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 constitute this association, such as Astarte, Hiatella, Mya and Trichotropis, are intolerant of the lowered salinities and high suspendedsediment 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 J0rgen Br0nlund Fjord, Greenland. In the latter fiord, shallowwater (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. On a recueilli des mollusques marins—comprenant des bivalves, des gastéropodes et des scaphopodes—par dragages effectués à des profondeurs allant de 3 à 82 m dans le fjord Expedition, situé dans l'île Axel Heiberg au Canada. Des analyses typologiques, établies sur les données de présence ou d'absence à 27 stations, ont permis de définir deux associations de mollusques à l'intérieur du fjord. Une association Portlandia-Thyasira, caractérisée par l'abondance de Portlandia arctica et de Thyasira gouldi, habite les substratums d'argile limoneuse à des profondeurs allant de 32 à 82 m dans le fjord tout entier. Une association Astarte, caractérisée par l'abondance de Astarte borealis et de Astarte warhami, habite les substratums de vase sableuse à des profondeurs allant de 3 à 32 m dans le milieu ou en aval du fjord. L'absence de cette association de mollusques à l'extrémité amont du fjord suggère que les mollusques se nourrissant d'éléments en suspension qui forment cette association, comme Astarte, Hiatella, Mya et Trichotropi