Joshua Learn, E&E reporter

Published: Friday, August 22, 2014

Coral larvae and fish looking for new homes are able to sniff out and
avoid areas degraded by overfishing, pollution or other problems,
according to research published yesterday in the journal Science.

Danielle Dixson, a biology professor at the Georgia Institute of
Technology in Atlanta and the lead author, said the study suggests that
designating protected marine areas may not always lead to healthier
reefs nearby.

Further intervention may be needed, she said, to help degraded areas
recover.

Researchers started by testing 15 fish species and three coral species
in the lab for their ability to smell healthy reef locations ripe for
colonizing based on seawater they injected into the water.

“We were really wondering what chemical cues makes them decide where to
go,” Dixson said in a telephone interview, adding that the species
showed “a very strong preference for water taken from the healthy reef
areas.”

The scientists then took tests out to waters in Fiji that have very
healthy and well-protected reef areas next to spots that have suffered
hugely from overfishing or other human-related activities.

“Coral are pretty much a living rock, they can’t move once they’ve
settled,” Dixson said.

Larvae, she said, will often scout settlement areas out before choosing
to lay down their roots and begin forming coral. But in Fiji they
tended to avoid areas plagued with too much algae.

In Fiji, she said, “degraded reefs are pretty much algal parking lots.”

The discovery is troubling, she said, because marine protected acres
(MPAs) are supposed to act as recovery points for wider areas, as fish
and other species don’t stick within their borders.

“The point of a marine protected area is not only to protect what’s
inside its area,” she said.

But in Fiji it’s not happening in some areas because larvae and the
fish that follow them once the coral has developed probably don’t ever
recognize that some algae-covered areas are habitat anymore.

“When two areas are too different from one another, the MPA might not
be working in the way that we think it should be working,” she said.
“That feedback loop is just not going to occur.”

Joana Figueiredo, a marine larval ecologist at the Oceanographic Center
at Nova Southeastern University in Fort Lauderdale, Fla., said the
study’s findings seem reasonable.

“Just by the scent of the water, the larva decided the water wasn’t
good,” she said, adding that the study is in agreement with things that
have been published before.

Both Figueiredo and Dixson said that as a result, conservationists need
to think about wider strategies than just demarcating protected zones.

“What she’s showing is that you cannot just protect a little small area
and not worry about the condition of all the rest. The overall quality
of the area needs to be high,” Figueiredo said. “It’s not just by
protecting one area that you will be able to save a reef.”

Dixson said ways to do this could include clearing the algae from areas
that would otherwise be appropriate for coral settlement, or even
learning more about the kinds of scents that different coral favor in
settlement, as some species will put up with a smellier home than
others.

It’s an important area of study, Dixson said, because once reefs go
past a certain point, we don’t know what we can do to help them.

She’s currently working on related studies testing the chemical
preferences of Caribbean coral species off the coast of Belize.