a day ago
Researchers study impacts of coral bleaching on Lord Howe Island
Researchers hope studies into the world's most southern coral reef at Lord Howe Island will help experts better understand how marine systems are adapting to changing oceans, and how to protect them.
The island's reefs, 600 kilometres from the Australian mainland, are on a boundary line between warm and cool environments.
They support a range of marine species found nowhere else in the world.
Their remote and southern location, away from stressors which impact other reef systems, means they are an important benchmark site when assessing the wider impact of warmer ocean temperatures.
Last February, Lord Howe experienced its most severe coral bleaching event, the fourth and worst recorded there since 1998.
Since then, a team of researchers from Sydney's University of NSW (UNSW) and University of Newcastle has been monitoring the recovery of the island's reefs.
"We are looking at understudied reef systems … what happens after a bleaching event, how do corals recover?" UNSW PhD candidate Paige Sawyers said.
"And are there different tolerances for recovery for different species?"
Ms Sawyers has observed the Lord Howe Island reef systems on four visits to the island since the start 2024.
She said a low tide anomaly at the island last May left coral exposed and further damaged and stressed the reef system.
Ms Sawyers said the reef was showing observational signs of recovery earlier this year, but was experiencing ongoing strain after an "incredibly challenging year".
"A lot of the reef was looking OK, unfortunately, the temperatures were higher than normal," she said.
"While we didn't reach bleaching thresholds or witness visible bleaching this year, the reef was still under thermal stress.
"Sea temperatures remained above the summer average of 24.06 degrees Celsius, sitting between 24 and 25 degrees for around four to five months.
She said the prolonged exposure occurred at a critical time when the reef needed to recover.
"Instead, what we're seeing is recovery being stalled just when it's most vital," she said.
Ms Sawyers said compared with tropical reefs, subtropical reefs such as Lord Howe typically recovered more slowly after bleaching.
She has been analysing her findings and said she hoped to visit Lord Howe in the coming months.
Lord Howe reef tour operator Dean Hiscox regularly monitors the island's ocean temperatures and coral health.
He said he was concerned about the impacts of residents living on the island, particularly on the marine park's water quality.
"We really need to get our head around sustainability, and we need some baseline information," he said.
Work is underway to gather that information.
Lord Howe Island Marine Park managers have been working with researchers from the Australian Institute of Marine Science (AIMS), Southern Cross University, and the University of NSW to investigate water quality and nutrient levels in the marine park, which can directly impact marine system health.
AIMS senior research scientist Shaun Wilson was part of a research trip to the island late last year to try and determine the level and movement of nutrients in the coral lagoon, and whether they were coming from human or natural sources.
Dr Wilson said there was evidence modern waste and sewage management had led to a reduction in nutrient levels in parts of the reef.
His team hoped to return in the next 12 months to collect more data.
"Lord Howe is one of our most temperate reefs," he said.
As part her research, Ms Sawyers has also been investigating bleaching and recovery in an understudied tropical reef system in Samoa, where a mass bleaching event also occurred in 2024.
"When we went back five months later, they'd [the corals] recovered," she said.
Ms Sawyers said she was comparing the Samoan reef's resilience with Lord Howe.
"This helps us identify patterns in resilience and recovery.
"The findings can then be used to inform predictions and management strategies for other Australian reef systems."
