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I'm a professor of marine ecology an UNC Chapel Hill and have been working on coral reef ecology and conservation for nearly twenty years. But I only recently became aware of the threat to reefs posed by ocean acidification.
New research indicates that the buildup of carbon dioxide in the atmosphere is slowing the growth of reef-building corals by increasing the acidity of the world's oceans. By burning immense amounts of fossil fuels, humans have increased the concentration of carbon dioxide (CO2) in the atmosphere by nearly 40%. Roughly a quarter of this CO2 is being absorbed by oceans, where it reacts with seawater to form carbonic acid, acidifying the upper layers of the ocean.
Several laboratory experiments suggest this could make it more difficult for corals and other organisms such as crabs and clams to secrete the calcium carbonate skeletons they depend on for survival. The increased acidity essentially makes it more energetically costly to secrete skeletons and could eventually literally dissolve them.
A new research article published today in Science magazine (De'ath, et al. 2009) and reported on msnbc.com takes the case for ocean acidification a step further. The article suggests that the recent man-made increase in ocean acidity has reduced the growth rate of reef-building corals. A team of scientists from the Australian Institute of Marine Science measured the growth of hundreds of corals from 69 reefs on the Great Barrier Reef (GBR) in Australia. The team took cores of the coral skeletons and measured annual growth rings going back 400 years. Their results indicate that the vertical extension of massive, long-lived corals has slowed by roughly 13% since 1990. This decrease in growth coincides with an increase in the acidity of tropical oceans.
I think this is a very important study. And the findings are frankly pretty scary.
Slower growth might not seem like a big problem, but reef scientists are concerned that this will exacerbate the impacts of other threats to coral reefs. For example, it will slow the vertical growth of corals, making it harder for them to keep up with rising sea levels. It could also slow recovery from other disturbances such as coral bleaching episodes and destructive storms.
We are increasing the concentration of CO2 in the atmosphere faster even than the IPCC worse-case-scenario. And there is a lag of many decades between the addition of CO2 and the resulting increase in ocean acidity. So we will almost certainly see this problem grow over the next few centuries. The only questions are by how much, how quickly corals can acclimate to climate change and what the broader impacts will be.
Corals create the physical structure that thousands of other species depend on. They play a role analogous to trees that create forests. When corals die, so do the fish and invertebrate animals that live on reefs.
When they are working properly, coral reefs provide human societies with massive economic benefits through fisheries, tourism and invaluable services like buffering from storms. I often refer to reefs as the ATMs of the sea. By allowing reefs to become degraded, we are forfeiting a gigantic natural service; an opportunity cost that will have to be paid by diverting revenue from other sources. If the dire forecasts about the impacts of climate change on coral reefs are accurate, it seems likely that millions of people will lose their livelihoods.
I just got back from a quick trip to Heron Island Research Station on the Great Barrier Reef , where I plan to live and work for nine months in 2010. It is an almost indescribably amazing place. The GBR may not be pristine, but it is the closest thing to an intact ocean ecosystem I have ever experienced. Top predators like sharks are plentiful and their prey are nervous. To an ecologist, those are important signs of a healthy food web. The corals are wildly diverse and relatively abundant. I usually work in highly degraded marine ecosystems. So seeing the GBR gave me a fresh perspective on the way the world use to be and a strong sense of hope that reefs can be saved.
What can we do to mitigate the impacts of climate change on coral reefs? I'd like to see more bikes, more solar panels, and more nuclear power plants. Better batteries wouldn't hurt either. I'd also be happy to have a permanent $1-$2 per gallon gas tax imposed in the US. This would encourage conservation and solidify the recent move to smaller cars. But more importantly, it would promote the development of alternate energy technologies by reducing market risk.
There are many technological and lifestyle solutions. I understand the hesitation people have in implementing them. But the threats are real and given the enormous value of natural ecosystems, the investment is a sound one. Think of it as changing the oil in your car or wearing your seat belt. Simple precautions to avoid potentially catastrophic consequences.
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Jim, Many or most my colleagues do think nutrient pollution and terrestrial runoff are one of the major causes of coral loss. I have worked on how nutrients can increase the severity of coral diseases, so I am sympatheic to the argument (you can download the paper here if you are …