“Researchers in Australia say the growth of coral on the country’s iconic Great Barrier Reef (GBR) has fallen since 1990 to its lowest rate in 400 years,” variations of this message have been repeated around the world from South Korea to London with global warming, and the associated acidification of oceans, claimed to be the cause.

These reports are repeating claims in an Australian Institute of Marine Science (AIMS) media release made just last Friday to coincide with the publication of research findings in the journal Science [1].

The media release also claimed the research to be “the most comprehensive study to date on calcification rates of GBR corals”.

Having followed GBR issues for many years I was surprised to hear global warming associated with slow coral growth rates, indeed AIMS’s researchers Janice Lough and David Barnes have published detailed studies concluding that coral growth rates increase significantly with an increase in annual average sea surface temperature [2]. Furthermore growth rates actually decrease from north to south along the GBR as this corresponds with a cooling temperature gradient of 2-3 degrees C.

If there has been a slowing in growth rates of coral over the last nearly 20 years, as suggested by this new research, a most obvious question for me would be: Have GBR waters cooled?

This new research paper in Science presents evidence for a decline in coral growth rates since 1990, but no credible reason for the decline. While the study hints that the cause could be ocean acidification no direct evidence is provided to support this claim – not even a correlation. Indeed no data is presented to suggest the PH (a measure of acidity) of GBR waters has changed, and based on modelling of hypothetical changes in PH associated with increases in atmospheric carbon dioxide there is a timing problem – the decline in calcification rates should apparently have started years earlier.

Confronted with a lack of evidence in support of this hypothesis – that ocean acidification has caused the drop in growth rates – the researchers suggest in the paper “synergistic effects of several forms of environmental stress” and implicate higher temperatures. But no data is presented in the paper to contradict the well established relationship between increasing temperature and increasing growth rates – though various confusing statements are made and it is suggested that global warming has increased the incidence of heat stress in turn reducing growth rates – while at the same time the researchers acknowledge higher growth rates in northern, warmer, GBR waters.

Marine Biologist Walter Starck has perhaps aptly described the research as part of “the proliferation of subprime research presenting low value findings as policy grade evidence” and has suggested this has “science headed in the same direction as Wall Street.”

Interestingly, Queensland Premier, Anna Bligh, has decided the “massive decline in the reef’s growth” will require new laws.

None of this, however, gets us any closer to understanding why there has been an apparent dramatic decline in the growth rates of GBR corals over the last 20 years.

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Notes

[1] G. De’ath, J.M. Lough and K. Fabricius (2009) Declining Coral Calcification on the Great Barrier Reef. Science. Volumne 323, pages 116-119

[2] J.M. Lough and D. J. Barnes (1999) Environmental controls on growth of the massive coral Porites. Journal of Experimental Marine Biology and Ecology. Volume 245, Issue 2, pages 225-243

Picture from Walter Starck’s collection.