Hard Coral Cover On GBR Near Record Lows In North, Declining In South
Hard coral cover on the Great Barrier Reef is near record lows in its northern stretch and in decline in the south, surveys by government scientists have found. A report card by the government’s Australian Institute of Marine Science says hard coral cover in the northern region above Cooktown is at 14% – a slight increase on last year but close to the lowest since monitoring began in 1985.
A series of “disturbances” – coral bleaching linked to rising water temperatures, crown-of-thorns starfish outbreaks and tropical cyclones – caused a 10% to 30% decline in hard coral cover across much of the world heritage landmark over the past five years.
Mike Emslie, the institute’s acting head of long-term monitoring, said the report included glimmers of hope: individual reefs, including those on the outer shelf in the Whitsunday Islands, were found to have lively communities and tiny juvenile corals were discovered across the 2,300km reef system. The density of juvenile coral suggested recovery was possible if there were not further disturbances. He said it indicated there was some resilience in the system but added: “The important thing is the absence of further disturbances. If we have more coral bleaching events all bets are off.”
Ed. - Emphasis added - "If"?
The Institute of Marine Science report warns the extent of hard coral in the north may be even lower than the 14% estimated due to skewed surveying – the greatest bleaching damage was on inshore reefs and they were under-represented in surveys due to safety concerns. The highest level of coral reef cover recorded in the north was 30% in 1988.
Emslie said the reef’s southern section had escaped the worst effects of coral bleaching and cyclones since 2009 but has been affected by a severe outbreak of crown-of-thorns starfish since 2017. Crown-of-thorns feed on coral and spawns so rapidly it is difficult to tackle once it takes hold. Its spread has been linked to nitrogen from fertiliser and pesticides in agricultural run-off.
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https://www.theguardian.com/environment/2019/jul/11/great-barrier-reef-hard-coral-cover-close-to-record-lows