Shellfishes emit CO2, what solutions exist?

In an article published in Reviews in Aquaculture, scientists reveal the idea that shellfish farms capture atmospheric carbon dioxide (CO2), is incorrect. In fact, shellfish emit CO2 as they build their shells. Returning shells to the water after the meat has been consumed, or cultivating algae with the shellfish, are promising ways of reducing CO2 emissions from shellfish farming.

Press release - Shellfish emit CO2, what solutions exist?

Scientists from Ifremer, CNRS, the University of Gothenburg in Sweden and the International Atomic Energy Agency's Radioecology Laboratory in Monaco, have reviewed 51 scientific papers that study the link between shellfish and CO2 . Thirty-six of them wrongly consider that shellfish production consumes CO2 because the idea is based on a misconception of carbonate chemistry.

"The main misunderstanding lies in the idea that the carbon in shells comes from atmospheric CO₂, whereas it is essentially derived from carbonate or bicarbonate ions from rock erosion. Their incorporation into shells therefore does not lead to the capture of CO₂ present in the atmosphere."

Fabrice Pernet, Ifremer researcher in marine organism ecology

In fact, it’s quite the opposite: far from absorbing CO₂, shellfish emit it. In addition to respiration, the calcification that forms the shell releases CO2 into the water, and the more CO₂ the ocean contains, the less it is able to absorb from the atmosphere.

However, the idea that shellfish production absorbs CO₂ has grown in the shellfish farming community and government policy, to the point of considering the granting of carbon credits to shellfish farmers. Although shellfish farming offers numerous environmental benefits (seawater clarification, nitrogen and phosphorus regulation, etc.), it does not contribute to CO₂ sequestration.

Return to the water of shells and co-culture with algae: two promising ways for reducing CO₂

However, the CO₂ emissions balance of the industry could be improved by returning shellfish to the ocean, or by developing algae co-culture on shellfish farming land.

"While the manufacture of shells produces CO₂, their dissolution consumes it. Unfortunately, today most shellfish waste is incinerated and thus transformed into atmospheric CO₂. Putting shells back in the water could therefore reduce CO₂ emissions from shellfish farming."

Fabrice Pernet, Ifremer researcher in marine organism ecology

On the other hand, through the process of photosynthesis, algae transform CO₂ into biomass. Their cultivation, combined with shellfish, could therefore capture some of the excess CO₂ produced by shellfish farming.

The development of these solutions opens up great prospects for reducing CO₂ production in shellfish farming, which remains, despite everything, the animal farming sector that emits the least carbon dioxide.

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