Long-Term Monitoring Program
Annual Summary Report of Coral Reef Condition 2022/23

A pause in recent coral recovery across most of the Great Barrier Reef

Published 9th August 2023

Download this Report | 3.7MB

Key Results

• This report summarises the condition of coral reefs of the Great Barrier Reef (GBR) from the Long-Term Monitoring Program (LTMP) surveys of 111 reefs conducted between August 2022 and May 2023 (reported as ‘2023’). 
   
• Over the past 37 years of monitoring by the Australian Institute of Marine Science (AIMS), coral reefs of the GBR have shown dynamic responses to cycles of disturbance and recovery.
   
• Despite small declines in 2023, regional hard coral cover was similar to that reported in 2022.
   
• Above-average water temperatures occurred from October to December 2022; however, an active monsoon trough stopped further heat accumulation of waters of the GBR from January to March 2023 and none to low coral bleaching was recorded during the 2023 summer.
   
• Over the past 12 months, survey reefs were exposed to minimal other stressors, i.e., there were no severe cyclones impacting the GBR and despite crown-of-thorns starfish outbreaks persisting on some Southern GBR reefs, the number of outbreaks on the surveyed reefs has largely decreased.
   
• Only one reef had hard coral cover <10%, while nearly half of the surveyed reefs (49 out of 111) had hard coral cover levels between 10% and 30%, and over a third of the surveyed reefs (43 out of 111) had hard coral cover levels between 30% and 50%. Eighteen reefs had hard coral cover between 50% and 75%.
   
• On the Northern GBR,region-wide mean hard coral cover declined slightly to 35.7% (32.1% - 39.6% 95% Credible Intervals [C.I.s]) compared with 36.5% (32.2% - 40.9% C.I.s) in 2022 but remained within the C.I.s.
   
• On the Central GBR region-wide mean coral cover declined slightly to 30.8% (27.6% - 34.2% C.I.s) from 32.6% (28.8% - 36.5% C.I.s) in 2022 but remained within the C.I.s.
   
• Region-wide mean hard coral cover on reefs in the Southern GBR declined slightly in 2023 at 33.8% (29.0% to 38.9% C.I.s) from 33.9% (28.6% - 39.3% C.I.s) in 2022 but remained within the C.I.s,despite ongoing crown-of-thorns starfish outbreaks that led to loss of coral cover on some reefs in this region.
   
• The accumulation of thermal stress during the 2022 mass coral bleaching event caused low levels of coral mortality, but this, coupled with likely sub-lethal effects (e.g., reduced growth) plus some mortality from crown-of-thorns starfish outbreaks and coral disease and Tropical Cyclone Tiffany in January 2022, has paused the recovery of hard coral cover on many reefs.
   
• Most coral reefs of the GBR demonstrate resilience in the absence of acute disturbances showing the ability to recover from events causing widespread mortality. However, as the 2022 mass bleaching event highlighted, and crown-of-thorns starfish outbreaks, coral disease and Tropical Cyclone Tiffany further emphasise, the reefs of the GBR continue to face cumulative stressors. Even without causing mass mortality, bleaching events can hinder hard coral growth. The future is forecasted to bring more frequent, intense and enduring marine heatwaves, alongside the persistent threat of crown-of-thorns starfish outbreaks and tropical cyclones.