IMAGE COURTESY OF PENN COVE SHELLFISH FARMClimate change is bad for commercial oyster and mussel growers. But until recently, researchers weren’t sure exactly how rising CO2 levels and the resultant ocean acidification—reduced pH—harmed the farmed bivalves. This week (December 15), researchers proposed an answer: it’s all about saturation state. In a paper published in Nature Climate Change, scientists from Oregon State University and state agencies reported that the larvae of Pacific oysters and Mediterranean mussels have a hard time forming their calcium carbonate shells as the surrounding seawater’s saturation state falls. Saturation state is a measure of how corrosive the seawater is to the shells that the larvae make as they grow, and as CO2 increases in the atmosphere, saturation state drops. A lower saturation state means more corrosive water.
“Biological oceanographers have speculated that early life stages of marine organisms might be particularly sensitive to ocean acidification, but the underlying mechanisms remain unknown for most species,” David Garrison, program director in the US National Science Foundation’s Division of Ocean Sciences, which funded the research through an ocean acidification competition, said in a statement. “This research is an important step in being able to predict, and perhaps mitigate, the effects of ocean acidification on coastal resources.”
The researchers exposed shellfish larvae to chemically manipulated seawater in the lab and tracked the effects of falling saturation state on their growth. They found that if water was too acidic, the free-swimming larvae had to expend too much energy on shell growth, which diverted energy from feeding and swimming activities. This was especially damaging because the developing mollusks have a brief, 48-hour window in which they must begin feeding at a rate that ensures their survival. “The hatcheries call it ‘lazy larvae syndrome’ because these tiny oysters just sink in the water and stop swimming,” lead study author George Waldbusser, an Oregon State University marine ecologist and biogeochemist, said in the statement. “These organisms have really sensitive windows to ocean acidification—even more sensitive than we thought.”