Selecting the optimal artificial reefs to achieve fish habitat enhancement goals

Managers and conservation practitioners commonly deploy artificial habitats to restore lost natural habitats or supplement existing natural habitats. These decision makers face logistical and financial constraints in determining which type of structure (e.g., size, material) to deploy, as well as the added complication that ecological evaluations of structure performance are sparse. As a result, deployed artificial habitats often fail to meet habitat restoration or supplementation goals, especially in marine systems. Here, we evaluated the ecological performance of four types of marine artificial reefs (metal ships, three types of concrete modules) relative to each other and to neighboring natural habitat (rocky reefs). Through diver-conducted fish surveys on twenty-three reefs offshore of North Carolina (NC), USA, we found that different reef types hosted distinct fish communities. Concrete modules performed similarly to rocky reefs, supporting similar fish abundance, biomass, and community composition. In contrast, metal ships supported different fish communities than concrete modules and rocky reefs. Further analyses revealed that these patterns may relate to the 'footprint' and structural complexity of reef structures. These findings suggest that managers should strategically deploy particular types of artificial reefs depending on their objectives. For example, concrete modules should be deployed if the objective is to mimic rocky reefs, whereas deploying ships may create habitats that surpass natural reefs in fish abundance and biomass but with different communities. Moving forward, managers and conservation practitioners must rely on the most recent and location-specific structure evaluations when deciding which types of artificial habitats to deploy given their management objectives.