08 November 2009

Why do some corals have glowing patches?

Like bright band aids, these flourescent areas appear to protect injured hard corals as they heal.
A recent study found that when a coral is broken or injured, it releases highly reactive oxygen (free radicals) to heal the wounds. Free radicals, however, can harm surrounding healthy coral cells. The glow is a result of fluorescent proteins, which in corals act as antioxidants to keep free radicals at bay.

Wow! I've seen these pink spots and patches on some of our hard corals. Such as this pink spot on a hard coral at an area where some burrowing animal seems to have bored into the living coral.
Hard coral (Porites sp.)

I wonder whether this also explains the brightly coloured mushroom corals that we sometimes see on our shores?
Circular mushroom coral (Family Fungiidae)

Circular mushroom coral (Family Fungiidae)

Glowing corals: Fluorescence Found to Aid Healing
National Geographic 4 Nov 09;
Injured corals develop colorful glowing "scabs" to help themselves heal, a new study has found.

When a coral is broken or wounded, it releases highly reactive atoms of oxygen known as free radicals to close up the gashes.

But these powerful molecules can also inadvertently kill off some of the coral's healthy cells. Hydrogen peroxide, for instance, is a common free radical in corals, and it can damage every part of the cell, from DNA to proteins.

Hurt corals have also been known to take on brightly colored glows, noted study leader and coral immunologist Caroline Palmer. Wounds on Acropora millepora corals appear blue, for example, while injured tissues on Porites species—like the raised and swollen patches seen in the photo above—are an "intense" bubble-gum pink.

To figure out why damaged corals glow, Palmer and colleagues took small fragments from seven species of healthy wild Caribbean corals as well as samples of injured and healthy tissue from coral colonies on Australia's Great Barrier Reef.

The researchers then studied the intensity of the glow coming from healthy and wounded corals. What they found is that corals with a brighter glow are best able to keep free radicals from damaging healthy cells.

The glow is a result of so-called fluorescent proteins, which in corals act as antioxidants to keep free radicals at bay, Palmer's team says.

The study is the first to show that corals use fluorescence to boost their immunity, added Palmer, of Australia's James Cook University and the U.K.'s New Castle University.

As invertebrates—a group of less complex creatures, including worms and snails—corals were thought to have very simple immune systems, said Palmer, whose study appeared October 6 in the journal PLoS One.

"However," she said in an email, "it's becoming evident that they have a wide range of defensive responses."

—Christine Dell'Amore

Photograph Caroline V. Palmer

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