Beyond Residence Time: Quantifying Factors that Drive the Spatially Explicit Filtration Services of an Abundant Native Oyster Population

The Guana-Tolomato-Matanzas (GTM) system is a well-flushed estuary in Northeastern Florida, USA, and characterized as having an extraordinarily high abundance of oysters that resembles the populations described by Euro-American settlers. Historically, dense populations of oysters, such as those found in GTM, are believed to play an important role in water filtration; however, most research teams seeking to simulate this role have not had access to such robust populations to parametrize their models. To quantify the filtration service (FS) of Eastern oysters (Crassostrea virginica) in GTM at several spatial scales (i.e., reef, watershed, estuary), we implemented a model that solves for the hydrodynamics and depletion of particulate matter passing over model oyster populations, the latter of which were derived from detailed bay-wide surveys. The model results suggested that oyster reefs populating the GTM play an important role in water quality by filtering ~60% of the estuary’s volume within its residence time. Our approach teases apart the role of reef size, residence time, particle concentration, and other physical factors on the generation of FS at different spatial scales. Downstream effects were found to be very important for estuary FS, which depend on the spatial distribution of the reefs in the GTM and local and estuarine-scale hydrodynamics. Therefore, the difference between “realized” FS and the “potential” FS of a given reef may be substantial when considering the complex hydrodynamic and connectivity among populations at several scales. Our model results provide clear and actionable information for management of these oyster populations and conservation of their ecosystem services.