GWEN IFILL: Next, what's happening to the Great Barrier Reef in Australia. A new study finds that one of the world's great natural wonders and its largest coral system is in decline.
Researchers at the Australian Institute of Marine Science say the reef has lost half of its coral cover over the past 27 years. There are multiple causes, including a destructive kind of starfish, shown here.
We look at what's behind it and what's at stake in Australia and around the world with Nancy Knowlton, a coral reef biologist and the chair of Marine science at the Smithsonian National Museum of Natural History right here in Washington.
NANCY KNOWLTON, Smithsonian National Museum of Natural History: Thanks.
GWEN IFILL: How has this -- how has all of this coral died off? Do we know what's causing it? Is it all that starfish we just saw?
NANCY KNOWLTON: Well, it's actually not all the starfish.
The starfish is about 42 percent. Typhoons, big strong storms another 48 percent, and then coral bleaching is the remaining 10 percent which is caused whenever the water gets too hot.
GWEN IFILL: So this is human-caused?
NANCY KNOWLTON: Yes. Most of it is human-caused.
I mean, a coral reef naturally goes through cycles of up and down. But it shouldn't be declining by half over the course of 27 years.
GWEN IFILL: I feel like we have talked before about the declining coral cover, but not -- but I'm wondering whether it's now picking up speed or whether this is just a natural deterioration that we should just be used to.
NANCY KNOWLTON: No, this is not a natural deterioration. And it's not natural in Australia and it's not natural around the world, where we have seen similar declines in a variety of places.
In the Caribbean, for example, we have lost 80 percent of the living coral just in the last 30 years.
And it's also not as if the Australians have been ignoring the Great Barrier Reef. That's an iconic reef for their society and their economy. And so they have put in place quite a few pleasures to actually take care of it.
And so losing half of it in 27 years, despite that effort, is actually quite shocking.
GWEN IFILL: So when you say it's human-caused, do you mean what we do with our waters, what we do with our fishing, what we do with our runoff from agricultural causes?
NANCY KNOWLTON: All of those things have a big role to play.
As you mentioned, the star -- this voracious predatory starfish has caused lot of the death on coral reefs. And that starfish is almost like a locust on reefs when it gets out of control. You can -- a swimmer can see 100 or even over 1,000 in a 20-minute swim when you have an outbreak going on.
And they can kill up to two-thirds of a reef just in a year when that happens. Now, what causes that is now increasingly well-understood. And in fact, information from the Great Barrier Reef is why we understand it.
On one hand, it's really important to have healthy fish communities there, because the fish eat the starfish and keep them under control.
And then you have to really worry about water quality because if there's too much nutrients in the water, then what happens is the baby starfish, when they're developing, do extra well. And then there's a big swarm of them as a result.
GWEN IFILL: Is there any evidence that this is happening besides just the Great Barrier Reef? Is it happening around the world as well?
NANCY KNOWLTON: Well, we have known about outbreaks of starfish since the 1960s. And it's quite clear from looking at the dynamics that this can't be a natural phenomenon.
And, as I mentioned, we have seen the declines in the Caribbean. We have seen the declines all throughout the Pacific.
Now, that said, there actually are places remote from human activities where the reefs are still really healthy, for example, in the Northern Line Islands, where there's -- they are protected by the United States, several of those islands. And there the cover of coral is very healthy. The fish populations are amazing. And you still see healthy corals.
But when there's a lot of interaction with people, then you get problems.
GWEN IFILL: If I'm an average American who may never get to see the Great Barrier Reef, unfortunately, why should I care about this? Why is it important?
NANCY KNOWLTON: Well, reefs in general are incredibly important in the ocean. Something like one-quarter of everything that lives in the ocean lives with coral reefs, which is amazing when you think of the fact that if you took coral reefs and squashed them down into just one place, it's only about the size of Texas or France.
And then they're also worth quite a bit of money. In the Australian context, for example, it's about five billion -- over five billion Australian dollars and about 50,000 jobs every year.
GWEN IFILL: So, how do you stop this die-off? What are we supposed to be doing about it?
NANCY KNOWLTON: Well, there are a couple of things that we can do. One is that we can continue the regulations on fishing. The Great Barrier Reef, one-third of it is protected from all fishing. And that's very important for controlling the crown-of-thorns starfish.
And then they have to do a better job with water quality. It's been -- it's been modeled in a way that suggests that now -- although now we get outbreaks about every 15 years, before agriculture was established, European agriculture was established, it was closer 50 to 80 -- once every 50 to 80 years. And so that's a big increase.
But in that -- those are the things that the Australians can do and are doing. But in a global sense, we also have to do something about carbon dioxide, because local protection buys you a lot of very valuable time. But, in the final analysis, if we don't stop global warming and stop ocean acidification, even the local efforts, heroic as they are in the case of the Great Barrier Reef, won't be enough.
GWEN IFILL: Is it possible for these -- for coral to regrow itself, to regenerate itself? It seems to me I have read that somewhere.
NANCY KNOWLTON: Yes. Corals are actually sort of like plants. And you can break them into little pieces just can the way you might separate something in your garden and plant them in different places and they regrow.
So, they are quite flexible in that way. If the conditions are good, corals will grow. And some of them actually grow fairly fast, although many of them are fairly slow. You can sort of think of them as trees in a way.
GWEN IFILL: So, if you can find some way to take away -- to stop the die-off, then they can come back?
NANCY KNOWLTON: Absolutely.
I mean, coral reefs in many parts of the world routinely get battered by typhoons and hurricanes and cyclones. But they come back when the conditions are good.
GWEN IFILL: Nancy Knowlton of the Smithsonian -- Smithsonian -- I don't know why I can't say that tonight -- Museum of Natural History, thank you for helping us out.
NANCY KNOWLTON: Thank you.