Dropstones On A Glaciated Continental Shelf As Key Habitat, Sabrina Shelf, East Antarctica

Glaciated margins on the Antarctic continental shelf comprise a mixture of substrate types, with areas of hard bedrock exposed by glacial erosion, glacial diamict deposits comprising mixed clasts, and dropstones deposited during ice sheet retreat and iceberg melt. Soft sediments accumulate in deeply eroded glacial troughs and depressions. Seabed substrates clearly delineate benthic habitats on the Sabrina Coast shelf, with significant increases in taxa diversity, abundance, and biological cover observed on hard substrates such as dropstones and areas of exposed bedrock, compared to soft substrates. Some taxa, including the hexactinellid sponge Anoxycalyx joubini, branching hydrocorals, several gorgonians, and colonial ascidians, were found only in areas of hard substrates. The largely random distribution of dropstones across glaciated shelves creates fine-scale habitat heterogeneity that is important not only for the distribution of the seafloor biota, but also for their dispersal.