Seasonal distribution of sympagic amphipods near Chesterfield Inlet, N.W.T., Canada

The seasonal distribution of sympagic amphipods was investigated in the Chesterfield Inlet area of northwestern Hudson Bay (63°30′N). Amphipod abundance was measured by photographic samples and species composition was determined by sweep net samples. Twelve species of amphipods were collected, the most common being Ischyrocerus anguipes, Pontogeneia inermis, Apherusa megalops and Weyprechtia pinguis. The major environmental variable affecting amphipod distribution was water depth. Amphipod abundance was highest near 20 m and near zero past 50 m. The maximum recorded abundance was 1367 m⁻². A minor factor affecting the distribution of amphipods was snow depth, through its modifying effect on light and thereby the growth of ice algae. Amphipods began to inhabit the sea ice shortly after its formation. From the beginning of March, the number of amphipods on the ice increased steadily to about the 3rd week of April, after which numbers declined. This pattern coincided with the seasonal ice algae abundance. Amphipods reduced ice algal biomass over 20-m depth by 63%. No evidence of diurnal changes in abundance was observed. Received: 15 May 1996 / Accepted: 4 November 1996