Perfect storm of weather events sees coral bleached at Abrolhos Islands off West Australian coast

Nice to see a coral bleaching event that is NOT being attributed to global warming. Why are similar processes not at work on the other side of Australia? Why are similar processes not at work on both the East and West coasts. There is no reason why. Water levels fluctuate on both coasts

In what's been described as an important natural process, thousands of hectares of coral at the Abrolhos Islands off the West Australian coast have been bleached after a combination of weather conditions repeatedly exposed the coral to strong cold winds.

Fisher and pearl farmer Jane Liddon has watched the ocean around her fall over the past few days from her home at Post Office Island in the southern group of the Abrolhos.

She said water levels had fallen to an unusually low level due to a combination of strong winds, a high-pressure system and new moon tides.

"When the coral first came out [of the water], it was bright and beautiful … the second day, the water was even lower and still very windy and cold. By the third day it was completely white," Ms Liddon said.

"The tops were bright white. It was like new islands have formed everywhere here."

Ms Liddon, who has spent her life at the Abrolhos, said in 50-odd years, she had often seen events where a low tide had exposed some stag coral, but this was unusual.

"It's a coincidence of having these weather events all come together that has made it extreme, this time of year you do get low tides in the middle of the day, that's common, but not as low as this event," she said. "The low tide is like a lawnmower on the coral.

"For three days we haven't been able to take our dingy off our jetty because our jetty was not in the water anymore, so we are marooned by low tide, which is very rare."

Murdoch University PhD student Jo Buckee is studying coral mortality events and the role that they play in determining coral cover on shallow reef platforms.

She said a similar coral bleaching event at Abrolhos Island due to low tide in 2018 impacted the 7,000-hectare area of shallow reefs and saw about 30 per cent of the coral die.

However, Ms Buckee said the coral was able to regenerate and recover relatively quickly and had re-established itself back to pre-2018 levels.

"The bulk of the corals that you'll see sticking out of the water are the fast-growing Acropora corals, branching and plating corals, and they are capable of fast growth rates," she said.

"This trimming off of the tops is a natural event, it looks very dramatic but it is a naturally occurring process. "It's important for keeping up with sea level rise, for providing the material for reef and island building."

Ms Buckee said sea level variability along with coral growth and mortality over thousands of years had formed the coral reefs and the Abrolhos Islands themselves and allowed them to remain in position.

"That is the material that you're walking on when you're walking on the islands, it's from previous periods when the sea level was slightly higher than it is now, but also fragments washed up from reef flats that surround the islands," she said.

"In order for the reef to keep up with sea level rise over time, it requires fragments of coral to be produced so that the overall height of the reef is able to change.

"These environments are very dynamic with a mixture of seaweed and coral, a reflection of the Abrolhos's position in the transition zone between tropical and temperate ecosystems."

Ms Buckee said with the diversification of land and water activities at the Abrolhos, leading to year-round visitation, previously unwitnessed coral bleaching events were now attracting interest and attention.

https://www.abc.net.au/news/2022-11-03/coral-bleached-abrolhos-islands-west-australian-coast/101608748

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