The effects of ocean acidification and parental history on eastern oyster (Crassostrea virginica) biomineralization and functional morphology

Ocean acidification (OA) negatively impacts biomineralization by reducing the availability of carbonate ions in seawater, which calcifying organisms use to build their shells or skeletons. Larval stages are particularly vulnerable because of their rapid rate of calcification and their increased exposure of crystal nucleation sites to seawater. Changes in the growth rate and function of larval shells could result in longer time to larval settlement, increased stress during metamorphosis, and increased susceptibility to predation and desiccation. Most previous studies have assessed the impacts of OA on larvae with parents naïve to the effects of OA. However, parental history could play a key role in determining larval response to OA through nongenetic inheritance mechanisms. We examined the effects of parental and larval exposure to OA on eastern oyster (Crassostrea virginica) biomineralization and functional morphology. Adult oysters were exposed to control (400 ppm pCO₂) or OA (2800 ppm pCO₂) conditions for 30 days. We produced zygotes using a North Carolina II cross design and exposed larvae from each cross to control and OA conditions for three days. Larval exposure to OA, regardless of parental history, resulted in more rounded larval shells and increased the proportion of larvae with visibly extruded cilia – indicating a potential change in the ability of the shell to contain soft tissue and thus prevent desiccation and/or exposure to predation. Parental history of exposure to OA did impact shell size, however, with larvae from naïve parents exhibiting a greater decrease in median shell length when exposed to OA than larvae from OA-exposed parents. These results suggest that parental exposure could reduce some of the negative impacts of OA. They also provide insights into the potential functional impacts of OA on early life stages of an ecologically and economically important species.