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The Impact of Ocean Acidification on the Pearl Oyster

Paper Reviewed
Liu, W., Yu, Z., Huang, X., Shi, Y., Lin, J., Zhang, H., Yi, X. and He, M. 2017. Effect of ocean acidification on growth, calcification, and gene expression in the pearl oyster, Pinctada fucata. Marine Environmental Research 130: 174-180.

Dissolution of atmospheric CO2 into the surface waters of the world's oceans is believed to have caused a slight decline in seawater pH of 0.1 unit over the past two centuries; and it is projected that future CO2 emissions -- if left unchecked -- could cause an additional decline of up to 0.3 pH units by the end of this century, a phenomenon referred to as ocean acidification. The impacts of this possibility, however, remain highly debated and a key topic of scientific inquiry.

The latest group to examine this topic is the eight-member Chinese research team of Liu et al. (2017), who studied the impacts of ocean acidification on the pearl oyster (Pinctada fucata). As both an ecologically and economically important bivalve species inhabiting the southern coasts of China, the pearl oyster has surprisingly not received much attention in this regard. Thus, it became the objective of the eight scientists to investigate the impact of ocean acidification on the shell growth, calcification and expression of calcification-related genes in pearl oyster specimens subjected to three levels of seawater pH over a period of 42 days.

Oysters were collected from a major growing area in Daya Bay Station on the southern coast of China and transported to aquaria in a controlled-environment setting. Following one week of acclimation, the oysters were divided into one of three pH treatments: a natural level of 8.10 representative of today's conditions, and two lower values (7.70 and 7.40). The 7.70 treatment was chosen to represent conditions that might exist at the end of this century, while the 7.40 pH treatment, which corresponded to a pCO2 value of approximately 3000 ppm, represented an extreme condition that may very well never be reached in the real world.

In describing their findings, Liu et al. report that "elevated pCO2 levels resulted in a significant decrease in shell length growth rate and total weight only when seawater was undersaturated [with] respect to aragonite and calcite," which undersaturation only occurred in the 7.40 seawater pH treatment. Additionally, the authors state that at the end of the 42 day experiment there was no significant difference in mean shell hardness, mean shell calcium content or the expression of calcification-related genes among the oysters growing in the 8.10 and 7.70 pH treatments. Thus, in light of their findings, the authors conclude that the pearl oyster "could acclimate to long-term exposure to low seawater pH (7.70)." And if it was able to accomplish that feat after being instantaneously shocked into its low-pH environment after just 42 days, imagine what it could accomplish following a period of a century or more of adaptation and evolution!

Posted 27 March 2018