The coral larvae, when in an attempt to find a place to settle, can smell the difference of a healthy reef to the damaged one, an interesting study reveals for the very first time.
Reason for this is because the damaged coral reef releases chemical cues that sicken the fish and young coral, thus discouraging them from dwelling in the destroyed habitat.
The seaweed emits chemical signals that discourage the young coral from finding home in seaweed-dominated area, while the young fish do not find themselves attracted to the smell of water from a damaged reef.
The researchers studied three marine areas in Fiji with neighboring fished areas. Fiji set up no-fishing areas in order to secure its healthy habitats and to allow recovery of damaged reefs. They used the previous method applied to test fishes as well.
They found that young fishes and corals were revolted by the chemical cues coming from seaweed-dominated and overfished reefs, yet attracted to cues from the coral-dominated areas where there’s prohibited fishing.
Fish and coral larvae, meanwhile, preferred specific chemical cues from coral species indicating healthy habitat and evaded particular seaweeds indicating damaged habitat.
"Not only are coral smelling good areas versus bad areas, but they’re nuanced about it," Mark Hay, senior author of the study, says in a statement. "They’re making careful decisions and can say, 'settle or don’t settle.'"
Because of these chemical signals that drive them away, results of the study suggest that it may not be enough to designate overfished coral reefs as marine protected area to help the overfished reefs recover.
“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,” study’s first author Danielle Dixson stated.
The researchers say they intend to do work in the future that will engage removing seaweed plots from destroyed reefs and will study how such effort affects reef recovery. They hope such move could bring fishes back to the area so that they settle and consume the seaweeds around the corals, for the latter to get bigger because of the absence of overgrown seaweed. The larger corals would, in return, mean being more attractive to more fishes.
"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," says Hay.
Hay and Dixson are both professors at School of Biology, Georgia Institute of Technology in Atlanta.
The study, “Chemically mediated behavior of recruiting corals and fishes: A tipping point that may limit reef recovery,” is published in the Science journal on Aug. 22.