Acidic water found to erode reef

Ocean acidification caused by increasing carbon dioxide levels in the atmosphere has been known to hamper the growth of coral reefs.

Thanks to an innovative study of coral skeletons conducted at the University of Hawaii at Manoa’s Hawaii Institute of Marine Biology, scientists now know that ocean acidity also contributes to the breakdown of reefs.

The finding confirms a "double whammy for coral reefs in a changing climate," according to the institute.

Researchers laid small blocks of dead coral skeleton along a 100-foot area of shallow coral reef in Kane­ohe Bay and measured their erosion after one year.

In previous studies, researchers weighed the blocks before and after their time in the ocean to determine erosion. This time the researchers used a high-resolution CT scan to create before-and-after 3-D images of each block, which provided a more accurate measure of erosion rates.

The study compared the influence of pH, resource availability, temperature, distance from shore and depth in determining that reefs experienced higher rates of erosion in more acidic water.

"It was surprising to discover that small-scale changes in the environment can influence ecosystem-level reef processes," lead author Nyssa Silbiger said in a statement Friday.

Coral reefs exist in a balancing act between construction and destruction.

As corals grow, they build the complex calcium carbonate framework that provides habitat for fish and other reef organisms.

Simultaneously, parrotfish, boring marine worms and other "bio­eroders" break down the reef structure into rubble and the sand that replenishes beaches.

For reefs to persist, rates of reef construction must exceed reef breakdown. Increasing atmospheric carbon dioxide causes ocean acidification that threatens that balance, scientists have concluded.