Researchers have discovered alarming evidence that mangrove forests, crucial for safeguarding tropical and subtropical coastlines, are sinking in the Maldives. Their study shows that since 2020, rising sea levels and a climate pattern known as the Indian Ocean Dipole have caused more than half of the mangrove cover on some Maldivian islands to disappear.
Researchers have uncovered concerning evidence that the mangrove forests, essential to protecting coastal regions in tropical and subtropical zones, are drowning in the Maldives.
The findings, released today (Tuesday 12 December) in Scientific Reports, reveal that the combination of rising sea levels and the Indian Ocean Dipole has resulted in significant losses of mangrove cover on various Maldivian islands since 2020.
The research team, led by experts from Northumbria University, cautions that these findings could have repercussions not just for the Maldives, but for island nations and coastal ecosystems globally.
In 2020, over a quarter of the Maldivian islands with mangrove forests experienced the gradual decline of mangrove trees, resulting in a phenomenon called dieback.
Satellite images of both populated and unpopulated islands highlighted the severity of this issue, revealing that some islands had lost more than half of their mangrove forests.
Mangroves are vital for coastal protection as they serve as natural barriers against storms, erosion, and flooding. They are also biodiversity hotspots, providing essential habitats for marine species such as crabs, prawns, and fish, which are critical for food security and the livelihoods of many coastal communities. Furthermore, they offer valuable resources, such as building materials for homes.
A research team, supervised by Lucy Carruthers and Vasile Ersek from Northumbria University’s Department of Geography and Environmental Sciences, used a combination of sea level data, climate data, and remote sensing, along with field studies of sediment composition and tree growth, to examine the mangrove dieback.
Their analysis of mangrove wood indicated that the dead trees showed greater levels of salinity stress compared to those that were still alive.
This stress reflects that the tree roots were struggling with increased salt concentrations, which played a significant role in their eventual demise.
According to the researchers, sea levels around the Maldives rose at an alarming rate of over 30mm annually between 2017 and 2020. During the latter part of this period, an exceptionally intense climate event known as the Indian Ocean Dipole occurred, leading to warmer sea surface temperatures and an increase in sea level in the Western Indian Ocean.
Although mangroves typically accumulate their own sediment to adapt to gradually rising seas, the pace of the sea level rise was too swift for them to keep up.
Because tidal movements are restricted in the regions where many mangrove forests are located, rising sea levels caused seawater to flood these areas, hindering the mangroves’ ability to build the necessary sediment to stay above water. Ultimately, they lost their resilience and succumbed to drowning.
Dr. Vasile Ersek, an Associate Professor in Northumbria University’s Department of Geography and Environmental Sciences, explained: “Dieback was first spotted in the central areas of low-lying basins before spreading outward. These basins have limited tidal flushing, so we observed rising sea levels inundating the forests with seawater, leading to increased salt concentrations over time.
“As the rate of sediment buildup by the mangroves slowed due to the rising sea level, the salinity of the soil exceeded what even these salt-tolerant trees could endure. Essentially, the mangroves were drowning.”
“The severe level of dieback we have seen in the Maldives starkly illustrates how climate change could drive natural ecosystems past their limits, resulting in profound effects on both the environment and human populations.”
Lucy Carruthers, now a postdoctoral scholar at East Carolina University’s Department of Coastal Studies, led this study while at Northumbria University. She stated: “The sea level in the area reached an unprecedented high according to tide gauge records coinciding with the dieback in 2020. This happened during a strong positive phase of the Indian Ocean Dipole, which can create extreme climate conditions for nations in the Indian Ocean.”
“As global temperatures continue to rise, we can anticipate that the Indian Ocean Dipole will become more frequent and severe, making events like this mangrove die-off more common.”
“These remarkable forests have flourished for centuries at the intersection of land and sea. Their survival amid the rapid changes in the forthcoming decades will largely depend on our proactive management of the climate crisis now.”
The researchers observed other documented cases of mangrove die-off around the Indian Ocean during the same timeframe, including in the Seychelles and Madagascar.
Given that mangrove forests sequester substantial amounts of carbon—typically three to five times more per equivalent area than tropical rainforests—the researchers expressed concern that the loss of these forests could lead to significant carbon emissions, exacerbating climate change.
She further commented: “Our research highlights the susceptibility of mangrove ecosystems to rapid sea-level rise and underscores the urgent need for adaptive conservation strategies in small island developing nations.
“Though it might seem like a localized issue, it serves as a cautionary tale for coastal areas worldwide. As climate change and extreme weather events escalate, some mangrove forests may struggle to adapt to the rising sea levels. The Maldives, being the lowest-lying nation in the world, could potentially serve as an early warning system for similar issues elsewhere.”
