Eastern Oysters, Crassostrea virginica, settle near inlets in a lagoonal estuary: spatial and temporal distribution of recruitment in Mid-Atlantic Coastal Bays (Maryland, USA)

Authors: FARMER, MADELINE - University Of Maryland Eastern Shore (UMES); Klick, Sabrina; CULLEN, DANIEL - University Of Maryland Eastern Shore (UMES); STEVENS, BRADLEY - University Of Maryland Eastern Shore (UMES)

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2023
Publication Date: 4/27/2023
Citation: Farmer, M.A., Klick, S.A., Cullen, D.W., Stevens, B.G. 2023. Eastern Oysters, Crassostrea virginica, settle near inlets in a lagoonal estuary: spatial and temporal distribution of recruitment in Mid-Atlantic Coastal Bays (Maryland, USA). PeerJ. 11:e15114. https://doi.org/10.7717/peerj.15114.
DOI: https://doi.org/10.7717/peerj.15114

Interpretive Summary: In recent decades, there have been an increase in efforts by federal, state, and non-government agencies to restore populations of the Eastern oyster in the Chesapeake Bay and the Coastal Bays of Maryland, Delaware, and Virginia. Restoration initiatives in the Maryland Coastal Bays (MCBs) require a series of evaluation studies in order to ensure success. This was the first study in the MCBs to map locations where natural larval recruitment and settlement could aid in restoration initiatives. Thirteen sites were chosen to test sampling methods to quantify oyster larvae populations and examine peak time and locations for larval recruitment in the MCBs during 2019 and 2020. Results showed that ceramic plate materials were the best method to facilitate larval recruitment and settlement. The highest oyster larval counts were located at sites closest to inlets and occurred between late-June and early-July. This was the first study evaluating Eastern oyster larvae populations in the MCBs and serves as baseline for future recruitment studies in other estuaries. Results from this study can be used to inform stakeholders on potential locations in the MCBs for restoration efforts.

Technical Abstract: Background. Declines of the Eastern oyster, Crassostrea virginica, and its numerous ecological benefits have spurred oyster restoration initiatives. Successful restoration of a self-sustaining oyster population requires evaluating the temporal and spatial patterns of recruitment (settlement and survival) of oyster larvae in the target waterbody. Restoration of the eastern oyster population in the Maryland Coastal Bays (MCBs), U.S.A., a shallow lagoonal estuary, is of interest to federal and state agencies, but the location and timing of natural recruitment is not known. Methods. We assessed the spatial and temporal variation in oyster larval recruitment throughout the MCBs using horizontal ceramic tiles and PVC plates. Newly settled oyster larvae (recruits) were monitored biweekly from June to September 2019 and 2020 at 12 sites in the MCBs and a comparison site in Wachapreague, Virginia. Water quality measurements collected included temperature, salinity, dissolved oxygen, pH, and turbidity. The objectives of this study were to determine 1) the most effective substrate design for monitoring oyster recruitment, 2) the spatial and temporal distribution of oyster larval recruitment in the MCBs, and 3) patterns in oyster larval recruitment that would be applicable to other lagoonal estuaries. Results. 1) Ceramic tiles were more effective than PVC plates for recruiting oyster larvae; 2) Peak settlement began during the period from late June through July, and oyster recruitment was greatest at sites closest to the Ocean City and Chincoteague inlets; 3) Areas near broodstock that have slow flushing rates to retain larvae may provide the best environments for recruitment of oysters to lagoonal estuaries. Discussion. As the first study on oyster larval recruitment in the MCBs, our results provide insight into their spatial and temporal distribution, methods that can serve as a foundation for future recruitment studies in other lagoonal estuaries, and baseline data that can be used to inform stakeholders and evaluate the success of oyster restoration projects in MCBs.