Abstract
Freshwater cyanobacterial blooms are mainly composed of Microcystis spp. Cyanobacteria settle down when their cellular activity declines and are subsequently deposited on the lake bottom. In this study, we investigated the process of decomposition of Microcystis spp. and its availability as a food source for macrobenthos, using Microcystis spp. labeled by 13C and 15N. Labeled Microcystis spp. settled immediately with re-suspended sediment. The decomposition rate of Microcystis spp. was increased by mixing with bottom sediment. However, the results of δ13C and δ15N analyses suggested that the organic matter of Microcystis spp. in the sediment remained as detritus or as heterotrophic bacteria. Moreover, the results of the feeding experiment of sediments, containing decomposed Microcystis spp., demonstrated that three kinds of macrobenthos, Chironomidae spp. larvae, Anodonta spp., and Corbicula leana, fed on the organic matter of Microcystis spp. origin. The results of feeding experiment on two kinds (fresh and old) of sediment containing decomposed Microcystis spp. suggested that Corbicula leana, and especially Chironomidae spp. larvae, fed on fresh Microcystis spp.
