Damage to the Great Barrier Reef will in future, be reported on a new scale ranging from one to five, similar to how tropical cyclone strength is reported, under a new framework announced by the Great Barrier Reef Marine Park Authority on Feb. 20.
A ranking of five would indicate a widespread bleaching event on the reef.
A single-celled algae, called zooxanthellae, lives inside coral, giving it both colour and food. But when the coral experiences stress it expels the algae, causing it to turn white. A bleaching event does not necessarily mean the coral is dead.
Stress can be caused by environmental changes such as increased water temperatures or a drop in salinity from freshwater flooding.
High Temperatures Blamed for Full Bleaching
If the reef experiences temperatures 16 degrees or more above the long-term average weekly temperature, it will be deemed a category five, with the impact likely to be full bleaching and death to many species across the ecosystem.Unlike cyclones, which are gauged by wind intensity and where the Bureau of Meteorology can forecast the severity, the category of coral bleaching will only be released at the end of the summer period.
“A tropical cyclone might happen over 24 hours as it crosses the Great Barrier Reef on our coastline, but the bleaching event might unfold over several months,” the Authority’s Mark Read explained. The new framework will help reef caretakers prepare for a bleaching event, and will provide a more detailed assessment after it occurs.
He said the categorisation framework will also be applied retrospectively to previous summers to demonstrate broader trends.
Several Adverse Events
So far this summer, the reef has been hit by two tropical cyclones and runoff caused by flooding—both of which are major causes of stress to corals.Mr. Read said parts of the Reef, near Cairns and Townsville, have experienced physical damage from wind and waves. Freshwater flooding and subsequent bleaching have also impacted some of the offshore reefs near Cairns this summer. However, other parts are in good condition.
The category of bleaching applicable to this summer is expected to be released in a few months.
Coral reefs are susceptible not just to bleaching, but also to disease and attacks by starfish. All blamed for stalling the Great Barrier Reef’s recovery last year.
One report stated that hard coral cover in the northern section of the reef, from Cape York to Cooktown, was at 35.7 percent, down from 36.5 percent in 2022.
Between Cooktown and Proserpine, the reef’s central region, coral cover was estimated at 30.8 percent, down from 32.6 percent in the previous year. And in the southern region, from Proserpine to Gladstone, coral cover was at 33.8 percent—virtually unchanged from the previous year.
