Ice scour disturbance to benthic communities in the Canadian High Arctic

Seabed scouring by ice is a large-scale disturbance to polar coasts. Grounding ice modifies seabed topography, reworks the sediment, and ploughs and crushes the seabed biota. The effects of ice scour on soft-sediment benthos were examined in Barrow Strait in High Arctic Canada. Due to the variability of ice keel depths in this area, the Barrow Strait coast was found to exhibit a gradient of ice scour disturbance to 30 m depth. The inshore shallows were highly scoured by the abundant shallow draft ice. Deeper water scours caused by icebergs and portions of ice shelves were less frequent. The benthos paralleled this disturbance gradient, with the inshore consisting of a disturbance-associated fauna. Four recently formed ice scours were studied at 3 locations. Despite differences in exposure to currents and water depth, all scours were dominated by the same disturbance-associated fauna and were distinctive from the benthos outside. Scavenging amphipods and gastropods consumed bivalves that were dislodged and damaged, while predatory amphipods and opportunistic polychaetes burrowed in the gouged and displaced clays. Our expectation was that the topography of the ice scours would select for different colonizing species. However, there was no evidence of preferential occupation of the raised berms by suspension feeders or of the troughs by deposit feeders. The species that dominated the 4 scours also dominated the less recently disturbed areas of the inshore, despite the fact that these areas were situated 300 to 400 m inshore and at shallower depth. The prevalence of species that associate with ice scours indicates that ice disturbance is an important factor that molds coastal benthic zonation at this Arctic location.