The temperature tolerance of corals

Maximum summer sea temperatures that are just 2-3°C above normal values can kill corals. The upper temperature limit for corals varies between species and places. Corals that usually live in cooler conditions, where summer maximum temperatures are 28°C, will bleach at lower temperatures than corals that usually live in hotter parts of the reef where summer temperatures reach 31°C.

Sea temperatures atr Halfway Island (in the Keppel group) during the 1998 and 2002 bleaching events were higher than the 10-year average. Graph courtesy R. Berkelmans, CRC Reef.

The extent of bleaching also depends on the length of time that the water temperature is raised. A coral which normally grows in summer temperatures of 29°C may show few signs of stress if exposed to temperatures of 32°C for
a few hours, but could bleach if temperatures reach 31°C for a week. It is a combination of the length of time, and the amount by which water temperature exceeds normal maximum values, that is critical in determining the extent of bleaching.

CRC Reef Research Centre Ltd was established and is supported under the Australian Government’s Cooperative Research Centres Program. Its mission is to plan, fund and manage world-leading science for the sustainable use of the Great Barrier Reef World Heritage Area. CRC Reef is a joint venture between Association of Marine Park Tourism Operators, Australian Institute of Marine Science, Great Barrier Reef Marine Park Authority, Great Barrier Reef Research Foundation, James Cook University, Queensland Department of Primary Industries and Fisheries, Queensland Seafood Industry Association, Sunfish Queensland Inc. The University of Queensland is an associate member.