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

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 South Sandwich Islands Marine Protected Area. However, under a context of major changes in the Antarctic region due to climate change, the biodiversity of the archipelago remains poorly studied. Here we used predators as biological samplers to study the bathyal communities of SSI. A total of 61 species including fish, cephalopods, crustaceans, were identified from the diet of 13 predators (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 vertical range increased. Fifteen fish and one crustacean appear to have SSI as the limit of their distribution. Community analysis found two major groups at SSI, one at north and one at south, with the southern group subdivided into two groups. This separation is related with 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) correlated with the communities’ dissimilarities. 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 the occurrence of non-native species and could lead to local extinction of some species exclusively found in the southernmost areas of the archipelago.