By Dr. Ryan P. Moyer
Oyster reefs, constructed primarily by the eastern oyster (Crassostrea virginica), provide critical ecosystem services to nearly all of coastal Florida. Over many years, multiple generations of oysters settle upon one another, constructing a large reef structure that stabilizes sediment and provides a hard substrate that is utilized as habitat by other species. Oyster reef habitats are crucial components to coastal ecosystems and provide substrate, habitat, and/or food sources to numerous species of gastropods, crustaceans, sponges, worms, fish and birds. Thus, their ability to support recreational and commercial fish species, improve water quality through filtration, and reduce shoreline erosion highlights their significance as critical species within estuarine ecosystems.
In Tampa Bay, continued coastal development, dredging, and historical harvests have led to a reduction in suitable hard substrate for oyster recruitment. Beginning in the early 2000s, several public and private organizations initiated the installation of artificial oyster reefs to mimic the natural substrate oysters need for settlement and growth. These reefs were constructed from shell, concrete domes and mesh shell bags, and were placed throughout Tampa Bay to increase available oyster habitat and oyster populations. In collaboration with Tampa Bay Watch and the Tampa Bay Estuary Program, the Florida Fish and Wildlife Research Institute (FWRI) Coastal Wetlands Research Program implemented a study to assess and monitor oyster growth on old (>5 years), moderate-age (2-5 years), and young (<2 years) constructed oyster reefs.
Physical assessments of oyster growth (e.g., oyster density, shell height, associated fauna) are coupled with real-time kinematic (RTK) Global Positioning System (GPS) surveys resulting in high-resolution (cm) elevation control of both the reefs and associated shorefaces being sheltered by the reefs. To date, 16 constructed oyster reefs in Tampa Bay with variable substrates (shell bags, concrete domes and loose shell) and ages (old, moderate and young) have been assessed, with young-age reefs being monitored bi-annually. In addition, three nearby natural reefs have been identified to serve as controls, and the same metrics used on created reefs are measured there. Physical oyster growth and faunal information at the 16 sites will be correlated to elevation (depth below mean tide level) and age (young, moderate, old) to further understand how these reefs mature over time.
Oysters are tolerant to prolonged areal exposure, however in order to release toxins and feed they must be submerged; therefore, it is imperative to maintain tight elevation controls during reef construction to ensure proper placement of substrate within the water column. As a result, reef sections situated above, or below suitable oyster settlement depths may experience reduced settlement, increased predation and reduced growth. The conclusions from this study will be used to maximize oyster growth potential and inform adaptive improvement in the planning and design phase of future oyster restoration projects to ensure maximum recovery of healthy oyster populations in Tampa Bay and around Florida.