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

Abstract

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 increa- sing concentrations of sediment on the oxygen con- sumption 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 O2g-1dm day-1) and further addition of sediments decreased respiration. Ccrit was 200 mg L-1 for A. challengeri (Omaxof 0.651 ± 0.238) and between 100 and 200 mg L-1for C. verrucosa (Omaxof 0.898 ± 0.582). Oxygen consumption of M. pedunculata increa- sed 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 the abundance of the sensitive ascidian M. pedunculata from areas strongly affected by glacial sediment discharge, whereas sea pens are increasing in abundance. Our investigation relates conse- quences (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.