Seawater carbonate chemistry and larval feeding physiology of the mussel Mytilus californianus

Ocean acidification (OA)—a process describing the ocean's increase in dissolved carbon dioxide ( pCO2) and a reduction in pH and aragonite saturation state (Ωar) due to higher concentrations of atmospheric CO2—is considered a threat to bivalve mollusks and other marine calcifiers. While many studies have focused on the effects of OA on shell formation and growth, we present findings on the separate effects of pCO2, Ωar, and pH on larval feeding physiology (initiation of feeding, gut fullness, and ingestion rates) of the California mussel Mytilus californianus. We found that elevated pCO2 delays initiation of feeding, while gut fullness and ingestion rates were best predicted by Ωar; however, pH was not found to have a significant effect on these feeding processes under the range of OA conditions tested. We also modeled how OA impacts on initial shell development and how feeding physiology might subsequently affect larval energy budget components (e.g. scope for growth) and developmental rate to 260 µm shell length, a size at which larvae typically become pediveligers. Our model predicted that Ωar impacts on larval shell size and ingestion rates over the initial 48 h period of development would result in a developmental delay to the pediveliger stage of >4 d, compared with larvae initially developing in supersaturated conditions (Ωar > 1). Collectively, these results suggest that predicted increases in pCO2 and reduced Ωar values may negatively impact feeding activity and energy balances of bivalve larvae, reducing their overall fitness and recruitment success.