Within and Cross-Generational Effects of Elevated Seawater pCO2 on Larval Bay Scallops Argopecten irradians (L)

Bivalve larvae are highly susceptible to ocean acidification (OA), but there is little knowledge of the capacity of bivalve species to acclimate or adapt to changing ocean conditions. It is challenging to compare results among studies of OA reported in the literature, as there is little consistency among studies in water chemistry across OA treatments used or how OA conditions were determined. In addition, it is difficult to predict from short-term experiments how populations might respond across generations. The bay scallop, Argopecten irradians, is a good model species for such experiments because of its short generation time and importance commercially and ecologically. Bay scallops were exposed to OA conditions from embryos to metamorphosis across two generations. Ocean acidification treatment levels included historical or preindustrial “low” (pCO2 ∼450 µatm), current average “moderate” (∼800 µatm), and future “high” (∼1,350 µatm). In the first generation, high OA had negative effects on larval performance, with no survival to metamorphosis, preventing its inclusion in the second generation. Moderate OA reduced performance (survivorship and growth) relative to the low OA. In the second generation, however, there was no difference in survival between the moderate and low OA treatments, but the difference in size at metamorphosis remained. These results suggest that over two generations, bay scallops either acclimated or adapted to moderate OA. Further work is needed to determine the extent to which long-term, generational adaptation to OA is possible in the bay scallop.