The ocean organism possibly most vulnerable to temperature change is coral.
Temperature is critical to reef building and controls the rate of coral reef growth. There is evidence that reefs will bleach (eject their symbiotic algae) at even a slight persistent temperature rise. Bleaching slows coral growth, makes them susceptible to disease, and can lead to large-scale reef die-off.
As a result of this prolonged increase in sea surface temperatures, the Great Barrier Reef has recently experienced a number of coral bleaching events. The most severe mass bleaching events spanned the summer seasons of 1997-98 and 2001-02, with over 50 per cent of reefs affected by bleaching, resulting in lasting damage to an estimated 5 per cent of reefs.
Rising sea surface temperatures are projected to result in more frequent and widespread coral bleaching events. An increase of more than 2°C would place 34 per cent of coral reefs above the critical limit for bleaching, and a temperature increase of around 3°C would lead to 65 per cent of coral reefs being above the critical limit for bleaching. Bleaching events are likely to diminish the ability of corals to recover and adapt, seriously threatening the ecosystem of the Great Barrier Reef.