Quantification of the potential spawning contribution from oyster (Crassostrea virginica) restoration projects: a comparative study among restoration sites and substrates in coastal Alabama

Abstract

Although numerous ecosystem services of oyster reef restoration have been documented, the contribution of larvae has not been previously quantified. In this study, we selected 5 restoration sites in coastal Alabama (Billy Goat Hole, Alabama Port, Coffee Island, Point aux Pins and Little Bay) with 6 different substrates materials (Reef Balls™, Reef Blocks™, bagged oyster shell, loose oyster shell and 2 types of Wave attenuation restoration materials (WARMs). In 2011, we sampled the oysters monthly during the presumed reproductive season (June to November), dividing the oysters into 2 size classes (> 30 & < 75 mm shell height, and > 75 mm), with up to 30 oysters collected per size class per sampling. Oysters were sexed by microscopic examination of the gonad, and the number of eggs per female was estimated using a modified method of Cox & Mann (1992). The result suggests that spawning primarily occurred from June to September 2011. And in both sizes oysters there are two observable spawning peaks, one is in June or July and the other one is in September. The sex ratio shows a dramatic decline of female oyster in October and November. Among all the conservation materials, WADs in Billy Goat Hole has the highest potential egg production per female in legal size oyster, while Reef Balls™ in Alabama Port is the highest in sub-legal size oysters. There is no significant different (p<0.05) among different sites for the potential egg production per female. For the potential spawning contribution per square meter and potential spawning contribution, WADs in Billy Goat Hole is the highest as well, and the significant difference (p<0.05) existing among different sites.