Oysters and eelgrass help each other out under increasing carbon dioxide levels

Increasing human output of carbon dioxide results in higher temperatures and in ocean acidification—the lowering of ocean pH and other chemical changes. Oysters are threatened by ocean acidification, while eelgrass may benefit from the higher carbon dioxide levels in the water. A new laboratory study asks whether culturing Pacific oysters (Crassostrea gigas) together with eelgrass (Zostera marina) can help both out. The idea is that the eelgrass uses up carbon dioxide in the water, which should buffer the effects of ocean acidification and increase pH levels; while oysters filter disease-causing organisms out of the water, which should improve eelgrass growth. In a series of recent experiments that tested these ideas, eelgrass wasting disease declined under higher carbon dioxide conditions, and was even more dramatically cut in the presence of oysters, resulting in faster eelgrass growth. In addition, in the presence of eelgrass, pH did increase, but the increase in oyster mass was not statistically greater than expected by chance. The new study was conducted by Maya Groner while at the University of Prince Edward Island, together with coauthors that include SAFS professor Carolyn Friedman, and is published in the journal Ecology.

Growing oysters with eelgrass should have two main effects: eelgrass uses carbon dioxide, thus increasing pH and reducing the effects of ocean acidification on oyster growth; and oysters filter out pathogens including those that cause eelgrass wasting disease, benefiting eelgrass growth.

 

When cultured with oysters, eelgrass grows faster (top panel), and eelgrass wasting disease (EWD, bottom panel) is greatly reduced, especially when carbon dioxide (pCO2) levels are high.

 

Levels of pH increase when eelgrass is grown, reducing the effects of acidification on oysters.
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