Noisy Reefs Preferred by Young Fish, Study Says

April 7, 2005

Travel brochures often use coral reef imagery to lure tourists to seemingly tranquil locales. Don't be fooled: Reefs are anything but quiet. And that's a welcome fact if you're a reef fish looking for a place to settle, scientists say.

Many reef fish coordinate their egg laying with the tides. That way, their baby fish, or larvae, drift out to sea upon hatching, explained Stephen Simpson, a tropical reef ecologist at the University of Edinburgh in Scotland.

"They do their development at sea, because it's a far safer place to be," Simpson said. The open waters are relatively predator free, allowing the larvae to grow and become strong swimmers before they brave life on the reef.

Once the larval fish are agile swimmers, the reef noise guides them back home, Simpson and his colleagues report in tomorrow's issue of the journal Science.

Stephen Swearer is a marine ecologist at the University of Melbourne in Australia. He said the finding adds to the growing body of evidence that "larval fish are far from the passive particles we used to think they were."

Until recently, scientists believed larval fish—typically under an inch (two centimeters) long—had little control over their environments and were at the whims of currents and tides.

Now research is showing that, as the larval fish develop, they become adept swimmers and can smell and hear reefs. By the time they reach the settlement stage, larval fish are aware of their environment, can react to predators, and are choosy real estate shoppers.

"What this study shows is that larval fish are using auditory information to make decisions about where to settle," Swearer said. "What we now need to determine is whether they use such information throughout the larval period."

Such knowledge, Swearer added, will provide insight to the question of whether larval fish tend to settle close to where they were born or venture to far-off reefs.

Artificial Reefs

To find out whether the reef ruckus might help guide larval fish, Simpson and his colleagues used dead coral to build 24 artificial reefs around Australia's Great Barrier Reef. On half of them, the researchers placed loudspeakers broadcasting reef noises.

The noises included the "frying bacon" sound of snapping shrimp. Other audio cues included grinding and popping sounds. Fish make the popping noises by sending air through different chambers of their swim bladders, the inflatable sacs that help fish float.

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