Oyster spat recruitment methods3/10/2023 ![]() ![]() Two stratum types were defined, Module and Face. The modular reef was sampled using a stratified random sampling design. Jensen) is deceased but gave verbal permission. Knick) in one of the manuscript photos have given written informed consent (as outlined in PLOS consent form) to publish the photo. The field sampling did not involve endangered or protected species. Permission to sample the reef was given by United States Navy Captain (Retired) Robert W. Individuals in the photo are, from left to right, Captain R. Top three modules of the modular reef that were sampled and immediately returned to the same location. In this study, we document density, abundance, biomass and size structure of the eastern oyster and hooked mussel Ischadium recurvum as a function of various features of the artificial reef, which can serve as a model for the use, performance and monitoring of artificial reefs in restoration efforts. Consequently, we provide one of the few exhaustive evaluations of experimental, subtidal artificial reef modules for the eastern oyster. ![]() In contrast, subtidal artificial oyster reefs have rarely been evaluated comprehensively. For subtidal shell and intertidal restoration reefs, there is ample evidence of their productive performance in restoring the eastern oyster. To ensure that effort and funds are expended judiciously for restoration, credible evaluation of alternative reef structures is critical. These reefs have demonstrated that alternative reef structures providing the stability and complexity of natural reefs can lead to higher abundance, biomass and diversity of species under restoration. Other benefits of these reefs are protection from illegal trawling and of biodiversity. ![]() Often such reefs serve a dual purpose, such as combined fish and bivalve habitat, and many of these reefs have enhanced commercial harvests, especially of bivalves. European countries have been experimenting with various types of subtidal artificial reefs over the past few decades. Unfortunately, the preferred substrate for oyster restoration, natural oyster shell, has become a limiting resource, which has spurred the use of alternative reef substrates such as concrete structures. These population declines have stimulated considerable restoration efforts, particularly in the Gulf of Mexico and estuaries along the Atlantic coast. In Chesapeake Bay, the eastern oyster has been reduced to approximately 1% of its previous abundance due to overfishing and oyster reef degradation. For instance, in North America the native eastern oyster ( Crassostrea virginica) along the Atlantic and Gulf of Mexico coasts and Olympia oyster ( Ostrea lurida) along the Pacific coast have declined by 88% in biomass and by 64% in reef area over the past 200 y. Native oyster reefs have been functionally extirpated worldwide. ![]() This modular reef is one of the most successful artificial reefs for eastern oyster and hooked mussel restoration, and details features that are conducive for successful settlement, growth and survival in subtidal habitats. Oyster density correlated positively in a sigmoid fashion with mussel density up to high densities, then declined. Oyster biomass (1663 g dry mass m -2 river bottom) and condition index were equally high, whereas parasite prevalence and intensity were low. Size structure of oysters reflected four year classes, with over half of oysters more than 1 y old and of reproductive age. These densities translate to 1085 oysters and 8617 mussels m -2 river bottom, which are the highest recorded for artificial oyster reefs. The reef was heavily colonized by 28-168 oysters and 14-2177 mussels m -2 surface area. After nearly 5 y (May 2005), we took 120 stratified random samples over the reef. We quantified population structure, density, abundance and biomass of eastern oyster and hooked mussel, Ischadium recurvum, on a concrete modular reef (75 m 2 surface area over 5 m 2 of river bottom) deployed subtidally at 7 m depth in the Rappahannock River, Virginia during October, 2000. Restoration efforts with native eastern oyster, Crassostrea virginica, in Chesapeake Bay and elsewhere have been limited by shell availability, necessitating the use of alternative structures as subtidal reefs, yet these have rarely been evaluated quantitatively. ![]()
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