The 2002 coral bleaching event

Coral bleaching Photo:GBRMPA

In 2002, the Great Barrier Reef suffered the worst coral bleaching on record.

Aerial surveys by scientists from the Australian Institute of Marine Science, CRC Reef and the Great Barrier Reef Marine Park Authority that covered more than 640 reefs found that nearly 60% of the reef area in the Marine Park was heat-stressed to some extent as indicated by bleaching. Not all reefs were bleached equally, and the bleaching was not evenly distributed throughout the Marine Park.

The coral bleaching episode in 2002 was probably worse than the 1998 event because more reef area was affected. The most severe bleaching occurred on reefs close to shore in both bleaching events, but the 2002 event affected a greater area of reefs further offshore.

The aerial surveys found that bleaching was worst in the Princess Charlotte Bay region, near the Turtle Island Group, on inshore reefs from Cape Upstart to the Whitsundays in some reefs in the Sir James Smith Group and in the Keppel Island area. Moderate to very high bleaching was seen inshore and offshore from around Cape Flattery to Mackay. Little or no bleaching was seen in the Far Northern Section from the tip of Cape York to the northern Princess Charlotte Bay area, in the Swains area and in the Capricorn Bunker Group.

The team also used SCUBA to confirm results and determine whether corals were likely to recover from bleaching or would die. The underwater surveys found that few reefs escaped bleaching, but it appears likely that most reefs will recover with only minor death of corals. However, some of the most severely bleached reefs were devastated with 50% and 90% of coral dead at some sites.

Australia has been lucky to see another major bleaching event without widespread death of corals but the devastation at some sites provides a vivid warning of what could happen if hot water events become more frequent and severe.

We may be witnessing the beginning of a slow-motion degradation of the reef system that will only get worse in coming decades. AIMS, CRC Reef and the GBRMPA will continue to keep a careful watch on the health of the reef and improve our understanding of the implications of global warming for reef management.