Species Unique to Tidal Marshes Face Threats

August 1, 2006
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Tidal marshes cover only about 45,000 square kilometers worldwide—about the area of Denmark. In comparison with other habitats, tidal marshes support few nonaquatic vertebrate species, but their unique characteristics have led to the evolution of species and subspecies that are found nowhere else on earth. These endemic species and subspecies, which seem to be largely restricted to North America, have adapted to life in a harsh environment in which seed abundance is low, salinity is high, and flooding is frequent. However, that environment—and thus the species endemic to it—is threatened by a broad range of human activities, from coastal development to rice production, say Russell Greenberg of the Smithsonian Migratory Bird Center and his coauthors in an article published in the August 2006 issue of BioScience.

Tidal marshes occur in mid to high latitudes, along coasts that are protected within estuaries or behind barrier islands. They are most common in North America and China. Some tidal marsh species are protected from high salinity by relatively impermeable skin, and others have kidneys that can concentrate salts from large volumes of water or specialized glands that exude salt. Many are gray or black in color, which is believed to be an advantage because it matches the dark color of the soils often found in tidal marshes. Why endemic tidal marsh species seem to be largely restricted to North America—which has 24 of the worldwide total of 25—is not clear: Although the skewed distribution could reflect differing taxonomic practices in different countries, it may be related to the history of glaciation or of agriculture.

Endemic tidal marsh species are vulnerable to coastal development and to sea level rise, both of which are rapidly reducing the area of tidal marshes. They are also threatened by toxic wastes and invasive species. Greenberg and his coauthors argue for an expanded research program to try to understand how species will respond to these threats.

The complete list of research articles in the August 2006 issue of BioScience is as follows:

Prospects for Developing Perennial Grain Crops. Thomas S. Cox, Jerry D. Glover, David L. Van Tassel, Cindy M. Cox, and Lee R. DeHaan.

A Thirty-Year Study of Phenotypic and Genetic Variation of Blue Tits in Mediterranean Habitat Mosaics. Jacques Blondel, Donald W. Thomas, Anne Charmantier, Philippe Perret, Patrice Bourgault, and Marcel M. Lambrechts

Tidal Marshes: A Global Perspective on the Evolution and Conservation of Their Terrestrial Vertebrates. Russell Greenberg, Jesus E. Maldonado, Sam Droege, and M. V. McDonald

Toward a Synthetic View of Extinction: A History Lesson from the North American Rodent. Kathleen LoGiudice

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