The Effects of Temperature on Microcystin-LR Toxicity to Bosmina Longirostris: Food Web Implications in the Chowan River, North Carolina

Abstract

In the Chowan River, North Carolina, the frequency of Microcystis aeruginosa blooms has increased over recent years with an average 1.9°C rise in June water temperatures since 1975. Zooplankton are an important trophic link for toxins to move up the food web. Bosmina longirostris, a dominant zooplankton in the Chowan River, consumes toxic M. aeruginosa cells. This study aimed to understand how microcystin-LR, produced from M. aeruginosa blooms, affects B. longirostris mortality under increasing temperatures. B. longirostris were resistant to microcystin-LR, demonstrating an LC50 of 26.3 [mu]g/L. Therefore B. longirostris can survive typical bloom microcystin-LR concentrations ranging less than 0.1 [micro]g/L to 2.0 [mu]g/L. As temperatures were increased from 25°C to 35°C, microcystin-LR mortality increased approximately 18% from 25-27°C; demonstrating that microcystin-LR was more toxic with increasing temperatures. Above 27°C, mortality also increased, but this was due to the effect of temperature rather than increased toxicity of microcystin-LR. This signifies that during spring, when temperatures are below 27°C and B. longirostris are most abundant, microcystin-LR may be most toxic and may have the greatest influence on the Chowan River food web. Under climate change conditions microcystin-LR may eliminate resistant zooplankton from the food web, putting pressure on larval fish and fisheries.