In early 2020, the Great Barrier Reef suffered its third major coral bleaching event in five years due to heat stress.
At Lizard Island, bleaching first became noticeable in mid-February. February is normally “wet season”, with clouds and rain that keep the sea temperature down despite the tropical summer heat. But this year, the weather was clear and mostly calm, just as it had been four years earlier in the lead-up to the 2016 bleaching event. That year, coral loss in this area was extreme – more than 75% died.
Initially, it seemed that we were in for a re-run of the devastating 2016 event. It was quite horrifying to see corals start to bleach en masse again, just as the recovery process was becoming really noticeable in some places.
Luckily, the weather pattern changed in time to avoid major mortality this time. In mid-March, Cyclone Gretel formed far offshore, bringing clouds, rain and wind which lowered the water temperature. In 2016, high temperature persisted for much longer and the accumulated heat stress was extreme, continuing to kill corals throughout winter.
A tiny proportion of corals have already died from the 2020 bleaching at Lizard Island but we don’t expect that to continue. And while many colonies are still bleached at present, many others are beginning to regain their colour and that will increase in the coming months.
These photos show changes over time in two sets of corals.
Corals at Lizard Island – and the legions of life that depend upon them – have dodged a bullet this time around. It was a close call. Unfortunately, it appears that other parts of the Great Barrier Reef have not been so lucky.
We have seen quite amazing levels of recovery since the 2016 and 2017 bleaching events. This is a welcome demonstration that reefs can regenerate themselves after extreme damage, given the right conditions. But how long can they continue to do so in a world where conditions that cause such extreme damage occur with increasing frequency?
Anne Hoggett, 4 May 2020
[Dr Anne Hoggett is a Director of the Australian Museum’s Lizard Island Research Station. Resident there since 1990, she has seen years when corals flourished; and years when they have been devastated by Crown of Thorns Starfish, direct-hit cyclones or bleaching sea temperatures. The history of the Station is told in its Annual Research Reports and in Lizard Island Research – a partnership.