Taxonomy, biogeography and ecology of Quaternary benthic Ostracoda (Crustacea) from circumpolar deep water of the Emerald Basin (Southern Ocean) and the S Tasman Rise (Tasman Sea)

Abstract

Benthic Ostracoda were recovered from 19 box core samples collected during the cruise SO 136 of the German R/V SONNE in the Tasman Sea and Southern Ocean (SW Pacific sector). The detailed taxonomic study of more than 10.000 specimens recovered from eleven box-corer samples from circumpolar deep water of the Emerald Basin (Southern Ocean) and the S Tasman Rise (Tasman Sea) led to the recognition of 34 genera and 63 species, of which 9 new to science. Additionally, ten key cosmopolitan and endemic taxa were re-studied and re-illustrated from type material from the Natural History Museum (London), the Utrecht Micropaleontological Collection, the Senckenberg Museum (Frankfurt) and the University of Canterbury (New Zealand). Oxygen and carbon isotopic values were measured on specimens from 17 samples from the Campbell Plateau and the S Tasman Rise. In particular, four podocopid ostracod genera were analysed: the infaunal Krithe and the epifaunal Fallacihowella, Poseidonamicus and Bradleya. The stable isotopes proxies provided useful indications about the microhabitats, the diets and the temperature sensitivity of each taxon. Additionally, different calcification rates and different microhabitats were claimed to explain the different isotopic signature of adults and juveniles of Krithe. Statistical analyses were performed on the relative abundance i n percentages of 73 species identified in 19 sediment samples. Both species (R-mode) and samples (Q-mode) were grouped by cluster analyses and detrended correspondence analyses (DCA) using the software package PAST (ver. 0.94). Q-mode cluster analyses partially supported the obser vations made by previous authors that the ostracod specific thresholds are controlled by the water mass characteristics. Q- and R-mode detrended correspondence analyses, on the contrary, indicated that distribution patterns must be driven by factors other than the water mass characteristics. Seven assemblages are recognised and the characteristic or most abundant species are discussed for their ecological demands. Bottom topography, sediment type, CaCO3 content, and flux of organic carbon interplay with the water mass characteristics creating a complex network of ecological gradients. Within each of the identified assemblages the species specific thresholds are not identical and often the range of the ecological gradients of the most abundant species do not include that of the characteristic species. Most likely, dynamics of co-occurring species take place which could involve Ostracoda and other benthic animals belonging to the same trophic groupings.