Artificial oyster reefs in the northern Gulf of Mexico: management, material, and faunal effects

Abstract

Artificial oyster reefs seek to restore reef ecosystem services, such as water filtration, shoreline protection, and habitat for nekton. This study established three objectives to address the dispersed nature of artificial reef information in the Gulf of Mexico (GoM) and lack of post-construction monitoring assessments. First, to document the extent of activities in the GoM, we developed a database of all inshore artificial oyster reefs created for restoration purposes. Of the 422 reefs in the resultant database, a third or less provided records of entities involved (27%), restoration goals (24%), area (20%), monitoring efforts (15%), relief (9%), and costs (8%). Material (89%) and age (66%) records showed reefs were primarily built with rock (48.6%, limestone or concrete) or shell (12.8%) materials; a quarter of projects (26%) occured after Hurricane Katrina (2005). Second, in a field study we examined the success of artificial subtidal reefs using the presence of (a) living oysters and (b) hard substrate as indicators of success. This field study sampled historic (N=7) and artificial shell (N=5) and rock (N=8) reefs in 8 bays along the northern GoM. Rock artificial reefs were more successful on average than shell, providing significantly higher mean adult oyster density and hard substrate volume. In addition to material effects, design (i.e., relief) and placement specific environmental variations (i.e., hydrodynamics) may have affected success. Lastly, to assess artificial reef use by nekton communities, we sampled nekton assemblages with 3 gear types (gillnet, castnet, and shrimp trawl), during 4 trips in summer 2011. Overall, abundance, richness and diversity were similar between historic reefs and both artificial reef materials (shell, rock). It is probable that biophysical variations may have affected nekton use, more than reef structure. Of the reefs sampled, only 65% of the artificial reefs were fully successful in providing reefs with hard substrate and living oysters, while all reefs provided similar nekton support. This project highlights the need to better track restoration projects in order to inform future activities. Identifying aspects of design and/or location that influence reef success is critical for improving restoration activities.