Discovery of a Giant Coral Colony on the Great Barrier Reef

Citizen scientists have identified what is believed to be one of the largest coral colonies ever documented on the Great Barrier Reef. This colony, a Pavona clavus coral, spans approximately 111 meters in length and covers an estimated area of 3,973 square meters, roughly half the size of a soccer field. The discovery was made by Jan Pope, who found the coral in waters a few hours offshore from Cairns as part of the Great Reef Census, a citizen science initiative managed by Citizens of the Reef.

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Pope, who has extensive diving experience on the Great Barrier Reef, described the underwater landscape as “a very surreal underwater landscape. It looks like a rolling meadow.” Her daughter, Sophie Kalkowski-Pope, who is also involved in the census project, noted the significance of the find, stating, “We had no idea that something so significant was right here on our doorstep.” The Great Reef Census aims to monitor coral cover across the reef, having surveyed about a quarter of it since its inception in 2020.

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The identification of this coral colony is crucial for understanding the resilience of coral ecosystems. Sophie Kalkowski-Pope explained that the project seeks to pinpoint key source reefs, referred to as “hotspots of resilience,” which can provide larvae to other reefs during spawning events. Dr. Tom Bridge, curator of corals at the Queensland Museum, emphasized the rarity of such large coral colonies, particularly in light of increasing coral bleaching events.

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To confirm whether the Cairns coral is a single organism or multiple colonies that have coalesced, genetic testing will be necessary. This testing requires over 300 individual samples from across the colony due to its size. The coral was mapped using photogrammetry, a technique that stitches together surface photographs into a 3D model, revealing that the coral is larger than initially estimated.

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Dr. Bridge noted that the species Pavona clavus is undergoing reclassification as part of a broader overhaul of coral taxonomy. Additionally, the University of Milano Bicocca runs another citizen science project called Map the Giants, which tracks giant coral colonies globally.

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While the discovery is celebrated, concerns remain regarding the long-term survival of such coral colonies. Dr. Bridge pointed out that for corals that are hundreds of years old, the likelihood of surviving increasing bleaching conditions and rising water temperatures is diminishing. This highlights the urgent need for conservation efforts in the face of climate change.

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• “It was quite glassy and I could see this very strange pattern in the water,” — Jan Pope, Citizen Scientist

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• “We had no idea that something so significant was right here on our doorstep,” — Sophie Kalkowski-Pope, Marine Operations Coordinator, Citizens of the Reef

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• “Bridge, also a senior lecturer at James Cook University, said: “Very large coral colonies are going to be exceedingly rare because we’re finding bleaching is increasing in severity but also in frequency.” — Dr. Tom Bridge, Curator of Corals, Queensland Museum

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This discovery not only adds to the understanding of coral ecosystems but also underscores the ongoing challenges they face in a changing climate.

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