Oyster aquaculture in an acidifying ocean: Effects of ocean acidification on Eastern Oysters (Crassostrea virginica) and the mitigation potential of seagrass (Zostera marina)

Description

Ocean acidification (OA) is  the decrease in oceanic pH and associated changes in marine carbonate chemistry resulting from increased oceanic uptake of atmospheric carbon dioxide (CO2). This process poses a threat to marine life, as shifts in oceanic pH can have negative physiological and behavioural consequences for a wide array of marine plants and animals.

This research monitored the pH and carbonate chemistry in Shippagan Bay, New Brunswick (NB), and assessed the biological effects of ocean acidification on hatchery-reared Eastern Oysters (Crassostrea virginica) at different stages of production. It also aimed to explore the importance of  eelgrass (Zostera marina) as a potential mitigation strategy against OA for hatchery operations.

This project provides valuable information on OA in the coastal zone of Atlantic Canada, identifying how OA impacts oysters in their early life history stages, and developing a sustainable and environmentally-friendly mitigation strategy against OA. It also implements research to support the use of emerging technologies to identify or alleviate associated environmental concerns, and to create more environmentally sustainable operations. Collectively, these research findings provide information to provide effective management strategies for oyster hatcheries in the advent of a potentially-detrimental global change stressor.

Findings

Shippagan Bay had relatively stable and optimal pH and carbonate conditions (pH≥8.0), which is likely attributable to the high abundance of healthy eelgrass (Zostera marina). In the hatchery-nursery pond where juvenile oysters are grown, pH conditions were highly variable and often declined following rain events. Regular tidal inflow from Shippagan Bay was important in maintaining optimal pH levels and boosting aragonite saturation levels. Under laboratory conditions, low pH (7.5-7.7) had positive effects on adult reproductive development and larval survival, but slight negative effects on larval size and shape at 48-h post-fertilization. Juvenile oyster growth was unaffected by exposure to highly variable pH conditions, including values in the 7.0-7.5 range.

The results suggest that Eastern Oysters in northern NB (Shippagan Bay) may be relatively tolerant to OA in comparison to other populations elsewhere in the western Atlantic Ocean. This robustness is attributed to a long history of variable pH conditions in the region (as coastlines of northern NB bays are largely comprised of peat, resulting in acidic runoff and transient low pH conditions). This suggests that ocean acidification may not have a substantial negative impact on the oyster industry in NB.

More research is needed pertaining to long-term larval survival and the combined effects of ocean acidification and other stressors (e.g., ocean warming, hypoxia, pollution, etc.) on both wild and commercially-reared oysters. The results also highlight the important role of eelgrass in buffering seawater pH in Shippagan Bay and protecting the oyster industry against ocean acidification.

Publications

• Clements, J.C., Carver, C.E., Mallet, M.A., Comeau, L.A., Mallet, A.L. (2021). CO2-induced low pH in an eastern oyster (Crassostrea virginica) hatchery positively affects reproductive development and larval survival but negatively affects larval shape and size, with no intergenerational linkages. ICES Journal of Marine Science 78: 349-359. https://doi.org/10.1093/icesjms/fsaa089

Program name

Aquaculture Collaborative Research and Development Program (ACRDP)

Years

2017 – 2021

Principal investigator

Jeff C. Clements, Biologist, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region
Email: Jeffery.Clements@dfo-mpo.gc.ca

Team member(s)

• Luc Comeau, Research Scientist, Fisheries and Oceans Canada, Gulf Fisheries Centre, Gulf Region
• Claire Carver, L'Étang Ruisseau Bar Ltd.
• Élise Mayrand, Université de Moncton
• Sébastien Plante, Université de Moncton

Collaborator(s)

• André Mallet, L'Étang Ruisseau Bar Ltd.