Predominant factors limiting the recovery of the eastern oyster (Crassostrea virginica) in western Mississippi Sound, USA

In addition to suitable substrate, successful oyster recruitment requires an adequate supply of planktonic larvae, followed by the subsequent survival and growth of early post-settlement stages. Substrate limitation, recruitment limitation and post-settlement limitation each played key roles in limiting the recovery of the eastern oyster, Crassostrea virginica (Gmelin 1791) within western Mississippi Sound between 2016 and 2019. Effects of a mortality event which eliminated the oyster spawning stock biomass from two major oyster reefs of western Mississippi Sound in 2016 carried over to the 2018 recruitment period. But the supply of larvae from outside the affected reefs was sufficient to provision spat to restored and reference sites within the 2018 study area. Thus, substrate limitation was inferred to be the primary limitation to early oyster recruitment in 2018. Moreover, variability in spat metrics from settlement samples implied potential post-settlement limitation in 2018. Spat density, mortality, size, and inferred growth varied on temporal, subregional, and microhabitat scales. In 2019, oyster spawning stocks were completely decimated throughout the western Mississippi Sound region by unprecedented freshwater discharge from the Bonnet Carré spillway. Consequently, early oyster recruitment was effectively eliminated, as evidenced by the lack of spat settlement across the entire oyster metapopulation of western Mississippi Sound. Within the course of a single year, the predominant deterrent to oyster recovery had shifted from substrate limitation to recruitment limitation.