Restoration of Oyster Reefs along a Bio-physical Gradient in Mobile Bay, Alabama

Abstract

Oyster reefs support a valuable commercial fishery based on the extraction of oysters from the biogenic reef matrix they form. This fact, combined with recent recognition of the many ecological services oyster reefs provide to estuarine ecosystems, has resulted in increased efforts to restore and/or enhance the spatial extent of oyster reefs. As part of a large-scale restoration effort in Mobile Bay, Alabama, we designed a field project to determine if the design and location across a bio-physical gradient of restored oyster reefs affect the recruitment of oysters and other sessile invertebrates. In January 2004, eight oyster reefs (625 m 2 each) were constructed in each of three areas of Mobile Bay (Cedar Point, Sand Reef, and Shellbank), which varied in water quality and spatial extent of existing oyster reefs. Four reefs were high relief ($1.0 m vertical relief) and four were low relief (0.1-0.2 m). Semiannual quadrat surveys and monthly assessments of oyster survivorship were designed to evaluate oyster recruitment, abundance, and mortality as a function of reef elevation and location. The two most abundant sessile invertebrates found in the quadrat sampling were eastern oyster (Crassostrea virginica) and recurved mussel (Ischadium recurvum). Recurved mussels were abundant on all restored reefs, but densities did not significantly vary with location or reef elevation. Oyster recruitment and abundance varied by location (Cedar Point> Sand Reef> Shellbank). Oyster recruitment was also higher on high relief reefs compared with low relief. The pattern of higher recruitment of oysters at high relief reefs suggests that in locations where oyster mortality is high (i.e., Sand Reef) or larval supply is low (i.e., Shellbank), high relief reefs are an important design element in successful reef restoration.