Rising water temperature not the only risk to reefs

Coral reefs are one of my favorite biotopes. It’s astounding the variety of flora and fauna you can find in a very small area of reef, with their attendant diversity in color. Plus sessile animals! Those of us paying attention know that these species are extremely sensitive to environmental changes, and that even a minor rise in water temperature – a degree or two – would spell disaster, and could result in mass extinctions. Unfortunately, temperature isn’t the only parameter changing – water chemistry is changing, too.

The world’s oceans are turning acidic due to the buildup of carbon dioxide (CO2) in the atmosphere, and scientists say the effects on marine life will be catastrophic.

In the next 50 to 100 years corrosive seawater will dissolve the shells of tiny marine snails and reduce coral reefs to rubble, the researchers say.

The scientists stressed that increased ocean acidity is one of the gravest dangers posed by the buildup of atmospheric CO2.

“Ocean chemistry is changing to a state that has not occurred for hundreds of thousands of years,” said Richard Feely of Seattle’s Pacific Marine Environmental Laboratory.

Already, Feely said, ocean acidity has increased about 30 percent since industrialization began spurring harmful carbon emissions centuries ago. Unless emissions are reduced from current levels, an increase of 150 percent is predicted by 2100.

Such an increase would make the oceans more acidic than they’ve been at any time in the last 20 million years, he added.

As oceans absorb CO2 from the air, the gas reacts with water to produce carbonic acid. The acid in turn consumes the carbonate that sea creatures need to build their shells.

Not just shells – coral skeletons. The structure of the reef itself. Hobbyists who keep reef aquariums know how critical carbonate levels, and water chemistry (pH, etc), are to maintaining animal health.

Mass extinctions of marine life in the distant past, he said, were probably caused by chemical changes similar to those happening today.

“It took coral reefs about four to ten million years to recover each time,” he added.

Unfortunately, Veron said, “the very corals that will escape mass bleaching are those most prone to the effects of ocean acidification.”

Perhaps even more alarming is the threat to marine snails called pteropods.

Populations of these tiny creatures can reach up to ten thousand individuals per cubic meter (35 cubic feet) in the Southern Ocean. Their loss, Orr said, would have far-reaching effects.

“They’re an integral component of marine food webs, a huge food source for many marine predators,” he said.

It’s not just the risk to biodiversity – it’s the risk to the food chain as a whole.

I’m glad I had the opportunity to snorkel in a Caribbean reef when I was younger. I feel like I should make it a priority to do the same on some South Pacific reefs before that is no longer an option.