Human aren't the only ones concerned abut the health of the world's ocean reef system, it turns out; baby fish and corals can "smell" a bad reef and avoid it, a study conducted in Fiji found.
When exposed to two different water samples in a lab -- one from a dying, depleted reef and one from a healthy one -- the creatures avoided the sample carrying the odor of seaweeds that typically invade dying reefs in preference for the water from a vibrant, healthy reef, researchers found.
The results suggest sea creatures can detect the chemical signals that tell them whether or not a reef is dying or degrading, the scientists report in the journal Science.
The results also suggest that just giving a marine protected zone designation to a reef may not be sufficient for it to recover if the smelly seaweed has already invaded it.
"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," says lead study author Danielle Dixson from the Georgia Institute of Technology.
Simply banning overfishing in a reef area may not be sufficient, the researchers say; controlling seaweed may also be a necessary step in efforts to repopulate reefs.
The study in Fiji looked at several marine protected zones that held healthy coral reefs but were immediately adjacent to heavily fished areas where seaweed had come to dominate.
Water taken from both areas was used in the laboratory experiments.
"We've got these fished and un-fished areas that are small and immediately adjacent to each other, so it's a nice experimental setting," researcher Mark Hay, a Georgia Tech biologist, says.
When exposed to the two different water samples, young fish of 15 different marine species preferred the water taken from the healthy reefs, spending 80 percent of their time at the "healthy" side of a test chamber.
The larvae of three species of coral also showed a strong preference, "swimming" toward the healthier water by moving tiny hairs known as cilia on the bodies.
"This is the first time that we've seen coral's ability to assess this on a large scale, when they're floating around," Hay says.
Hay notes that floating coral larvae are pretty much at the mercy of ocean currents and can't make much swimming headway against them.
What they might be do, he says, is let themselves drift through different reefs, "and if it smells good, they go down" to attach themselves to the surface.
