Freshwater input and ocean connectivity affect habitats and trophic ecology of fishes in Arctic coastal lagoons

Arctic coastal lagoons are important habitats for unique assemblages of diadromous and marine fishes. Many of these fishes are vital to the food security of rural and indigenous communities. However, human impacts on coastal Arctic habitats, as well as climate change, weaken ecosystem resiliency and threaten the sustainability of fish stocks as a component of local food security. Identifying how habitat characteristics influence fish ecology may allow for predictions of changes in fish abundance and availability in response to these threats, and may help illuminate strategies for responding to negative impacts. Consequently, we endeavored to link habitat characteristics likely to be most-impacted by climate change to fish assemblage trophic metrics in four lagoons within Cape Krusenstern National Monument, Alaska where subsistence fishing commonly occurs. This was done through calculating trophic metrics including mean nitrogen (δ15N) and carbon (δ13C) stable isotope values from fish muscle tissue samples collected from the study lagoons. Lagoon habitat characteristics were quantified including ocean connectivity, freshwater input, and surface area using satellite imagery. Finally, associations between fish assemblage trophic metrics and habitat characteristics were evaluated using linear regressions, and trophic metrics were compared between lagoons with ANOVA and Tukey post-hoc tests. Model results showed that increased freshwater input resulted in longer duration of lagoon ocean connectivity. Additionally, longer duration of ocean connectivity was associated with an increase in mean δ15N and δ13C across all lagoon fish species. Finally, there were significant species-specific differences in fish trophic metrics among lagoons with varying habitat characteristics. Overall, freshwater input and ocean connectivity of coastal Arctic lagoons appear to be important drivers of fish trophic ecology, and should be carefully monitored in the face of anticipated changes in the region, to conserve important subsistence harvest species.