Distribution and transport of Olympia oyster, Ostrea lurida, larvae in northern Puget Sound, Washington, USA

As efforts for restoring Olympia oyster (Ostrea lurida) populations have expanded, there is an increased need to understand local factors that could influence the long-term success of these projects. To address concerns over potential limitations to recruitment at a restoration site in northern Puget Sound, Washington, USA, a study was developed to characterize physical processes governing larval transport in conjunction with larval abundance and environmental factors. Larval presence was not associated with tide cycle, season, or a combination of tide cycle and season. In terms of location, larvae were more likely to be present at offshore and intertidal sites versus the estuarine lagoon where the adult population resides. Larval density was higher during late summer ebbs versus early summer floods. Across sampling dates and locations, larval sizes ranged from 184 to 263 µm, indicating that larvae were released into the water column throughout the reproductive season and retained in the embayment for at least ~16 days. Throughout different tidal cycles in Skagit Bay, acoustic Doppler current profilers were used to measure current direction and velocities, concurrent with plankton sampling. Surface currents in the study area alternated between a clockwise and counterclockwise gyre during initial ebb and flood tides, respectively. Larvae exported from the source population during initial to mid-ebbs are swept into a northward gyre, and potentially retained at intertidal sites alongshore. These results will provide resource managers attempting to restore native bivalves with the ability to expand populations by identifying optimal areas for habitat enhancement through natural recruitment.