A steep decline in coral cover right across the Great Barrier Reef is a phenomenon that “has not been observed in the historical record”, a new report by the Australian Institute of Marine Science says.
The institute, Australia’s government-backed marine research agency, periodically releases results of a long-term reef monitoring program. Each reef along the Queensland coast is visited by researchers every two years to assess its condition and coral cover.
The latest results, released on Tuesday, detail how major bleaching events in 2016 and 2017 have impacted on different sections of the reef. AIMS said it had no previous record of bleaching events occurring in successive years.
“Over the 30-plus years of monitoring by AIMS, Great Barrier Reef reefs have shown their ability to recover after disturbances, but such ‘resilience’ clearly has limits,” the report says.
“The predicted consequences of climate change include more powerful storms and more frequent and more intense bleaching events.
“More intense disturbances mean greater damage to reefs, so recovery must take longer if the growth rate remains the same. At the same time, the intervals between acute disturbance events are decreasing and chronic stresses such as high turbidity and high ocean temperatures can slow rates of recovery.”
Survey reefs in the northern section, the worst hit by climate-induced marine heatwaves, have lost about half their coral cover. The impacts of the most recent heatwave is not fully represented in the results, as the most recent AIMS surveys have been in the central and southern sections.
The central section “sustained significant coral loss due to coral bleaching and the continued southwards spread of the current wave of crown-of-thorns starfish outbreaks”. Total coral cover decreased from 22% in 2016 to 14% in 2018.
“The geographic scale of recent bleaching means that breeding populations of corals have been decimated over large areas, reducing the potential sources of larvae to recolonise reefs over the next years,” the report says.
“It is unprecedented in the 30-plus year time series that all three regions of the [reef] have declined and that many reefs have now very low coral cover.
“The prognosis of more frequent disturbances, each causing greater damage to reefs, combined with slower rates of recovery will inevitably lead to less living coral on reefs.”
Imogen Zethoven, from the Australian Marine Conservation Society, said the report highlighted the unprecedented scale of coral loss on the reef.
“We need the government to see this as a national crisis, which it is. We are responsible for the protection and conservation of this world treasure. We have a legal and moral obligation to look after it.”
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