Abstract
Seagrasses provide various ecological services including water filtration, sediment stabilization, provisioning of food and habitat, and carbon sequestration. However, seagrasses are declining globally, largely due to decreases in optical water quality. Estero Bay is a shallow estuary in Southwest Florida and has historically had extensive seagrass beds. Anecdotal reports suggest that seagrasses are seriously declining in the Bay, but trends in the monitoring data are difficult to interpret. In this analysis, we updated and integrated all available seagrass data for Estero Bay, as well as analyzed trends in seagrass abundance in relation to available environmental factors. In addition, we developed a new, Bay-wide monitoring technique to quantify seagrass health and extent, and utilized the method quarterly for a year (2017-2018). This monitoring effort was paired with water quality data collection to relate seagrass abundance to spatial and short-term temporal variation in environmental conditions. Optical water quality was measured as light attenuation and was also partitioned into three main components: chlorophyll a, turbidity, and colored dissolved organic matter. Analysis of historical transect monitoring data and aerial photography demonstrated that seagrass abundance and density are in serious decline in the Bay. Seagrass losses from 2003-2016 were best predicted by temperature and total phosphorus concentrations, which had negative and positive relationships with seagrass abundance, respectively. Analysis of our 2017-2018 data indicated that seagrass abundance was positively correlated with light availability and inversely correlated with macroalgae cover and turbidity. Both analyses were consistent with the hypothesis that eutrophication is a major contributor to poor optical water quality and seagrass declines, implying that efforts to reduce nutrient loading into the system are strongly needed.
