Slowest Growth In 400 Years

The image you see at the top of the post is a section of Australia's Great Barrier Reef-- the largest coral reef in the world, roughly parallel to the coast of Queensland, Australia, for almost 2,000 km--which began growing approximately 500,000 years ago. The Great Barrier Reef is the Earth's largest biological structure, so large it can be seen from space.

But researchers looking at the reef recently discovered that it is growing at its slowest rate for at least 400 years. Professor Glenn De'ath (I know, I know... what an ominous name to accompany this report), who carried out the research at the Australian Institute of Marine Science, believes that increased ocean acidification due to the absorption of carbon dioxide from the atmosphere is the main culprit.

The team, which published the findings in the journal Science, looked at a total of 328 coral colonies spanning the reef. They found that calcification rates (rate at which coral polyps secrete their limestone skeletons) increased 5.4 per cent between 1900 and 1970, but have dropped 14.2 per cent from 1990 to 2005, mainly due to a slowdown in growth from 1.43 centimetres per year to 1.24 centimetres per year.

But wait. Couldn't the decreased calcification rates correlate to some other causes such as land-based sources of pollution or water quality? Nope, says Australian coral-climate expert Ove Hoegh-Gulberg, "The very fact that the effect is seen on inshore as well as offshore reef sites rules out [the chance that] the observed decline has been due to declining coastal water quality".

Decreased growth rates aren't just being tracked in the Pacific, either. As reported this past summer at the 11th International Coral Reef Symposium, growth and calcification rates of brain coral colonies in Bermuda have shown a 25% decline since 1959. Clive Wilkinson, global coordinator of the Global Coral Reef Monitoring Network in Townsville remarked that calcification decline in coral reefs is "here and now and over the past decade, not some time in the future, as we predicted." "This has been happening under our noses," he said.

I've written extensively on the threats to our ocean from acidification. For another take, check out Miriam's Quick and Dirty Guide to Ocean Acidification as guest blogger at The Reef Tank.