Source: Environment News Service

11/24/06 

SANTA BARBARA, CALIFORNIA - The increasing violence of storms associated with global climate change, as well as future tsunamis, will have major effects on coral reefs, according to a paper published this week in the international scientific journal "Nature."

Shape and size of the corals are key variables, according to the authors, scientists with the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara.

"Coral reef experts have long had a general sense of which coral shapes are more vulnerable during storms than others," said first author Joshua Madin. "However, to really predict how these events impact the dynamics of coral reefs we needed a way to quantify these vulnerabilities."

The authors created the world's first engineering model to predict how much damage a reef is likely to suffer when confronted with the forces of a turbulent sea.

They used mathematical models to calculate the forces such as waves, storm surges, or tsunamis and the probability of coral colonies being ripped from the seabed.

Working with co-author Sean Connolly, Madin developed the model at the Centre of Excellence for Coral Reef Studies at James Cook University, Australia. Connolly is also a senior lecturer at James Cook University.

How coral assemblages respond to the power of the sea is essential for understanding the natural distribution of coral types on present-day reefs as well as for projecting how they will change in response to more violent or frequent storms, according to the researchers.

"Our study offers a solution to this longstanding problem by factoring in the shape of different coral colonies, the strength of the sea-bed to which they attach, and the change in force of the waves as they move across the reef," said Madin. "This enables us to predict the likely changes in composition of the coral in response to present and future storms or tsunamis."

The study introduces 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 being dislodged.

The scientists found that the most vulnerable corals are "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.