The noisier, the healthier

CORAL reefs that offer exotic ocean views can be surprisingly noisy places, with tiny fish and invertebrates like lobsters, sea urchins, squids and corals producing a relentless cacophony of squeaks and grunts. UK scientists recently listened to these noises and found the noisier the reef the better is its health; meaning, the reef has more living corals, offering shelter to large numbers of fish and other marine animals.

With the help of acoustician Marc Holderied and marine scientist Steve Simpson of University of Bristol, Emma Kennedy, a student at University of Exeter, analysed noise recordings of 11 coral reefs in the Las Perlas archipelago in Pacific Panama. Some reefs were noisier than others—in fact, each reef produced a different cacophony of noise. To understand the difference, they dived to the reef sites, surveyed them and compared the data on the number of fish and benthic communities with reef noise recordings.

Analysis showed reefs producing low frequency sounds had more number of fish living in it, while those with high frequency sounds had rich diversity of living corals, the scientists noted in the study yet to be published in the Journal of Experimental Marine Biology and Ecology. This is the first time noise by individual reefs is linked to the specific habitats that are subtly different from each other depending on size and composition of the resident communities.

The finding explains how fish can move around reef environments and locate their settlement, often at night, when vision is of no use, said Simpson. His previous work shows after spending first few weeks out in the plankton, larval fish and corals listen out for reef noise to return to the very reef on which they were spawned. “Learning about reef noise could help managers detect changes in reef health caused by, say, overfishing or select the best locations for protected areas,” Simpson said. “Reefs broadcast a lot of information out into the sea,” said Kennedy.

Understanding the information might lead to the development of new tools for rapid monitoring of the fragile ecosystem that is under threat from global warming and pollution. Based on the finding, acoustical classifications can be done to create a database for coral reefs across the world, said A K Saran, scientist at the National Institute of Oceanography, Goa. This would help monitor and manage the reefs, Saran added.

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