Rare salt marsh endemics threatened.

29/03/2007 00:00:00 There are only about 45,000 square kilometres of Tidal marshes left worldwide—roughly the size of Denmark. Tidal marshes support relatively few non aquatic vertebrate species, but their unique characteristics have meant that many species and subspecies, such as Saltmarsh snake, Swamp sparrow and the Louisiana swamp rabbit, are specialists and are not found outside of this particular habitat.

These endemic species and subspecies, which are mostly restricted to North America, have adapted to a harsh environment where seed abundance is low, salinity is high, and flooding is frequent. That environment, and the species endemic to it, is threatened by a wide range of human activities, including coastal development and rice production, according to Russell Greenberg of the Smithsonian Migratory Bird Centre in the August 2006 issue of BioScience.

Tidal marshes are found in mid to high latitudes, on coastlines 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 colour, which is believed to be an advantage because it matches the dark colour of the soils often found in tidal marshes. Why endemic tidal marsh species are mostly restricted to North America, which contains 24 of the worldwide total of 25, is not clear.

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 co-authors argue for an expanded research program to try to understand how species will respond to these threats.