IRA FLATOW, HOST:
This is SCIENCE FRIDAY, I'm Ira Flatow. Australia's Great Barrier Reef is in trouble. In the last 27 years, the world's largest coral reef system has lost 50 percent of its coral cover, and if this trend continues, the amount of coral could halve again by 2022.
According to researchers at the Australian Institute of Marine Science, 10 percent of the loss was from coral bleaching, which is primarily caused by warming ocean temperatures; 48 percent from storm damage; and 42 percent of the loss was caused by hordes of starfish that prey upon the live coral.
Why are these starfish such voracious predators? What needs to be done to save the Great Barrier Reef? Mark Eakin is the coordinator of the Coral Reef Watch Program at the National Oceanic and Atmospheric Administration in College Park. Welcome to SCIENCE FRIDAY.
MARK EAKIN: Thank you, very glad to be with you, Ira.
FLATOW: You're welcome. Are you surprised by the amount of coral cover that has been lost in this, 50 percent in 27 years?
EAKIN: Well, you know, it's a combination of two things. We look at it, and it's shocking when you see something this big this fast. But the sort of declines that we're seeing are things that we've been expecting to happen to coral reefs because of all of the threats that are facing them.
So shocking in a way but not entirely unexpected.
FLATOW: Tell us about this starfish that seems to be a voracious predator there.
EAKIN: Well, crown-of-thorn starfish are found across much of the Pacific Ocean and Indian Oceans. They are - they're about dinner-plate size, multiple arms, have little thorn-like spines coming out of them. They're also quite venomous. So the last thing you want to do is touch one and have it prick you, and it can cause paralysis.
But the important part for the corals is that these things are wonderful eating machines. They move slowly across the reef. They actually invert their stomach onto the corals and dissolve the coral tissue, you know, digesting it as they go. And they leave (technical difficulties) white behind them as they move forward.
FLATOW: So they're like little bulldozers.
EAKIN: Yeah, it's sort of like bulldozers. It's almost more like having a wave of people with flamethrowers going through the brush. You know, the coral physically is left behind, but it's all dead.
FLATOW: Do they have any natural enemies that might, you know, come out and eat them?
EAKIN: They do, but they won't help much in this case. There's a type of snail that eats them that unfortunately is also popular in the curio trade, but their numbers were never huge. There's some - actually some very small shrimp that will eat them, but, you know, there's only so much they can do.
When you have these outbreaks, the numbers of starfish are so much that it's beyond what any of their predators can do anything about.
FLATOW: And these are not your run-of-the-mill, see-them-on-the-beach five-legged starfish, are they?
EAKIN: No, no, I mean, they look like monsters. If you wanted to - you know, if you were to blow one of these things up really big, you could use it in a sci-fi movie.
FLATOW: No kidding? It's that ferocious-looking?
EAKIN: They look nasty. I mean, they're not your, as you say, your friendly hang-on-the-wall starfish. This is a thorny-looking, multi-armed feeding machine.
FLATOW: So if they don't have any natural enemies that can decrease their population, what can you do about them?
EAKIN: Well, this is really getting at the question not just for the starfish but for what you can do for coral reefs. So we've been working, in fact, with the Australians for a while, dealing with the issues of resilience to climate change. And the two things we need to do is we really need to deal with those local stresses to coral reefs to make the reefs healthier so that while we're working on solving the climate change issues, reducing the amount of CO2 in the atmosphere - we're already at too high a level.
So getting that down, getting it to the point that bleaching isn't such a problem, we've got to do that, but in the meantime we've got to take care of the local threats. Well, what they're looking at in Australia, because they've got really these issues of climate change, bleaching, they've got cyclones that are always a problem for coral reefs, it's a natural problem, they're looking at two things.
One is perhaps going out and manually finding ways to remove or kill the crown-of-thorn sea stars. You don't chop them up into little pieces, though, because like any starfish, you cut them up into little pieces, you get more of them. So you've got to find something to kill them, remove them.
But at the same time, the other big thing they're doing in Australia is looking at improving water quality because there has been an indication, absolute proof isn't there yet, but a real strong indication that poor water quality, especially high nutrients, can lead to more sea stars. So you can lead to these big outbreaks that they're having.
So they're looking at going out and removing them, improving their water quality, which is a win-win situation no matter what happens, you know, cleaner water on the reefs is good. And at the same time, of course they like everyone else are looking at what we can do to resolve some of the issues where climate change is going to be so important to reefs in the long term.
FLATOW: Obviously there's some niche that the starfish occupy. Should we be worried if - what we might do to the ecosystem if we get rid of these starfish?
EAKIN: You know, I think it would only be in the dreams of a few people that they might possibly be able to get rid of all of them. What they're trying to do is cut back on the numbers. So they're going to remove as many as they can, but you're still going to have some out there.
And these sea stars are out there on a lot of reefs in the Pacific in low numbers. You can see little trails of white, dead corals that they've left behind as they've gone along feeding, and that will continue to happen. They're not going to get rid of every last one of them.
But the increase in numbers, I mean, you're talking about going onto reefs and having hundreds to thousands times as many starfish on a reef as you normally would see, and that's a big difference.
FLATOW: Yeah, and you think of some of the runoff that might be coming onto the reef.
EAKIN: There's a lot of evidence that it is. The smoking gun hasn't been found yet, but there's a lot to think that the runoff may be contributing to this. We're definitely - the Australian data show that they're seeing more frequent outbreaks of these sea stars in recent decades, and they think that especially nutrients but other parts of runoff may be to blame.
FLATOW: If you can get them - get the die-off under control, how much of a recovery could we expect from the reef system?
EAKIN: Well, you know, that's one of the nice things that this study did is they actually found that you - if you were to remove the damage from the crown-of-thorn starfish that they would be seeing a one-percent increase in coral cover per year.
Remember what we're talking about on these reefs is the overall Great Barrier Reef has dropped from somewhere around 30 percent to somewhere around 15 percent over the last 27 years. So if you turn that around, and you had it going up by just one percent a year, that would be significant.
And so yeah, we could see some recovery. It's a decadal-scale recovery, unfortunately, but yeah, we could see a recovery if that problem were eliminated but only, again, as bleaching becomes more of a problem, and we see more corals dying from high temperatures, we've got to deal with that issue, or removing the starfish won't be enough.
FLATOW: OK, that's a long-term problem we can all appreciate.
EAKIN: Afraid so.
FLATOW: Thank you, Mark, for taking time to be with us today.
EAKIN: Thanks a lot for having me on.
FLATOW: Mark Eakin is coordinator of the Coral Reef Watch Program at the National Oceanic and Atmospheric Administration in College Park.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.