The researchers' model uses mathematical models borrowed from engineering theory to translate the movement of storm waves into mechanical stresses on the coral in different parts of the reef, incorporates the various shapes of coral colonies and calculates whether they will be dislodged during extreme weather.
The research introduces a new concept ?colony shape factor (CSF) ?to translate the myriad shapes and sizes of coral colonies onto a simple scale that measures their vulnerability to dislodgment. Any severe event, like a cyclone, imposes a threshold that can be scored on the same scale, allowing scientists to determine which corals will live and which will die.
The most vulnerable corals are the table corals which have a broad flat top supported by a narrow stalk, making them more susceptible to strong wave forces than bushy or mounded corals. Vulnerability also depends on whether the coral grows on the front, crest, flat or the back of the reef, where the force of the waves progressively dies away.
The team ran a field test at Lizard Island, in the northern part of the Great Barrier Reef, taking digital photographs of corals, and calculating their vulnerability.
They found that the threshold imposed by the previous year's biggest storm predicted the pattern of coral sizes and shapes almost perfectly. "There were a lot of table corals present that went right up to the threshold from the last big storm, and then suddenly nothing above it," says Dr Connolly, a CoECRS researcher and Senior Lecturer at James Cook University. "They even followed the predicted trends from the reef crest to the reef back."<