Larval Growth of Oysters in a Warming and CO2-Accreting World
Thiyagarajan, V. and Ko, G.W.K. 2012. Larval growth response of the Portuguese oyster (Crassostrea angulata) to multiple climate change stressors. Aquaculture 370-371: 90-95.
As the air's CO2 content rises in response to ever-increasing anthropogenic CO2 emissions, and as more and more carbon dioxide therefore dissolves in the surface waters of the world's oceans, the pH values of the planet's oceanic waters are projected to gradually drop, leading many scientists to question how this chain of events might impact the oceanic biosphere. In one such study, Thiyagarajan and Ko (2012) conducted a number of laboratory studies designed to see how the larval growth stage of the Portuguese oyster responds to various "climate change stressors," as they describe them, by investigating the effects of low pH (7.9, 7.6, 7.4) at ambient salinity (34 ppt) and low salinity (27 ppt), while "the combined effect of pH (8.1, 7.6), salinity (24 and 34 ppt) and temperature (24°C and 30°C) was examined using factorial experimental design."
In describing their findings, the two researchers say that, "surprisingly, the early growth phase from hatching to 5-day-old veliger stage showed high tolerance to pH 7.9 and pH 7.6 at both 34 ppt and 27 ppt," while they report that "larval shell area was significantly smaller at pH 7.4 only in low-salinity [italics added]." Then, in the 3-factor experiment (see figure below), they observed that "shell area was affected by salinity and the interaction between salinity and temperature but not by other combinations [italics added]." And they discovered that "larvae produced the largest shell at the elevated temperature in low-salinity, regardless of pH [italics added]."
Mean shell area of the Portuguese oyster larvae exposed to a low-pH or elevated carbon dioxide treatment for 5 days at two levels of salinity (ambient and low-salinity) and temperature (ambient and elevated). Each bar represents the mean ± S.D. of four replicate cultures. Adapted from Thiyagarajan and Ko (2012).
In light of these several positive findings, Thiyagarajan and Ko conclude that "the growth of the Portuguese oyster larvae appears to be robust to near-future pH level (>7.6) when combined with projected elevated temperature and low-salinity in the coastal aquaculture zones of [the] South China Sea."