Deep-sea isopod biodiversity, abundance, and endemism in the Atlantic sector of the Southern Ocean—Results from the ANDEEP I–III expeditions

Three expeditions were performed in the framework of ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonisation history and recent community patterns) in order to understand the Southern Ocean (SO) biodiversity of the Isopoda and to investigate faunal connections with other deep-sea areas in the world oceans. We sampled mainly in the Atlantic sector of the SO (Drake Passage along the Shackleton Fracture Zone, off Elephant Island, in the South Shetland Islands area, in the northwestern Weddell Sea, and at the South Sandwich Islands), but also took two stations in each Bellingshausen Sea and Cape Basin.In total, three expeditions yielded 13,046 specimens of Isopoda. During ANDEEP I–II 5525 specimens and 317 species of Isopoda were sampled, and 7521 specimens and 496 species were discriminated from the ANDEEP III material. Overall, Isopoda comprised 35% of all Peracarida sampled, and we identified 674 isopod species from the 40 deep SO stations. Eighty-nine of these species (13%) were known, the others (585 species) were new to the area, and most of these were new to science, 43 genera being recorded for the first time. Asellota comprised 97% of all ANDEEP Isopoda, and Munnopsidae were the most dominant family, followed by the Desmosomatidae, Haploniscidae, and Ischnomesidae. To our present knowledge 87% of the SO deep-sea Isopoda are apparently “endemic”. Most species did not occur frequently in the samples. Abundance was higher at the shallower ANDEEP stations and highest in the Powell Basin at station 133, and generally decreased with increasing depth. Species richness was highest with 92 species at the bathyal station 80-9 in 3100 m off Kapp Norvegia, in general, species richness was highest at around 3000 m depth with 216 species found at all ANDEEP stations, and 92 species sampled at a single station in 3100 m depth.The cluster analysis of the isopod composition from ANDEEP revealed in general terms that the abyssal Weddell-Sea stations build one cluster. Depth turned out to be the most important abiotic factor for the species composition reported. Most of the species frequently occurring at the abyssal stations are Munnopsidae, which can swim.The SO deep sea differs in faunal composition from the shelf, and few isopod species occur at many stations, while most species only occur at few. The reasons for these findings are unknown. Future studies should focus on the functional role of the frequent species of the SO deep-sea ecosystem and food-web.