Fish and corals can "smell" a bad neighborhood and avoid making their homes in a damaged reef. 

Damaged coral reefs emit chemical cues that offend fish and corals, driving them away, Georgia Institute of Technology reported. The study shows for the first time that coral larva can detect the difference between damaged and healthy reefs. 

Coral reefs are declining around the world, mainly because overfishing is depleting the number of herbivorous fish that eat damaging seaweed off the reefs. The study looked at how chemical signals from the seaweed repel young young coral from settling in the area; the smell of the water around damaged reefs is also believed to ward off the fish. The findings suggest designated overfished coral reefs as protected may not be enough because crucial fish will still be driven away. 

"If you're setting up a marine protected area to seed recruitment into a degraded habitat, that recruitment may not happen if young fish and coral are not recognizing the degraded area as habitat," said Danielle Dixson, an assistant professor in the School of Biology at the Georgia Institute of Technology in Atlanta, and the study's first author.

To make their findings the researchers conducted studies in Fiji, which has designated a number of marine areas as protected. 

The team put water from healthy and unhealthy habitats into a flume that allowed fish to swim towards one or the other; the fish showed an eight times greater preference for the healthy water. Coral water were found to prefer healthy water five-to-one over degraded water. 

The team also soaked seaweed and water and tested fish and coral preference. They found the seaweed-soaked water reduced the attractiveness of the water by 86 percent for fish and 81 percent for coral larvae. 

"Corals avoided that smell more than even algae that's chemically toxic to coral but doesn't bloom," Dixson said.

"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," said Mark Hay, a professor in the School of Biology at Georgia Tech and the study's senior author. 

The findings were published August 22 in the journal Science.