Climate variability and change: monitoring data and evidence for increased coral bleaching stress

Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water temperatures, light, salinity, nutrients, bathymetry and the aragonite saturation state of seawater (Buddemeier and Kinzie 1976; Kleypas et al. 1999; Hoegh-Guldberg 2005). Their natural environment, at the interface of land, sea and the atmosphere, can vary quickly and potentially be stressful. Reef organisms have, over millions of years, evolved strategies to cope with occasional environmental disturbances (such as tropical cyclones). Given sufficient time between disturbances, damage or destruction would normally be followed by recovery and regrowth (Buddemeier et al. 2004). As documented in numerous scientific studies and reports, the world's coral reefs are "in crisis" as a result of direct local- and regional-scale human impacts on their environment. These impacts include overfishing, destructive fishing practices, changed land-use that increases sediment, nutrient and pollutant flows into reef waters, and poorly designed coastal development. This ecosystem degradation is largely occurring in the many tropical countries whose increasing populations are heavily dependent on coral reefs yet have insufficient resources to develop appropriate, sustainable management practices (Wilkinson 2004). Coral reefs are now confronted with additional global-scale stresses due to the introduction of enhanced greenhouse gases that are rapidly changing coral reefs' environmental envelope through both ocean acidification and increased thermal stress due to climate change (Hoegh-Guldberg et al. 2007)