Investigating the influence of sea ice cover on benthic community and trophic structure

The extent of Antarctic sea ice has decreased rapidly since 2014, reaching a record low of 10.7 × 106 km2 in 2017. The duration and extent of sea ice cover are directly linked to primary production and the subsequent vertical transfer of organic matter to the deep sea. Through this close benthic-pelagic coupling, climate-driven variability in the upper ocean can therefore be expected to directly impact benthic macrofaunal community composition and diversity. To investigate the impact of sea ice cover and primary productivity on community structure, food sources and trophic levels of benthic macrofauna, benthic sampling and experimentation was carried out at 4 stations in the Weddell Sea along a gradient of sea ice cover and primary productivity. Here, community structure parameters (abundance and biomass) were compared between the station with the longest (station 6) and shortest (station 38) period of ice coverage (>50%). Both abundance and biomass were significantly higher at station 38. Polychaetes were more dominant at station 38 and together with larger bivalve specimens strongly contrasted the more varied taxonomic distribution at station 6. In addition, the expected identification of decreasing levels of biomass and abundance with increasing sediment depth were confirmed. Furthermore, stable isotope signatures (δ13C and δ15N) and community parameters were compared between station 6 and the Prince Gustav Channel (PGC). Overall, the benthic community at the PGC was dominated by polychaetes, attributed to higher productivity levels benefiting polychaete families, particularly the Maldanidae family. This pattern of polychaete dominance in terms of biomass and abundance was not as pronounced for station 6. The depleted δ13C and δ15N signatures at the PGC demonstrate the increased variation in food sources utilised at the PGC, including the possibility of a chemosynthetic and/or terrestrial input in the area. The polychaete family Cirratulidae, in particular, showed a significantly higher δ13C signature. As a result of climate variability it is to be expected that the identified community shift of increasing biomass and abundance as well as changing taxonomic distributions and stable isotope signatures with varying sea ice cover will be more pronounced in the future. This study provides a baseline for how benthic polar macrofaunal communities will change in response to increasing open water conditions.