Climate change is disrupting the shape and presence of coral islands across the Indo-Pacific, creating uncertainties for legal maritime zones and small states, say legal experts.
Atolls and reefs naturally grow and shrink due to complex processes yet to be fully understood.
However global warming is disrupting them further and leading to fresh uncertainties, according to research conducted at the University of Sydney.
Lead author Dr Thomas Fellowes says new technologies and approaches coupled with expanded analysis of coral behaviour may be needed to help dispel some of the precariousness and solidify claims.
"Coral reef islands are the legal basis for many large maritime zones," he said.
"Hence, continued climate disruptions may have substantial impact not only for small island states but in hotly contested boundary disputes in places like the South China Sea.
"It's a perfect storm that is bringing instability and uncertainty to what are already difficult boundaries to determine with any great accuracy."
The rules for atolls and reefs in international law - already murky and subject to interpretation due to their shifting nature - will be under greater stress as sea levels rise and acidification disrupts reef integrity.
Agreed by 167 nations and almost universally recognised, they govern territorial seas up to 12 nautical miles from a coast reef as well as exclusive economic zones up to 200 nautical miles.
Their potential loss of baselines is a serious concern for nations like Kiribati, as well as larger ones like Australia, who depend on reefs and islands to maintain their claims, according to fellow author Frances Anggadi.
"But there is still no clear agreement whether changes to the structural integrity of coral reef islands due to climate will lead to legal vulnerabilities," he said.
"They may not and that's what many Pacific island countries believe."
What's clear is that more detailed understanding of coral reef island behaviour is needed, along with rethinking of the rules.
The researchers say one way to buttress existing claims is by defining reef baselines with geographic co-ordinates like GPS or remote sensing approaches like satellite bathymetry.
Another would be to better understand how climate change will affect island habitability.
For these approaches to work, tough, further data on each reef system is needed to more accurately delineate the scope and resilience of existing claims and better understand how climate change might affect them.
Climate change is disrupting reef systems in four ways: sea-level rise, warming oceans, ocean acidification and increased storminess.
Each has an impact on the interconnected biophysical processes that allow their creation, retreat and overall structural stability.
For example, higher temperatures trigger the expulsion of algal symbionts in corals and other invertebrates (like giant clams), leading to coral bleaching, which can cause reef collapse.
In the decades ahead, this could lead to a shrinkage of the outer low-water line of the reef, reducing the basis for a maritime claim.
Oceans acidify as they absorb more carbon dioxide, reducing their mineral saturation and making it harder for corals to form.
As the reefs grow and expand, they become either fringing, barrier or atoll reefs.
Fringing reefs are the most common, projecting seaward from the shore, forming borders along shorelines and surrounding islands.
Barrier reefs do this at greater distance, separated from land by a lagoon of often deep water.
If a volcanic island sinks below sea level and its coral keeps growing, an atoll forms.