Increased Carbon Dioxide Levels Damage Coral Reefs

Scientists have been worried about coral reefs for years, since realizing that rising temperatures and rising ocean acidity are hard on organisms that build their skeletons from calcium carbonate. Researchers on Australia's Great Barrier Reef are conducting an experiment that demonstrates just how much corals could suffer in the coming decades.

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As we burn fossil fuels - we're talking about oil, gas and coal - carbon dioxide builds up in the atmosphere. Now, there are debates about how quickly that is changing the global climate, but there is no question that billions of tons of carbon dioxide have soaked into the ocean. That's making waters more acidic, which puts some ocean ecosystems at risk, particularly coral reefs. We sent NPR science correspondent Richard Harris to Australia's Great Barrier Reef to look into these consequences. His first stop was a research station on Heron Island.

(SOUNDBITE OF WATER SPLASHING)

RICHARD HARRIS, BYLINE: Heron Island is surrounded by a reef that is home to sea turtles, sharks, rays, brilliantly colored fish, and hundreds of other species. The spectacular scenery draws snorkelers from around the world. The island also hosts one of the world's major coral reef labs, run by the University of Queensland, and research there shows that the reefs are in trouble. Scientist Sophie Dove plunges her arms into a tank the size of a kettle drum.

SOPHIE DOVE: OK. We'll start with the plates. Uh-huh.

HARRIS: She and research assistant Annamieke van den Heuvel are weighing chunks of coral.

ANNAMIEKE VAN DEN HEUVEL: Two hundred and forty-six point nine.

DOVE: Do you want to just check the zero when I take this away?

HARRIS: Dove has recreated a simplified version of the coral ecosystem in a dozen large tanks.

DOVE: And so in each tank here we basically - I can lift up the lid - this is one of our - this is our present-day tank, if you like.

HARRIS: The water temperature and the carbon dioxide levels match the conditions on the present-day reef.

DOVE: We've got little mushroom corals, fungia, brain corals, stylophera pistolata there. It's a very common coral around the world. We've got these corals that look like bunches of flowers. They're called lobophelia.

HARRIS: The corals in this tank look healthy. And as she weighs them, she seems that they've been growing since she transplanted them here nearly a year ago. Then she opens the next tank.

DOVE: We'll hop from present day, and the next one along here is the worst of the future with a thing we call business as usual or do nothing tank.

HARRIS: Dove is pumping much warmer water with lots of added carbon dioxide into this tank. This is what the world's oceans are likely to look like later in this century when the schoolchildren visiting this island today reach middle age.

DOVE: And as you look into here, it looks quite different, as you will see.

HARRIS: Oh yeah.

DOVE: OK. So there's lot of this slimy, yucky mess(ph) of cynobacteria.

HARRIS: Clumps of black gunk swirl along the surface of the tank.

DOVE: We find that cynobacterial (unintelligible) tend to do really well in the future. The slippery slope to slime seems to be the way to go.

HARRIS: Not so for the coral. Most of it has either died or turned white, which means the organisms that live inside the coral have moved out.

DOVE: So as you see, the future is not a great place. Here's - the needle(ph) coral is underneath here. It's gone. And there's really not very much left alive.

HARRIS: In all there are four sets of tanks here: the healthiest coral are in a tank that simulates pre-industrial conditions. The present day tank looks almost as good, but the coral looks progressively worse in tanks with increasing carbon dioxide and temperature.

DOVE: We can make this a little bit (unintelligible)...

HARRIS: Now, plenty of small-scale experiments in the lab have shown that corals suffer in hotter waters and in more acidic conditions. This experiment puts those two threats together, since that's what the reefs of the future will face. Dove tries to be dispassionate about her findings, but the site touches the human chord.

DOVE: I feel pretty sad when I look into this. You know, I look at the others, the control tank, and I think, well, that would be nice if we could at least stay like that.

HARRIS: But doing so would mean civilization would have to stop burning fossil fuels immediately. That's not going to happen. Instead, once the carbon dioxide concentrations get high enough in the ocean, the stony structure of the reef actually starts to dissolve. That's bad news for the vibrant life that lives on the reef.

DOVE: There's no reef building going on here. It's reef dismantling that's going on here. Maybe some fish can survive in this type of environment, but I think we're going to lose a lot of the fish capabilities, you know, for fishing and everything. So people who are trying to live off what the reef offers them, this is going to be much harder. From a tourist's point of view, I don't imagine this is something that tourists would feel that attracted to come and see.

HARRIS: And as the reefs erode, they will offer less protection from the storm surges generated by the typhoons that sweep ashore here in Australia and throughout the South Pacific.

ANDREAS ANDERSON: Millions of humans are dependent on the reefs today.

HARRIS: Andreas Anderson is a reef scientist at the Scripps Institution of Oceanography in San Diego. He says increasing ocean acidity is a big threat to the millions of people who depend on the fish that in turn depend on the reef. He says experiments like the one on Heron Island suggest the reefs face bad times ahead later in this century, but the weakness of studies like this is that they change conditions for the corals in one sudden shock.

ANDERSON: So what we don't really understand is, you know, how quickly will this happen, to what extent will it happen. Will organisms be able to acclimatize or adapt to this over a longer time scale?

HARRIS: The best case is that the change will be slow.

ANDERSON: If it breaks down very rapidly, we are definitely in big problems. But if it takes thousands of years, then, you know, perhaps it's not so bad.

(SOUNDBITE OF WATER SPLASHING)

HARRIS: Sophie Dove knows no experiment is perfect, but hers is designed to look for hints that corals can adapt to their new circumstances, and she doesn't see any sign of that. We will have more definitive answers soon enough because this experiment isn't simply confined to tanks at research stations - it's playing out on every coral reef in the world. Richard Harris, NPR News.

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