Cooperative Fish and Wildlife Research Units Program: Louisiana
Education, Research and Technical Assistance for Managing Our Natural Resources

In the northern Gulf of Mexico, reefs built by the eastern oyster, Crassostrea virginica, provide critical habitat within shallow estuaries, and recent efforts have focused on restoring reefs to benefit nekton and commensal populations. Nekton and commensal invertebrate communities are compared at historic reefs, and newly-created (< 5 yrs) and old (> 6 yrs) shell and rock substrate reefs. Using baited crab traps, gill nets, otter trawls, cast nets, and commensal invertebrate collectors, 20 shallow reefs (<5 m) in the northern Gulf of Mexico were sampled throughout the summer of 2011. We compared nekton and commensal community abundance, diversity and richness across reef types. While there were few differences in nekton assemblages, commensal invertebrate assemblages had the lowest diversity and abundance on old shell substrate reefs. Old rock substrate reefs had greater diversity, most likely due to greater amount of structure remaining, compared to shell reefs over time. To determine the refuge value of oyster reefs for commensals compared to bare bottom, we tested preferences of juvenile crabs across depth and refuge complexity, in the presence and absence of adult blue crabs. Juveniles were more likely to use deep water when predators were present, but only in the presence of oyster structure. Both our sampling and the laboratory study suggest that structural refugia result in higher commensal richness and diversity on reefs. Reef restoration therefore needs to use substrate materials that support long-term sustainability.