Marine Mollusca from Expedition Fiord, Western Axel Heiberg Island, Northwest Territories, Canada

Marine molluscs, including bivalves, gastropods and scaphopods, were recovered by dredging at depths of 3 - 82 m in Expedition Fiord, Axel Heiberg Island, Canada. Cluster analysis, based on presence/absence data at 27 stations, defined two mollusc associations within the fiord. A Portlandia-Thyasira association, characterized by the abundance of Portlandia arctica and Thyasira gouldi, inhabits silty clay substrates at depths of 32 - 82 m throughout the fiord. An Astarte association, characterized by the abundance of Astarte borealis and Astarte warhami, inhabits sandy mud substrates at depths of 3 - 32 m in the middle and outer fiord. The absence of this mollusc association at the fiord head suggests that the suspension-feeding molluscs that const itute this association, such as Astarte, Hiatella, Mya and Trichotropis, are intolerant of the lowered salinities and high suspended- sediment concentrations created by the discharge of Expedition River into the fiord-head environment. The Expedition Fiord molluscan fauna is compared to the molluscan fauna recorded in Jørgen Brønlund Fjord, Greenland. In the latter fiord, shallow- water (5 - 19 m) molluscan faunas are characterized by the abundance of Portlandia arctica and Hiatella arctica, while deep-water (22 - 48 m) faunas are characterized by the abundance of Thyasira dunbari. Molluscs recovered live in both of these fiords are distributed widely in high-latitude fiord and continental shelf environments.