Environmental characteristics of the South Shetland Islands Archipelago (Western Antarctic) that promote the occurrence of pelagic amphipod Themisto gaudichaudii

Themisto gaudichaudii belongs to the pelagic amphipods which can be very abundant in the Antarctic waters and can be an important food source for many Antarctic predators. T. gaudichaudii is generally associated with relatively warmer, ice-free waters, although it may co-occur with Euphausia superba and can also occur at low densities in colder regions. Over the past few decades, Antarctic krill has been declining in some regions of the Southern Ocean, which may lead predators to seek alternative food sources. Due to the tendency of Themisto species to occur in aggregations and at high densities, these species may represent such an alternative. However, detailed studies on the ecology of this crustacean are still lacking. The present research was carried out during the expedition PS112 on R/V Polarstern in 2018 in the vicinity of Elephant Island, Weddell Sea, South Shetland Islands, and in the Bransfield Strait from March to May. The average recorded abundances of T. gaudichaudii were high in the areas under the direct influence of Antarctic Circumpolar Current, and the highest abundances were observed in the Elephant Island region, probably due to its location and unique hydrological conditions. The population was dominated by juveniles presumably because the samples were collected after the spawning period.