Globally, seawater pH is decreasing as the oceans absorb excess carbon dioxide from the atmosphere.
“The oceans are a massive sink for atmospheric carbon dioxide,” says Jeff Clements, lead author of the study. “All of this extra CO2 is changing the chemistry of the oceans, with potentially deleterious effects for marine shellfish.”
While ocean pH is not actually acidic by definition, the change in ocean pH presents a challenge for marine life. A major consequence is that shellfish like oysters have a harder time making shells. Although studies have reported negative effects of ocean acidification on oysters in the eastern United States, how oysters in Atlantic Canada may be affected remains unknown.
To fill this knowledge gap, the researchers studied Eastern oysters (Crassostrea virginica) at the L’Étang Ruisseau Bar oyster hatchery in northern New Brunswick. They found that adult oysters actually increased their reproductive development under low pH. In addition, while juvenile oysters were smaller and had a higher percentage of deformities under low pH, their survival was actually higher.
“To our knowledge, this is the first study showing such positive effects of low pH on this species of oyster, which is quite promising,” says Clements.
The researchers attribute the toughness of the oysters in this region to a long history of exposure to low pH conditions.
“The estuarine waters in which these oysters have evolved are very dynamic and show large natural fluctuations in pH due to events like freshwater runoff and daily fluctuations driven by photosynthesis - these waters regularly experience episodes of low pH,” says Martin Mallet, co-author of the study and hatchery manager at L’Étang Ruisseau Bar.
Clements and Mallet both admit that there are some caveats to the study that are important to note. For example, the relatively short time periods to which the oysters were exposed to low pH means that longer-term studies are needed to see if there are any effects of chronic exposure.
Overall, however, they think their results provide room for cautious optimism in the region and hope to follow this study with more work in the future.
“This isn’t just good news for the oyster industry in Atlantic Canada, but it’s also great news for industry and government research in the region,” says Clements.
Mallet agrees. “We have a great relationship and plan to continue working on research projects together in the future.”