NCWQ Environment Report: July 2021

NCWQ Environment Report July 2021

By Pat Pepper, NCWQ Environmental Adviser

Environment Summary

Researchers at the Australian Institute of Marine Science (AIMS) have shown that without major disturbances from cyclones, coral bleaching and crown-of-thorns starfish outbreaks, coral reefs can recover as measured by hard coral cover.  But that the composition of coral species can change.  However, if the frequency and severity of disturbances increases, as expected from climate change, recovery could be more difficult.


Update on Great Barrier Reef

Since 1985 AIMS researchers have surveyed the condition of selected reefs across the Great Barrier Reef (GBR).  The average hard coral cover is now at 27%, 26% and 39% in the Northern, Central and Southern GBR Regions indicating that coral reefs still have the capacity to recover during periods of low disturbance, such as this last year when no major cyclones or prolonged heat stress events resulting in coral bleaching, occurred. Also, despite ongoing crown-of-thorns starfish outbreaks in the Southern region, outbreaks decreased across much of the GBR.


Coral reef trends
Trends in average hard coral cover (with 95% confidence limits) from underwater surveys from the AIMS Long-Term Monitoring Program.


In the Northern region the hard coral cover appears to have recovered from the cumulative effects of severe tropical cyclones in 2014 and 2015, crown-of-thorns starfish outbreaks and the 2016 mass bleaching event. In the Central Region, after recovering from the 2011 severe tropical cyclone Yasi, coral cover had decreased in 2019, largely due to mass coral bleaching in 2016 and 2017 and crown-of-thorns starfish outbreaks. No outbreaks were recorded on the survey reefs this year, probably due to the Crown-of-thorns Control Program removing substantial numbers of starfish.  In the Southern region, coral cover which had recovered from the 2009 tropical cyclone Hamish, was reduced in 2018 by crown-of-thorns outbreaks.

Exposure level of the 127 LTMP reefs surveyed in 2021 to accumulated heat stress during the austral summer of 2020. Widespread bleaching is expected above 4 DHW, while coral mortality is predicted above 8 DHW. Source: NOAA/NESDIS/STAR Coral Reef Watch program

Fast-growing branching and table corals (Acropora species) which were mainly responsible for the increase in hard coral cover are vulnerable to wave damage, like that generated by strong winds and tropical cyclones as well as to coral bleaching and are the preferred prey for crown-of-thorns starfish.

Surveys recorded shifts in coral communities on some outer shelf reefs in Northern & Central Regions following 16/17 mass coral bleaching event. Pocillopora corals became more dominant than the more typical Acropora corals. AIMS scientists are monitoring selected reefs to detect changes and how that will influence the reef ecosystem

Climate change is predicted to cause more severe cyclones and more frequent and intense heatwaves, so the AIMS warns the observed recovery could easily be reversed.


Long-Term Monitoring Program Annual Summary Report of Coral Reef Condition 2020/2021


Pat Pepper, NCWQ Environment Adviser.


photo credit: Acropora corals at Forrester Reef near Cooktown

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