Drowning mangroves: Climate change is pushing nature past its limits

Researchers have discovered that mangrove forests – a shield against destructive storms across many coastlines – are now suffocating underwater in the Maldives.

The data shows that the combination of an escalating sea level and a shift in Indian Ocean conditions has caused some Maldivian islands to lose more than half of their mangrove cover since 2020.

The researchers, led by Lucy Carruthers and Dr. Vasile Ersek of Northumbria University, noted that this isn’t a singular incident affecting only the Maldives.

The experts said that extreme climate events represent an emerging threat to mangroves and coastal ecosystems worldwide.

Slowly deteriorating mangroves

In 2020, the mangroves on more than a quarter of the Maldives islands started showing signs of slow deterioration, sliding into a state known as dieback, before bidding the world adieu.

The intensity of this mangrove loss phenomenon was captured by satellite imagery. The experts found that some islands had lost more than half of their mangrove cover.

For their investigation of mangrove dieback, the researchers combined evidence from sea level, climate data, and remote sensing. Field observations of sediment geochemistry and dendrology were also taken into consideration.

Signs of salinity stress in mangroves

According to the results, the dead trees exhibited increased signs of salinity stress when compared to their living counterparts.

This stress gives us a clue that the tree roots were having a tough time dealing with the heightened salt levels, which played a key role in their demise.

The scientists concluded that sea levels around the Maldives had risen at an escalated rate of over 30mm per year from 2017 to 2020.

Adding fuel to the fire, there was a particularly intense shift in the Indian Ocean Dipole during this period. This brought along warmer sea surface temperatures and a sea-level increase in the Western Indian Ocean.

Limited tidal movement

While mangroves do have a way to cope with slow and steady rising seas by building up sediment, they found the pace of sea level rise over the past few years too fast to keep up with.

Due to limited tidal movements in the basin areas where many mangrove forests grow, the rising sea levels essentially drowned them.

The lack of tidal movement and the consequent flooding obstructed the mangroves from building the sediment they needed to stay above water.

Extreme magnitude of forest dieback

Dr. Vasile Ersek is an associate professor in Northumbria University’s Department of Geography and Environmental Sciences.

“Dieback was first observed in the center of low-lying basin areas before gradually spreading outwards,” said Dr. Ersek.

“As these basin areas have something we call limited tidal flushing we saw evidence of the rising sea level inundating the forests with seawater. This prolonged exposure created higher concentrations of salt.”

“As the mangroves’ build-up of sediment slowed down due to the pace of the rising sea level, the soil salinity increased beyond what even these salt-tolerant trees could handle. Essentially, the mangroves were drowning.”

Dr. Ersek noted that the extreme magnitude of dieback seen in the Maldives is a vivid illustration of how climate change may push natural systems past their limits, with cascading consequences for both nature and people.

Future of mangroves in a warning climate

Lucy Carruthers, the study’s lead author, is now a postdoctoral scholar in East Carolina University’s Department of Coastal Studies.

“Sea level in the region reached its highest point on tide gauge records when the dieback occurred in 2020. This coincided with an intense positive phase in the Indian Ocean Dipole which can induce climate extremes for countries within the Indian Ocean,” said Carruthers.

“As our planet continues to warm, we can expect to see the Indian Ocean Dipole occurring more frequently and at higher magnitude, meaning events like this mangrove die-off may become more common.”

“These remarkable forests have thrived at the interface of land and sea for many centuries. Whether they can survive the rapid changes of the coming decades will depend largely on our actions in managing the climate crisis today.”

The study is published in the journal Scientific Reports.

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