Recolonization of soft-sediment ice scours on an exposed Arctic coast

Ice scour is the most disruptive and widespread physical disturbance that naturally affects the coastal benthos in polar waters, where it creates a mosaic of disturbances in various stages of recolonization. The purpose of this study was to (1) determine the timing and sequence of biotic recovery following ice scour disturbance of soft sediment and (2) test the general hypothesis that ice scour increases biotic diversity in high-latitude benthic communities. The study area was a 6.6 km length of Barrow Strait along the exposed coast of Cornwallis Island in High Arctic Canada. Corecollected (0.0075 m2) macrofauna (≥0.5 mm) inhabiting 19 scours at 12 to 28 m depth were sampled during open water in August of 1991 to 1996 and again in 1999. We repeat-sampled 2 scours for 6 summers, 3 scours for 3 summers, and 2 for 2 summers, while the other 12 scours were sampled once. Sampling was severely limited by availability of open water which was constrained by frequent invasion of the study area by drift ice. Young ice scours were refugia for the dorvilleid polychaete Ophryotrocha spatula. Its numbers declined precipitously as the scours aged. Other early colonists maintained or increased their abundance. Most of the later colonists significantly increased in abundance as the scours aged despite the presence of the early colonists. Abundance, biomass and species richness increased progressively with scour ageing but did not significantly exceed that in the unscoured community. Thus, although the scours differed from the unscoured reference community in species composition, they were not havens for species-rich or highly different assemblages (at least not among core-collected macrofauna). Recolonization of ice scours ≤9 yr old fitted a linear model. Assuming that further colonization would continue to be linear, the 2 scours monitored the longest had achieved 65 to 84% recolonization by Ages 8 to 9. The unscoured reference community was significantly more diverse, massive and abundant where disturbance was a chronic but infrequent occurrence, compared to where it was protected from ice scour by an offshore rise. Thus, ice scour appears to have a positive effect on the benthos of this coast.