INTERACTING EFFECTS OF RECRUITMENT, EELGRASS (ZOSTERA MARINA), AND HUMAN ACTIVITY ON RESTORED OLYMPIA OYSTER (OSTREA LURIDA) BEDS AND THEIR PROVISION OF ECOSYSTEM SERVICES

Oysters are foundation species utilized in Living Shorelines projects due to their potential to attenuate wave energy and stabilize shorelines. These potential benefits have created recent interest in restoring Olympia oysters (Ostrea lurida), the only oyster species native to the US west coast. However, little is yet known about what site characteristics are necessary to successfully restore functional, self-maintaining Olympia oyster beds. Furthermore, the degree to which Olympia oyster beds attenuate wave energy is not yet known. I examined the effects of annual recruitment, eelgrass presence, and human activity on restored oyster bed integrity and adult oyster density at four sites in Newport Bay, California between 2019-2021. I assessed wave attenuation and shoreline stabilization by measuring the height of boat wakes passing over oyster beds and associated control plots and by tracking changes in grain size profiles upshore of the oyster beds. Oyster beds at sites with higher levels of destructive human activity experienced more rapid bed breakdown, but breakdown was reduced when eelgrass density was higher. Oyster density increased with higher larval recruitment during the previous year, but this relationship weakened as bed breakdown increased. I did not find evidence of wave attenuation by the restored beds. The results of my study suggest that Olympia oyster beds restored at sites with high levels of human activity require additional protective measures to prevent premature breakdown, especially when year-to-year recruitment is variable.