Evolution of Antarctic biodiversity in the context of the past: the importance of the Southern Ocean deep sea

Abstract

Present day Southern Ocean benthic biodiversity is the result of climatic changes based on the break-up of Gondwana in the Cretaceous and the Cenozoic and the physiological potential of the fauna to cope with the climatic deterioration. Though many taxa survived the thermal drop in ocean bottom temperatures, zoogeographic ranges changed and some faunal elements even became extinct, e.g. benthic decapods and teleost fish, opening up new ecological niches and the potential for enormous adaptive radiations within some taxa, like the amphipods and isopods (peracarid crustaceans) and notothenioid fish. Ice-sheet extensions and retreats might have enhanced speciation processes as well as eurybathy. Biodiversity on the Antarctic shelf is high within the polychaetes, molluscs, and echinoderms, and within the amphipods and isopods possibly due to the Cenozoic extinction of the benthic decapods. Moreover, some shelf areas are characterized by accumulations of large suspension feeders like poriferans, bryozoans, ascidians, gorgonians, and hydroids. Palaeoclimatic changes also caused that many taxa of the modern, present day Southern Ocean benthic organisms are characterized by gigantism, slow metabolism, longevity, and a reduced number of offspring combined with late maturation. However, our biological knowledge is mainly confined to Southern Ocean shelf organism; we do not know much about the composition, biodiversity and zoogeography of the Southern Ocean deep sea animals. On this background the deep sea expeditions ANDEEP were born and the background and first results of these are presented herein.