Spatial and temporal variation of coastal Ross Sea macrozoobenthos

Antarctic shallow-water communities are projected to undergo considerable changes in the coming decades due to the impacts of climate change on the prevailing environmental conditions. A clear understanding of these communities’ vulnerability to change requires that the current relationships between environmental conditions and species assemblages be well understood. The benthic environment of the Ross Sea is subject to constant changes, including but not limited to changes in ice formations, salinity, light intensity, food types and food availability. The aim of this study was to quantify the temporal and spatial differences in macrozoobenthos between four coastal sites within the Ross Sea and determine the impact these abiotic factors could have on macrozoobenthic ecology. The macrozoobenthic communities in four Ross Sea coastal sites (Cape Armitage and Cape Evans within the McMurdo Sound, and two sites within Terra Nova Bay, designated as Gondwana and Mario Zucchelli) were investigated, with multiple video transects taken from each site over the space of several years. Transects were taken at depths of 19 to 23 m, between late December and early January. 15 quadrats were selected at random for each of the transects, scaled to a size of 0.25 m². Cape Armitage had the highest species diversity (Simpson’s Diversity Index), while Mario Zucchelli had the lowest. Cape Evans and Gondwana shared a similar diversity. Cape Armitage was the most ecologically diverse, with most macrozoobenthos visible through the Cinachyra barbata spicule mat in evenly spaced clusters of diverse species. Cnidaria was the dominant phylum at Cape Armitage, while the remaining three sites were dominated numerically by two Echinoderms Odantaster validus and Sterechinus neumayeri, which were mainly observed on gravel and cobble substrates. Macrozoobenthos species composition varied significantly between all four locations (One-way PERMANOVA p >0.001). A SIMPER analysis showed that Echinodermata (S. neumayeri and O. validus) and Cnidaria (Alcyonium antarcticum and Artemidactis victrix) were the main drivers of these differences. Only the Mario Zucchelli site showed a significant temporal difference over time, and there the change was marginal (p = 0.048). The change was largely due to an increase/decrease in the density of the main urchin species (S. neumayeri) between sequential year sampling. When data from all sites were combined, the species composition varied significantly across substrates (Two-way PERMANOVA, p >0.001), though it was hard to determine the underlying substrate in Cape Armitage due to spicule mats. This research highlights the diverse benthic biota within the Ross Sea, and supports previous conclusions that assemblages are site-specific but rather stable over time. In terms of ongoing conservation and monitoring of the Ross Sea benthic environment, it points to the need for increased understanding of ecology in the Ross Sea for maintaining the diverse faunal communities found within the Southern Ocean