Dr. Jane M Caffrey

Seagrass beds are important to the health of estuaries around the world, and often these grasses are keystone species for their environments. Water quality conditions controlling light availability such as total suspended solids (TSS), phytoplankton biomass, and the color of the water are important in understanding seagrass health. Six locations from the Pensacola Bay System in Santa Rosa Sound and Big Lagoon with extensive seagrass beds were sampled monthly between May and October 2023. Water quality was measured, and surveys of seagrass beds were conducted at each site. Linear models were developed to attempt to explain K d from water color, phytoplankton biomass, and TSS, as well as their impact on the percent cover of the seagrasses. Seagrass cover increased over the growing season. K d varied between 0.3 /m and 1.8 /m, and across all study sites only color was significantly (p < 0.1) related to light attenuation, although it could not explain much variability (R 2 =0.08). While water depth was significantly related to percent cover of Halodule wrightii and Thalassia testudinum, depth integrated values of light available and factors related to light attenuation explained little variability in percent cover despite significance levels (p < 0.1). Sites in Santa Rosa Sound and Big Lagoon were similar. Larger scale surveys with more opportunistic sampling (e.g. following rain events) in addition to planned collection days, might provide data with clearer relationships to light attenuation and seagrass cover. Surveys that extend to the deepwater edge of the seagrass beds should also be done in the future to provide a clearer picture of the habitat and changes in the beds.

Seagrasses protect coastlines from erosion, improve the water quality, shelter juvenile marine species, and are an important part of the estuarine environment. Seagrasses are responsible for nutrient cycling within the estuary, such as carbon fixation and burial, and nitrification and denitrification. Pensacola Bay System’s seagrasses were studied to see how seagrass coverage, water quality, and nutrient concentrations changed during the 2024 growing season. Three locations in Santa Rosa Sound, home to the most seagrass coverage, were used to collect samples. Measurements of seagrass cover and water quality were made, along with samples for overlying water and pore water. The average seagrass cover
at these locations was 57% with Halodule wrightii dominating in shallow water and Thalassia testudinum dominating in deeper water. Porewater was analyzed for dissolved inorganic phosphate (DIP), sulfide, iron, and ammonium. Ammonium and DIP concentrations from May and June had consistently lower overlying water concentrations compared to the porewater. DIP was in excess compared to ammonium assuming Redfield stoichiometry, perhaps due to seagrasses taking up nitrogen from the porewater. This data will be used to find how seagrass growth effects the nutrient concentrations of estuarine sediment.

Seagrass beds provide numerous services, including coastal protection, erosion control, carbon sequestration, and habitat for ecologically and economically important species. Many factors influence the growth of seagrasses, with one of the main factors being nutrient availability. The aims of this study are to quantify the recycling of key nutrients such as nitrogen, phosphorus, iron, copper, zinc and manganese by 3 dominant faunal species from different trophic levels found in seagrass beds in Santa Rosa Sound, FL and Grand Bay, MS. Fecal samples were collected from spotted seatrout (Cynoscion nebulosus), pinfish (Lagodon rhomboides), and blue crabs (Callinectes sapidus) from each location and analyzed for carbon, nitrogen, and phosphorus, along with sediment and seagrass samples from each location. Trace metal analyses were also conducted on all samples. Results from this study provide a
method for identifying ecologically important species that contribute to the health and continued growth of seagrass beds.