For healthier shellfish, add lime

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With oceans quickly acidifying due to carbon dioxide emissions, aquaculture farmers face a serious threat to the health of calcifying sea organisms like crabs, clams, mussels and shellfish that we enjoy at the dinner table.

“It’s becoming harder and harder for these organisms to build their calcium carbonate shells in larval stages because there are fewer free carbonate ions in acidic seawater,” explained SFU environmental sciences graduate student Carolyn Duckham.

Duckham has discovered however that the missing carbonate ions can be restored by adding hydrated lime, an inexpensive, abundant compound that increases pH and could neutralize acidic seawater. During a two week long experiment, Duckham found that shellfish larvae growing in limed water — where the pH is at 7.65, close to pre-industrial levels — grew significantly larger shells than those in acidic seawater.

“However, we found no impact — positive or negative — on shellfish survival or the level of deformities in larvae with the use of hydrated lime,” says Duckham. “But, its use does help them grow. And when you look at other research, you see that those that grow bigger tend to do better.”

It seems natural to extrapolate these results and assume that liming the whole ocean would be feasible and effective — but, Duckham explained, this is not the case. “You’d have to add so much lime into the ocean to do that. It would ramp up the pH and take years to circulate around the ocean, so from that aspect, it’s only useful [at the hatchery level].”

In the future, she notes, carbon dioxide emissions and water acidity in nature will likely increase until shells begin dissolving into seawater. Though other studies indicate that hatchery shellfish are more resilient to ocean acidification than wild shellfish, scientists are still raising concern over their general ability to adapt to these harsher conditions.

“I think the fear for most scientists is that environmental change is occurring so fast, and we don’t know if these organisms can adapt quickly enough,” said Duckham.

Similar acidification reversal strategies are already in place in East Coast aquaculture to control invasive tunicates. Duckham’s strategy is soon to be tested by the Center of Shellfish Research on a hatchery-wide scale — this will involve larger sample sizes and tests on different species of shellfish than her lab tests.

“In some ways, my method is a temporary, bandaid solution,” concluded Duckham. “But for now, these findings could really help the shellfish industry until we figure out what we’re going to do about the world’s fossil fuel emissions.”

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