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Coral uses slimy mucus to donate food


The Great Barrier Reef in all its glory (Image: Ray Berkelmans, AIMS/CRC Reef)

Coral has snot-like mucus that transports food to its neighbours, researchers have found.

The mucus transports any spare food, synthesised when the coral's photosynthetic algae use energy from sunlight, for nearby fish and other organisms to eat.

Dr Anke Klueter of the Australian Institute of Marine Science (AIMS) in Townsville and colleagues report their study in this week's issue of the journal Nature.

Mucus, which you can see dripping off coral as it is lifted out of the water, plays a role in cleaning the coral of dirt. It also protects coral from bacterial infection.

"It looks a little bit like snot," biochemist Klueter told ABC Science Online

Coral produces a lot of mucus and until now researchers were not sure why it would spend so much energy making it.

Each day the main type of hard coral on the Great Barrier Reef, Acropora, exudes 4.8 litres of mucus per square metre of reef, the researchers said.

The research team, led by Dr Christian Wild of the Max Planck Institute for Marine Microbiology in Germany, analysed the composition and tracked the movement of the mucus in a lagoon off Heron Island.

The mucus was stacked with carbohydrates produced by the photosynthetic algae living in symbiosis with the coral.

Abundant light means the algae produce a lot of food but coral normally only uses half of it; the rest is spare.

The researchers found that between 56% and 80% of the mucus dissolved into the reef water immediately around the coral where microscopic life used it up.

The rest of the mucus floated away undissolved and joined with other particles to form nutrient-rich pellets that fish and other organisms ate.

"The mucus is not just a lost production from the coral. It is actually utilised by the whole ecosystem. It isn't wasted," said Klueter.

The discovery that coral mucus helps prevent nutrients from being lost from the reef helps answer the long-standing question of why coral bothers to produce so much seemingly wasteful slime, the researchers said.

Cyclone saves reef from bleaching

In related news, scientists report that the Great Barrier Reef was spared from devastating bleaching this summer by the recent Cyclone Fritz, which hit the Gulf of Carpentaria.

Bleaching is caused by the heating of water which causes a breakdown of the symbiosis between the coral and its algae.

According to Dr Ray Berkelmans of AIMS, sea temperatures had been rising and scientists feared a repeat of the 2002 bleaching event which affected 55-60% of the 3000 reefs on the Great Barrier Reef.

"But the cyclone in the Gulf of Carpentaria cooled waters in the reef two degrees in the space of a fortnight," Berkelmans told ABC Science Online.

"The cyclone cooled the reef waters by bringing rain, cloud cover and winds strong enough the mix the water column but not strong enough to disturb the corals."

While temperatures have again since crept up, the cooling effect of the cyclone helped prevent an accumulation of heat in the ocean. And traditionally sea temperatures would fall off in March, said Berkelman said. "We're crossing our fingers we've seen the end of the heating."

Cyclones during the summer months usually cool reef water temperatures, said Berkelman. But there had been no cyclones in the area in the past two summers; scientists did not know why.

Once killed by bleaching, corals take years to recover. A report last month said most of the reef's coral would be dead by 2050 because of global warming.

Tags: climate-change, marine-biology