Recordings of coral reef sounds attract fish
Pied Pipers of the Reef
Tina Butler, mongabay.com
May 24, 2005
Many coral reef fish species are spawned on the reef, with eggs developing under the care of parent fish until hatching, but mature elsewhere. Some species of larval reef fish relocate to the open sea after hatching to avoid predation by other reef organisms. Previous studies have discounted the belief that reef fish larvae are merely passive passengers on ocean currents. Feeding on plankton, the larvae mature into juveniles, moving back onto the reef when they are larger and less vulnerable. Even though these young fish spend at least four weeks at sea, traversing significant distances, young coral reef fish eventually find their way back to a reef to make a permanent home.
|Heron Island on Australia's Great Barrier Reef|
The research team behind the study, headed by Dr. Stephen Simpson, from the University of Edinburgh's School of Biological Sciences, was stationed on Lizard Island, located near the northern end of the Great Barrier Reef. After building 24 patch reefs near the island, researchers broadcasted imitation reef noises on half of the patch reefs using an innovative submersible speaker system developed in New Zealand. The noise the marine biologists simulated consisted of a series of pops, bangs, whoops and trumpet sounds used by nocturnal fish to communicate as they hunt. There was an additional recording used that played a background crackle noise, like that made by the claws of snapping shrimp.
Simpson and his colleagues studied two families of reef fish, damselfish and cardinal fish, believed to be most important in the reef habitat. Experimenting on both silent and noisy,' speaker-assisted artificial reefs produced illuminating evidence on fish behavior. Fish not only locate settlement sites using reef sounds, but also discriminate between different sounds. Their aural memories from inside the egg, known as acoustic conditioning, may imprint the particular noises of their natal reef on fish. The marine biologists found that the studied damselfish, also known as clownfish, were drawn to the high frequency noise of snapping shrimp, while the cardinal fish responded to both high and low frequency noises produced by shrimp and other fish. Whatever the frequency, the affect of the noise is so strong that the number of fish arriving on noisy reefs was six times that for the silent reefs.
Researchers behind the study warn that foreign and unnatural noises created by shipping and drilling may be depleting fish stocks in sensitive areas. Overfishing and damage to natural habitat are also serious threats to coral reef fish. In order to manage these fish species effectively, scientists need to understand their behavior, especially during the open water developmental stage in relation to sound. Reefs are noisy environments, full of crackles and snaps from other inhabitants like shrimp and various fish species, combined with the ambient sounds of surf, wind and rain. The underwater cacophony of clicks, clacks and pops is a powerful navigation tool for juvenile reef fish to find their way home. Scientists hypothesize that larval crabs and rock lobster probably use the same acoustic cues to find the coast from out at sea. In light of these findings, human activities such as drilling may be seriously impacting fish populations that can no longer rely on their aural memory because it is drowned out by foreign sounds.
|Great Barrier Reef fish. Photo by Brian Mathy.|