Bioaccumulation of a cyanobacterial toxin, microcystin, on Stenopsyche marmorata and the ecological implications for its impact on the ecosystem of the Tenryu River, Japan

Abstract

The upstream region of the Tenryu River (the outflow river of the hypertrophic lake Lake Suwa) has the world's largest population of the net-spinning caddisfly, Stenopsyche marmorata. The river water often contains huge amounts of the toxic cyanobacteria Microcystis and hepatotoxin microcystin that originate from the lake during spring- to -autumn blooms. The seasonal changes in microcystin concentrations in S. marmorata larvae from the river and the bioaccumulation and depuration of microcystin in S. marmorata were investigated. The toxic contents of the larvae correlated with the toxicity of volatile suspended solids in the river water. The younger larvae of S. marmorata contained higher concentrations of microcystin than the older ones. This tendency is probably caused by the differences in their food preferences. The prepupae, pupae and adults of S. marmorata showed only low levels of microcystin. Furthermore, the results of excretion experiments suggested that microcystin remained in S. marmorata tissues throughout the experimental period. These findings indicate that S. marmorata is a vector of microcystin in the river ecosystem, and that there is the potential for a transition of the cyanobacterial toxin to higher levels in the aquatic food chain and terrestrial habitat.