When it comes to real estate on a coral reef, young fish may be looking for noise, noise, noise.
Most reef fish spend the first stage of their lives as specks in open water away from any reef. Just how these fish larvae, which resemble crumb-size shrimp, end up on a reef as adults has long intrigued biologists and conservationists.
Now, an experiment using artificial reefs at Australia’s Lizard Island has tested the idea that the clamor of other reef creatures attracts the youngsters. Researchers broadcast recordings of fish and shrimp noises from some of the reefs but not from others. More young settlers homed in on the noisy reefs, say Stephen Simpson of the University of Edinburgh and his colleagues.
The evidence of noise attracting larvae is “compelling,” comments Stephen Swearer of the University of Melbourne in Australia.
For their experiments, the researchers heaped dead coral onto sand flats to make 24 small artificial reefs. Most young fish settle on a reef at night, so the researchers broadcast nightlong concerts from half of their rubble piles. In the morning, the researchers checked for new arrivals. At reefs broadcasting sound, about 80 larvae of the cardinalfish family showed up in a typical night. Only half as many appeared on silent reefs.
Swearer welcomes the new work as part of what he sees as a changing view of fish youth. Until the end of the 1990s, he says, biologists considered fish larvae as hapless particles swept hundreds, even thousands, of miles from their hatching sites by ocean currents. After weeks or months at sea, the little fish, in theory, just drifted into some reef and settled down.
A case is now building that larvae don’t necessarily travel far and that they’re not passive, Swearer argues. His own work, for example, used chemical signatures in fish-ear bones to trace the origins of juvenile fish on reefs off St. Croix in the Caribbean. Roughly half of the fish on certain reefs had returned to their natal regions after a youthful phase at sea.
More evidence comes from studies by others of larval swimming ability. This work shows that larvae quickly develop considerable swimming strength.
Simpson has focused on the next question: If young fish control their fate, how do they find and choose their reefs? That’s where sound could come in, he says. After all, sound travels well underwater and reef creatures make a lot of it. Snapping shrimp make choruses of little pops that have been compared to the sizzle of frying bacon. Other fish click their jaws or make low-frequency rumbles.
Simpson and his colleagues describe their evidence for the alluring role of sound in the April 8 Science.