Multiple drivers of interannual oyster settlement and recruitment in the lower Chesapeake Bay

Despite global investment in shellfish restoration activities, relatively little attention has been given to predicting optimal restoration sites and testing these expectations. We used a coupled biological-physical connectivity model as a guide to plant two distinct hatchery-spawned strains of the eastern oyster, Crassostrea virginica, in the Lafayette River, Virginia during the summer of 2013 at two locations corresponding to virtual spawning locations within the connectivity model. We utilized single nucleotide polymorphism markers to test the model predictions by genotyping oysters recruited after planting two hatchery-spawned strains and examining interannual recruitment variability for two successive years. Two spat were identified as hybrids of one of the planted strains and resident oyster genotypes. We also observed a genetic influence from an oyster strain used previously for restoration. Differences in environmental conditions between the two years of monitored recruitment likely affected larval dispersal and survival, contributing to observed interannual differences in the newly recruiting cohorts. Oyster spat from 2013 were genetically more similar to resident adults sampled in the Lafayette River, while the 2014 spat exhibited genotypic frequencies more similar to adults from surrounding rivers. The winds during the spawning seasons differed between years providing conditions for retention in 2013 and mixing of water masses in 2014. We recommend that the monitoring of restoration activities should consider relevant environmental conditions and observe multiple years of recruitment to assess the genetic impacts of restoration plantings and variable reproductive success