Ocean acidification

While Andrew Bolt continues his character assassination, let's get back to the facts. There are several misconceptions about ocean acidification that require correction, both here and elsewhere.

1.     “Ocean acidification is not a problem because organisms show a variety of responses (both positive and negative).”

The fact that not all organisms or physiological processes respond in the same way to ocean acidification is well known (Hendriks et al. 2009).  This does not, however, logically lead to the conclusion that ocean acidification is not a problem. Organisms like reef building corals, for example, show a consistent 15-54% reduction in calcification with a doubling of atmospheric CO2.  This is a problem irrespective of whether some other groups ( e.g. some bivalves) don't show this type of response.  Given that corals build and maintain coral reefs, the impacts on this group of organisms alone are likely to be large and negative.  

2.     “Ocean pH varies greatly in time and space.  This variability is much greater than any potential effect of carbon dioxide.”

It is true that ocean pH and carbonate ion concentrations do vary over time and space.  The issue, however, here is whether or not average pH is changing over time.  This is essentially the same distracting argument that some people have about the weather (i.e. day-to-day variability in temperature - "it was cold today, therefore climate change is happening.") and climate change (i.e. long-term trends in average temperature). 

3.     “Organisms like corals have been around for hundreds of millions of years, over which time atmospheric carbon dioxide has varied greatly. Therefore, we don't need to be concerned about ocean acidification.”

The fact that corals have survived as a group over long evolutionary time periods is irrelevant to whether or not current changes in ocean pH will impact their ability to build coral reefs. Having a long evolutionary history, gives little information about whether or not marine calcifiers like corals were rare or not at any particular time. Extinction has never been the issue here.  The issue is as follows:  If corals become rarer (and/or calcify less) due to ocean warming and acidification (e.g. (Bruno and Selig 2007; De'ath et al. 2009) then their ability to build and maintain coral reefs will be diminished. This in turn will decrease the ability of coral reefs to provide ecological services and support to over 500 million people worldwide. 

4.     “Carbon dioxide has been high in the past year coral reefs have continued to lay down calcium carbonate”.

This is not supported by the bulk of scientific studies.  Most of the evidence, reveals that marine calcifiers like corals did not form carbonate reef systems during periods of high CO2 in the past (Veron 2008 etc.).  There are big gaps in the depositions of carbonate during these periods.

5.     “We don't understand how the ocean works hence we do not have good evidence that ocean acidification is occurring.”

Modelling studies based on what are essentially simple geochemical processes have matched the observed decline in ocean pH.  Essentially, while we are there is still much to learn about how the ocean works, there are many empirical studies that show that ocean pH is changing rapidly. An excellent description of this work can be found in Doney et al. (2009).  Ocean acidification is occurring at rates which dwarf anything seen over the recent past.

Bruno, J. F. and Selig, E. R. 2007. Regional decline of coral cover in the indo-pacific: timing, extent, and subregional comparisons. PLoS ONE 2 (1):e711.

De'ath, G., Lough, J. M., and Fabricius, K. E. 2009. Declining Coral Calcification on the Great Barrier Reef. Science 323 (5910):116-119.

Doney, S., Fabry, V., Feely, R., and Kleypas, J. 2009. Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Science 1:169-192.

Hendriks, I., Duarte, C., and Álvarez, M. 2009. Vulnerability of marine biodiversity to ocean acidification: A meta-analysis. Estuarine, Coastal and Shelf Science.

 Veron, J. 2008 Mass extinctions and ocean acidification: biological constraints on geological dilemmas. Coral Reefs 27:459-472.

Posted by Ove Hoegh-Guldberg on Wednesday, 23 June, 2010

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