The impacts of climate change on Antarctic nearshore mega-epifaunal benthic assemblages in a glacial fjord on King George Island: Responses and implications

We examined the impacts of climate change on Antarctic nearshore marine benthic communities on the West Antarctic Peninsula, one of the most rapidly warming regions on earth. We surveyed the epibenthic megafaunal assemblages of Marian Cove, a representative fjord on King George Island. We collected specimens by SCUBA diving at varying distances from the retreating glacier front during the 2013/2014 austral summer. Based on presence/absence data from the collected taxa, we determined species richness (S), taxonomic distinctness (TD) and functional diversity (FD) and further analyzed differences in assemblages in relation to environmental characteristics. Faunal assemblages in the inner cove (ice-proximal zone) were compositionally distinct from those in the outer cove. Species number and FD were also lower in the inner cove and tended to increase toward the outer cove. Nonetheless, TD values were similar among sites, indicating that all sites were distinct taxonomically. This may be because glacier retreat affected organisms of lower taxonomic levels the most. Multivariate and univariate analyses demonstrated that these differences were significantly related to distance from the glacier, substrate grain size, and organic content. The high correlation (R = 0.909, P < 0.01) of assemblages with distance from the glacier front suggests that physical disturbance by ice is a major process shaping benthic communities. Thus, we provide evidence that glacier retreat and its consequent processes impact the structure and function of communities. With their spatial pattern significantly associated with environmental suites, nearshore megabenthic communities respond sensitively and measurably to climate-induced impacts, suggesting their utility as long-term biomonitors. As a small but confined glacial cove with very distinct environmental gradients related to climate-induced processes, Marian Cove could serve as a model ecosystem for assessing climate impacts on Antarctic nearshore benthic communities.