Polychaete assemblages on the Magellan and Weddell Sea shelves: comparative ecological evaluation

Similarities between the soft-bottom polychaete assemblages on either side of the Drake Passage and spatial patterns of these assamblages were analysed based on data from 273 corer samples collected in the Magellan region (42 to 55° S, 254 m mean water depth) and on the Weddell Sea shelf (70 to 71° S, 263 m mean water depth). Paraonidae, Ampharetidae and Maldanidae were the most abundant families in the Magellan region, while in the Weddell Sea, Syllidae, Terebellidae and Spionidae were most abundant. The total species number found in the Magellan region (199) was higher than in the Weddell Sea (163), and significantly higher values of heterogeneity diversity, species richness and density were found in the Weddell Sea. At most of the Weddell Sea stations, all 3 trophic guilds (suspension feeders, detritus feeders and predators) were present, whereas suspension feeders were almost absent in the Magellan samples. The species abundance distribution showed a high number of species represented by only 1 specimen in both regions. This causes low dominance and similar high values of evenness in both regions. We suggest that the polychaete assemblage structures in both regions are influenced by environmental stress through ice and the physical complexity of the areas, which results in many different habitats.