The amount of damage a coral reef will suffer in the face of stormy seas can be predicted by a new engineering model.

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SYDNEY: The amount of damage a coral reef will suffer in the face of stormy seas can now be predicted by an engineering model developed by Australian scientists.

In a paper published today in the British journal Nature, researchers from James Cook University in Townsville use mathematical models to calculate the forces that coral is subjected to by waves, storm surges or tsunamis. They also calculate the probability of the coral being destroyed.

"The predictive tool we have developed allows managers to assess the vulnerability of their reefs to extreme wave events," said lead author Joshua Madin, now at the University of California in Santa Barbara.

"The ability to estimate the potential damage on a reef for different disaster scenarios could help managers plan for economic losses, as well as promote strategies that help the reef recover," he said.

The model predicts the probability that coral will be dislodged in any given year, based on only three factors: the colony's shape, the strength of the reef to which it is attached, and the likelihood that there will be a storm that exceeds the critical level that year.

The researchers borrowed from engineering theory to translate the movement of waves into the mechanical stresses that would be felt by coral in different parts of a reef.

They also introduced a new concept - 'colony shape factor' - to translate the myriad shapes and sizes of coral colonies onto a simple scale that measures their vulnerability to dislodgment. Any severe weather event can be scored on the same scale, allowing scientists to determine which corals will live and which will die.

The most vulnerable are table corals: their broad, flat top and narrow supporting stalk make them more susceptible to strong wave forces than bushy or mounded corals.

In the model, vulnerability also depends on whether the coral grows on the front, crest, flat or back of the reef, where the force of the waves progressively dies away.

The team ran a field test of their model at Lizard island, in the northern part of Australia's Great Barrier Reef, taking digital photographs of corals, and calculating their vulnerability. Using data from the previous year's biggest storm, they found that their model predicted the pattern of coral sizes and shapes almost perfectly.

According to the researchers, global warming will have a dramatic impact on coral reefs, but not only because of the increase in severe storms. "Corals are adapted to life in stormy seas. Even the vulnerable species are quite stable when they're young," said co-author Sean Connolly. "They also tend to grow and mature quickly, so the species can recover before the next big storm arrives."

However one effect of the increased production of greenhouse gases is an increase in the acidity of the ocean. This is likely to reduce the stability of coral reefs, and amplify the damage done by tropical storms in coming decades.

Unusually hot temperatures can also cause coral bleaching, where the symbiotic algae that corals depend on is lost, and coral cells become toxic.

"To predict how coral reefs will look under different future scenarios, and to plan accordingly, we needed to know exactly how wave forces impact who lives and who dies on the reef," said Connolly. "These new models provide us with that essential tool."