The Superior Substrate: The Effects of Shell Type on Oyster Restoration

The eastern oyster, Crassostrea virginica, is a critical ecological and economic organism within the Galveston Bay estuary. Oysters prevent shoreline erosion, filter the surrounding water, and provide a three-dimensional habitat for hundreds of marine organisms. In the last century, however, multiple stressors have led to declines in oyster populations. Cataclysmic storm events are one particular stressor that has caused oyster mortality through freshwater input and sediment deposition. The shells entombed in sediment turn “black” in the anoxic environment and no longer provide settlement substrate for larval oysters. With limited oyster shell for large scale restorations after major storm events, resource managers have dredged up the black shell to provide settlement substrate; however, the effects of black shell on larval recruitment is extremely limited. The primary purpose of this experiment was to determine the impact of different shell types for oyster larval recruitment: white sun-cured shell commonly used with oyster restoration, sun-cured “black” shell, and fresh “black” shell on larval recruitment. Recruitment trays containing ten pieces of one of the three treatments of shell were deployed on restored intertidal oyster reefs (n=5) in Sweetwater Lake, Galveston Bay, Texas. Further, background densities were quantified for each of the five reefs in July 2019. The recruitment trays will be retrieved towards the end of the recruitment season (mid-October) and one reef had significantly higher oyster density than the other four reefs. Providing the restored reefs receive adequate recruitment, these results have the potential to influence future oyster restoration efforts, as this could indicate to resource managers the value of exposing black shell for a settlement substrate, or the value of leaving the shells buried and using other materials for restoration efforts.