Benthic macrofauna communities of the submersed Pleistocene Elbe valley in the southern North Sea

Abstract

Macrozoobenthic community structure was studied in two surveys along a transect of 13 stations following the submersed Pleistocene Elbe valley in the south-eastern North Sea during May to June 2000 and March 2001. Two replicates of bottom samples were taken with a van Veen grab of 0.1 m 2 sampling size. In order to analyse the benthic macrofauna communities, the animals obtained were identiWed and counted, and MDS and cluster analysis were performed. Out of 200 taxa identiWed, 84 were polychaetes, 46 molluscs, 40 crustaceans, 15 echinoderms, and 15 belonged to other groups. Mean abundance was 4,860 individuals per m 2 , mean biomass 32.9 g ash free dry mass per m 2 . Mean diversity was 1.76 and mean evenness 0.54. The macrofauna of the Pleistocene Elbe valley is composed of three associations according to the cluster analysis. Each association is described by a combination of characterizing and discriminating species. An Amphiura-brachiata·Tellimya-ferruginosa-association was found in the south-eastern part of the depression, whereas a transitional association with elements of both assemblages lead to an Amphiura-Wliformis·Galathowenia-oculata·Nuculoma-tenuis-association in the north-western part of the valley. In the context of the entire southern North Sea, both associations are small-scale substructures, and as such are contained in the Nucula-nitidosa-community and the Amphiura-Wliformis-community, respectively. A northwestward shift of the community of the southern Elbe valley was found and discussed as a possible consequence of warm winters of the last decades.

Introduction to the Assessment—Characteristics of the Region

“…Total macrobenthic biomass decreases northward from 51.5°N while biodiversity and density increase (Heip et al 1992). Rehm and Rachor (2007) also showed benthic biomass to decrease with distance from the coast. According to Heip and Craeymeersch (1995), northern species of the macrobenthic community extend southward to the northern slope of Dogger Bank and southern species extend northward to the 100 m depth contour.…”