Many coral reefs will be unable to keep growing fast enough to keep up with rising sea levels, posing another potential problem for low-lying tropical islands under climate change.
That's according to a new study by an international team of researchers, including University of Auckland coastal geomorphologist Professor Paul Kench, who investigated how rising seas compared to the maximum upward growth rates of coral reefs.
The growth of coral reefs was strongly influenced by the amount and types of coral living on the reef surface - and was now being hampered by a combination of coral disease, worsening water quality, fishing pressure and climate change-driven impacts like coral bleaching.
For many reefs across the Caribbean and Indian Ocean regions, where the study focused, rates of growth are slowing due to coral reef degradation.
Meanwhile, rates of sea-level rise are increasing – and the results suggest reefs would be unable to keep up, meaning water depths above most reefs would increase rapidly through this century.
Even under modest climate change prediction scenarios, only about three per cent of Indian Ocean reefs would be able to track local sea-level rise projections without sustained ecological recovery.
And under the worst scenarios, most reefs would experience water depth increases of more than half a metre.
The researchers said the issue was of critical concern, given reefs played a key role as natural sea defences by limiting the impact of wave energy.
They said efforts to tackle climate change must therefore be coupled with careful management of fishing and water quality protection to prevent "widespread submergence" through this century.
Kench said the study was important in that it investigated the combined result of changes that could affect a reef's structure - and therefore what could happen to low-lying islands.
But he noted that, as the study had focused on only the Caribbean and Indian Ocean regions, it wasn't a complete given that the same impacts would be seen in Pacific reefs closer to New Zealand.
"I think one of the really novel aspects of this study is that there have been very few efforts, globally, to actually look at what reefs are actually doing."
Another co-author, Professor Peter Mumby of the University of Queensland, nonetheless said it was crucial, now more than ever, to limit global greenhouse gas emissions.
"Our predictions, even under the best-case scenarios, suggest that by 2100 the inundation of reefs will expose coastal communities to significant threats of shoreline change," he said.
"Healthier coral reefs will reduce the rate of seawater inundation."
Study lead author Professor Chris Perry, of the University of Exeter, echoed the concern.
"The most worrying end-point scenario in this respect is that if predictions of increasing bleaching frequency are realised, many reefs may become locked into permanent low-growth-rate states, leading to more submergence under all future sea-level rise scenarios."