UH research: Warming's dark twin, acidification, eroding reefs.

Global warming’s dark twin, ocean acidification, is disrupting life in the oceans as dangerously as warming itself.

A recent study by University of Hawai`i researcher Nyssa Silbiger and her colleagues indicates that coral reefs are eroding as increasingly acid oceans eat away at their calcium carbonate structures.

(Image: MicroCT scan of experimental blocks reveals bioerosion scars. Credit: N Silbiger, M Riccio/Cornell.)

Corals are always in dynamic tension, as the building work of coral polyps is balanced against the destructive work of parrotfish and boring marine worms. But studies at the University of Hawai`i Institute of Marine Biology shows that acidification is tipping the scales toward destruction.

The paper, Reefs shift from net accretion to net erosion along a natural environmental gradient, by Silbiger, and co-researchers Òscar Guadayol, Florence I. M. Thomas and Megan J. Donahuein, is in the journal Marine Ecology Progress Series.

Researchers placed coral blocks onto the Kane`ohe Bay reef for a year, measuring them before and after by both weight and high-resolution computed tomography (CT) scans. Different parts of the reef have different levels of acidity, current flow, temperatures and other variables.

They found that the big predictor of coral erosion was acidity of the water. And since oceans are expected to continue to acidify from carbon-dioxide loading, that’s bad news for reefs.

And particularly bad news for reef areas subject to higher levels of acidity. The study found that rather than being uniform, acidity levels vary both in place and time.

“It was surprising to discover that small-scale changes in the environment can influence ecosystem-level reef processes. We saw changes in pH on the order of meters and those small pH changes drove the patterns in reef accretion-erosion,” Silbiger said in a news release.

What does it all mean?

“Our findings suggest that increases in reef erosion, combined with expected decreases in calcification, will accelerate the shift of coral reefs to an erosion-dominated system in a high-CO2 world. 

"This shift will make reefs increasingly susceptible to storm damage and sea-level rise, threatening the maintenance of the ecosystem services that coral reefs provide,” the researchers write.

A video of the erosive process is here.

Citation: NJ Silbiger, O Guadoyal, FIM Thomas, MJ Donahue (2014) Reefs shift from net accretion to net erosion along a natural environmental gradient. Marine Ecology Progress Series, vol. 515, doi: 10.3354/meps10999

© Jan TenBruggencate 2014