By Abbas Nazil
Coral reefs are unlikely to migrate quickly enough to escape the destructive effects of climate change, as rising ocean temperatures, acidification and frequent bleaching events threaten their survival, according to scientific modelling examining the future of coral ecosystems worldwide.
The findings suggest that although some coral species may gradually expand towards cooler waters closer to the poles, natural migration and adaptation alone will not protect the majority of the world’s reefs from rapidly changing ocean conditions.
Scientists warn that immediate and substantial reductions in global greenhouse gas emissions remain essential to limiting further damage to coral reefs, which support marine biodiversity and provide important ecological benefits.
Rising greenhouse gas emissions have pushed tropical ocean temperatures to unprecedented levels, placing increasing pressure on coral reefs and encouraging marine organisms to shift towards higher latitudes in search of more favourable conditions.
Researchers have long recognised that marine species tend to move towards the poles as oceans warm, with fossil records indicating that coral reefs expanded their geographical ranges during previous periods of climate change.
However, scientists have faced uncertainty over whether such movements could occur quickly enough to protect coral ecosystems from the unprecedented pace of modern global warming.
To investigate this question, researchers from multiple institutions used advanced computer simulations conducted on the University of Hawaiʻi’s Koa supercomputer to assess how coral reef networks could respond to climate change over extended periods.
The modelling incorporated evolutionary processes and connections between coral populations to provide a broader understanding of how reefs might respond to changing environmental conditions.
Dr Lisa McManus, an assistant research professor at the Hawaiʻi Institute of Marine Biology and a co-author of the study, said the approach offered an unprecedented long-term perspective on the response of complex coral ecosystems to climate change.
The simulations indicated that coral larvae could disperse towards cooler regions through ocean currents, but the process would generally be too slow to compensate for the extensive losses expected in tropical waters.
Researchers also identified additional challenges that could limit the establishment of coral reefs in higher-latitude environments.
Although cooler temperatures may initially provide suitable conditions, these areas can experience greater ocean acidification and lack the established ecological relationships needed to support thriving coral communities.
Consequently, corals reaching these locations may struggle to survive even when temperatures appear more favourable.
Corals possess some natural mechanisms that help them cope with environmental stress, including the dispersal of larvae through ocean currents and changes in the composition of symbiotic microalgae living within their tissues.
These changes can sometimes improve heat tolerance and offer temporary protection against elevated temperatures.
However, such adaptations generally occur gradually, while marine heatwaves and associated coral bleaching events can develop rapidly and cause extensive damage.
The growing difference between the speed of biological adaptation and the rate of environmental change is increasing the risk of coral reef degradation before many populations can adjust to new conditions.
Scientists expect that some small coral patches may eventually become established in higher-latitude waters, but such developments are unlikely to replace the extensive reef systems threatened by warming in tropical regions.
The findings highlight the limitations of relying on natural migration as a solution to climate change and reinforce the need for urgent action to address its underlying causes.
Reducing greenhouse gas emissions could help slow ocean warming and limit the environmental pressures facing coral ecosystems, while conservation measures could support the resilience of reefs already experiencing climate-related stress.
Without stronger climate action, scientists warn, the ability of coral reefs to move into cooler waters will offer only limited protection against the accelerating threats facing these vital marine ecosystems.
