Coral bleaching categories

Assessing and monitoring coral bleaching

Discover how the Reef Authority, together with our science and management partners, Traditional Owners, and tourism operators assess coral bleaching events and their extent, severity and prevalence on the Reef.

Bleaching impact framework

As part of the summer Reef health response, marine managers and scientists from the Reef Authority, Australian Institute of Marine Science, and James Cook University developed a framework to describe and categorise coral bleaching on the Great Barrier Reef.

This framework describes bleaching events in a clear and consistent way — and enables comparisons to be made between years, over time, and across the Reef.

It considers the four key components that contribute to coral bleaching: exposure, colony response, spatial extent, and prevalence.

Exposure: satellites, weather stations, gliders and data loggers provide information on the duration of heat stress — how hot, how long, and where.
Colony response: once coral has been exposed to temperatures, in-water surveys are used to consider how the coral responds — severity, loss of zooxanthellae, mortality, survival.
Prevalence: in-water and aerial surveys look at what area and what parts of the Reef have been impacted e.g. is it just the reef flat or a bigger area — what percent is impacted, which habitats, at what depths.
Spatial: broadscale aerial surveys and in-water observations are used to determine whether the scale of impacts — local, regional, widespread, or the total Reef area.