Effects of propagule pressure, environmental factors, and climate change on success and impacts of benthic aquatic invasions

Nonnative species introductions are linked to anthropogenic drivers, including transport of species into novel habitat(s), changes in local environmental factors that may facilitate invasions, or large-scale shifts in abiotic conditions with climate change. In freshwater ecosystems, transport of nonnative species often occurs via boats (e.g., trailers, boat props, bilge water). Environmental factors include differences in watershed land use and water quality (e.g., transparency, nutrient and chlorophyll-a concentrations, pH, and conductivity). Climate change may increase water temperatures, affecting lake stratification, and causing low or pulsed dissolved oxygen concentrations. Both understanding factors causing spatial variability of invasive species and assessing potential negative impacts to ecosystems are important. For example, some invasive species are more tolerant or adapted to increased water temperature or lower dissolved oxygen, and may persist in such environments, while natives decline. This research assessed propagule pressure, environmental factors, and climate change, focusing on benthic macrophytes and macroinvertebrates. First, propagule risk (proxy for propagule pressure, capturing extent to which invasives might be introduced from different populations) and environmental conditions were correlated with richness and abundance of invasive macrophytes in 20 lakes; results suggest that propagule risk was the driver of invasive macrophytes in the lake communities studied. Negative impacts on macrophyte communities from the introduction of a dominant macroalgae, Nitellopsis obtusa, were also evaluated. Increased abundance of N. obtusa was correlated with reductions in total and native macrophyte richness, a pattern consistent across depths, suggesting that N. obtusa can displace species in lake communities. Finally, bioenergetics and nutrient/trace metal sediment release from the nonnative oligochaete, Branchiura sowerbyi, were compared to those of native benthic invertebrates (Hexagenia and Chironomus riparius) under various water temperature and DO concentrations, to understand ecosystem implications of B. sowerbyi’s introduction. Results suggest that B. sowerbyi may be more tolerant of conditions under predicted future climate, and thus may spread and become more dominant in benthic communities, with implications for sediment nutrient and contaminant dynamics. Results of this research offer insight into ecological processes involved in benthic aquatic invasions, including factors that may lead to their success, and the consequences for ecosystems and native species once established