Mapping the world’s tidal marshes

For the first time, the world’s tidal marshes have been mapped, providing scientists, researchers and planners the opportunity to monitor and understand the important role they play in our ecosystems.

What are tidal marshes?

Tidal marshes are wetland ecosystems located in the intertidal zone, the area between high and low tides, along the coast. These marshes act as a crucial interface between terrestrial and aquatic environments. It houses a variety of plant species such as grasses, sedges and rushes, and is subject to periodic inundation due to tidal cycles.

This fluctuation in water levels creates a unique habitat that supports a wide range of animals, including different species of fish, crustaceans and birds. Tidal marshes also perform essential ecological functions, such as nutrient cycling, water purification, and carbon sequestration. Like barrier islands, tidal marshes also act as a buffer against coastal erosion and flooding, providing protection to inland areas.

Tidal marshes at the mouth of Plum Island, Massachusetts. Image: USGS, public domain.

Tidal marshes are valuable as habitats for a variety of wildlife while protecting coastal areas from harmful floods. They also store carbon and can help achieve long-term goals of reducing carbon dioxide levels on the planet. Tidal marshes also act as a buffer against coastal erosion and flooding, thus providing protection to adjacent upland areas.

Where are tidal marshes found around the world?

The new tidal map was created using 2020 Sentinel 1 and 2 data with classification techniques trained on images to automate tidal marsh areas, with an accuracy measured at over .85 using this approach.(2)

The new map shows that approximately 45% of tidal marshes are in North America and northern Europe, but there are important areas in South America, East Asia and Australia.

Map of tidal marshes of the world will help in environmental conservation

Now, with a new map showing the main areas where tidal marshes are located, we can better track how protected they are and perhaps plan to expand the areas where they can be found. The new map was produced by the Nature Conservancy and the University of Cambridge. . The map has been published at a resolution of 10 meters and is available on Google Earth.(1)

Gray shaded map of countries with a gradient from yellow to green to blue to dark purple, showing the extents of tidal marshes.
Tidal marsh extents around the world based on 2020 Earth observation data. Map: Worthington et al., 2023, CC BY 4.0.

The main purpose of this map is to facilitate research and provide a better understanding of tidal marshes while aiding in their conservation. We know that tidal maps are important for various habitats, human well-being, climate and biodiversity. In addition, areas where tidal marshes need restoration can be identified using the new map.

There have been several mapping projects before for tidal marshes, such as the well-known Chesapeake Bay area that has been studied by scientists for decades, but many areas have remained mysterious. This world map allows a better overall perspective on the global importance of tidal marshes.

Over the past century, tidal marshes have been cleared, drained and built up, resulting in less than 53,000 square kilometers of tidal marsh area remaining today worldwide. This is less than the size of West Virginia.

Benefits of tidal marsh restoration

There is hope that restoration efforts will yield beneficial results for the tidal marshes. For example, the Lightning Point restoration project in Alabama helped restore a degraded tidal marsh to attract seabirds and wildlife back to the area. Over time, this habitat could also become a useful storehouse of blue carbon and help protect the coastline from erosion and hurricane damage.

There is also an economic benefit as fishermen avoid damage to their vessels due to storms, as tidal marshes act as a natural sponge during storms, and the habitat becomes rich again for more sustainable forms of fishing.(3)

Lightning Point is considered a huge success by the Nature Conservancy and the non-profit wants to see it serve as a blueprint to encourage other coastal communities to similarly restore tidal marsh areas. The new map can aid in this effort by identifying the best areas to reshape tidal marshes.

Mapping the world’s mangroves helps conservation efforts

A similar precedent may show that there is potential benefit to creating a global map of tidal marshes. In 2010, researchers came together to create the world’s first map of global mangroves. This has since played an important role in encouraging their conservation and enabled policy makers to make better and informed decisions in mangrove management.

Home of red mangroves, Everglades National Park.  Image: NPS
Home of red mangroves, Everglades National Park. Image: NPS, public domain.

Like tidal swamps, mangroves play an important role in local ecosystems and in broader carbon reduction efforts. With a focus on environmental conservation that helps benefit local communities and ecosystems and provide an overall global benefit in storing potentially harmful atmospheric carbon, planners can take advantage of the new map and see how tidal marshes can be part of countries’ national and international carbon reduction commitments. And preserve the environment. Protecting ecosystems. As Lightning Point’s efforts have shown, this also means benefiting communities socially and economically.(4)

It may seem that a global map of tidal marshes may not provide much benefit outside of having professionals with a tool for knowing where tidal marshes are located. However, it is clear that maps provide ways for many stakeholders to benefit from them, and are also important tools for conservation and restoration efforts.

These global maps of wetland ecosystems provide a perspective that is difficult to see from the local level, but can serve as a platform to start new conversations about the ways in which we can better improve our efforts to protect vital ecosystems, improve our communities, and even reduce some of the negative impacts of increasing Carbon in the atmosphere.


(1) The Google Earth Engine website can be found here:

(2) A recent presentation on the new tidal marshes map and its benefits can be found here: An academic presentation on the benefits can be found here: Worthington, TA, M. Spalding, E. Landis, TL Maxwell, A. Navarro, LS Smart, and NJ Murray. 2023. Distribution of global tidal marshes from Earth observation data. com.bioRxiv doi: 10.1101/2023.05.26.542433.

(3) To learn more about the Lightning Point restoration project in Alabama, see:

(4) For more information on global mangrove mapping efforts, see:



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