Risks to the North American beaver from exposure to the algal-bloom toxin microcystin

Abstract

My paper is a risk assessment of the effects of the algal-bloomcyanotoxin, microcystin, on the North American beaver, Castor canadensis. Microcystins are not only the most common cyanotoxins detected in the Great Lakes, but also in freshwater lakes worldwide.I have specifically focused on the population of beavers on Isle Royalein Lake Superior because cyanobacteria blooms have become more frequent on Isle Royale’s inland lakes and have recently begun to appear in the surrounding Lake Superior area. Isle Royale’s inland lakes have been gradually warming for decades and the beavers help foster a nutrient-loaded, slow-moving water area for those blooms to occur. Beavers tend to be a keystone species for an ecosystem, and they are generally seen as an indication of good ecosystem health. Isle Royale is isolated far from the mainland with few opportunities for new organisms to immigrate or ecosystem recovery; therefore,I estimated the risks of microcystin to the North American beaveron Isle Royale. I reviewed toxicity, estimated dietary exposure, projected concentrations of the toxin in the Isle Royale lakes for future years, and compared estimated exposures to toxicity thresholds to characterize risks using a risk quotient (RQ) approach. An RQ is the ratio of estimatedexposure to an effect threshold to identify if an organism’s exposure exceeds the threshold. My results indicate RQs rangedfrom < 0.01 to 0.02 for 2022. This means that exposures I calculated were less than 2% of the no-adverse-effect level and the beavers are at negligible risk of adverse health effects from microcystin in the lakes on Isle Royale. Projected microcystin concentrations and RQ values for 2030 and 2040 also indicate a similar level of negligible risk.