Vertical distribution of pelagic polychaetes in the Bransfield Strait and northwestern Weddell Sea in austral summer of 2022

Despite the wide distribution of holopelagic polychaetes, very little is known about their ecology and role in communities, particularly their vertical patterns. Data on pelagic polychaetes from the Southern Ocean are especially scarce. The aim of our study was to address both issues. The pelagic polychaete taxocene was sampled at 30 stations in the West Antarctic with different gears. A 5-net Multinet was used at 18 stations to study vertical structure; qualitative gears with large mouth areas were used at all stations to obtain more complete faunistic information. The horizontal distribution of polychaetes had no correlation with water masses and was likely driven by seasonal succession. Although four groups of species were distinguished by the differences in their vertical distribution patterns, their common (and most notable) property was their complete absence in the uppermost water layer, down to the depth of 50–100 m. This layer corresponded to the chlorophyll a maximum. Based on the relation between the pelagic polychaete distribution and the dominant phytoplankton species group, we consider the latter to be one of the main drivers of this pattern. Vertical profiles of polychaete abundance and species number at deep-water stations had relatively uniform shapes. At the same time, vertical profile shapes in shallow waters varied greatly, apparently reflecting the more diverse conditions and finer scale heterogeneity of the neritic zone environment.