Fram Strait Polychaeta (IPOE), 1994-1995

The macrobenthic fauna of the East Greenland continental margin was investigated between 74 N and 82 N in summer and autumn 1994 and 1995 with a main emphasis on polychaetes. A major goal was to describe the community structure (distribution, composition, diversity, abundance, biomass) in relation to environmental factors. Samples were collected during two expeditions with RV ‘Polarstern’ in July 1994 (ARK X/1) and September/October 1995 (ARK XI/2) with a giant box corer and a multiple corer. Stations were located on two down-slope transects across the continental shelf break at 75 N (200 to 2700 m depth) and at 79 N (200 to 2000 m depth) and at latitudinal transect at 2000 m depth between 79 N and 80 30'N. In total 33 box corer samples (0.0625 m2) and 4 multicorer samples from 15 positions were analysed. For analysis of vertical distribution of macrofauna in the sediment, samples were divided into two layers (0–1 cm, 1–6 cm). Macrofaunal abundance was assessed, biomass was estimated by wet weight and biometric modelling. Additionally, sediment properties like grain size, Corg content and C:N ratio were analysed. Macrofauna samples included Porifera, Brachiopoda, Sipunculida, Nemertini, Priapulida, Aplacophora, Bivalvia, Gastropoda, Polychaeta, Acari, Crustacea, Ophiuroidea and Holothuroidea. For Polychaeta, 81 species were identified. At the shelf stations (200 to 400 m) mean macrobenthic abundance (biomass) was 5673 ind. m-2 (0.55 g C m-2), at mid-slope stations (800 to1400 m) 2047 ind. m-2 (0.20 g C m-2) and at deep-sea stations (2700 m) 1800 ind. m-2 (0.13 g C m-2). Macrofaunal abundance and biomass values were in the same order of magnitude as those from other continental margins and revealed an exponentially decrease with increasing water depth. There was no general correlation between community patterns and sediment parameters like grain size, Corg content, C:N ratio or chl a content. The macrofaunal organisms were concentrated to the upper centimeter of the sediment. This layer accounted on average for 66 % of total abundance and 48 % of total biomass. Vertical distribution patterns of animals reflected life strategy and food supply to the benthos. The polychaete community consisted mainly of Atlantic faunal elements and was characterized by a low number of species. Species diversity decreased with increasing depth and was low compared with more temperate areas. Multivariate statistics revealed a depth zonation with 3 distinct polychaete assemblages at shallow (200 to 400 m), mid-slope (800 to 1400 m) and deep-sea stations (> 1400 m) for the two down-slope transects along 75 N and 79 N. On the continental shelf between 74 N and 79 N the assemblages were rather similar in composition. With increasing water depth the similarity between the transects decreased. Stations from the latitudinal transect at 2000 m depth were rather different from the stations at the down-slope transects. A correlation analysis showed that the structure of the polychaete assemblages was mainly related to water depth. However, not depth per se but depth-dependent factors like hydrography, food input and sediment structure are thought to be most important. The regional patterns of community structure at the East Greenland continental margin can be explained by the large-scale hydrography and the temporal and spatial heterogeneity of particle sedimentation.