Growing oysters in the face of climate change

Learning from the life history of the European flat oyster (Ostrea edulis) as a SEANET (Sustainable Ecological Aquaculture Network) intern at the University of Maine's Darling Marine Centre.

Brooding Oysters

Ocean acidification (OA) is a threat to many marine organisms, especially calcifying mollusks that need to build shells. However, previous studies have shown that the larvae of the Ostrea genus are capable of resisting declines in pH, and may represent survivors as oceans acidify (1). Ostrea edulis is a brooding oyster species that can retain larvae internally in a brood chamber. Past research has suggested that this internal environment can reach low pH conditions when mothers isolate their chamber from the overlying water (2). Adverse conditions inside the brood chamber may have inadvertently applied evolutionary pressure on larvae to develop in low pH environments. Here we investigated O. edulis' brood chamber oxygen and pH content to better understand how this species might fare as oceans acidify.

CO₂ reacts with the ocean to create a weak acid that increases the number of protons in the water. This makes it harder for calcifying animals to form shells (3)

Brood Chambers can be Low in Oxygen and Create an Acidic Environment

Oxygen content in O. edulis was found to steadily decline over time in conditions with no food. The data suggested that the brooding oyster gradually ventilated less and closed up the brood chamber, possibly as a protective and energy saving response. After forcing an oyster shut, pH declined rapidly. Such closures happen naturally after changes in environmental conditions. Image analysis revealed trends in which a closed oyster caused internal pH to decline when closed and pH to increase when open and ventilating.

Brooding O.edulis at the Darling Marine Centre, Maine (4)

Resistance to Ocean Acidification?

The internal environment of Ostrea edulis therefore appears to be capable of reaching significantly lower and variable pH and oxygen content than ambient seawater. This is especially true when mothers close up and seal themselves from the external environment for extended periods of time. Low pH conditions found in the brood chamber suggests an evolutionary pressure for larvae to adapt to low pH environments. This data suggests that O. edulis may be a "winner" amidst changing ocean acidification and may become an important species to the oyster aquaculture industry in Maine due to climate change (5).

References

1. Waldbusser G, Gray M, Hales B, Langdon C, Haley B, Giminez I, Smith S,Brunner E, Hutchinson G (2016) Slow shell building, a possible trait for resistance to the effects of acute ocean acidification.

2. Chaparro O.R, Segura C.J, Montory J.A, Navarro J.M, Pechenik J.A (2009) Brood chamber isolation during salinity stress in two estuarine mollusk species: from a protective nursery to a dangerous prison.

3. Image courtesy of “Marine Science Today”- http://marinesciencetoday.com/2014/03/12/ocean-acidification-the-devastatingtruth/

4. Image courtesy of Dr. Matthew Gray (University of Maryland).

5. Gray, M. W., Chaparro, O., Huebert, K. B., O’Neill, S. P., Couture, T., Moreira, A., & Brady, D. C. (2019). Life History Traits Conferring Larval Resistance against Ocean Acidification: The Case of Brooding Oysters of the Genus Ostrea. Journal of Shellfish Research, 38(3), 751. https://doi.org/10.2983/035.038.0326