Cohort adaptation is a within-generation population response to spatial variation in selection below the scale of average dispersal. C ohort adaptation can provide a dynamic response to temporal and spatial environmental heterogeneity and maintain spatially balanced polymorphisms. Using Eastern oysters Crassostrea virginica as a model, this study seeks to test for genomic signatures expected from cohort adaptation along the Delaware Bay salinity gradient. A wild transect of adult samples was sampled in 2019 after precipitation generated a protracted period of low salinity leading to substantial oyster mortality on up-bay beds . Based on whole genome sequence comparisons we found very low population differentiation (FST pairwise average 3e-4), underscoring the dominant role of homogenizing gene flow within the estuary . We hypothesized that hypo-salinity selection was strong enough up-bay to increase the frequency of tolerance traits and genes contributing variation to those traits. A model-based single generation selection (SGS) test was implemented to detect significant allele frequency differences between the transect end samples , beyond that expected from genetic drift in a single population (e.g., sweepstakes reproduction) and sampling error . Thousands of single nucleotide polymorphism (SNP) candidates were identified, distributed across the genome with low to moderate allele frequency change magnitudes. Challenge experiments were used to identify and compare genomic changes resulting from extreme hypo-salinity selection on adults, but parallel responses are only expected for genes of large effect. Therefore, additional metrics were compared between SGS candidate vs. control loci to increase confidence in a cohort adaptation inference.