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, are being reported this week in the journal Nature Climate Change.
“Bivalves have been around for a long time and have survived different geologic periods of high carbon dioxide levels in marine environments,” said George Waldbusser , an Oregon State University marine ecologist and biogeochemist and lead author on the study, “The difference is that in the past, alkalinity levels buffered increases in CO2, which kept the saturation state higher relative to pH.”
“The difference in the present ocean is that the processes that contribute buffering to the ocean cannot keep pace with the rate of anthropogenic CO2 increase,” added Waldbusser, who is in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences. “As long as the saturation state is high, the oysters and mussels we tested could tolerate CO2 concentrations almost 10 times what they are today.”
The idea that early bivalve development and growth is not as physiologically linked to CO2 or pH levels as previously thought initially seems positive. However, the reverse is actually true, Waldbusser noted. Larval oysters and mussels are so sensitive to the saturation state (which is lowered by increasing CO2) that the threshold for danger will be crossed “decades to centuries” ahead of when CO2 increases (and pH decreases) alone would pose a threat to these bivalve larvae.
Learn more
- Read the full story from OSU News & Research Communications
- Related Sea Grant-funded research by Dr. Waldbusser and colleagues: