Evaluating coastal protection benefits of restored oyster reef designs

Wave attack is the driving force behind erosional processes causing marsh retreat in shallow coastal bays. Sea level rise and increased storminess are expected to heighten wave energy, escalating coastal erosion problems and intensifying vulnerability of coastal communities to storm damage. Thus, wave attenuation is a critical part of any coastal protection and resilience plan. Previous efforts to protect shorelines have largely involved bulkhead and seawall construction, both of which can be detrimental to nearshore habitats. Recent efforts have shifted towards the use of “living shorelines”, such as restored oyster reefs, as nature-based solutions for coastal protection that stabilize shorelines and enhance oyster populations and the ecosystem services they provide. This study evaluated restored oyster reefs as a nature-based solution for attenuating waves, thus alleviating storm wave impacts, and stabilizing marsh edges in Wachapreague, Virginia. Different substrates, including oyster castles and new reef designs developed by Sandbar Oyster Company that consist of biodegradable hardscapes, were placed adjacent to a marsh island that affronts the Town of Wachapreague. Direct field measurements were collected before and after reef construction to quantify changes to the wave, morphologic and ecologic environments related to reef presence and development. Oyster reefs in this study successfully dissipated wind-wave energy, but only when water depths were near or below reef crest heights. In-situ measurements of reef-lined and un-lined marshes showed reefs at this location significantly reduced rates of marsh edge erosion. This study demonstrates that marsh morphology and elevation are at least as important as the presence of fringing oyster reefs in reducing wave energy reaching marsh edges and stabilizing shorelines. Both artificial reef designs in this study successfully fostered larval recruitment and oyster growth, with significantly higher oyster densities recorded on Sandbar substrate than oyster castles. The presence of constructed reefs had no significant effect on infaunal communities and sediment properties within the study period, highlighting the need for continued restoration monitoring. The current reef configurations at this location seem to be effective restoration designs for stabilizing the marsh edge and enhancing the oyster population. Results from this study supplement our understanding of the combination of restored oyster reefs and marshes as a nature-based solution to threats associated with storms and sea level rise.