Role of a Unionid Clam Population in the Calcium Budget of a Small Arctic Lake

Growth rate and morphometric parameters were estimated for the Anodonta grandis (Pelecypoda, Unionidae) population in Shell Lake, N.W.T. (68°N), based on sampling during the summer of 1972. Variation in density and size of Anodonta within the lake as a function of varying depth and slope of bottom was estimated by SCUBA during the summer of 1973. Predictive models based on these data estimate total calcium in shells of the Anodonta population to be 10.1 Mg, which is approximately half the amount of calcium dissolved in Shell Lake water. The youngest four or five year-classes are missing from the estimated age distribution, and recent pollution may be a factor. Independent estimates of calcium used for shell growth, and of calcium released by death of individuals and subsequent shell dissolution, approximate 50% (of the calcium in the Anodonta population) per year. This implies a mean residence time in the Anodonta population of approximately 2 yr.