Diver teams have detected highly variable but widespread coral bleaching across the Great Barrier Reef Marine Park, with cloud cover and heavy rain in the central and southern regions providing some relief from the heat stress that has caused corals to bleach.
The extent and severity of bleaching on a regional level in the far north have prompted the Great Barrier Reef Marine Park Authority to increase its surveys, particularly in areas experiencing the greatest heat stress.
Chairman Dr Russell Reichelt said the area around Lizard Island, situated 250 kilometres north of Cairns, and sites further north, had fared the worst.
“This is the result of sea surface temperatures climbing as high as 33 degrees Celsius during February,” Dr Reichelt said.
“In the far north, the surveys found severe bleaching on inshore reefs, along with moderate bleaching on mid-shelf reefs.
“Further south in the Marine Park, mid-shelf and outer reefs that were surveyed are generally displaying minor to moderate bleaching, some of which is typical for this time of year.
“At this stage, coral mortality also remains low and has only been detected on a small number of reefs.”
Dr Reichelt said it was likely that cloud cover and heavy rain over the past fortnight had lessened the risk of bleaching in the central and southern regions of the 344,400 square kilometre park.
“Satellite readings have been interrupted by the cloud cover, meaning it’s difficult to gauge where sea surface temperatures may have come down and by how much. It will be some months before we know the full effects on the Reef,” he said.
“The events on the Great Barrier Reef are part of the global pressure on coral reefs during a strong El Niño weather system which also affected reefs in Hawaii and the Caribbean. During past bleaching events in 1998 and 2002, about half the shallow corals of the Reef were bleached and about five per cent died as a result.
“Bleaching is a vivid reminder of the need for all of us to continue building the resilience of coral reefs to give them the best chance of dealing with increasing climate change impacts.
“I would urge Marine Park users to help promote coral recovery through simple measures such as not anchoring close to corals, preventing and reducing marine debris especially discarded fishing lines, and abiding by zoning rules that provide strong direct protection over very large areas of the Great Barrier Reef.”
Heat stress can cause corals to expel tiny algae, called zooxanthellae, which live inside their tissues and provide corals with most of their colour and energy needs. If bleaching persists, corals begin to starve and eventually die.
The strong El Niño weather pattern has further elevated high sea surface temperatures usually present at this time of year. Dr Reichelt said in the long term, climate scientists had predicted a trend of increasingly severe El Niño weather patterns.
Divers from the Great Barrier Reef Marine Park Authority are partnering with the Queensland Parks and Wildlife Service and a range of research institutions to survey the extent and severity of bleaching.
The agency is also being assisted by the tourism industry and the public who are are providing reports of bleaching through the Eye on the Reef program.