SEASONAL DISTRIBUTION OF SYMPAGIC AMPHIPODS NEAR CHESTERFIELD INLET, NWT, CANADA

The seasonal distribution of sympagic amphipods was investigated in th e Chesterfield Inlet area of northwestern Hudson Bay (63 degrees 30'N) . Amphipod abundance was measured by photographic samples and species composition was determined by sweep net samples. Twelve species of amp hipods were collected, the most common being Ischyrocerus anguipes, Po ntogeneia inermis, Apherusa megalops and Weyprechtia pinguis. The majo r environmental variable affecting amphipod distribution was water dep th. Amphipod abundance was highest near 20 m and near zero past 50 m. The maximum recorded abundance was 1367 m(-2). A minor factor affectin g the distribution of amphipods was snow depth, through its modifying effect on light and thereby the growth of ice algae. Amphipods began t o inhabit the sea ice shortly after its formation. From the beginning of March, the number of amphipods on the ice increased steadily to abo ut the 3rd week of April, after which numbers declined. This pattern c oincided with the seasonal ice algae abundance. Amphipods reduced ice algal biomass over 20-m depth by 63%. No evidence of diurnal changes i n abundance was observed.