Seagrass meadows around the world are facing growing threats as ocean temperatures continue to rise. A new study published in the journal New Phytologist, December 2025 finds that tropical seagrasses are the most vulnerable to marine heatwaves, raising concerns about the future of one of the planet’s most important coastal ecosystems.
The research was led by Nicole Said, a Ph.D. candidate at Edith Cowan University, along with an international team of scientists. The team examined the thermal tolerance of six seagrass species along a latitudinal gradient spanning about 1,000 kilometers on Australia’s west coast, from temperate to tropical waters.
Seagrasses are flowering plants that live fully submerged in shallow marine waters. They form extensive underwater meadows that provide nursery habitat for fish and invertebrates, stabilize sediments, store significant amounts of carbon—often referred to as blue carbon—and protect coastlines from erosion. But as marine heatwaves become more frequent and intense, these ecosystems are increasingly at risk.
Differences of Up to 10 Degrees Celsius
The study found striking differences in heat tolerance among species. Across species, thermal tolerance varied by as much as 10 degrees Celsius. Even within a single species, populations living only a few kilometers apart showed differences of up to 4 degrees Celsius in their temperature thresholds.
“Some populations are better prepared to cope with heat, and in some cases, the more tolerant ones grow just a few kilometers away from more vulnerable populations,” Said said in a statement released with the study.
These findings suggest that seagrass responses to ocean warming are far from uniform. While some species or local populations may withstand higher temperatures, others are already living close to their upper thermal limits.
The research also showed that tropical seagrasses are particularly at risk. Species growing in warmer, lower-latitude regions are already near the maximum temperatures they can physiologically tolerate. As a result, even relatively small increases in sea surface temperature during marine heatwaves can push them beyond critical thresholds.
From mountains to oceans, delivered to you. Follow us on Lingkar Bumi WhatsApp Channel.
Marine Heatwaves on the Rise
Marine heatwaves are prolonged periods of unusually high sea surface temperatures that can last from days to months. Their frequency, duration and intensity have increased significantly in recent decades due to climate change.
When temperatures spike, seagrass photosynthesis can become impaired. Cellular damage, reduced productivity and tissue die-off may follow. In extreme cases, entire meadows can collapse.
Professor Marnie L. Campbell, Executive Dean of Science at Edith Cowan University and a senior author of the study, said conservation and restoration strategies must adapt to this new climate reality.
“The way we protect and restore seagrass needs to change as the climate continues to warm,” Campbell said.
The loss of seagrass meadows has far-reaching consequences. Beyond biodiversity impacts, degraded meadows may release stored carbon back into the water column and atmosphere, undermining their role as carbon sinks. Fisheries that rely on seagrass habitats for spawning and nursery grounds could also be affected.
Toward Climate-Ready Restoration
One of the most significant insights from the study is the variation in thermal tolerance at the population level. This local-scale variation opens the door to climate-informed restoration strategies.
According to Said, identifying and using heat-tolerant populations in restoration efforts could help build “climate-ready” seagrass meadows. By sourcing plant material from populations that demonstrate higher heat tolerance, managers may increase the resilience of restored meadows in warming regions.
However, the researchers caution that restoration cannot be one-size-fits-all. Different species have different ecological requirements, including depth preferences and sediment conditions. Effective management must account for these biological and environmental factors.
The team also stressed that natural adaptation has limits. If global warming continues unchecked, even the most heat-tolerant populations may eventually exceed their physiological thresholds. (Wage Erlangga)
