97% coral at Australian island wiped out in 3 months

The worst mass coral bleaching event in the world’s biggest reef system has wiped out at least 97 per cent of the coral at Australia’s Lizard Island in three months, according to a recent drone analysis.

Located in the north of the Great Barrier Reef in Australia, Lizard Island has become ground zero for studying the effects of rising sea temperatures. Scientists from various institutions used before and after high-resolution drone images from the same location to estimate the extent of bleaching and death on the island’s coral reef, which was captured between March and June this year.

The imagery revealed a horrifying decline, with nearly all the coral succumbing to bleaching and dying, the scientists wrote for nonprofit news source The Conversation.

This news comes on the heels of an announcement by the United States-based National Oceanic and Atmospheric Administration (NOAA) on May 23, 2024. NOAA reported that over 70.7 per cent of coral reefs worldwide have been impacted by bleaching-level heat stress since January 1, 2023. This surpasses all previous global mass bleaching events.

The drone image results are the first quantitative assessment of coral deaths from the previous mass bleaching event, Jane Williamson, Professor of Marine Fisheries Ecology at Macquarie University wrote in The Conversation.

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“We don’t know how much coral died beyond this reef. But we do know that, according to other aerial surveys, almost one-third of the Great Barrier Reef experienced ‘very high’ and ‘extreme’ levels of coral bleaching last summer,” she wrote. Australia’s summer months are December, January and February.

The Great Barrier Reef has undergone five mass bleaching events, with the ongoing coral bleaching being the fifth in the past eight years alone.

Coral bleaching occurs when corals expel algae from their tissues into the water in response to extreme heat stress. As a result, the corals appear white and become vulnerable to diseases. Often, corals can recover when water temperatures decrease, but some may die immediately or due to prolonged heat stress.

In March, images were captured using drones flying at 20 metres altitude over the North Point Reef of the island, the authors said. The same area was covered with drone imagery in June. The researchers then snorkelled down to observe the situation first-hand.

The earlier maps showed corals bleached or appearing brightly coloured, also known as fluorescing, as they expelled algae. The numbers peaked at 97 per cent mortality in June.

This revelation comes against the backdrop of the United Nations Educational, Scientific and Cultural Organization expressing its “utmost concern” regarding the mass coral bleaching, appealing to the Australian government to make the data and extent of coral death public as soon as possible.

The Australian Institute of Marine Science is expected to release its annual report on coral reef conditions in the coming months.

A statement from the Reef Authority said, “Sea surface temperatures across the Reef are now below the threshold that typically causes heat stress to corals. However, sea surface temperatures were still about 0.8°C above the May average and are currently about 0.7°C above the June average.”