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Mass bleaching

Mass bleaching was first recorded in early 1980 in the Caribbean and surrounding seas (notably in Jamaica and the Bahamas), the far eastern Pacific (Panama and the Galápagos Islands) and in isolated instances in the Pacific (notably French Polynesia and Thailand) and the Great Barrier Reef.

There have been seven major bleaching events on the Great Barrier Reef, the three spanning the summer seasons of 1981/82, 1997/98 and 2001/02 being the most widespread. However, it was the 1981/82 mass bleaching event that really drew attention to the association between ocean temperature and bleaching. A community of bleached coral. Photograph: Katharina Fabricius. A community of bleached coral. Photograph: Katharina Fabricius.

The 1997/98 mass bleaching event was extraordinarily widespread. It affected reefs in over 50 countries throughout the Pacific and Indian Oceans, the Red Sea and the Caribbean, and even affected corals in high latitudes including those of the Arabian Gulf.

On the Great Barrier Reef, this mass bleaching coincided with the highest sea surface temperatures ever recorded. It was also at this time that 500-year-old Porites died, strong evidence that mass bleaching had human causes. A bleached Porites colony several hundred years old. Photograph: Katharina Fabricius A bleached Porites colony several hundred years old. Photograph: Katharina Fabricius.

The third major mass bleaching event took place in 2001/02, again affecting many countries. By this time it had become clear that there was a causal link between the periodicity of global bleaching and changes in ocean temperature associated El Niño Southern Oscillation cycles. The gap between these events appears to be closing as the difference between El Niño years and non-El Niño years diminishes, a process that has started occurring and is destined to continue on into this century. Significantly, while 2006 was not an El Niño year, there was significant mass bleaching of corals on the Great Barrier Reef. Extensive mass bleaching occurred in several countries of the Caribbean in both 2005 and 2006. Present indications are that increases in global temperatures will lead to mass bleaching in all years by 2030 at the latest.

J.E.N. Veron