Comparative analyses of plastid sequences between native and introduced populations of aquatic weeds Elodea canadensis and E. nuttallii

Elodea mediates juvenile salmon growth by altering physical structure in freshwater habitats

Invasive species introductions in high latitudes are accelerating and elevating the need to address questions of their effects on Subarctic and Arctic ecosystems. As a driver of ecosystem function, submerged aquatic vegetation is one of the most deleterious biological invasions to aquatic food webs. The aquatic plant Elodea spp. has potential to be a widespread invader to Arctic and Subarctic ecosystems and is already established in 19 waterbodies in Alaska, USA. Elodea spp. has been found to alter ecosystem processes through multiple pathways; yet little is known about the impact of Elodea spp. on fish life history. A primary concern is the effect of Elodea spp. on juvenile Pacific salmon (Oncorhynchus spp.), because this invading plant can form dense stands in littoral zones, potentially impacting important freshwater rearing habitats used by juvenile fish for foraging and refuge from predators. We used a field experiment to test the effect of Elodea spp. on juvenile coho salmon (O. kisutch) growth in an infested lake near Cordova, Alaska, USA. We found that Elodea spp. stands result in reduced growth and a lower trophic position for juvenile coho salmon over the summer compared to habitats dominated by a native assemblage of aquatic plants. While infested sites were not associated with significant changes in water condition or primary productivity compared to sites dominated by native vegetation, zooplankton densities were reduced, and Elodea spp. height and vegetation richness increased macroinvertebrate densities. Combined, these results indicate that Elodea spp. may alter the flow of energy to juvenile salmon by restructuring space and affecting prey resources for rearing fish. Furthermore, these results suggest that widespread establishment of Elodea spp. may alter the quality of habitat for juvenile salmon and, by affecting juvenile fish growth, could lead to population-level impacts on salmon returns.

Integrating subsistence practice and species distribution modeling: assessing invasive elodea's potential impact on Native Alaskan subsistence of Chinook salmon and whitefish

Alaska has one of the most rapidly changing climates on earth and is experiencing an accelerated rate of human disturbance, including resource extraction and transportation infrastructure development. Combined, these factors increase the state's vulnerability to biological invasion, which can have acute negative impacts on ecological integrity and subsistence practices. Of growing concern is the spread of Alaska's first documented freshwater aquatic invasive plant Elodea spp. (elodea). In this study, we modeled the suitable habitat of elodea using global and state-specific species occurrence records and environmental variables, in concert with an ensemble of model algorithms. Furthermore, we sought to incorporate local subsistence concerns by using Native Alaskan knowledge and available statewide subsistence harvest data to assess the potential threat posed by elodea to Chinook salmon (Oncorhynchus tshawytscha) and whitefish (Coregonus nelsonii) subsistence. State models were applied to future climate (2040-2059) using five general circulation models best suited for Alaska. Model evaluations indicated that our results had moderate to strong predictability, with area under the receiver-operating characteristic curve values above 0.80 and classification accuracies ranging from 66 to 89 %. State models provided a more robust assessment of elodea habitat suitability. These ensembles revealed different levels of management concern statewide, based on the interaction of fish subsistence patterns, known spawning and rearing sites, and elodea habitat suitability, thus highlighting regions with additional need for targeted monitoring. Our results suggest that this approach can hold great utility for invasion risk assessments and better facilitate the inclusion of local stakeholder concerns in conservation planning and management.