Written By: Salt marshes are some of the most fascinating yet overlooked coastal landscapes. Stretching between land and sea, these wetlands are alive with movement, from shifting tides and rustling grasses to the calls of wading birds.
For travelers wandering boardwalk trails or paddling through tidal creeks, salt marshes offer a different way to experience the coast. These ecosystems shelter wildlife, protect shorelines, filter water, and store large amounts of carbon in their soils.
Read on to discover what defines a salt marsh, the plants and animals that shape its food web, the climate benefits they provide, and how restoration is helping to protect these important coastal wetlands.
Key Takeaways
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What Are Salt Marshes?
Salt marshes are coastal wetlands regularly flooded with salty seawater brought in by ocean tides. Salt-tolerant plants, such as grasses, sedges, and reeds, sprout up from the soggy ground, painting the landscape with shades of gray, brown, and green. Their mucky soils are composed of mud and peat, the latter of which is a spongy material made up of decomposing plants.
Salt marsh plants must withstand stresses such as salty water, heat, and low oxygen in wet soils. Because water levels vary across the marsh, different areas face different challenges. This creates natural “zones,” each with plant species specially suited to handle the conditions in that area.
Salt marsh plant adaptations include glands in the leaves that secrete excess salt and a strong root system that anchors the plants in place.
Where Are Salt Marshes Found?
Salt marshes are found worldwide on every continent except Antarctica and are estimated to cover between 5.4 and 99 million acres (2.2 and 40 million hectares). They are most common in temperate climates and at higher latitudes, typically in sheltered locations.
Why Are Salt Marshes Important?
Coastal Protection from Storms and Flooding
Beyond their quiet beauty, salt marshes perform one of the most valuable jobs along our coasts. They provide natural protection against floods and extreme weather, which are becoming increasingly frequent due to climate change. Their dense grasses absorb wave energy and slow rushing water, while their peat soils act like a giant sponge, soaking up floodwaters and storing water during high tides and storms.
Just one acre of marshland can absorb up to 1.5 million gallons of floodwater — more than twice the volume of two Olympic-size swimming pools. The plants’ thick root networks stabilize the soil and trap new sediment, preventing erosion and allowing the marsh to build up higher as sea levels rise. During storms, salt marshes can reduce property damage in nearby communities by up to 20%. The coastal wetlands that line U.S. shorelines provide an estimated $23 billion in storm protection each year.
That same ability to trap and hold sediment also makes salt marshes natural filters. As water moves through the marsh, plants and soil filter out pollutants before the water reaches the sea. In doing so, salt marshes help keep coastal waters cleaner.
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Carbon Storage in Marsh Plants and Soils
Salt marshes don’t just protect coastlines; they also fight climate change by locking away carbon. Salt marshes capture carbon not just from living plants but also by trapping sediments and decaying matter. Over time, this forms thick, mucky soils rich in carbon. Because these wetlands are waterlogged and oxygen is scarce, decomposition happens slowly, allowing vast amounts of carbon to remain buried for centuries.
Salt marshes are known as blue carbon ecosystems, a category that also includes mangroves and seagrass meadows. All three of these coastal habitats share a remarkable ability to store carbon in their soils. An estimated 95% of the carbon stored in salt marshes lies underground. These belowground reserves make salt marshes powerful carbon sinks that sequester more carbon per acre than tropical forests and keep it stored for much longer.
Wetland Habitats and Food Webs
Salt marshes are dynamic ecosystems teeming with life and movement. Their constant tidal exchange brings in nutrient-rich waters, creating fertile feeding grounds in adjacent estuaries and coastal waters. The mix of shallow water, dense vegetation, and muddy soils provides food and shelter for everything from tiny crustaceans to large flocks of migratory birds.
Juvenile fish, shrimps, and crabs hide from predators beneath their waving grasses before moving into open waters. These wetlands provide habitat for more than 75% of fisheries species, making them essential to food security and fishing-based livelihoods.
Above the waterline, salt marshes attract a variety of animals. Herons, egrets, ospreys, and kingfishers hunt in the shallows, while migratory bird species stop to rest and refuel during long journeys. Mammals such as otters and raccoons hunt along the shoreline while snakes weave through the grasses.
Coastal Tourism and Outdoor Recreation
Salt marshes add depth and diversity to coastal tourism, offering something different than the typical beach experience. Their wide horizons and wildlife attract birdwatchers, kayakers, anglers, and photographers. By reducing erosion and pollution, they also keep nearby beaches and marine habitats more inviting for recreation.
In many regions, salt marshes anchor eco-tours, fishing charters, and wildlife excursions that bring revenue to coastal communities. In South Carolina, where hundreds of thousands of acres of marshes and wetlands stretch along the coastline, coastal tourism contributes $9 billion annually and supports nearly 100,000 jobs.
Salt Marsh Decline
Globally, salt marshes are declining, having lost between 25% and 50% of their historical global coverage. Between 2000 and 2019, they experienced a net global loss of about 560 square miles (1,450 square kilometers) — roughly the equivalent of one soccer field disappearing every hour.
Salt marshes’ threat level varies by region and the local extent of loss. For example, the Yellow Sea tidal flats in China, North Korea, and South Korea are an endangered ecosystem.
What’s Driving Salt Marsh Loss
A combination of human-driven pressures, including climate change, coastal development, and pollution, causes salt marsh degradation.
Sea Level Rise and Coastal Squeeze
Salt marshes naturally build elevation as they trap sediment and organic matter, allowing them to grow upward and keep pace with the gradual rise in sea level. But when water levels rise too quickly, marsh plants may not be able to add soil fast enough to stay above the tides. Scientists estimate that over 90% of the world’s salt marshes could be submerged or lost by 2100 due to sea level rise.
In healthy systems, marshes can adapt by migrating inland, allowing new vegetation to take hold on higher ground. However, when they’re bordered by infrastructure such as roads or seawalls, that movement becomes impossible — a phenomenon known as coastal squeeze. One study found that marshes next to bulkheads eroded nearly three times faster than those without them. When this happens, marshes eventually drown.
Coastal Development
Historically, salt marshes were often viewed as wastelands, making them prime targets for development and exploitation. For centuries, people filled in marshes to build towns, shipping ports, and infrastructure.
The fertile, nutrient-rich soils of salt marshes also made them valuable for farming, and many marshes were drained and diked to create agricultural land. In other places, marshes were converted for aquaculture, such as shrimp ponds, oyster farms, and fish pens.
Across Europe, it’s estimated that more than half of all salt marshes have been lost to coastal development alone.
Runoff and Pollution
While salt marshes help keep coastal waters clean, they’re often left polluted like a used filter. Runoff from farms and cities carries fertilizers, pesticides, oil, pathogens, and heavy metals into these wetlands.
Over time, this pollution takes a heavy toll on salt marshes. It weakens the roots and soils that hold them together, causing the ground to break apart and once-vegetated areas to collapse into mudflats. Severe contamination, such as oil spills, can cause years of damage and double the rate of erosion. Pollutants also spread into nearby waters, making them unsafe for swimming, fueling algal blooms that suffocate fish, and contaminating shellfish with toxins.
Invasive Species
Salt marshes also face pressure from biological invaders that come from other regions. When invasive plants or animals move in, they threaten the ecosystem’s delicate balance. These new residents can outcompete native species, alter soil and water conditions, and disrupt the web of life. Over time, such invasions can transform marshes into more uniform landscapes and reduce their ability to support wildlife and buffer coastlines.
In China’s Yancheng salt marsh, an invasive cordgrass has rapidly spread, replacing much of the native Suaeda salsa, a salt-tolerant shrub that once dominated the tidal flats. Over the past few decades, Suaeda salsa has declined by more than 82%, changing the habitat.
Invasive green crabs are one of the world’s most damaging coastal species, disrupting ecosystems across North America. In Maine’s salt marshes, their constant digging tears up the roots of grasses that hold the soil in place. This leaves creek banks weaker and more prone to erosion. Green crabs are also voracious predators. A single crab can eat up to 40 clams a day. Their growing numbers have devastated Maine’s soft-shell clam industry, with harvests falling by nearly 75% over the past 40 years.
Salt Marsh Restoration and Protection
Efforts to conserve and restore salt marshes are growing worldwide. Common strategies include restoring tidal flows, planting native grasses, adding sediment to rebuild elevation, and managing invasive species.
- Restoring Water Flows: Reestablishing natural water circulation can involve removing manmade blockages like dikes or seawalls, regulating tidal flows through gates, and creating pools or digging channels to prevent stagnant water. The Valle Paleazza project in Italy’s Venice Lagoon demonstrates this approach, using traditional water management to restore wetlands. The project also helps mitigate climate impacts by enhancing the marsh’s capacity to store carbon.
- Adding Sediment: Depositing soil or sand raises the land’s elevation. Doing so helps the marsh keep up with rising sea levels and creates a stable foundation for vegetation and wildlife to return.
- Planting Native Grasses: Actively replanting salt-tolerant species in areas where natural recovery is slow can speed up marsh restoration.
- Controlling Invasive Species: Efforts to manage invasive species often involve a combination of removal and natural population control. In some areas, restoring native predators can help keep invaders in check. For example, the recovery of sea otters in a California estuary has helped control invasive green crabs.
Take Action for Salt Marshes
Conservation isn’t just the work of scientists or environmentalists. Everyone has a role in protecting and restoring salt marshes. Here are three simple actions to get you started:
- Tread Lightly: Choose guided tours or nature walks that use boardwalks and stay on designated pathways to avoid trampling sensitive vegetation. Get more tips by downloading our Sustainable Marine and Coastal Tourism guide.
- Support Restoration: Back projects that restore or protect marshes. One way to do this is to offset your travel emissions via our carbon calculator. Your contribution funds verified blue carbon projects, such as Valle Paleazza, as well as other ecosystem conservation and climate initiatives.
- Access Business Tools: Membership with Sustainable Travel International provides tourism businesses with tools and resources that make it easier to reduce your footprint and care for coastal destinations.
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