concern in several countries
Coral islands and reefs grow and shrink through natural biological and physical processes that researchers still strive to fully understand. Today, climate change adds new uncertainties to these systems, especially in ocean regions and small island states where maritime boundaries matter and may be redefined as sea levels and weather patterns shift.
Experts argue that advancing research into the behavior of coral reef islands, supported by new technologies and fresh methodologies, will help clarify many of these uncertainties.
A study from researchers at the University of Sydney, published in Environmental Research Letters, suggests that rules governing atolls and coral reefs in international maritime law—already intricate and open to interpretation—will face greater pressure as sea levels rise and ocean chemistry changes threaten reef integrity.
“A perfect storm of instability and boundary ambiguity that is already hard to pin down will intensify,” notes Thomas Fellowes, a postdoctoral fellow in the School of Geosciences at the University of Sydney and the study’s lead author.
“There are geopolitical implications too. Coral reef islands form the legal basis for many large marine areas. Climatic disturbances we are witnessing now and those likely in the coming decades could significantly affect not only small island states but also hotly contested border regions, such as in the South China Sea,” he adds.
global concern across nations
There exists a near-universal treaty, signed by 167 countries, that governs everything from territorial seas to the low-water line of reefs, extending 12 nautical miles to 200 nautical miles of exclusive economic zones. It also sets out freedom of navigation and allows nations to use, protect, and regulate resources within their territorial waters.
“In coral islands, the outer low-water line of the reef serves as the legal basis for defining marine zones,” states a student from the University of Sydney.
“Potential loss of marine areas due to shifts in reef baselines caused by climate change raises serious concerns for countries like Kiribati and larger states such as Australia that rely on reefs and islands to sustain their claims,” he warns.
Although there is no final agreement on whether climate-induced changes in reef structure create new legal vulnerabilities, many Pacific Island nations believe so. What is clear is that the behavior of coral reef islands requires deeper study, together with a revision of legal norms that govern them. Friends say the issue is timely and urgent.
“Coral reefs only develop within a particular range of biophysical, oceanic, and climatic conditions. Yet shifts in sedimentation due to climate change could expand some reefs and alter maritime claims,” Fellows observes. “It isn’t guaranteed that there will be only losers.”
the danger to coral reefs
Researchers propose ways to define reef baselines using geographic coordinates through GPS or remote sensing, including satellite bathymetry. A parallel line of inquiry looks at how climate change might affect a reef island’s habitability and the ability to sustain human life and economic activity, which are central to treaty claims.
For these approaches to work, more data on each coral reef island system are essential to accurately map the scope of current claims and understand how climate change may affect them in the future, according to the University of Sydney.
Great Barrier Reef, Australia. Katerina Katopis/Ocean Image Bank
Scientists identify four key ways climate change alters coral reef systems and potentially shifts maritime borders: rising sea levels, warmer oceans, ocean acidification, and more intense storms. Each factor influences the interconnected biophysical processes that drive reef creation, growth, removal, and overall structural stability.
For example, higher temperatures can trigger the expulsion of symbiotic algae and other organisms, causing coral bleaching and the death of reef-building life. As oceans absorb more carbon dioxide, they become more acidic, reducing mineral saturation and hindering coral skeletal formation. This compromises the reef’s structural integrity as many reef-building species adapt by changing their skeletal chemistry.
Note: this analysis reflects current scholarly work and practical observations from multiple fisheries and marine law centers. The study from Environmental Research Letters provides a framework for understanding the legal and ecological intersections of coral reef islands under climate pressure.
Great Barrier Reef, Australia. Katerina Katopis/Ocean Image Bank
Overall, climate-driven changes impact not just natural systems but the legal maps that nations rely on for claiming and protecting marine resources. The ongoing research emphasizes the need for precise reef baselines and robust data to guide future policy decisions and treaty interpretation.