Watching marine scientists the great Barrier Reef They say they have recorded the highest levels of coral cover in 36 years in the northern and central regions, but they caution that any recovery could be quickly capsized by global warming.
The annual long-term monitoring of the Australian Institute of Oceanography Report He says fast-growing corals that have pushed coral cover upward are also most at risk from marine heat waves, storms, and crown-thorn starfish (COTS).
Global heating has been accepted by scientists as the greatest long-term threat to coral reefs.
earlier this year, Unusually hot ocean temperatures caused the first-ever mass bleaching within a year of a La Niña A natural climatic phase that should have given the corals a rest period.
The first mass bleaching on the reef was recorded in 1998, but since then the reefs have been infected in 2002, 2016, 2017, 2020 and again earlier this year.
Predicting the future of coral reefs under climate change, the report said, was one of the increasingly frequent and long-lasting marine heat waves, with the continuing risk of COTS outbreaks and tropical cyclones.
“Mitigating these climate threats requires immediate global action on climate change,” the report said.
“The fact that we’ve had four bleaching events in the last seven years and the first in La Niña is really worrying,” Dr Mike Emsley, who leads the Australian Institute of Marine Sciences’ monitoring programme, told the Guardian.
Surveys are conducted by dragging divers over reefs at a standard rate, recording corals, bleaching levels, COTS and number of trout and sharks.
About half of the 87 corals surveyed for the report were conducted before the last bleaching event occurred in February and March of this year.
“The effects of the 2022 mass bleaching event are still unfolding, and its impact will only be known over the coming months,” the report said.
aerial surveys The Australian Institute of Marine Science and the Great Barrier Reef Marine Park Authority in March covered 750 individual reefs.
fast growing Acropora He said that the branching, plate-like corals species that were pushing the coral cover up were also preferred prey for the plants of the Red and Green Sea islands.
In the northern parts of the reef, monitoring data showed an average coral cover of 36% – a record high, with the region’s lowest levels at 13% recorded in 2017.
Coral cover averaged 33% in the central region – another record high compared to the 2019 low of 14%.
In the southern region, average coral cover decreased from the 2021 estimate from 38% to 34%.
And while bleaching spread across the reefs in February and March, Emsley said heat stress had not reached levels likely to cause coral death.
To get the effects [of the latest bleaching] We won’t know until we do surveys in the water over the next few weeks.
“But the bleaching has non-lethal effects and will affect the physiology of the corals because during bleaching they were starving.”
He said there is evidence that even when corals do not die from bleaching, this phenomenon can reduce their ability to reproduce, slow their growth and make them more susceptible to coral diseases.
It may take a year or more for those non-lethal effects to become apparent, he said.
Because bleaching events occur so often, he said, future bleaching events could “reflect the observed recovery in a short period of time.”
The latest mass bleaching coincided with a United Nations coral reef monitoring mission requested by the Morrison government in an attempt to combat a recommendation to put the reefs on the World Heritage List in danger.
The status of coral reefs will be discussed at the next World Heritage meeting, but no date has yet been set after a meeting scheduled for June was canceled due to the Russian invasion of Ukraine. The meeting was scheduled to be hosted by Russia.