Epibiotic assemblages on seaweeds in the German Wadden Sea (North Sea)

After detachment from benthic habitats, the epibiont assemblages on floating seaweeds undergo substantial changes, but little is known regarding whether succession varies among different seaweed species. Given that floating algae may represent a limiting habitat in many regions, rafting organisms may be unselective and colonize any available seaweed patch at the sea surface. This process may homogenize rafting assemblages on different seaweed species, which our study examined by comparing the assemblages on benthic and floating individuals of the fucoid seaweeds Fucus vesiculosus and Sargassum muticum in the northern Wadden Sea (North Sea). Species richness was about twice as high on S. muticum as on F. vesiculosus, both on benthic and floating individuals. In both seaweed species benthic samples were more diverse than floating samples. However, the species composition differed significantly only between benthic thalli, but not between floating thalli of the two seaweed species. Separate analyses of sessile and mobile epibionts showed that the homogenization of rafting assemblages was mainly caused by mobile species. Among these, grazing isopods from the genus Idotea reached extraordinarily high densities on the floating samples from the northern Wadden Sea, suggesting that the availability of seaweed rafts was indeed limiting. Enhanced break-up of algal rafts associated with intense feeding by abundant herbivores might force rafters to recolonize benthic habitats. These colonization processes may enhance successful dispersal of rafting organisms and thereby contribute to population connectivity between sink populations in the Wadden Sea and source populations from up-current regions.

Benthos fauna in the North Sea from 2 surveys in 1986 and 1987

During two surveys in the North Sea, in summer 1986 and in winter 1987, larger epibenthos was collected with a 2 m beam trawl. The distributions of the species were checked for average linkage by means of the JACCARD-index cluster analysis. In summer two main clusters can be recognized. These are situated to the north and to the south of the Dogger Bank. In winter two main clusters may be recognized as well, but these clusters divide the North Sea into a western and an eastern part. We conclude, that these differences of epibenthos characteristics are correlated with seasonal changes in water body distributions.

Selected Devonian/Carboniferous boundary profiles in the Sauerland area (Rhenish massif)

Selected sections, containing Devonian/Carboniferous boundary beds, are described from the northern and northeastern margin of the Rhenish massif, especially from the Seiler region near Iserlohn and the Warstein area. These sections are from prospecting trenches, quarries and road cuts. The dominantly carbonate sequences were investigated in regard to the development of conodonts. The Devonian/Carboniferous boundary could be placed precisely in both areas by means of the phylogenetic transition from Siphonodella praesulcata to S. sulcata. Compared investigations lead to the following conclusions: - The basal part of the Hangenberg limestone is heterochronous. - The Devonian/Carboniferous boundary lies distinctly below the Hangenberg limestone, i. e. at the same stratigraphical level as the Stockum limestone. - The Imitoceras limestone lens of Stockum and the Stockum limestone represent a special facies within the Hangenberg schists. 80th belong either to the praesulcata- and sulcata-zone or are restricted only to the sulcata-zone. - Protognathodus kuehni appears together with Siphonodella sulcata. Where S. sulcata is lacking, P. kuehni may be considered as a valid index conodont indicating the beginning of the Carboniferous. - The upper part of the Wocklum beds, following above the Wocklum limestone, usually consists up to the lower Carbonilerous boundary in a more or less consistent facies, that of the Hangenberg schists. Only in the section 01 the northeastern wall of the eastern Provincial Quarry at Drewer and in the road profile Rüthen - Nuttlar, the Devonian/Carboniferous boundary is to be placed in a continuous carbonate sequence. - The eastern Provincial Quarry at Drewer is therefore proposed as a new candidate section for the Devonian/Carboniferous boundary stratotype. - In many places the carbonates at the Devonian / Carboniferous boundary and the Hangenberg limestone are characterized by an impoverished conodont fauna. - Using platform conodonts, biofacies models are developed, permitting to conclude on the position of the respective setting 01 sedimentation area, either close to a rise or a basin.