Seasonal variations in calorific values of some littoral benthic invertebrates of the Ottawa River, Ontario

Abstract

The calorific values of several groups of littoral benthic invertebrates of the Ottawa River varied significantly from June-Sept. 1974. Observed variation over this period amounted to 8% of the minimum caloric value in the amphipod Gammarus fasciatus (3934-4258 cal/g dry wt), 19.5% of the minimum caloric value in the amphipod Hyallela azteca (3611-4315 cal/g dry wt), 22.4% of the minimum caloric value in the isopods of Asellus spp. (3252-3981 cal/g dry wt) and 12.1% of the minimum caloric value in midge larvae. Chironomidae spp. (4176-4737 cal/g dry wt). Two patterns of change in calorific value were observed. In G. fasciatus and Asellus spp. significant (P .ltoreq. 0.05) variations were noted in both calorific value (calories per gram dry weight) and the relative size of the ash fraction (percentage ash) but not in the calorific value of the organic fraction (calories per gram ash-free dry weight). In H. azteca and Chironomidae spp. larvae, variation in all 3 parameters was significant (P .ltoreq. 0.05).