Climatic and biotic thresholds of coral-reef shutdown.

Climate change is now the leading cause of coral-reef degradation and is altering the adaptive landscape of coral populations. Increasing sea temperatures and declining carbonate saturation states are inhibiting short-term rates of coral calcification, carbonate precipitation and submarine cementation. A critical challenge to coral-reef conservation is understanding the mechanisms by which environmental perturbations scale up to influence long-term rates of reef-framework construction and ecosystem function. Here we reconstruct climatic and oceanographic variability using corals sampled from a 6,750-year core from Pacific Panamá. Simultaneous reconstructions of coral palaeophysiology and reef accretion allowed us to identify the climatic and biotic thresholds associated with a 2,500-year hiatus in vertical accretion beginning ∼4,100 years ago. Stronger upwelling, cooler sea temperatures and greater precipitation-indicators of La Niña-like conditions-were closely associated with abrupt reef shutdown. The physiological condition of the corals deteriorated at the onset of the hiatus, corroborating theoretical predictions that the tipping points of radical ecosystem transitions should be manifested sublethally in the biotic constituents. Future climate change could cause similar threshold behaviours, leading to another shutdown in reef development in the tropical eastern Pacific. [ABSTRACT FROM AUTHOR]