Wave Exposure Structures Oyster Distribution on Natural Intertidal Reefs, But Not on Hardened Shorelines

Abstract

Intertidal oyster reefs can protect estuarine shorelines from wave erosion and sea-level rise, and recognition of these ecosystem services has fueled global efforts to conserve and restore these reefs. Although intertidal oyster reefs are valued for attenuating wave erosion, little attention has been paid to the effects of wave exposure on their distribution. The present study characterized the role of wave exposure in determining the distribution of natural intertidal oyster reefs and of oysters on hardened shorelines (bulkhead and riprap revetments). Wave exposure was determined using the National Oceanic and Atmospheric Administration (NOAA)-developed Wave Exposure Model (WEMo), which integrates adjacent water depth, fetch, and processed wind information, among other variables. Field mapping of oyster reefs, defined as ≥10 oysters m−2, in Pamlico and Core sounds, North Carolina, USA, was conducted in summer 2014. Hardened shorelines and associated oyster densities were mapped for Pamlico Sound only. A narrow wave exposure threshold (~500 J m−1) was identified above which natural intertidal reefs did not occur and below which reef presence was apparently dependent on other structuring variables, such as salinity at the time of sampling and the grain size of surrounding sediments. Wave exposure was not correlated with the presence of oysters on hardened shorelines. The application of WEMo in the present study should be useful for selecting locations and materials for intertidal oyster reef restoration.