ROBERT SIEGEL, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

MICHELE NORRIS, host:

And I'm Michele Norris. A new report says that those pristine-looking coral reefs you see on National Geographic specials are actually extremely smelly places, if you are the larvae of a certain kind of reef fish, that is. As NPR's John Nielsen reports, researchers say larvae floating in the open ocean sometimes follow these smells back home.

JOHN NIELSEN: Consider the predicament faced by the larvae of your average cardinal fish, a pretty red thing that darts in and out of shallow coral reefs all over the South Pacific. The larvae of this fish is no bigger than the tip of your fingernail, but by the time it learns to swim, it is already lost at sea, thanks to tides that pull it off its reef, out into the ocean. Surely, there is no chance that these larvae will ever see another coral reef, and yet, amazingly, they find a way.

Mr. JELE ATIMA(ph) (Ecologist, Boston University): You begin to wonder how in the world can they do that?

NIELSEN: Jele Atima, an ecologist with Boston University, says these larvae actually do more than merely find the nearest reef. Like salmon returning to the streams where they were born, cardinal fish can swim more than 100 miles back to the reefs where they were born. Atima says larvae find their way through rough-and-tumble oceans by riding ocean currents in much the same way that lots of people use the New York City subway system.

Mr. ATIMA: We don't want to walk all the way across all of New York to go back home so we go to the subway system, and we carefully look for the right train.

NIELSEN: In this case, the right train is a current headed straight to the home reef. But how exactly does a larvae know the difference between the line that takes him to Penn Station and the line that leads to Yankee Stadium? After all, there aren't any signs out in the ocean. But Atima says there are a lot of smells, and for a long time, he's been wondering whether some larvae follow them home.

That thought first hit him 10 years ago, when he looked out of a boat and saw a dusty-looking trail of water flowing out of an Australian coral reef.

Mr. ATIMA: And I thought wait a minute, that's a visible plume of dust that can go kilometers as a sort of a highway, streaming out of the reef into the open ocean. There must be odor in there, and there must be fish in there.

NIELSEN: Since then, Atima's been part of a team of researchers studying watery odor trails. In one experiment, the team put cardinal fish larvae into the aquatic equivalent of a subway station, which allowed the fish to chose between two different water trains, one of which was from their home reef. Almost every time, the larvae jumped into the stream that smelled like home, even when Atima tried to trick one of them.

Mr. ATIMA: And I switched - bad guy I am - switched the odor on him, and then he gets nervous and swims immediately over to the other side, back to his home odor.

NIELSEN: The study was published in the Proceedings of the National Academy of Sciences, and it has attracted critics. They say one big problem is that the chemical compounds that might be creating these odors are never identified. But evolutionary biologist Richard Zimmer of the University of California at Los Angeles says this study raises some intriguing possibilities. For instance, if these smelly currents do turn out to exist, they could be used to lure fish back to reefs that are now facing all kinds of problems.

Mr. RICHARD ZIMMER (Evolutionary Biologist, University of California Los Angeles): So there's tremendous interest in knowing what processes get fish to a particular reef so that ultimately, reefs can be more effectively managed.

NIELSON: Atima's team is trying to help by learning more about how smelly currents work. John Nielsen, NPR News, Washington.

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