IMPERILED PRIMATES: The peculiar proboscis monkey is just one of the endangered animals unique to mangrove forests.
ISTOCKPHOTO/KJORGEN

In the watery limbo between sea and river, where salt and fresh water mingle in the roots of mangrove trees, a handful of uniquely adapted species—terrestrial and aquatic—have evolved to fill the novel niche.

But more than 40 percent of the land-dwelling animals that live in mangrove forests are now under pressure from habitat loss, concludes an analysis published this week in BioScience.

"Mangroves are threatened by development, pollution, mariculture and changes in sea level and salinity," wrote David Luther, an ecology researcher at the University of Maryland, College Park, and Russell Greenberg, head of the Smithsonian National Zoo's Migratory Bird Center. The impact on creatures that depend on mangroves remains poorly documented.

Tangled woody mangrove forests cover about 65,637 square miles (170,000 square kilometers) around the world, but they're quickly disappearing. A 2007 United Nations report noted that 20 percent of the globe's mangrove forests had vanished in the 25 years between 1980 and 2005, a rate that the U.N. Food and Agriculture Organization's director called "alarming."

Here's a look at the forests and some of the animals that are now threatened by their rapid disappearance.

Slide Show: Vanishing Animals of the Mangroves