The dreamy quiet of coral reefs screeches to a halt at dusk. Daytime waters come alive with the clanks, groans, knocks and pops of hunting fish and snapping shrimp--a din that can be heard several kilometers from shore. New research suggests this nighttime clangor serves a critical function: guiding adolescent reef fish back home.
After hatching, infant reef fish can drift far from their homes. Yet, to mature, they must return home or find another reef suitable for food and mating. Previous research has shown that adolescent fish have excellent hearing. So fish ecologist Stephen Simpson of the University of Edinburgh, United Kingdom, wondered whether young fish might follow a trail of sound to find the reefs.
To test the idea, Simpson and colleagues placed 24 piles of coral rubble on an underwater sandy plain near Australia's Great Barrier Reef. The team played recorded reef fish noises over a period of six nights at half the piles, and left the others alone. In the mornings, the researchers collected the fish loitering near each reef. Many more fish turned up near the noisy piles than near the quiet ones, the scientists report today in Science. The researchers then played the high-frequency sounds of snapping shrimp at some piles, and the lower-frequency noises of fish at other piles. Damselfish showed no frequency preference, while cardinalfish preferred the higher frequency sounds. This suggests fish groups may have different hearing capabilities or head for different reef conditions, say the researchers.
"We think fish can use sound to get a sneak preview of the reef before settling onto it," Simpson says. "Reefs are essentially a wall of mouths waiting to eat young fish. So listening to the animals that reside there might be a way to pick the right reef."
"These fishes are definitely cuing in on sound as they make the final approach to the reef," says fish ecologist Peter Doherty of the Australian Institute of Marine Science in Townsville, Queensland, who notes that the fish may also be guided by odor and other cues. Understanding how far young fish drift, and how they home in on corals, he adds, can help biologists design marine reserves that can protect fish at critical stages in their life cycles.