What inhabits the South Sandwich Islands deep-sea? Biodiversity and biogeography of bathyal communities using predators as biological samplers

Understanding the biodiversity of an ecosystem is crucial to determine its structure and resistance to climate change. The South Sandwich Islands (SSI) are located in the Scotia Sea (Southern Ocean), within the South Georgia and the South Sandwich Islands Marine Protected Area. However, the biodiversity of the archipelago remains poorly studied, whilst climate change has the potential for wide-ranging impacts in the Antarctic and Subantarctic regions. Here we used predators as biological samplers to study the bathyal communities of SSI. A total of 61 species including fish, cephalopods and crustaceans, were identified from the diet of 13 predatory taxa (11 fish and two cephalopod). Common Subantarctic and Antarctic species were found, with Moroteuthopsis longimana being the species with the highest density (1.74 individuals per stomach at Montagu Island). Eleven fish and one cephalopod species were recorded for the first time at the archipelago. Furthermore, 16 fish species had their bathymetric range increased. Fifteen fish and one crustacean appear to have SSI as the northern or southern limit of their distribution. Community analysis found two major groups at SSI, one in the north and one in the south, with the southern group subdivided into two groups. This separation is related to the environmental conditions at the archipelago that abruptly change at Saunders Islands. Latitude (correlated with sea surface temperature) and sea surface height (proxy for upwelling) both correlated with the dissimilarity between communities. These results suggest that climate change may affect the biodiversity at SSI in the future as warming waters of the Scotia Sea and changes in the upwelling system may favour range extensions of more northerly species into the archipelago. Furthermore, it could lead to local extinctions of some species exclusively found in the southernmost areas of the archipelago.