Past environmental conditions associated with a shut-down of coral-reef expansion in Pacific Panama are reported online this week in Nature Climate Change. The study suggests that future human-induced climate change could lead to another reef shutdown in the tropical eastern Pacific.

Coral reefs are important underwater ecosystems that are home to a wide variety of marine life. In response to changing climate and ocean conditions, several coral reefs in Panama and other locations in the Pacific ceased development for 2,500 years beginning about 4,100 years ago. By analysing the geochemistry of coral skeletons, Lauren Toth and colleagues reconstructed the environmental and physiological states leading up to and following this hiatus of the 6,750-year-old reef at Contadora Island. They found that changes in temperature and precipitation (which can reduce water clarity and thus the amount of light reaching the reef) ultimately drove the corals to thresholds beyond which normal development could not be sustained. The El Nino/Southern Oscillation, which is predicted to increase in frequency and severity in the coming years, was associated with the shut-down. Photosynthetic activity and the structural integrity of the corals deteriorated just before the hiatus, supporting the prediction that ecosystems exhibit early warning signs prior to collapse..

The authors report that average sea temperatures at Contadora Island are now approaching the maximum temperatures that supported coral growth before the previous hiatus. Increases in thermal stress are expected to cause enormous damage to coral reefs in the near future.