Role of algae in the diet of Chironomus plumosus F. semireductus from the Bay of Quinte, Lake Ontario

Abstract

The importance of algae and different algal species to the chironomid diet was investigated through examination of the guts of chironomids taken from 5 locations in Big Bay (Bay of Quinte, Lake Ontario) at 6 times during the ice-free period. A comparison of the density and condition of algal cells at the two ends of the gut provided information on the digestibility of each algal species and the algal biomass assimilated by the chironomids. Diatoms and two species of green algae were assimilated over much of the summer, but the blue green algae were digested only late in the season when their populations were aged and/or dying. In terms of energy contribution, diatoms, especially Stephanodiscus spp. and Melosira spp., were most important in May (99% of all algal biomass assimilated), August (98%), and Octobr (92%), while the blue green species, Microcystis aeruginosa, was predominant in September (76%). Only a few small greens were assimilated in June and July. The contribution of algae as a food source to chironomid energetics was small, and reached a maximum in August and September (15%–34%). It is postulated that bacteria are a more important food source.