NDER STRESS: A diver surveying coral bleaching at Lizard Island, where a large part of the reef flat has been affected.PICTURE: AUSTRALIAN MUSEUM
THE worst coral bleaching to hit Lizard Island in nearly 15 years has scientists worried about how badly the Great Barrier Reef will be affected by warmer waters in coming weeks.
Researchers estimate 80 per cent of coral on the reef flat surrounding the island, about 220km north of Cairns, is showing signs of bleaching.
A wide variety of corals are bleaching but the branching, bushy and plate corals – which are highly sensitive to bleaching – are the worst-affected.
The Australian Museum’s Lizard Island Research Station director Dr Anne Hoggett said the station recorded similar levels of bleaching in 2002.
“We haven’t got a white fields of coral year but we’ve certainly got some corals that have gone completely white and a very large number that are fluorescing; they’re on their way to becoming bleached,” she said.
“We’ve got utterly perfect weather for bleaching here at the moment.
“It’s hot, it’s calm and it’s clear.
“That’s the worst possible combination for the corals.”
Sea temperatures have been up to 1.5C above average for this time of year at Lizard Island, and are expected to peak on the Great Barrier Reef later this month.
Researchers have warned the current El Nino weather patterns are mirroring those that caused widespread coral bleaching along the Reef in 1998.
Dr Hoggett believed the bleaching at Lizard Island would likely become worse in coming weeks.
She said it was particularly bad for the island’s reef ecosystem, which was still recovering from a recent crown-of-thorns starfish outbreak, and two major cyclones.
“It’s quite serious. We’re all worried about this coral bleaching,’’ she said.
“We had fingers and toes crossed hoping it wouldn’t happen, but it is happening exactly as predicted.”
Coral bleaching occurs when corals expel tiny algae that live inside them, mainly because of thermal stress.
ARC Centre of Excellence for Coral Reef Studies director Professor Terry Hughes said Lizard Island so far appeared to be the worst-hit location throughout the Great Barrier Reef this year.
“We’re quite close to the time of the year where the temperatures will start to peak and then drop,’’ he said.
“That should be the end of the bleaching, so it really comes down to what the local weather will look like in the next two weeks, whether bleaching will happen at a particular place or not.
“So we’re sort of down to the wire in terms of the summer maximum temperature upon us.”
Great Barrier Reef Marine Park Authority reef recovery director Dr David Wachenfeld said reports of low level bleaching in the northern sector of the marine park was not surprising, given the hot and often still conditions.
“It’s consistent with El Niño weather conditions,’’ he said.
“The weather over the next two to four weeks will be critical, as March is considered a high-risk period for mass coral bleaching.
“To alleviate thermal stress on corals, we need sea surface temperatures to come down.
“To achieve that, we ideally need a good deal of rain and cloud cover.”