Exploring Native Oyster Shell Microchemistry to Characterize Population Connectivity in Puget Sound, W

Olympia oysters (Ostrea lurida), a species of concern in Washington State, have failed to fully recover after both overexploitation and environmental degradation. State agencies, tribal nations, and environmental groups in Washington have made it a priority to restore O. lurida because they are the only native oyster on the west coast of North America and provide key habitat and ecosystem services to the Puget Sound. Despite this interest, our understanding of O. lurida larval dispersal patterns remains limited. The early life stage of Olympia oysters play a key role in their restoration because it is the only time when they can disperse to other populations. While being 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 providing a way to track their larval connectivity patterns. However, collecting brooded larvae from a species undergoing restoration efforts poses procedural challenges because it traditionally requires sacrificing significant numbers of adults to find enough reproductive females. The first objective of this study, therefore, was to develop a non-lethal sampling approach to collect brooded larvae. Exposure to magnesium sulfate (MgSO4) was assessed in lab trials as an anesthetization method to allow for the non-lethal collection of brooded Olympia oyster larvae. In the field, over 14,000 oysters were then anesthetized to assess reproductive status and validate the procedure. The anesthetization method of 45 min air exposure followed by 45 min submersion in 100 g/L MgSO4 was found to have a success rate > 80% in the field. This anesthesia method for O. lurida allows for non-lethal sampling of assessing reproductive status and collection of brooding larvae, as well as for obtaining tissues for genetic analysis, biopsy for diseases. The second objective of this work was to determine the viability of elemental fingerprinting for tracking larval dispersal patterns of O. lurida . 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. Unique elemental fingerprints of O. lurida larval shells were found in three regions in Puget Sound. This provides an approach to quantifying larval dispersal that can be used to determine the extent to which these O. lurida populations self-seed, seed other sites, and exchange larvae with other populations.