Morris, R.L., et al. Evaluation of wave attenuation and shoreline stabilization by US Atlantic and Gulf coast oyster reef living shorelines. Ecological Applications.
One of the paramount goals of oyster reef living shorelines is to achieve sustained and adaptive coastal protection, which requires meeting ecological (i.e., develop a self-sustaining oyster population) and engineering (i.e., provide coastal defence) targets. In a large-scale comparison along the Atlantic and Gulf coasts of the United States, the efficacy of various designs of oyster reef living shorelines at providing wave attenuation and shoreline stabilization was evaluated. Historical aerial imagery (to quantify shoreline change) combined with on-ground wave attenuation measurements of 15 oyster reef living shorelines, and paired controls, was analyzed. Oyster reef living shorelines varied in age, construction material (oyster shell or pre-cast concrete units), reef dimensions (i.e. length, width, height) and placement (i.e., tidal height, wave exposure, distance from shore) among sites. At six sites oyster reefs showed significantly greater wave attenuation than the paired controls, and the reduction in wave height at those oyster reefs varied between 13 – 55%. The oyster reefs in the other sites were not effective at wave attenuation and substantial continued shoreline erosion was observed. Wave attenuation was greatest at reefs where either (1) the crest height was at or above the water depth; or (2) the reef had a wider footprint. However, some of the tall reefs exceeded the tolerable aerial exposure for oysters (i.e., the amount of time a reef can spend out of the water) and, thus, the peak of such reefs was not suitable oyster habitat. There is, therefore, a trade-off between maximizing coastal protection or oyster habitat when designing an oyster reef living shoreline. Yet our results provide evidence that oyster reefs may be designed to deliver both substantial coastal protection and oyster habitat through further study of the relationship between reef structural attributes (height and width) and oyster habitat suitability. Verification of these observations under storm conditions, which drive erosive events, will be important to inform appropriate design and wider implementation of living shorelines globally.