Climate change will increase the erosion of coral reefs

Jeremy Hance, mongabay.com 28 Jul 08;

Coral reefs are particularly susceptible to climate change. Warming waters have been shown to bleach coral, killing off symbiotic algae that provide them with sustenance, and often leading to the death of the coral itself. Much attention has been placed on bleaching coral, but now scientists have discovered an additional danger to coral reefs in a warming world: erosion.

A study published in this week's issue of PNAS has shown that coral reefs in the waters off Panama and Galapagos, which live in a naturally acidic and high CO2 environment, contain dangerously low percentages of cement to hold them in place.

The researchers believe that these reefs are a vision into the future of reefs worldwide, since their environment replicates the expected increased in acidity and CO2. Oceans have already absorbed about one-third of all carbon dioxide released into the atmosphere since the industrial revolution.

The researchers believe that early marine cementation is key to a coral reefs "rigidity and stability".

Studying early marine cementation in three test sites, one in Galapagos and two in Panama, the researchers searched interskeletal pores for evidence of cementation. They found that cementation was in 1.5 to 16.1 percent of these reef's pores. The Galapagos was the most cement-free with six samples showing no cement whatsoever. The researchers also took samples from a reef in the Bahamas. In these less acidic and less CO2-rich waters, 60 percent of coral contained cementation: four times more than the most cement-rich coral found by scientists in the waters off Panama. Bearing out the link between less cementation and risk of erosion, the scientists note that erosion rates in the Galapagos and Panama "are among the highest measured for any reef system to date".

Coral reefs are bombarded by threats. A recent study from the IUCN showed that nearly one in three coral species in the world are endangered. Threats included human disturbance, coastal development, sedimentation from land erosion and deforestation, high nutrient run-off from agriculture causing algae blooms, over-fishing, and bleaching due to warming oceans. This new study reveals yet another vulnerability, the increasing instability of reefs in face of climate change.

"Poorly cemented coral reefs of the eastern tropical Pacific: Possible insights into reef development in a high-CO2 world," by Derek P. Manzello, Joan A. Kleypas, David A. Budd, C. Mark Eakin, Peter W. Glynn, and Chris Langdon. PNAS.