Oyster Demographics in a Network of No-Take Reserves: Recruitment, Growth, Survival, and Density Dependence

Central to ecology and resource management is knowledge of the spatiotemporal scales at which demographic rates vary and the ecological consequences of demographic variation, such as that due to density dependence. We quantified the spatiotemporal variation in eastern oyster Crassostrea virginica recruitment, density, growth, and survival and assessed density dependence within a network of no-take reserves in Pamlico Sound, North Carolina. From 2006 to 2008, average oyster recruitment and total density increased 15- and fivefold, respectively. The unprecedentedly high oyster densities in certain reserves (up to 6,500/m(2) at the end of the study) modified demographic rates such that further density increases were regulated by density-dependent survival. Oyster demographic rates varied significantly among reserves at relatively small spatial scales (20 km). Certain reserves were the strong "recruiters," others the fast "growers," and yet others the high "survivors." Cohort dynamics altered the demographic rank order such that the demographically "best" reserves varied intra- and interannually. From a management perspective, the prevalence of density-dependent survival suggests that the oysters in this system are habitat rather than recruitment limited, which may minimize the utility of stock enhancement programs. Addition of habitat (i.e., artificial reefs) should focus on reserves characterized by high recruitment but density-dependent growth and survival. This study (1) supports the efficacy of marine reserves in rapidly increasing the density and age-size structure of protected species, (2) highlights the need for spatially explicit demographic data to support multifaceted management objectives, and (3) when combined with evidence of reserve larval connectivity, provides support for applying metapopulation concepts to this reserve system.