The mortality of larval Pacific oysters in Northwest hatcheries has been linked to ocean acidification, yet the rate of increase in anthropogenic carbon dioxide in the atmosphere and the decrease of pH in near-shore waters have been questioned as being severe enough to cause the die-offs. However, a new study of Pacific oyster and Mediterranean mussel larvae found that the earliest larval stages are directly sensitive to saturation state, not carbon dioxide (CO2) or pH. Saturation state is a measure of how corrosive seawater is to the calcium carbonate shells made by bivalve larvae, and how easy it is for larvae to produce their shells. It is important to note that increasing CO2 lowers saturation state, the researchers say, and saturation state is very sensitive to CO2; the challenge interpreting previous studies is that saturation state and pH typically vary together with increasing CO2. The scientists utilized unique chemical manipulations of seawater to identify the direct sensitivity of larval bivalves to saturation state. Results of the study, which was funded by the National Science Foundation, have been reported in the journal Nature Climate Change.
