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Do corals and fish 'sniff' their ways home?

A young fish in a choice chamber, choosing between water from healthy and degraded habitats.
[Credit: Danielle Dixson]

Efforts to restore degraded coral reefs that have been overrun by seaweed could be complicated by some new findings in this week's issue of Science. Danielle Dixson and colleagues studied coral larvae and young reef fish from the coastal waters of Fiji and found that both of these aquatic drifters were attracted to chemical signals released by healthy corals and repulsed by similar cues coming from seaweed.

The researchers compared water from protected areas, where fishing had been outlawed, to water from non-protected areas, where few fish—but lots of seaweed—lived. Time and time again, the researchers found that their young corals and fish chose to explore the water from protected areas while avoiding as best they could the water from non-protected areas.

This discovery suggests that some aquatic species that appear to be simply floating through the water may in fact be making active choices about where to settle. But, if young fish and corals always head for reefs dominated by healthy corals while avoiding seaweed that's known to cover degraded reefs, how are degraded reefs ever supposed to recover?

Dixson and her team suggest that some degraded reefs might have to be managed so that they produce the signals that attract—rather than repel—new fish and coral larvae. Especially since more and more reefs around the world appear to be losing their corals and gaining more seaweed, they say.