Spread and impacts of freshwater invasive invertebrates in North America

The human-assisted transport of species around the world threatens to profoundly impact the physical, chemical, and biological environment, economic prosperity, and human health. My dissertation investigates the spread and impacts of a group of invasive aquatic invertebrates in stream ecosystems - an invasive gastropod (Chinese mystery snail), bivalve (zebra mussel), and crustacean (rusty crayfish). These aquatic invasive invertebrates represent organisms with differing life history characteristics and roles within aquatic food webs, which are important to understand when evaluating complex impacts resulting from species invasions.

I have examined the extent to which streams serve as pathways for the dispersal of invasive species, over both temporal and spatial scales. I have shown that zebra mussels and rusty crayfish are able to spread through streams, but that populations persist in the highest densities clustered at the lake-outflow and decline with distance downstream. Where streams have been invaded, I investigated the impacts on stream food webs and ecosystem processes. Exclusion experiments were conducted that showed that rusty crayfish increase the rate of leaf litter decomposition, reduce the abundance of benthic invertebrates, and may also indirectly reduce fish abundances. High densities of invasive species can also accelerate nutrient cycling, as in the case with the Chinese mystery snail. Biomass-specific release rates show that Chinese mystery snails are able to overwhelm nutrient release by native species. Finally, I summarized for the first time the state-of-the-knowledge on the distribution of aquatic invasive invertebrates in the U.S. and identified current invasional hotspots. This study shows that the epicenter of aquatic invertebrate invasions in the U.S. is in the Great Lakes region, likely due to high levels of domestic and international trade.

Overall, my research suggests that high densities of invasive invertebrates reduce the abundance of native congeners, increase the rate of ecosystem processes, reduce resource availability, and may indirectly affect higher trophic levels. The combined results of my dissertation highlight the importance of invasive invertebrates in altering historical stream food webs and ecosystem processes and the critical need to understand where species have invaded before we can successfully address management options.