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 larvae 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 parameters (temperature, salinity, dissolved oxygen, turbidity, and pH) were also measured. 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 larvae recruitment in the MCBs, and 3) patterns in oyster larvae 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 long flushing rates to retain larvae, may provide the best environments for recruitment of oysters to lagoonal estuaries.

Discussion. As the first study on oyster larvae 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.