Megabenthos habitats influenced by nearby hydrothermal activity on the Sandwich Plate, Southern Ocean

The Sandwich Plate is known as one of the tectonically most active regions in the Southern Ocean and Antarctica, characterised by a subsurface chain of active volcanic islands (the South Sandwich Arc), submarine volcanic features, an earthquake rich area along the South Sandwich Trench and hydrothermal vents on segments of the East Scotia Ridge. In 2013 and 2019 we investigated eight potential hydrothermally active sites in the forearc, island arc and back arc of the Sandwich Plate from shallow (60 m) to abyssal (3886 m) depths. All Protector Seamounts sites, Protector Shoal, Quest Caldera, and an unnamed submarine volcano, showed thermal anomalies, as did the East Scotia Ridge segment E5 back arc site. At Quest Caldera, chimney structures, bacterial mats and mineral precipitates were observed in a depression on the caldera rim. The investigated forearc sites showed hydroacoustic, but not temperature anomalies. None of the sites showed evidence of megafauna associated with hydrothermal venting or hydrocarbon seep sites, but did have evidence of both unexpectedly dense and sparse communities of Southern Ocean taxa in the vicinities of the anomalies. Overall, our investigations showed that the benthic habitats and communities of the Sandwich Plate are still barely known.