Third consecutive rare La Niña event could lead to more coral bleaching along WA’s Ningaloo Reef, scientists say

Marine scientists fear confirmation of another La Niña weather event this year could lead to increased coral bleaching along the northwest coast of Western Australia over the summer.

Although there are signs of recovery, researchers have confirmed significant bleaching events along the World Heritage-listed Ningaloo Reef, including Turquoise Bay and Coral Bay.

Australian Institute of Marine Science researchers James Gilmour and Luke Thomas monitor sections of the marine park for coral bleaching.

Further south, scientists have detected between 20 and 30 percent coral bleaching in Turquoise Bay.

But there are signs of recovery from last summer’s marine heat wave.

Marine Park Coordinator Sallyann Gudge of the Department of Biodiversity Conservation and Attractions (DBCA) regularly monitors the area.

“There are a few corals that haven’t fully recovered, but there’s definitely growth there, and we’re seeing baby corals and recruits, so that’s a really good sign as well,” he said. she stated.

A double whammy for the reef

Warm ocean temperatures and light winds created a double impact on WA’s Ningaloo coast earlier this year.

A marine heatwave caused bleaching at Bundegi and Turquoise Bay, while an unrelated coral spawning event at the same time led to massive fish kills at Coral Bay in April.

Ms Gudge said the massive fish kills occurred due to oxygen depletion in the shallow waters.

“The eggs and reproductive cells of corals rise to the surface and cause a slick, which usually disperses into the ocean,” she said.

“But this year, given the weather, he actually just dragged him into Bill’s Bay, and he was there for a week.

“And those conditions caused oxygen depletion out of the water.

“Unfortunately the corals there have also been stressed and bleached.”

Not the first time

The DBCA says that since it began monitoring the area, Bill’s Bay has experienced fish kills and coral bleaching due to anoxic (lack of oxygen) events in 1978, 1989, 2002, 2005, 2008 , 2019 and 2022.

And they say marine heatwaves have caused coral bleaching in Ningaloo before, particularly in 2011 and 2013.

Although there are signs of recovery, scientists fear that this third consecutive La Niña weather event, confirmed by the Bureau of Meteorology, could again lead to higher ocean temperatures and light winds along the coast. northwest this summer.

Dr Gilmour said the mass bleaching happened once the temperature was two degrees above normal for several weeks.

However, he says, a bleached coral is not necessarily a dead coral.

“It can be any type of stress, but it’s usually warm water where the corals expel or spit out the tiny algae cells that live inside their tissues. And the cells algae really provide a food source for the corals,” he said.

“It’s called bleaching because you can see the white skeleton through the translucent fabric.

Take care of our reef

As ocean temperatures continue to rise, Dr Thomas says they are using DNA technology to help find heat-tolerant corals on the Ningaloo Reef and learn from them.

“[We are] trying to focus on how temperature tolerance varies across the reef,” Dr Thomas said.

“What are the mechanisms driving this variation? Can we harness this natural variation?

“Can we find pockets of heat-tolerant corals?”

The coral is already renowned for its fragility, but with sections of the reef in recovery mode, the DBCA urges people to be careful when visiting the reef.

For now, the DBCA and researchers say they will continue to monitor Ningaloo Reef this summer.