Influence of substrate, elevation, and environment on eastern oysters Crassostrea virginica on artificial intertidal reefs in Tampa Bay, Florida

The extent and distribution of the Eastern oyster Crassostrea virginica has notably declined over the past century in the USA. Restoration efforts seek to increase oyster populations in substrate-limited areas by creating artificial reefs with the hard substrate needed for spat settlement. Numerous intertidal oyster reefs have been created in Tampa Bay, on the central Gulf coast of Florida, using 3 primary substrates: bagged shell, loose shell, and concrete oyster reef balls. This study monitored 16 artificial oyster reefs (1-14 yr old) and 3 natural oyster reefs in Tampa Bay. Live oyster density, shell height, gastropod predator density, reef elevation, burial by sediment, spat recruitment, water quality, and reef rugosity were monitored annually or biannually for 2 yr. The density of live oysters ranged from 7-1180 oysters m -2 across reefs. Higher elevation sampling plots had significantly higher live oyster density, less sediment burial, and lower gastropod predator density. Oyster populations on low-elevation reefs were less dense but larger in size. Shell bags had higher oyster density and lower predator density compared to oyster reef balls. Placement of new artificial oyster reefs in the higher intertidal zone (with inundation frequency of 54-70%) may support higher numbers of oysters and facilitate adaptation to rising sea levels. However, oysters on low-elevation reefs (with inundation frequency of >90%) reach larger sizes and are important for water filtration and spat production. Construction of a variety of substrate types at multiple elevations and locations will maximize the chances of long-term survival of oyster populations.