New research from China suggests that oysters can be good at removing carbon dioxide from oceans, making the bivalves both an important food source and a potential tool in the fight against climate change and ocean acidification.
Scientists have long debated whether oysters are a net source or sink of carbon dioxide (CO2) in the marine environment. That’s because when oysters build their shells using calcium and other elements in the seawater, they release CO2, raising concerns that they may be a source of marine carbon, which reduces the ocean’s ability to absorb atmospheric CO2. However, the recent study finds that overall, oysters help capture and lock away nearly 2.4 times more carbon than they release when forming their shells.
Researchers conducted the study using large outdoor tanks, each held different densities of Pacific oysters (Crassostrea gigas). Over a span of 120 days between June and October 2023, they monitored the growth of phytoplankton, carbon levels and the amount of organic carbon within sediments, including oyster waste, deposited at the bottom of each tank. Oysters consume algae and other tiny pieces of organic matter in seawater and effectively deposit the carbon they contain on the seafloor, largely in the form of oyster waste.
Analyzing data, the team determined the amount of carbon sequestered by oysters compared with carbon released during shell formation.
The researchers found that a moderate density of 1-2 oysters per square meter (10.8 square feet) in the experimental tanks sequestered the most carbon, capturing more than twice as much carbon as they released in forming their shells.
“This is indeed a very interesting and ambitious study, probably one of the most compelling in the field,” Fabrice Pernet, a researcher with the French Institute for Research on the Exploitation of the Sea , not involved with the study, told Mongabay in an email.
However, Pernet added that he sees two “major flaws” with the study. First, the research was conducted from June to October, and all the samples were collected in the daytime, when photosynthetic activity of phytoplankton is high, “which likely lead to an overestimation of CO₂ uptake and/or an underestimation of CO2 outgassing,” he said.
The study was also conducted at a single location, so Pernet cautioned that the results shouldn’t be used to generalize the potential of oyster farming as a whole.
Still, the study’s authors write that their results show potential for oysters to be an effective nature-based solution for several global challenges, such as rising food demand and ocean acidification, “making it a critical component of sustainable marine resource management.”
Banner image of shucked oysters. Image by Dr 방원장 via Wikimedia Commons (CC BY 4.0).
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