Mangroves grow at the edge of sea and land, their form shaped by the pull of both. Vibrant green foliage rises above a tangled lattice of partially submerged roots that seem less anchored than poised – planted, but not entirely still, as if they might unspool themselves and walk away at any moment. At high tide, water slips through them; hours later, the landscape rearranges itself, leaving the forest exposed.

It’s not an easy place to exist, yet these forests do more than endure at the edge of the sea. They hold it together.

A System that Sustains Life and Stores It

Mangroves begin their work below the surface. Their roots – arching and knotted, like many thousands of arms reaching down into the mud– turn open water into shelter. Juvenile fish slip between them. Crustaceans settle into the sediment. For many species, this is where their life will start: protected from predators, buffered from currents, and given time to grow.

Many of the fish that pass through mangroves will later move offshore, into reefs and open waters. Some of those fish will one day feed people far from the coast. A mangrove forest, in this sense, is less a place than a phase – a beginning that sustains systems elsewhere.

Amidst this bustle, mangroves are quietly managing something less visible and far more expansive: carbon. They pull it from the atmosphere and trap it in both their above-ground vegetation and in the oxygen-poor sediments that lie beneath them, where decay slows to a crawl. Layer by layer, year after year, carbon accumulates in the soil, locked away in sediment that lasts for centuries.

Few systems do this as efficiently. Mangroves “punch above their weight”, storing disproportionate amounts of carbon for their size. They cover less than 0.1% of the Earth’s surface, yet they are among some of the most productive ecosystems in the world.  It is estimated that mangroves may be responsible for holding as much as 5.72 billion metric tons of carbon globally. They are, in effect, small forests doing large atmospheric work.

The benefits of mangroves’ hard work extend to people as well. By breaking waves and binding sediment, mangroves soften storm surges and reduce coastal erosion. In places exposed to cyclones and rising seas, they can make the difference between damage and protection, loss and survival.

This combination of function – nursery, carbon sink, coastal buffer – reveals something else. Mangroves hold together multiple systems simultaneously: biological, climatic, and human.

And they are doing so under increasing strain.

Where Pressures Converge

Mangroves grow where land, sea, and human activity overlap. Across the tropics, these forests are cleared for aquaculture ponds, converted into farmland, or replaced with infrastructure. The drivers of these changes are familiar: food production, development, and economic growth. But their effects extend beyond the shoreline.

Recent research shows that mangrove loss is not just local, but global in origin. While shrimp farming and crop cultivation remain major contributors, other industries such as forestry, mining, and construction also play a role. And through global supply chains, distant consumers become part of the equation: it’s estimated that exports tied to international demand account for roughly one-fifth of blue carbon losses in mangrove regions.

These pressures are not acting alone. Climate change is altering the conditions mangroves depend on, raising sea levels, shifting temperatures, and intensifying storms. In many regions, rising seas and coastal development are combining to restrict mangroves’ ability to migrate inland, a process often described as “coastal squeeze,” where forests are left with little room to adapt.

Under these conditions, mangroves’ survival depends not just on where they grow, but also on how they remain connected.

An Interconnected System

It is tempting to think of mangroves as fixed – rooted in place, bound by shorelines. But their existence has always depended on connection.

Mangroves reproduce by releasing propagules, buoyant seedlings that drift with ocean currents until they find suitable substrate. Where those currents flow, mangroves can follow. Where they do not, forests can become isolated.

Research from the Centre of Marine Sciences at the University of Algarve suggests that these connections between forests are not random. One of those researchers, Eliza Fragkopoulou, is using her training in climate modeling to understand what drives connectivity between mangrove populations. 

“They connect through ocean currents, where the seeds can be transferred from one area to the other, depending on whether the currents are constantly flowing in one direction or the other. And [this] can actually dilute and mix the genetic signatures of the different populations,” explains Fragkopoulou. 

Using global biophysical models, her work shows that ocean currents structure how mangrove populations are linked, shaping the distribution of genetic diversity across regions – often more strongly than geographic distance alone.

This reframes mangroves as part of a dynamic network. Some regions act as hubs, maintaining genetic diversity and dispersing propagules across long distances. Others rely on these connections to persist, receiving the flow of genes and individuals that allow populations to recover and adapt.

Under climate change, this system is becoming less certain. Ocean currents are shifting, reshaping the pathways through which mangroves disperse, expand, mix, and maintain genetic diversity. When those pathways weaken or even accelerate, new populations may establish themselves. Others become fragmented, less able to adapt, and less able to recover.

How a mangrove forest responds to change depends not only on ocean currents but also on the conditions it experiences locally.  “For example, if mangrove populations are under pressure from coastal development and you’re constantly destroying the forest by being isolated, it means that it’s actually prone to more stressors, internal stress, [such as] diseases. If there is a huge heat wave and the temperature goes to extremes, then this population will not be connected with other populations to receive seeds, and then try to recover. So in this way, being isolated might impede recovery.”

Peering into the Future

The research group Fragkopoulou works with is now expanding this work to ask how climate change may reshape global patterns of mangrove biodiversity. “[So now what] we are doing is modeling the distribution of the different species and evaluating how these are changing under different climate change scenarios. Then, when we combine the different distributions of the multiple species, we can get global biodiversity patterns.”

These patterns can be used to explore areas of species richness where biodiversity may be lost, where species may expand into new areas, and how those changes could reshape ecological interactions. Fragkopolou notes that this will look different on local scales compared to global ones. ” In the Gulf of the Caribbean region, nowadays, five species of mangroves can be found. Will they all react in the same way to climate change?”

Whether those species persist, decline, or reorganize into new communities will depend on processes unfolding far beyond any single coastline. Mangroves have always existed at the shifting boundary between land and sea. Fittingly, their persistence has always depended on movement—of propagules, genes, and the ocean currents that connect forests across vast distances. Understanding those connections may prove just as important as protecting the forests themselves.

Quotes have been edited for length and clarity.

An Article by Natalie Testa, Title Photo by: Anita Kainrath / Ocean Image Bank / Mangrove Photography Awards