Tidal Marshes: A Global Perspective
By Gregory Gough
Tidal marshes line temperate coastlines around the world. Their combined area is roughly 45,000 square kilometers, about the size of Denmark.
Distribution of Tidal Marshes
| Continent | Coastline | Area (km2 | Vegetation |
|---|---|---|---|
| North America | Atlantic, Pacific, Gulf | 16,440 | Spartina, Phragmites, Salicornia |
| South America | Atlantic | 2,300 | Spartina, Juncus |
| Europe | All | 1,400 | Salicornia, Spartina, grasses |
| Asia | Pacific | 25,000 | Chenopods, Phragmites |
| Australia, New Zealand, Tasmania | Southern (temperate) | 772 | Sarcocornia, other chenopod shrubs |
| South Africa | Southern | 70 | Sarcocornia, Spartina, grasses |
Although the tidal marsh habitat is saline and floods regularly, it is quite productive. However, much of that productivity occurs below the ground and in the water. Therefore, tidal marshes have few terrestrial animals that regularly inhabit them.
Ipswich Marshes, (painting), Name: Heade, Martin Johnson, Date: 1860s
The vegetation typically consists of grass-like or salt-tolerant plants near the water, and taller grass-like plants and shrubs nearer the land.
Approximately 25 species (or subspecies) of birds, reptiles, and mammals live only in tidal marshes—and 24 of them are confined to North America. It is unknown why there are so many endemics in North America as opposed to the rest of the world but it may be because refuges existed during recent Ice Ages.
Tidal marshes are fragile habitats and face threats from: coastal development, sea-level rise, invasive species, and toxins and pollutants.
This article summarizes the information in this publication:
Greenberg, Russell S., Maldonado, Jesus E., Droege, S. and McDonald, M. Victoria 2006. Tidal Marshes: A Global Perspective on the Evolution and Conservation of Their Terrestrial Vertebrates. Bioscience, 56(8): 675-685.
Globally, tidal marshes are found in small pockets or narrow hands totaling only approximately 45,000 square kilometers. The comhination of salinity, low floristic and structural complexity, and regular tidal inundation, as well as unpredictable catastrophic flooding, provides a unique selective environment that shapes local adaptations, including those that are morphological, physiological, demographic, and behavioral. Although tidal marshes support a low diversity of nonaquatic vertebrate species, a high proportion of these inhabitants, at least along North American coastlines, are restricted to or have subspecies restricted to tidal marshes. Tidal marshes and their endemic fauna face broad threats from a variety of human-caused environmental changes. Future research should focus on global inventories, intercontinental comparative work, and investigation to determine why almost all presently described endemic taxa appear to be found in North America.
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