Fish and corals can each smell bad reefs from far away when searching for a place to settle.

Coral reefs damaged by overfishing and other causes release a chemical warning signal to other marine life. Fish are essential in removing seaweed that collects on damaged reefs. Without the animals to remove the marine algae, the reef can become encompassed. In extreme cases, the seaweed can completely choke the damaged reef, and prevent the growth of new members of the colony.

Coral larvae, searching for a habitat, can sense chemical signals given off by damaged reefs, and avoid taking up residence in the compromised environment.

Fish and coral larvae each head out into the ocean after being born, carried by the current, in search of new habitats. Many of these marine animals normally take up residence in healthy coral reefs.

Fish in Fiji were examined in the study, comparing their reactions to waters from near both healthy and damaged reefs. Researchers took water samples from each, and created water that "smelled" like each variety in the laboratory.

A flume tank, a design commonly used in marine research, was utilized to create areas where which possessed chemical signatures similar to those near damaged and healthy coral reefs. Fish and baby coral were given the chance to swim toward one or the other water system. The animals headed toward water smelling of healthy coral reefs, while avoiding the odor of damaged and overfished reefs and seaweed.

Sargassum polycystum, a seaweed known to take over coral reefs, was studied in the experiment. When the smell of this form of algae was introduced to water, it became 81 percent less attractive to coral larvae and 86 less appealing to fish.

Up to 90 percent of the corals in the Carribean and half the population in the Indo-Pacific have been lost in the last 30 to 40 years, according to environmentalists.

"What this means is we probably need to manage these reefs in ways that help remove the most negative seaweeds and then help promote the most positive corals," Mark Hay of the School of Biology at Georgia Tech and senior author of the study, said.

A video explaining how baby corals and fish can judge the health of coral reefs by their smell is available on the Georgia Tech YouTube page.

Laws providing protection of compromised coral reefs may not be timely enough to prevent damage done to the clusters of invertebrates. Chemical signals warning of damage could discourage new growth of reefs, even long after legal protections are put in place.

Investigation of chemical signals from damaged coral reefs and how they could affect larval coral and fish was detailed in the journal Science.