Coral Crisis: New Data Highlights Great Barrier Reef Decline After Summer Disturbances
The Great Barrier Reef, one of the world’s most iconic marine ecosystems, is reeling from a series of climate-driven disturbances. According to new data from the Australian Institute of Marine Science (AIMS), coral cover has plummeted across numerous reefs, underscoring the dire impact of rising global temperatures, extreme weather events, and their growing intensity.
The Findings: Significant Coral Loss
AIMS’ latest in-water surveys, conducted during August and October 2024, reveal a stark reality. Coral cover declined on 12 of 19 reefs surveyed between Lizard Island and Cardwell, with losses ranging from 11% to a staggering 72%. These figures reflect the first routine assessments of these sites since a catastrophic summer of back-to-back mass bleaching, cyclones, and flooding from December 2023 to March 2024.
The Cooktown-Lizard Island sector recorded the largest annual decline in hard coral cover in the 39 years of AIMS monitoring, with levels dropping from a high of 31.4% to just 19.3%. Meanwhile, the Cairns sector saw a similar decline, losing over a third of coral cover across surveyed reefs. In contrast, the Innisfail sector’s coral cover remained relatively stable, highlighting the variability of impacts across different regions.
The Culprits: Bleaching, Cyclones, and Heat Stress
Dr. Mike Emslie, leader of AIMS’ Long-Term Monitoring Program (LTMP), attributed the widespread losses to a confluence of climate change-induced stressors:
- Mass Bleaching: Prolonged heat stress during February and March 2024 triggered extensive coral bleaching across surveyed reefs. Some areas experienced such severe heat stress that mortality was inevitable.
- Tropical Cyclones Jasper and Kirrily: These cyclones battered the reefs with wave heights exceeding four meters, causing physical damage and compounding the bleaching effects.
- Flooding and Freshwater Inundation: Flooding brought additional stress to already vulnerable coral systems, particularly in nearshore areas.
“The impact from these events is significant coral mortality in those areas hardest hit,” Dr. Emslie noted. He explained that while some reefs escaped severe loss, others, particularly inner and mid-shelf reefs in the Cooktown-Lizard Island sector, saw devastating declines. One inner shelf reef lost nearly three-quarters of its pre-summer hard coral cover.
Resilience and Vulnerability: A Complex Picture
The surveys highlight a mixed picture of coral resilience:
- Vulnerable Species: Fast-growing table Acropora corals, instrumental in recent reef recovery, were among the most affected.
- Hardy Survivors: Massive corals like Porites showed greater resilience, emphasizing the variable response of coral species to climate stressors.
- Depth Variations: Corals in deeper reef slopes often fared better than those in shallow areas, where heat stress and cyclonic waves were more pronounced.
Interestingly, outer shelf reefs exhibited little to no coral loss, likely due to their community composition and the cooling effects of oceanic upwellings.
A Global Crisis with Local Implications
Dr. Manuel Gonzalez Rivero, AIMS’ acting Research Program Director, contextualized the findings within a broader global crisis. “The 2024 mass bleaching event on the Reef, its fifth since 2016, forms part of the fourth global bleaching event impacting reefs across more than 60 countries and territories worldwide.”
The increasing frequency and intensity of bleaching events underscore the vulnerability of reefs to climate change. “Despite these losses, coral cover on most reefs is at moderate levels of between 10 and 30%, but the resilience of the Reef is being severely tested,” Dr. Gonzalez Rivero said. He stressed the urgent need for strong greenhouse gas emissions reduction and innovative approaches to help reefs adapt to and recover from these impacts.
Looking Ahead
The LTMP continues its critical monitoring work, with further surveys planned for the Cairns and Innisfail sectors and potential additional assessments in the Cooktown-Lizard Island region. AIMS is also gathering detailed data on reef physiology, genetics, and community dynamics, with findings expected to inform future management strategies.
Comprehensive results from the 2024 surveys will be available by mid-2025. In the meantime, policymakers, scientists, and the public can access preliminary data through the AIMS Reef Monitoring Dashboard.
About AIMS and the LTMP
The Australian Institute of Marine Science has been at the forefront of tropical marine research for over 50 years. Its Long-Term Monitoring Program is a cornerstone of efforts to understand and protect the Great Barrier Reef, providing critical insights into coral health, species abundance, and the impacts of disturbances such as bleaching and cyclones.
To learn more about the ongoing work to safeguard the Great Barrier Reef, visit AIMS.
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