated.Natural as well as artificial tubes had positive effects on numbers of macrofaunal species and individuals. Yet, juvenile Mya arenaria were the only species appearing in higher numbers in both L. conchilega aggregates and artificial tube fields. They used the tube structure to attach themselves with their byssus threads. The polychaete Malmgrenidla lunulata only occurred in natural L. conchilega aggregates and was ofien found inside the polychaetes' tubes. It is possibly a commensal associated to L. conchilega. In artificial mbe fiel&, opportunistic spionids and Capitella capitata settled in higher numbers. This might be due to colonisation ofsediment accumulating in the tube fiel&, utilisation of the tubes as an attachment sufface or refuge from predation. However, two predatory polychaetes, Eteone Ionga and Nereis diversicolor, were also found in higher abundance in natural or artificial tube fields.Nematode abundances were considerably higher next to ~ndividual L. conchilega tubes ata distance of 0.5 cm. This distribution was mainly caused by a group ofthreadlike species with a thin cuticle, which are thought to be adapted to epidermal uptake of dissolved organic matter.Ir is suggested that there might be a linkage between predatory polychaetes and the distribution partero found for nematodes around the tubes ofL. concbilega.