Evaluating biodegradable alternatives to plastic mesh for use in small-scale oyster reef restorations

Oyster reefs have been in decline due to disease, overharvest, and habitat loss. In turn, the ecological and economic benefits of the reefs are threatened, and there are efforts to restore what has been lost. Small-scale and community-based restoration activities traditionally use plastic mesh bags filled with recycled oyster shell to form a three-dimensional substrate for new oyster recruitment. However, plastic pollution is a major concern, and there is a need to develop new restoration approaches that decrease the introduction of plastics to the marine environment. The goal of this study was to evaluate the functionality of biodegradable mesh alternatives for use in small-scale oyster reef restoration efforts. Experimental reefs were constructed in shallow (< 0.5 m)and deep (>1 m) areas using recycled oyster shells placed into four different mesh bag types:the traditional polyethylene plastic mesh and three biodegradable alternatives (cellulose, cotton, and jute). Reefs were monitored for seven months to assess the ecological community and condition of the bag material. Cellulose, cotton, and jute bags fully degraded within two months of deployment, while plastic bags remained intact. Oyster and fauna recruitment were greatest in plastic bags, and we suspect that the persistence of structure influenced this result. Rapid degradation of the materials in the field was further investigated in laboratory-based experiments, which suggested that herbivorous grazing played a large role in degradation. Plastic bags resulted in the greatest benefit-cost ratios, though accurate valuation of environmental and societal costs is unclear. Cotton was the most cost-effective biodegradable alternative, but recruitment of oysters and fauna to biodegradable treatments cannot be attributed to structured bags, rather, to loose shell post-degradation. The results of this study highlight the need for developing cost-effective, environmentally-friendly materials not only for daily consumer use, but also for sustainable habitat restoration.