Benthic hydroids (Cnidaria, Hydrozoa) from the Ross Sea (Antarctica) collected by the New Zealand Antarctic expedition BioRoss 2004 with RV Tangaroa

During the New Zealand BioRoss 2004 survey, with RV Tangaroa, sampling of marine communities on the Ross Sea shelf was undertaken. Samples were obtained employing several sampling gears (Van Veen grab, epibenthic sled, rough bottom trawl, and beam trawl). Among the numerous benthic samples obtained, a large and important collection of hydroids was present. Sixty-one species, four of them new to science (Monocoryne antarctica sp. nov., Halecium tangaroa sp. nov., Staurotheca gracilis sp. nov. and Symplectoscyphus densus sp. nov.) have been recorded. Oswaldella blanconae sp. nov. is also described. “Anthoathecata” are represented by ten species belonging to the families Bougainvilliidae, Candelabridae, Clathrozoellidae, Hydractiniidae, Eudendriidae and Tubulariidae. Leptothecata are dominant, with 51 species belonging to the families Campanulariidae, Campanulinidae, Lafoeidae, Haleciidae, Hebellidae, Kirchenpaueriidae, Schizotrichidae, Staurothecidae, Symplectoscyphidae and Zygophylacidae. Symplectoscyphidae is the richest family with 19 species (31%), followed by Staurothecidae with eight (13%) and Haleciidae with seven species (11%). At the generic level, Symplectoscyphus with 14 species (two of them identified only at the genus level), Staurotheca with eight species (one identified to genus level) and Halecium with seven species are the most speciose genera. Twenty-two species (including the four new species) constitute new records for the Ross Sea, thus raising the number of valid, known species of the area to 77.

Climatology and decadal variability of the Ross Sea shelf waters

The World Ocean Database 2001 data located in the Ross Sea (named WOD01 and containing data in this region since 1928) are merged with recent data collected by the Italian expeditions (CLIMA dataset) in the period November 1994-February 2004 in the same area. From this extended dataset, austral summer climatologies of the main Ross Sea subsurface, intermediate and bottom water masses: High Salinity Shelf Water (HSSW), Low Salinity Shelf Water (LSSW), Ice Shelf Water (ISW) and Modified Circumpolar Deep Water (MCDW) have been drawn. The comparison between the WOD01_1994 climatologies (a subset of the WOD01 dataset until April 1994) and the CLIMA ones for the period 1994/95-2003/04 showed significant changes occurred during the decade. The freshening of the Ross Sea shelf waters which occurred during the period 1960-2000, was confirmed by our analysis in all the main water masses, even though with a spatially varying intensity. Relevant variations were found for the MCDW masses, which appeared to reduce their presence and to deepen; this can be ascribed to the very limited freshening of the MCDW core, which allowed an increased density with respect to the surrounding waters. Variations in the MCDW properties and extension could have relevant consequences, e.g. a decreased Ross Ice Shelf basal melting or a reduced supply of nutrients, and may also be indicative of a reduced thermohaline circulation within the Ross Sea. Shelf Waters (SW) having neutral density γn > 28.7 Kg m-3, which contribute to form the densest Antarctic Bottom Waters (AABW), showed a large volumetric decrease in the 1994/95-2003/04 decade, most likely as a consequence of the SW freshening.

Macrobenthic communities of the north-western Ross Sea shelf: links to depth, sediment characteristics and latitude

In early 2004 the Victoria Land Transect project sampled coastal north-western Ross Sea shelf benthos at Cape Adare, Cape Hallett, Cape Russell and Coulman Island from 100–500 m deep. We describe the benthic macrofaunal assemblages at these locations and, to assess the use of seafloor sediment characteristics and/or depth measures in bioregionalizations, determine the extent to which assemblage compositions are related to measured differences in these factors. Percentages of fine sand and silt, the ratio of sediment chlorophyllato phaeophytin, and depth were identified as important explanatory variables, but in combination they explained only 17.3% of between-location differences in assemblages. Consequently, these variables are clearly not strong determinants of macrofaunal assemblage structure. Latitudeper sewas not a useful measure of community variability and change. A significant correlation between both number of individuals and number of taxa and sediment phaeophytin concentration across locations suggests that the distribution of the benthos reflects their response to seafloor productivity. A number of factors not measured in this study have probably influenced the structure and function of assemblages and habitats. We discuss the implications of the results to marine classifications, and stress the need to incorporate biogenic habitat complexity into protection strategies.