Impaired development of offspring of eastern oysters Crassostrea virginica deployed in urban versus non-urban estuaries

The eastern oyster Crassostrea virginica , a keystone species in estuaries along the Atlantic and Gulf coasts of the USA, holds significant economic and ecological importance globally. Despite ongoing oyster restoration efforts, challenges persist in urbanized estuaries. We examined the reproductive success of 18 mo old oysters deployed for 12 mo in 2 highly urbanized sites, Newark Bay and New York Bay, USA, and a reference site in southern New Jersey (Great Bay). Developmental endpoints of second-generation oysters were observed after strip spawning field-deployed oysters and rearing fertilized eggs through juvenile stages in a controlled laboratory setting. Our results highlight transitional larval phases, including the rarely recognized blastula and gastrula stages. Due to lower rates of fertilization and spat production, reproductive success for oysters deployed at the 2 urban sites was one-fourth to one-half of that for oysters deployed at the reference site, and the progeny of oysters deployed at the urban sites had poorly mineralized, eroded, and malformed shells. We observed that trochophore larvae from adults deployed at the urban sites had irregular shapes, underdeveloped embryonic ectoderm, and poor mineralization. Exposure of adults in the urbanized estuaries to chemical contamination, or to low salinity, dissolved oxygen or calcium carbonate saturation states, separately or in combination, may have impaired oyster reproduction. Our results indicate that while eastern oysters can tolerate environmental stress, the synergistic effects of multiple stressors may hinder their successful reproduction and limit the re-establishment of oyster populations in urban estuaries.