Benthic community response to iceberg scouring at an intensely disturbed shallow water site at Adelaide Island, Antarctica

Abstract

Disturbance is a key structuring force influencing shallow water communities at all latitudes. Polar nearshore communities are intensely disturbed by ice, yet little is known about benthic recovery following iceberg groundings. Understanding patterns of recovery following ice scour may be particularly important in the West Antarctic Peninsula region, one of the most rapidly changing marine systems on Earth. Here we present the first observations from within the Antarctic Circle of community recovery following iceberg scouring. Three grounded icebergs were marked at a highly disturbed site at Adelaide Island (-67 degrees S) and the resultant scours were sampled at <1, 3, 6, 12, 18 and 30 to 32 mo following formation. Each iceberg impact was catastrophic in that it resulted in a 92 to 96% decrease in abundance compared with reference zones, but all post-scoured communities increased in similarity towards 'undisturbed' assemblages over time. Taxa recovered at differing rates, probably due to varying mechanisms of return to scoured areas. By the end of the study, we found no differences in abundance between scoured and reference samples for 6 out of 9 major taxonomic groups. Five pioneer species had consistently elevated abundances in scours compared with reference zones. Variability between the reference zones was high and scour assemblages became comparable to those at reference zones after just 12 mo of recovery. The study site is intensely disturbed by icebergs and the relatively simple infaunal community is well adapted to recover rapidly from disturbance events. Water movements induced by wave action and iceberg groundings at the site are likely to advect small fauna into newly formed scours and promote recovery.