AIMS - Coral Bleaching on the Great Barrier Reef: Early video footage of coral recovery from Middle Reef, Townsville

Early video footage of coral bleaching and recovery from Middle Reef, Townsville

We now believe that bleaching occurs when corals are exposed to sea-surface temperatures (SST) in excess of maximum temperatures normally experienced. Solar radiation, extreme low tides and reduced salinities are also believed to be additional triggers of bleaching. Often these triggers act in combination. Corals become bleached when they lose their zooxanthallae and/or their pigments. Where adverse environmental conditions are severe or prolonged, bleached corals may not recover (Hyne, J 1998).

Bleaching The Great Unknown

AIMS has a comprehensive monitoring program in place on the Great Barrier Reef (GBR) with data on fish and coral communities since 1992 and on crown-of-thorns-starfish (COTS) extending back to 1985. The program provides information on the status of fish, coral and COTS populations on the GBR and trends through time. These data provide the principal management agency, the Great Barrier Reef Marine Park Authority (GBRMPA), with a perspective on the overall health of the reef associated fish and coral populations.

AIMS surveys conducted between January and June of 1998 revealed variable levels of bleaching with inshore reefs showing considerable bleaching, particularly in the Central GBR, while outer shelf reefs were largely unaffected. One of the reefs that the AIMS surveys each year is Middle Reef. This reef lies just off the coast of Townsville, a large regional city in Queensland.	Click on this image to view a video of the bleaching event in May 1998. (20 second MOV file)
Annual surveys have been conducted on Middle Reef since 1993. Coral cover has remained fairly constant since surveys began, with 36% hard coral cover observed in September 1997. However, significant bleaching was observed during the May 1998 survey. Bleaching was detected in most coral families, particularly Agariicidae, Pocilloporidae, and Poritidae. A large percentage of soft corals (mostly Sinularia spp) were also bleached.
Middle Reef was resurveyed in August 1998 to examine the impact of the bleaching event. Low levels of mortality were observed in the two dominant hard coral families Agariciidae and Poritidae. Many soft corals appeared to have recovered their original colouration though cover did show a decline between surveys. Note that many inshore reefs have shown much less recovery than has occurred at Middle Reef.	Click on this image to view a video of the same area of reef in August 1998 following the bleaching event. Significant recovery of hard and soft coral is evident. (20 second MOV file)

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