Effects of Oyster Castle reefs on shoreline erosion and sediment composition

Abstract

Declines in wild oyster populations and the growing need to protect coastal communities have led to the creation of novel reef substrates for use in oyster reef restoration. However, innovations in alternative substrates have outpaced scientific research quantifying their efficacy, leaving managers without the information needed for widespread adoption. To assess the effects of Oyster Castles, a concrete-based oyster restoration structure, on rates of horizontal and vertical shoreline erosion and sediment composition, we constructed replicate reefs just offshore of a medium-energy eroding salt marsh shoreline in North Carolina. We monitored vertical accretion of sediments and sediment composition behind reefs versus control shorelines and also measured rates of horizontal shoreline change over a two-year period. Our results show that reef and control sites did not differ significantly in terms of vertical sediment accretion, horizontal shoreline change, or sediment composition. The lack of differences between our reef and control sites may be due to our reef design choices or to the short study period. To fill the data-gap marine managers face when choosing reef designs, we recommend monitoring restoration sites over longer timeframes (> 5 years) and assessing efficacy differences between reef designs and spatial scales.