Sydney, March 10 (IANS) For the first time scientists have unravelled how corals can survive or perish in the face of climatic onslaught.
An international team led by Ken Anthony of the ARC Centre of Excellence for Coral Reef Studies and the University of Queensland have developed a technique to assess the chances of corals surviving a bleaching crisis.

Bleaching is caused when warm water circulates over the reef, causing them to shed the symbiotic algae they normally rely on for energy. If they cannot recover their algae in time, the corals starve to death.

“It mostly comes down to how well-fed the corals are before the bleaching event strikes,” Anthony said. “If they have high levels of lipids - or fats - in their system, it gives them the energy to hang on until they can re-establish their symbiotic relationship.”

The new technique offers scientists and reef managers a better understanding of the processes that can lead to high mortality rates among corals affected by bleaching - and also an explanation for why some reefs appear to bounce back quickly while others never recover.

The main factor is the amount of energy stored as fat in the coral’s tissues, Anthony said. This in turn depends on the level of the food supply in the water prior to the bleaching event, how recently the corals spawned and whether or not there have been other disturbances - such as human activities, storms, low tides and competition from weeds.

After the bleaching event itself, coral survival may also depend on the amount of plankton available in the surrounding water which the corals can subsist on until they can recover their algae partners, said a statement.

“We believe corals on coastal reefs are generally better able to recover from devastating bleaching events because there is often enough food in the water to keep them going,” explained Andrea Grottoli, coral physiology expert from Ohio State University.

“The research shows clearly that malnourished corals with little or no plankton in the water to rely on have a higher mortality risk - whereas those which are fat before the event and have plenty of food around afterwards have a higher chance of survival,” said Mia Hoogenboom, who co-developed the mathematical models.

The research appeared in the journal Functional Ecology.