The structural and functional diversity of the shallow-water benthic community at Cape Evans

The biodiversity of the seafloor community at Cape Evans was investigated to determine the structural and functional diversity of the benthic community and resurveyed over several seasons to assess year to year variability (01-09). A minimum of three sites, separated by at least 50m and accessed through separate dive holes were surveyed. Two 20m transect lines were laid on the seafloor within the 15-25m depth stratum starting from haphazardly chosen starting points. The transects were videoed using a diver-held digital video camera at a fixed height of (a) 70cm above the bottom (for the broader scale analysis of habitat structure) and (b) 40cm above the bottom (to allow for more accurate species identifications). Along one of the 20m transects, core samples were collected from five randomly chosen positions. At each position, two small sediment cores (20mm diam., 50mm deep) were collected, one to determine sediment grain size and benthic chlorophyll a content and one to determine the natural stable isotope signature of the sediment. Also at each position, one large core (70mm diam., 100mm deep) was collected to estimate the abundance and diversity of the benthic macrofauna. Additional collections include: a) three surface sediment scrapes to determine the species composition of microalgae, b) three individuals of each of the numerically dominant epibenthic species, for growth measurements and to determine the stable istope signatures and c) additional specimens of animals and plants and organic material (eg seal gaeces) for isotopic analysis to provide a more complete picture of the trophic structure of the community. Algae on the undersurface of the sea-ice were sampled to determine their isotopic signature using five small cores (20mm diam., 100mm deep). Another 9 cores were obtained for the determination of chlorophyll a and species composition of sea-ice algae. Video sampling was stratified by habitat and additional footage was taken of biota in the study area for a general picture of the site. Physical background variables (sea-ice conditions, light colour and intensity) were measured at 15m depth and water currents estimated. In the 03-04 season sediment traps, fluorometers and light meters were installed between depths of 15-25m. The sediment trap arrays were deployed at depths of 15, 20 and 25m. Each array consisted of three replicate tubes which were recovered the following season and analysed for algal species composition, relative abundance, total biomass and pigments to ascertain the relative contribution of phytoplankton and ice-algae as potential food sources for benthic invertebrates. Additional samples of ice algae were collected to compare and add to the list of ice algae taxa. The fluorometer were installed to measure temperature and water column chlorophyll fluorescence. It was deployed at 20m depth and programmed to measured phytoplankton chlorophyll fluorescence every two hours. Light sensors and data loggers were installed to record changes in photosynthetically available radiation (PAR). In the 04-05 season, sea urchins Sterechinus neumayeri were collected over a range of depths and analysed gut contents and size-frequency. In all seasons, the site was resurveyed using the above diver-held video camera. The site was resurveyed in the 2005-06 and the 2008-09 field seasons.