Drift Algal Accumulation in Ice Scour Pits Provides an Underestimated Ecological Subsidy in a Novel Antarctic Soft-Sediment Habitat

SIMPLE SUMMARY: Whereas several studies have documented the destructive effects of ice scouring on the seabed and its strong role in structuring benthic communities in Antarctica, none have highlighted the potential of seabed furrows (i.e., “ice pits”) produced by this disturbance as a novel habitat that is created by the accumulation of drift algae. This work documents the distribution and dimensions of ice pits to evaluate their relationships with the biomass and species composition of the accumulations of drift algae within them. Moreover, the temporal dynamics of algal deposition and advective loss in ice pits over time are assessed. These investigations show that ice pits provide hitherto underestimated ecological subsidies of food and shelter for other benthic organisms. Further research is needed to better understand the role of ice pits in the overall functioning of Antarctic marine benthic ecosystems. ABSTRACT: Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m(2)) that would otherwise be transported to deeper water accumulate inside these features, representing an underestimated subsidy. Our work documents the distribution and dimensions of ice pits in Fildes Bay, Antarctica, and evaluates their relationship to the biomass and species composition of algae found within them. It also assesses the rates of deposition and advective loss of algae in the pits. The 17 ice pits found in the study area covered only 4.2% of the seabed but contained 98% of drift algal biomass, i.e., 60 times the density (kg/m(2)) of the surrounding seabed. Larger ice pits had larger and denser algal accumulations than small pits and had different species compositions. The accumulations were stable over time: experimentally cleared pits regained initial biomass levels after one year, and advective loss was less than 15% annually. Further research is needed to understand the impacts of ice scouring and subsequent algal retention on ecosystem functioning in this rapidly changing polar environment.