Toxic Microcystis in western Lake Erie: Ecotoxicological relationships with three non-indigenous species increase risks to the aquatic community.

摘要

Cyanobacteria blooms have recurred in western Lake Erie. Recent blooms have been dominated by Microcystis aeruginosa, a non-nitrogen fixing species. Bloom dominance by non-nitrogen fixing species is significant because it has happened after declines in external sources of phosphorus loading led to significant declines in cyanobacteria blooms dominated by nitrogen-fixing species in the 1970's. Recent blooms coincide with the introduction of non-indigenous mussels, Dreissena polymorpha and D. bugensis, to Lake Erie. In ecologically similar lake systems invaded by Dreissena species, bloom formations dominated by M. aeruginosa have also occurred. My examination of trends in cyanophyte abundance and species composition suggest an interconnection between Microcystis blooms and high nitrate concentrations, selective filtration, and excretions of ammonia and phosphate by dreissenids, and extended periods of high summer temperatures.; Further, concern about M. aeruginosa blooms in western Lake Erie is founded in the production of hepatotoxins (microcystins) by this species. We examined the fate of microcystin produced by M. aeruginosa in western Lake Erie by testing whether microcystin is passed through and/or accumulated by three non-indigenous, interconnected species that have become established in Lake Erie. Dreissenid mussels, amphipods (Echinogammarus ischnus), and round gobies (Neogobius melanostomus), served as a model trophic cycle in which to follow the fate of microcystin. Our surveys of Lake Erie water showed that microcystin was present during Microcystis blooms. Mussels, amphipods and fish species collected during blooms accumulated the toxin in guts and/or liver tissue. We determined that microcystin is made more available to benthic organisms by deposition of microcystin-laden pseudofeces by dreissenids.; Further indirect effects caused by the introduction of dreissenid mussels may be negative feedback effects associated with toxic Microcystis blooms. I developed a dynamic programming model of D. polymorpha filtration behavior to determine if fitness is influenced by blooms of M. aeruginosa. In the model, bioenergetic parameters of mussels were influenced by assumed ecological conditions. Model outcomes suggest small mussels experiencing bloom conditions will have reduced fitness. In addition, size-frequency of populations may be shifted toward dominance by larger sizes, potentially having greater algal consumption and pseudofeces production rates.