Use of Biodegradable Coir for Subtidal Oyster Habitat Restoration: Testing Two Reef Designs in Northwest Florida

Oyster reefs are among the most threatened habitats in the world having suffered cosmopolitan decline, and studies evaluating reef construction materials and designs are critical to their successful restoration and management. Current restoration practice commonly employs the use of high-density polyethylene (HDPE) plastic materials to contain oyster shell (cultch); however, as scientists begin to understand more about the problematic ecological and health effects of microplastics in marine environments, testing alternatives to these materials has become increasingly important. In this study, we used biodegradable coconut fiber (coir) materials to construct a network of subtidal oyster reefs and evaluate two reef designs in West Bay, St. Andrew Bay, Florida. These designs differed in the quantity of cultch used and therefore overall reef height. Through an analysis of changes in reef area and reef height, as well as mollusc coverage, density, and size-frequency distribution over a 5-year period, we compare the performance of low- and high-profile reef construction designs and assess the suitability of coir for subtidal oyster reef restoration. Results indicate that a high-profile reef design involving a perimeter wall of coir oyster bags and a loose cultch interior is suitable for creating oyster reef habitat in the low-wave energy, subtidal conditions of St. Andrew Bay. Coir adequately contained cultch until live oysters could colonize the surface, indicating a viable alternative to using HDPE plastic materials in subtidal oyster reef restoration. Results also show the importance of reef height to sustaining oyster habitat at restoration sites subject to mobile sediments.