Garing, Madeline R., McWilliam, Mike J., Tebbett, Sterling B., Levering, LeightonZ, and Pratchett, Morgan S. (2025) Coral bleaching and crown-of-thorns starfish modulate long-term changes in coral cover and composition across reef zones at Lizard Island, northern Great Barrier Reef. Coral Reefs, 45. pp. 649-663.

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Abstract

Coral reefs are naturally subject to disturbances, but widespread and sustained coral loss over recent decades suggests that contemporary disturbance regimes have exceeded their capacity for resilience. Here, we explore long-term changes in coral cover and composition at Lizard Island, Great Barrier Reef, Australia. During the study period (1995–2025), reefs were exposed to three population irruptions of crown-of-thorns starfish (CoTS), six mass bleaching events, and two severe cyclones. Mean hard coral cover declined from 25.0% (± 1.3 SE) in 1995 to 14.4% (± 0.8) in 2025, but this decline was not consistent over the 30-year period. Rather, there were three distinct periods of coral loss, each of which coincided with a population irruption of CoTS, followed by recovery periods. Average hard coral cover declined by ~ 32.0% during the first period of coral loss (1999–2002), ~ 67.17% during the second (2009–2017), and ~ 31.8% during the third (2023–2025). Coral loss during bleaching events was generally concentrated in shallow zones (flat and crest), while coral loss attributable to CoTS irruptions occurred in deeper zones (crest, slope, and base). The cumulative impact of multiple disturbances between 2009 and 2017 resulted in substantial coral loss across every site and zone, and overall coral cover fell below ~ 10%. These declines were accompanied by shifts in community structure, with major declines of tabular Acropora and massive Porites, and proportional increases in corymbose Acropora and Pocillopora. This study shows that the persistent effects of CoTS are being conflated by other major disturbances, leading to sustained changes in the structure of coral assemblages.

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