Abstract
Seagrass beds in the Caloosahatchee Estuary have declined with increased human development in the watershed, which has altered the timing and volume of freshwater and nutrient inputs. Overgrowth of epiphytic algae may contribute to seagrass declines. Small invertebrate grazers (mesograzers) are thought to aid seagrass through removal of excess epiphytes. The goal of this study is to look at the indirect impacts of freshwater releases on seagrass health in the CRE, as mediated by increased nutrients and reduced mesograzer abundance and diversity. To do this we recorded seagrass abundance, epiphyte levels, and mesograzer abundance bimonthly for two years at two sites in the Caloosahatchee Estuary. We then compared these responses to seasonal and site variations in salinity related to freshwater discharges. Seagrass was most abundant at the highest salinity site and during the summer months. Epiphyte levels did not exhibit a clear seasonal or salinity-related pattern but showed interesting correlations with mesograzer abundance. Mesograzer species richness was positively correlated with salinity at all sites. Multivariate data analysis found a clear separation between sites, except during the wet season of 2013, where grazer community structure was heavily impacted at both sites. Because prior studies have demonstrated a link between mesograzer richness and epiphyte grazing efficacy, we propose that reductions in mesograzer diversity by high freshwater discharge events could exacerbate problems of epiphyte overgrowth. Understanding these impacts can aid in improving water management plans for the Caloosahatchee Estuary in order to protect its valuable seagrass beds.
