Distribution patterns of Canadian Beaufort Shelf macrobenthos

Variation in macrofaunal composition in relation to sediment and water variables was analysed in nine regions of the western Canadian Arctic on the Beaufort Shelf and in Amundsen Gulf. We hypothesized that benthic community composition was distinctive (1) in a recurrent polynya in Amundsen Gulf and (2) in upwelling regions (Cape Bathurst and Mackenzie Canyon) and (3) changed in a linear gradient across the Beaufort Shelf. Analysis was based on 497 taxa > 0.4 mm from 134 samples at 52 stations sampled over 2002–4 in 11–1000 m water depth. Abundance ranged from 490.7 m− 2 in eastern Amundsen Gulf to 17,950 m− 2 off Cape Bathurst. (1) Community composition in Amundsen Gulf was not significantly different from the Beaufort Shelf at similar depth, indicating a lack of benthic effect of the polynya in Amundsen Gulf. (2) The Mackenzie Canyon macrofauna, although abundant and diverse, were similarly indistinct from the shelf community at similar depth. However, there was a 10-fold increase in inshore abundance in the upwelling region of Cape Bathurst due to large numbers of the amphipod Ampelisca macrocephala and the polychaete Barantolla americana, species that were not abundant elsewhere. (3) In the inshore fast ice and flaw lead regions of the Beaufort Shelf, under the influence of ice scour, storm effects, coastal erosion and the Mackenzie River, the macrofauna were dominated by the bivalve Portlandia arctica and the polychaete Micronephthys minuta. Offshore, where these influences were less and upwelling of deep Atlantic water occurred, the polychaete Maldane sarsi dominated. Faunal distribution across the Beaufort Shelf correlated with depth, water and sediment changes but was not significantly linear.