ANTARCTIC FJORD BIODIVERSITY HOTSPOTS, SEAFLOOR ECOSYSTEM FUNCTION, AND RESPONSE TO CLIMATE CHANGE

Subpolar fjords with tidewater glaciers are warming rapidly in both the high Arctic and along the West Antarctic Peninsula (WAP). Arctic-fjord studies indicate reduced species richness and benthic faunal abundance, with steep declines from the open shelf to inner fjord basins as a consequence of high inner-fjord glacial sedimentation. Climate warming is predicted to reduce sedimentation in Arctic fjords, enhancing benthic community abundance/biodiversity. We use seafloor photosurveys, coring and stable isotope (delta-¹³C and delta-¹⁴N) analyses to show that, in contrast to the subpolar Arctic, inner-middle fjords along the WAP are hotspots of mega- and macrobenthic abundance and beta diversity; these hotspots appear to be sustained by spatial food-web subsidies from immigrating krill, and from macroalgal detritus cascading down fjord walls. We suggest that the WAP fjords support important ecosystem functions by providing seasonal habitat for krill and foraging baleen whales, and by maintaining regional benthic biodiversity. Currently, WAP fjords experience limited glacial sedimentation disturbance, and we speculate that climate warming will lead to enhanced glacial melt and sedimentation, “snuffing out” these WAP fjord hotspots by increasing burial disturbance and water-column turbidity. Because productivity/biodiversity hotspots such as WAP fjords can play disproportionate roles in the feeding and reproduction of mobile species (krill, baleen whales, juvenile fish) and in maintaining biodiversity in heterogeneous ecological landscapes, there is an urgent need for better understanding of the function and climate sensitivity of these WAP subpolar fjord ecosystems.