Disturbances related to freshwater management activities are known to affect the functioning of coastal ecosystems. Coastal lakes in the Everglades have experienced major reductions in freshwater inflows, resulting in higher salinities and nutrient levels relative to pre-drainage conditions of the Everglades. These changes in water quality have caused a state shift from SAV-dominated to phytoplankton-dominated primary production in some coastal lakes. In this project, we compared two lake systems with different prevailing primary production, one enriched phytoplankton-driven lake system (PLS) and one benthic-driven lake system (BLS), to assess how freshwater induced habitat changes influence movement and trophic interaction dynamics of mesopredators. We hypothesized higher residence time of mesopredators, along with a wider niche width and higher trophic level in the less enriched, BLS. To test this, we quantified the movement and trophic dynamics of Common Snook (Centropomus undecimalis), an economically important mesopredator and sportfish, by coupling acoustic telemetry and stable isotope analysis (SIA).
Results/Conclusions
We observed limited connectivity between the two lakes systems with only a small portion of tagged Snook using both systems. Snook in the BLS used more lakes than those in the PLS, but Snook in the BLS were found to move larger distances on average. A higher proportion of detections were also observed in the upstream lakes within the BLS whereas the majority of detections in the PLS system occurred in the downstream lakes. The SIA showed that the BLS Snook subpopulation had a wider isotopic niche width and higher trophic level in comparison to the PLS subpopulation. Based on a mixing model, we determined that epiphytes were the major basal energetic source in both systems, but BLS individuals used more algae based material and shifted away from relying solely on epiphytes. These results suggested that habitat disturbances induced by water supply modifications can drive consumer-mediated dynamics with possible implication on the fitness and management of fisheries in coastal environments.