Oyster recruitment and growth increases wave attenuation by breakwaters.

Coastal protection structures that incorporate reef-building organisms, such as oysters, are increasingly used to reduce wave energy, while also enhancing ecological function. However, it remains unclear how recruitment and growth of living organisms alters wave attenuation, and ultimately coastal protection, over time. Here, we present the first field-based quantification of changes in wave transformation over a living oyster breakwater following two seasons of recruitment. Using wave gauge deployments and oyster surveys at two sites, we observed a 10-15% increase in wave attenuation after oyster recruitment. The increase in wave attenuation was associated with oyster-induced increases in surface roughness and reductions in structural porosity. A standard breakwater transmission model was adapted using fitted ecological parameters, and oyster length emerged as an informative predictor of effective structural diameter. Our results highlight how ecological dynamics shape the evolving performance of nature-based coastal defenses and demonstrate a path toward adaptive, hybrid design frameworks.