The coral cays of the Great Barrier Reef are more than just picturesque, sandy islands. They are dynamic, living systems that play a crucial role in the health of the reef and support a wide range of biodiversity, from nesting seabirds to critical turtle habitats. However, their ever-changing nature, shaped by ocean currents, storms, and rising sea levels, makes it essential to monitor these cays closely. Drone technology has emerged as a vital tool in this effort, offering exceptional detail in capturing their shifting landscapes.
At GeoNadir, we collaborated with the Queensland Department of Environment, Science, and Innovation (Queensland Parks and Wildlife Division) as well as Dr Stephanie Duce and Professor Scott Smithers from James Cook University to not only map the cays but also establish standard practices for drone data capture and processing.
Monitoring these islands isn’t just about capturing their beauty from the sky—it’s about preserving ecosystems that are increasingly at risk. The Great Barrier Reef’s coral cays are dynamic, and keeping track of their changes through advanced geospatial techniques is essential for their future conservation.
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What exactly is a cay?
A cay is a small, low-elevation island formed mostly from coral debris, sand, and shells. It sits on top of coral reefs and forms when ocean currents and waves deposit sediments in a concentrated area. Unlike larger islands, cays are dynamic and can shift, erode, or grow over time, depending on tides, winds, and storms.
People often confuse cays with larger islands, but cays are generally more fragile and shaped by constant changes in the ocean’s environment. The terms “caye” and “key” refer to the same type of landform but are used in different regions. “Caye” is commonly used in Belize and parts of the Caribbean, while “key” is the term most often heard in places like Florida. Despite regional differences in the name, these landforms are all created in the same way—by the buildup of reef-based sediment on coral platforms.
In the Great Barrier Reef, cays play an important role in supporting wildlife and maintaining reef health. Monitoring them helps us understand their unique processes and their response to environmental changes, making their study essential for conservation efforts.
Why island monitoring matters
Monitoring cays is essential because they are dynamic environments that constantly change due to waves, wind, and sea levels. Just check out how much Taylor Cay changes within a few short weeks from the image sequence from Dr Duce and Emily Lazarus below! By tracking these shifts, we gain critical insights into how these fragile formations evolve over time and respond to environmental changes like storms and rising sea levels. Monitoring helps identify risks, such as erosion or loss of habitat, which are crucial for both wildlife and the broader reef system.
We use drones to collect high-resolution data that captures these island shifts in detail. GeoNadir, for example, supports drone-based monitoring to track geomorphic changes, map vegetation, and document shoreline shifts. Drone technology offers a cost-effective way to monitor large, remote areas while capturing data with precision. Using ground control points (GCPs) ensures accuracy, particularly when creating digital elevation models (DEMs) to monitor elevation changes.
The ability to frequently and accurately capture drone data means we can compare changes over time and identify trends. This provides a clearer understanding of how cays are impacted by both natural and human-induced factors. Monitoring, therefore, plays a vital role in informing conservation efforts and making data-driven decisions about the future of these dynamic reef islands. In this project, GeoNadir advised the team on the ideal data capture techniques to develop standard operating procedures (SOPs). We also processed all imagery to create analysis ready data.
‘Oh Cay’ collaborative drone mapping
Monitoring coral cays requires more than isolated data collection. GeoNadir’s platform allows multiple groups to contribute drone imagery, greatly expanding the available data. Even imagery that had been captured for different purposes is useful.
GeoNadir facilitated this collaboration by providing a space for contributors to upload, process, and share data. By making our data FAIR (findable, accessible, interoperable, and reusable), we ensure it can also be used for future research and conservation. Our collaborative approach enriches the overall dataset, improving our ability to monitor these dynamic landforms more comprehensively and accurately.
Collaboration also allows for a wider range of expertise to be brought to bear on the monitoring process. This, in turn, leads to more robust data and better-informed decisions on how to manage and protect the cays over time.
We are currently hosting drone mapping data from 34 of the 233 cays on the Great Barrier Reef. This includes data from our key project partner Queensland Department of Environment, Science, and Innovation, as well as Birdlife Australia; University of Wollongong; James Cook University; Macquarie University; The University of Sydney; and Monash University. You can see a selection of these cays and their diversity below.
Using Ground Control Points for cay monitoring
Ground Control Points (GCPs) are essential for ensuring accurate drone-captured data, especially when creating digital elevation models (DEMs) and orthomosaics. Placing GCPs on the ground during drone surveys (or using natural GPCPs) ties aerial data to real-world coordinates. This improves both horizontal and vertical precision.
For dynamic coral cays, even slight changes in elevation or shoreline position can indicate environmental shifts, making accuracy crucial. Without sufficient GCPs, elevation models might not detect subtle changes, such as sand erosion or accumulation, which are vital for understanding how these fragile landforms are evolving.
GeoNadir supported researchers from JCU (shout out to Hulwa Khaleel!) to determine the optimal number of GCPs needed to create accurate DEMs for monitoring cays. Stay tuned for these results when we publish them! Combining GCPs with advanced drone technology allows us to track elevation changes with precision. This helps us to detect even the smallest shifts, enabling more informed conservation and management decisions.
This accuracy is key for tracking the impacts of storms, sea-level rise, and other factors that affect these islands’ location, shape, and volume.
The future of island monitoring
Coral cays are more than picturesque sandy islands. They are dynamic landforms that play a vital role in the ecosystems of the Great Barrier Reef and other reefs worldwide. As these fragile formations respond to environmental pressures, it becomes increasingly important to monitor their changes accurately and consistently. By using drone and geospatial technology, the GeoNadir platform, and collaborative contributions from multiple stakeholders, we have taken significant steps to advance our understanding of these unique islands.
From developing best practices for drone data capture to ensuring the data are FAIR, our efforts are helping to create a more complete and accessible picture of how coral cays evolve. Integrating ground control points (GCPs) ensures that our elevation models and maps are accurate enough to detect even the most subtle shifts in the landscape, providing critical data for conservation and management decisions.
As we look to the future, continued collaboration and innovation in geospatial technologies will be key to protecting these cays. By staying at the forefront of monitoring efforts, we can help safeguard these invaluable ecosystems and the diverse species they support.
This work was partly funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, with support from the Reef Joint Field Management Program.
