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Salt Marshes

salt marsh area

Whenever I hear the word marsh, I think of a flat, dead landscape  shrouded in thick, damp, dismal fog, peopled only by smugglers. (Too many English horror stories as a child maybe?) In reality, salt marshes are busy, productive ecosystems teeming with a variety of life and offering a wealth of ecosystem services to us.



A marsh is a wetland that is dominated by herbaceous rather than woody plant species (like in a mangrove forest). At the coast, marshes become salt marshes. A salt marsh is also referred to as a tidal marsh because it occurs in the area between the low tide mark and the high tide mark.

Salt Marsh Distribution

Salt marshes can be found along coastal regions throughout the world,  except where ocean water level and land levels are markedly different e.g. where there are cliffs. They are less common in tropical regions where they are likely to be replaced by mangrove swamps. So typically, they occupy salty, shallow waters of bays, estuaries and lagoons in the temperate regions of the world.

salt marsh ecology

Salt marshes are visually dominated by grasses and salt-tolerant herbaceous plants, such as rushes, sedges and succulents. The exact composition of species varies from region to region. Salt marsh are home to many animals. Hidden within the tangle of plants are animals in various stages of life. Animals can hide from predators in marsh vegetation, because the shallow brackish area physically excludes larger fish.


Nutrient recycling

Although animals do eat the bounty of fresh vegetation in salt marshes, the real food chain engine is the high volume of dead and decomposing materials that are moved in and out with the tides. This nutrient rich material forms the foundation of a broad web of invertebrates, fish, shellfish, birds and mammals. The abundance per square meter of one species of fiddler crab or snail routinely reaches 100–400 individuals, at times over 1000.

Carbon storage

We are just starting to understand "blue carbon" importance.   Current studies suggest that mangroves and coastal wetlands annually sequester carbon at a rate ten times greater than mature tropical forests.  It has been estimated that the global average carbon accumulation rate (CAR) at 242.2 g of carbon per metre per year in saltmarsh sediments. They also store three to five times more carbon per equivalent area than tropical forests. Most coastal blue carbon is stored in the soil, not in above-ground plant materials as with tropical forests. This soil is not a potential source of CH4 emissions.


Buffering and filtering services

Tidal marshes are also extremely important because of their capacity to buffer storms and their pollutant filtering actions. The dense roots and stems hold the unstabilized soils together, reducing the impacts of storm surge. The plants, animals, and soils filter, absorb, and neutralize many pollutants before they can reach adjacent marine and estuarine communities.1


Summary of services provided for us

  • Amelioration of coastal erosion
  • Carbon sequestration
  • Habitat for many fish and crustaceans with commercial value
  • Recreational and educational value
  • Nutrient processing
  • Water quality improvement

Threats to the services?

  • Draining, filling in salt marsh areas to create new suburbs and to extend agricultural land.
  • Locating industries adjacent to wetlands areas and risking contamination of the surrounding vegetation e.g. oil spills from refineries
  • Introduction of invasive species which damage members of the community.
  • Activities such as burning fossil fuels which results in sea level rises and water temperature rises.
  • Increased frequency of drought which causes starvation as plant fail to thrive.

What can we do to retain these services?

  • Recognise the significance of blue carbon as part of our attempt to limit global warning, and learn more about the functioning and importance of salt marshes.
  • Stop clearing salt marsh areas for housing developments and agriculture. As salt marshes were diked, drained and filled in during the twentieth century to create farmlands and bayside suburbs, this dynamic ecosystem was greatly disturbed which affected a wide range of species.
  • Prevent industries adjacent to salt marsh areas from polluting the marsh with poor waste disposal tactics. In places where industry has made serious efforts to reduce the emission of pollutants, new vegetation has been observed to re-colonize bare mud and re-develop a salt marsh.

Dig deeper

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