The coastal distribution of seagrass and macroalgae make them particularly susceptible to anthropogenic eutrophication and increased sedimentation as a result of coastal development. The increasing resident and tourist populations of the Florida Keys are a source of anthropogenic disturbance via increased development, waste production, and careless diving and boating practices. Seagrass monitoring began in the Florida Keys National Marine Sanctuary in 1996 to determine the effects of heavily managed freshwater flow on the coastal ecosystems within the Sanctuary. Florida Bay and coastal waters located oceanside of the Florida Keys were divided into approximately three-hundred polygons, and within each polygon five sites were randomly selected. At each site, abundance, frequency, and density of seagrass and macroalgae were estimated using a modified Braun-Blanquet scale. Abiotic measurements along with tissue samples were taken and analyzed for carbon, nitrogen and total phosphorus content.
Results/Conclusions
Preliminary analyses of Braun-Blanquet data indicate that seagrass species have shown no significant increases or decreases in density at this landscape scale. Calcareaous green algae (Halimeda sp., Penicillus sp., and Udotea sp.) and other green algae (Avrainvillea sp., Dasycladus sp., Batophora sp., etc.) have been increasing significantly since 1996 (all p<0.05). Sargassum sp. has also increased significantly; however, other brown algae (including Dictyota sp.) have significantly decreased (p<0.05) followed by a significant increase (p<0.05) for no net change (p=0.98) in density. Studies of macroalgal distribution at permanent sites (30 total) sampled quarterly since 1996 showed similar trends and correlated these trends with local nutrient availability. Our preliminary results suggest that this trend is not merely a local phenomenon, but is occurring at the landscape scale.