At the whim of the tides: Measuring population connectivity of Olympia oysters (Ostrea lurida) in Puget Sound

Targeting restoration efforts to promote population connectivity, the exchange of individuals among geographically separated subpopulations, is a key element of successful management of declining marine species. Olympia oysters (Ostrea lurida), a species of concern in Washington State, have failed to fully recover after both over exploitation and environmental degradation. Although state agencies and environmental groups have made it a priority to restore O. lurida because they are native to the west coast of North America and provide key habitat and ecosystem services to the Salish Sea., our understanding of O. lurida population connectivity remains limited, in part because little is known about their migratory larvae. Brooded Olympia oyster larvae incorporate trace elements present in estuarine waters into their shell, creating a chemical “signature” of their natal site before release and dispersal. With the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the provenance signatures of larvae and recruits can be compared, and potentially matched, to signatures of source populations. In this study, larval source and recruitment were investigated via plankton pumping and settlement monitoring at two populations of O. lurida in Puget Sound: Fidalgo Bay, an enhanced subpopulation, and Dyes Inlet, one of the few remaining natural oyster beds. To create a base map of chemical signatures in Puget Sound, brooded larvae were collected from 13 distinct O. lurida locales. While sampling for brooded larvae we collected comprehensive reproduction and shell size data on Puget Sound populations of O. lurida. The results of this study will directly influence management efforts to restore O. lurida; resource managers will be able to identify both source populations of larvae, where seed enhancement would be the most effective restoration tool and sink subpopulations where habitat enhancement would be more beneficial.