Coral Find Ways to Fight Off Warming Effects Overly warm water can cause "coral bleaching," in which coral die and lose their pigmentation, leaving only ghostly skeletons behind. New research suggests that by actively engaging in 'tentacle feeding' on small marine organisms, some coral may be able to resist bleaching events.
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Coral Find Ways to Fight Off Warming Effects

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Coral Find Ways to Fight Off Warming Effects

Coral Find Ways to Fight Off Warming Effects

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You're listening to TALK OF THE NATION: Science Friday. I'm Ira Flatow. The world's coral reefs are dying. Often called the Rain Forests of the Oceans, they are home to millions of species of sea creatures. And, like the rain forests--the terrestrial rain forests--they continually face threats caused by humans: pollution, over-fishing, and the latest threat, rising ocean temperatures from global warming. Warm ocean waters make the corals spit out their colorful co-habitants, the green algae that help them eat. And when the algae leave home, they leave the coral white, or bleached, and much weaker and much hungrier.

For years scientists have been watching coral reefs shrink as more and more corals die off. Just this winter, record warm temperatures in the Caribbean contributed to an unprecedented die-off. But my guest today has found a coral species that seems to have found a strategy to defend itself during a bleaching event, and it does that by gorging itself on food.

Here to talk about her findings out in this week's issue of the journal, Nature, and the problems of the coral bleaching events is Andrea Grottoli. She is an assistant professor in the department of geological sciences at Ohio State University in Columbus, and she joins us by phone.

Welcome to the program Dr. Grottoli.

Dr. ANDREA GROTTOLI (Assistant professor Ohio State University): Hello, Ira.

FLATOW: Tell us a little bit about corals and the bleaching. What happens there?

Dr. GROTTOLI: Well, bleaching is a stress response. And so warming is one of those stressors, and it's becoming ubiquitous as the planet warms. The coral are living closer and closer to their thermal maximum threshold, and more susceptible than to be exposed to elevated temperatures that can cause bleaching.

FLATOW: Yeah, I think, you know, lots of us, the only time we see coral is, it is a white rocky substance on a shelf in the tchotchke store someplace. And we don't realize that it's a living animal.

Dr. GROTTOLI: That's right. It's a living animal. They're related to jelly fish and anemones. And this animal lays over a calcium carbonate skeleton and it's that skeleton you see in the store. And inside it lives unicellular algae. So it's a symbiotic organism with algae, an animal that excretes a skeleton.

FLATOW: Uh huh. And under stress, as you say, and part of that's just being warm water, the coral gets rid of that algae. What does the algae do for the coral?

Dr. GROTTOLI: Right. Well, under normal conditions, when the coral is healthy, those little algae are photosynthesizing, and they photosynthesize a lot more than what they actually need, and they give the coral host the bulk of that photosynthetic product. And this provides the coral host with nutrition--with food. When they are bleached, they lose those algae, and therefore that source of food. Coral can also get food by eating zooplankton, which are tiny little critters that live in the water column. And when they're bleached, they have to either rely on the energy reserve they have in their tissues, their fats, or they can feed.

FLATOW: And you've discovered that they go binging.

Dr. GROTTOLI: Well, one species.

FLATOW: One species. Right.

Dr. GROTTOLI: One species turns out when it is bleached can actually crank up it's feeding rate and meet all of its energetic needs, all of its food requirements, by eating more zooplankton. And then, as soon as they start to recover, or once they've recovered to a certain level, they switch back to being dependent on the photosynthetic source. The other two species we looked at were not able to increase their feeding. They just stuck with using up their energy reserve and waited until they started to recover and would then used photosynthetic product again.

FLATOW: Uh huh. That is, if they recover.

Dr. GROTTOLI: That is, if they'd recover, right.

FLATOW: Where do we find these species that are able to binge and to survive?

Dr. GROTTOLI: Well this one species is in Hawaii. It's called Mon Tipera Capitata(ph). That's its species name. And it is the only one of the three we looked at that was capable of doing this. And we don't know if there are others that can do it, but for now, we just know of this one.

FLATOW: Uh huh. So there might be others? They just haven't been discovered.

Dr. GROTTOLI: There might be others. There are thousands of species of corals, and it is possible that there are others that can do this. We hope there are, because it provides a mechanism for resilience. If they're not dependent on photosynthesis for food during bleaching, if they can get food elsewhere by eating the zooplankton, they are maintaining their energy reserves, they're a little more robust, and it is a mechanism for possible resilience. For being able to sustain themselves while they're bleached. And so if we find other species like it, it offers a little bit of hope that this might actually - there might be some resilience out there.

FLATOW: Uh huh. And might you also find a gene that regulates this increased eating habit?

Dr. GROTTOLI: Yeah. I mean, that's certainly po… I mean something is, it's got to be gene-regulated.

FLATOW: Right.

Dr. GROTTOLI: Years(ph) and those kind of activities are regulated by genes and what gene that is is--I don't know.

FLATOW: I know. I'm already thinking generations ahead, down the road. Fixing these other species. Because I don't think we're reversing cause--global warming very soon, any time soon.

Dr. GROTTOLI: Right. Right.

FLATOW: And these die-offs are going to continue. It's amazing how much of the coral is dying when you look at the records of these things.

Dr. GROTTOLI: It's an incredible amount. And large bleaching events can cause catastrophic damage, where 100 percent of the corals die in a single season, just due to warmer sea-water temperatures. And it's not even that much warmer. It's a degree and a half to two degrees warmer for as little as two weeks, you start seeing bleaching stress. The longer that the warm-water temperatures persist, the more stressed they become because they're in that bleached state, and then they start to die.

FLATOW: Well, good luck to you. And, you know, I don't know what to say. I'm glad you found about the corals, something good about the corals. If we can only open, sit back and make sure, or hope that they can recover. Or you find more of these kinds of corals.

Dr. GROTTOLI: We hope so.

FLATOW: Thank you very much, Dr. Grottoli.

Dr. GROTTOLI: Thank you so much.

FLATOW: Andrea Grottoli is an assistant professor in the department of Geological Sciences at Ohio State University in Columbus.

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