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Natural protectors: Mudflats, mangroves and marshes

Tamsin Walker
January 13, 2020

As sea levels rise, the planet's natural bulwarks against the ocean could help protect the coastline. But these very habitats are also under threat.

Stones covered in seaweed on a mudflat. The sun is setting in the background
Image: Imago/Priller&Maug/J. Meyer

The Wadden Sea — a unique habitat between land and water

More than a third of the global population lives within 100 kilometers of the world's coastline. But one stretch of coast can vary greatly from the next, and as such, each faces different challenges as sea levels rise in our warming world. Widely understood to protect the land from the water, though, are the habitats that spring up along coastlines: mudflats, mangroves and salt marshes. 

Read more: Hotter, higher seas to worsen extreme floods without 'urgent and ambitious' action, United Nations warns

What are mudflats and why do they matter? 

Mudflats are areas of land that are flooded at high tide and are formed by a buildup of sediment carried in by tides and rivers. Found all over the world in sheltered locations such as estuaries and bays, mudflats ­— also known as intertidal zones — are rich ecosystems that serve as breeding and nesting terrain for numerous native and migratory birds, as well as nursery grounds for many fish species. But they also provide a service to humankind, by acting as a barrier between land and the sea, thereby helping to prevent coastal erosion.

A mudflat with houses from above
The Wadden Sea in Germany's Lower Saxony is also a national park and includes the East Frisian Islands, salt marshes and mudflatsImage: picture-alliance/dpa/I. Wagner

Salt marshes

Salt marshes are also typically found in coastal regions in some parts of the word. They tend to be found along the shores in cooler regions, and are dominated by salt-resistant shrubs and grasses that grow on top of deep mud. They are often found close to intertidal zones, and like mudflats, they protect against coastal erosion by breaking the intensity of waves crashing against the shore, while also serving as carbon storage.

Grassy salt marsh
Only the toughest, most salt-resistant species can thrive on salt marshesImage: WWF/J. Fröhlich

Read more: Young mangrove defenders fight to save Panama's wetlands


There are between an estimated 50 and 110 species of mangrove tree. Though they range greatly in height, from just 2 to 10 meters, they are all able to live in ocean waters by excreting salt through their leaves. They also all serve the same environmental functions, which includes helping to limit erosion through their system of deep roots. According to Conservation International, they cover a total area of more than 137,000 square kilometers along the saltwater coasts of 118 tropical and subtropical countries. Indonesia has dense mangrove coverage, which contains as much as five times the amount of carbon per hectare as its tropical forests.

Mangrove trees
A mangrove lagoon in Sri Lanka's Mannar district, which is home to eight different species of mangrove plantImage: DW/C. Davison
Mangrove trees at high tide
Image: picture-alliance/Arco Images GmbH/W. Dolder

Read more: The war widows protecting Sri Lanka's mangroves

A sea at risk of drowning

The Wadden Sea, which stretches for some 500 kilometers (311 miles) along the coastlines of the Netherlands, Germany and Denmark, is one of the largest intertidal zones in the world. At low tide, its 10,000 square kilometers of mudflats become accessible to migratory birds, which both feed and breed there. As ocean levels rise, the Wadden Sea itself is at risk of disappearing. One idea to prevent this from happening involves dropping sand in strategic places so the sea can wash it onto the mudflats, thereby helping them to grow apace with rising water levels.

A photo of a bird called the bar-tailed godwit in water
The bar-tailed godwit is just one of many birds to leave its footprints in the sand of the mudflatsImage: picture-alliance/imageBROKER
Bird footprints in the sand
Image: DW/T. Walker

Read more: Germany's coastal lowlands under the shadow of climate change

Mont Saint-Michel

Rising from some 500 square kilometers of mudflats and salt marshes in a northern French bay is the UNESCO World Heritage site of Mont Saint-Michel. But life within the bay is every bit as spectacular. Home to hundreds of birds, plant and marine species, including honeycomb worms, which have built an expansive reef known as "Le Banc des Hermelles." The largest "bio-construction" in Europe, its surface area covers more than 100 hectares. The bay is also known for the highest tides in continental Europe.

A built-up island in the sea
Mont Saint-Michel is a Benedictine abbey off the coast of France built on a rocky islet and exposed to powerful tides Image: picture-alliance/dpa

Banc d'Arguin

Another UNESCO World Heritage Site is the sprawling coastal wetland and national park of Banc d'Arguin in West African Mauritania. The park, which comprises dunes, islands, shallow coastal waters and swamps, is home to a huge variety of flora and fauna, including whales, dolphins and turtles. The park represents the largest feeding, breeding and nursery area in West Africa. Expansive sea grass coverage helps to prevent erosion and enhance water quality as well as providing shelter to marine species.

Boats behind a bank of sand
Low tide at the Banc d'Arguin National ParkImage: Imago Images/photothek/T. Imo
Flamingos taking flight from the beach
Flamingos are one of the many species of bird that stop off at Banc d'ArguinImage: Imago Images/alimdi

Read more: Destruction of wetlands: swamp rats eating away at Louisiana's fragile coastline

Archipelago dos Bissagos

A satellite photo of Guinea-Bissau Archipelago dos Bissagos
The mangrove swamps of Archipelago dos Bissagos are fertile grounds for fish, birds and other animalsImage: picture-alliance/dpa/ESA/USGS

Comprised of 88 islands and a vast intertidal area of mangroves and mudflats, the Archipelago dos Bissagos is located off the coast of Guinea Bissau. The 76,000 and 35,000 hectares of mudflats and mangroves respectively are revealed twice daily by the retreating tide. During the winter, as many as 700,000 birds congregate in the area to nest, breed and feed.