Futuristic Ocean Acidification Levels Reduce Growth and Reproductive Viability in the Pacific Oyster ( Crassostrea gigas  )

In this study, we investigated the effects of futuristic pH because of climate change on the growth and reproductive viability of the Pacific oysters. The futuristic pH levels to which adult oysters were exposed are 7.5 and 7.8 (as extreme case) and 8.1 (as moderate case), with pH 8.2 serving as the control. We monitored growth and reproductive viability over a four-week exposure period. The reproductive viability of the oysters exposed to each pH level were assessed based on the sperm motility and egg viability. Throughout the exposure period, the induced acidified nature of each treatment aquaria was maintained. Data obtained from this investigation revealed significant decrease in weight of oysters exposed to pH 7.5 and 7.8 compared to the groups exposed to pH levels 8.1 and 8.2 (p < 0.05). Groups of oysters exposed to pH 7.5 recorded as much as 10.49% decrease in weight, with specific growth rate (SGR) of -0.4 %/day. Reproductive viability was significantly compromised in groups exposed to pH 7.5 and 7.8 as evident with reduced sperm motility and percentage of ruptured eggs in these groups of oysters. We therefore postulate that climate change will have significant impact on the recruitment of oysters in coastal waters as growth and reproduction will be impaired at extreme levels of futuristic ocean acidification.

Keywords
Ocean acidification; climate change; growth; reproductive viability; Crassostrea gigas