Respiratory responses of three Antarctic ascidians and a sea pen to increased sediment concentrations

Glacial retreat and subglacial bedrock erosion are consequences of rapid regional warming on the West Antarctic peninsula. Sedimentation of fine grained eroded particles can impact the physiology of filter feeding benthic organisms. We investigated the effect of increasing concentrations of sediment on the oxygen consumption of suspension feeding species, the ascidians Molgula pedunculata, Cnemidocarpa verrucosa, Ascidia challengeri, and the pennatulid Malacobelemnon daytoni in Potter Cove (South Shetland Islands, Antarctica). In A. challengeri and C. verrucosa oxygen consumption increased gradually up to a critical sediment concentration (Ccrit) where species oxygen consumption was maximal (Omax in mg O2 g-1 dm d-1) and further addition of sediments decreased respiration. Ccrit was 200 mg L-1 for A. challengeri (Omax of 0.651 ± 0.238) and between 100 and 200 mg L-1 for C. verrucosa (Omax of 0.898 ± 0.582). Oxygen consumption of M. pedunculata increased significantly even at low sediment concentrations (15-50 mg sediment L-1). Contrary to the ascidians, sediment exposure did not affect oxygen consumption of the sea pen. The tiered response to sedimentation in the four species corroborates recent field observations that detected a reduction in abundance of the sensitive ascidian Molgula pedunculata from areas strongly affected by glacial sediment discharge, whereas sea pens are increasing in abundance. Our investigation relates consequences (population shifts in filter feeder communities) to causes (glacial retreat) and is of importance for modelling of climate change effects in Antarctic shallow coastal areas.