If given the choice, most people won’t move into a bad neighborhood that is on the decline. Apparently fish and coral feel the same way. New research led by assistant professor Danielle Dixson of the School of Biology at the Georgia Institute of Technology in Atlanta demonstrates that chemical cues emitted by damaged reefs drive away young fish and coral.

Coral reefs around the world are in decline. One of the primary causes of this decline is overfishing. A lack of herbivorous fish causes a spike in seaweed, which can choke out coral in the reef.

In many countries, Marine conservation areas have been established in an effort to restore the reefs. The problem is that chemical cues given off by the seaweed may discourage young fish and coral from moving in.

“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 Dixson in a statement.

Researchers examined three protected areas in Fiji that were adjacent to fished areas.

The team tested 20 fish each from 15 different species, allowing the fish to choose to swim in one of two streams with different chemical cues being emitted from the end of each. They found that eight of every nine fish, chose to follow water flowing to healthy areas. When they tested coral larvae, they found that they too chose the healthy water at a five-to-one ration.

“Not only are coral smelling good areas versus bad areas, but they’re nuanced about it. They’re making careful decisions and can say, ‘settle or don’t settle,” said Mark Hay, a professor in the School of Biology at Georgia Tech and the study’s senior author.

In addition to chemical cues emitted from the seaweed, the researchers found that the coral in the reefs emitted cues of their own. Cues from the Acropora nasuta coral strongly attracted fish.

Acropora corals are sensitive to algae competition and are strongly prone to other stresses. The presence of this type of coral in a reef is a strong indicator that it is a healthy environment. Cues from stronger corals, which can grow even in heavily damaged environments were less attractive.

When researchers tested the seaweed Sargassum polycystum, which can easily bloom and take over a reef, reduced the attractiveness of a reef by 86 percent.

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

The researchers concluded that a small amount of hands on intervention in the right place at the right time could jump start reef recovery. If fish can be persuaded to return and eath the seaweed, the corals would then get bigger and the reef would send out more positive chemical cues.

“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 Hay.

The research can be found in the August 22nd edition of the journal Science.