How does rising atmospheric CO2 affect marine organisms?

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Individual and Combined Effects of Warming and Ocean Acidification on Young Corals

Paper Reviewed
Chua, C.M., Leggat, W., Moya, A. and Baird, A.H. 2013. Temperature affects the early life history stages of corals more than near future ocean acidification. Marine Ecology Progress Series 475: 85-92.

In a paper published in Marine Ecology Progress Series last year, Chua et al. (2013) note that climate change is projected to increase ocean temperatures by at least 2°C and decrease levels of pH by ~0.2 units (ocean acidification, OA) by the end of this century. And they write, in this regard, that "while the effects of these stressors on marine organisms have been relatively well explored in isolation, possible interactions between temperature and OA have yet to be thoroughly investigated," which shortcoming they thus set about to remedy.

Very briefly, the four researchers tested "whether temperature might act in combination with OA to produce a measurable ecological effect on fertilization, development, larval survivorship or metamorphosis of two broadcast spawning species, Acropora millepora and A. tenuis, from the Great Barrier Reef." This they did by means of four different treatments: (1) control, (2) higher, by 2°C, temperature, (3) high partial pressure of CO2 (700 ppm), and (4) a combination of high temperature and high pCO2, "corresponding to the current levels of these variables and their projected values for the end of this century under the IPCC A2 scenario."

This experiment, in the words of Chua et al., revealed "no consistent effect of elevated pCO2 on fertilization, development, survivorship or metamorphosis, neither alone nor in combination with temperature." And they indicate that the 2°C rise in temperature also "had no consistent effect on fertilization, survivorship or metamorphosis." However, they found that it actually increased larval development rates. And in light of these several discoveries, they concluded that "OA is unlikely to be a direct threat to the early life history stages of corals, at least in the near future," while holding out the possibility that warming might possibly be of some minor benefit.

Posted 12 November 2014