Effects of ocean acidification on early developmental stages of the Pacific oyster (Crassostrea gigas) in an aquaculture setting

Ocean acidification is a great concern worldwide. It has important impacts on the shellfish industry. However, more information is needed to assess the impacts of ocean acidification (OA) on economically important shellfish in a realistic industry setting. The goal of this thesis was to determine the effects of OA on the early developmental stages of the Pacific oyster, Crassostrea gigas. To better represent industrial-scale oyster production than is possible in small-volume, short-term laboratory studies, experiments were conducted at the Island Scallops hatchery facility using large volume containers and appropriate time scales. In Chapter 2, I investigated the effects of acidification on fertilization and larval development to explore the potential links between vulnerability at these life stages and documented mass mortality events in hatcheries in the past. Elevated pCO₂ contributed to increased egg fertilization. However, not all fertilized eggs were viable, and elevated pCO₂ reduced the likelihood of further development to later embryonic stages, resulting in decreased overall fertilization success in C. gigas. Increased pCO₂ levels also negatively affected oyster larvae by reducing growth and reducing the production sufficiently large to be suitable for aquaculture rearing practices. Larval deformity and mortality also showed a trend towards increases in acidified conditions whereas feeding was reduced. In Chapter 3, I assessed early development in benthic juveniles to test for potential for carry-over and/or acclimation effects of prior larval exposure to elevated pCO₂. Settlement did not depend on pCO₂ conditions during the larval phase. However, metamorphosis was reduced when larvae had been exposed to elevated pCO₂ levels. Juvenile growth and condition were both reduced after juvenile’s exposure at higher pCO₂ levels, but shell strength was unaffected. ii Overall, these findings suggest that OA had negative impacts on multiple life history stages in C. gigas. However, the lack of larval exposure effects on juvenile growth or condition suggests an absence of carry-over effects or acclimation for juveniles. These results have important implications for the aquaculture industry and for the development of best practices for combating the effects of ocean acidification.

Picard M., 2014. Effects of ocean acidification on early developmental stages of the Pacific oyster (Crassostrea gigas) in an aquaculture setting. MSc thesis, The University of British Columbia, 90 pp. MSc thesis.

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