Reddish egrets, pictured at right perched on a mangrove tree, are restricted to a narrow fringe of mangrove forest along the coastlines of the southeastern United States, Mexico, Central America, and the West Indies. They depend on mangroves for nesting and foraging habitat—but mangroves are not doing well.
Worldwide, their range declined 2% a year from the early 1980s to 2001. At that rate, mangroves could be gone within 100 years, and so would the animals that depend on them.
Mangroves grow around the world in the salty waters of the tropics and subtropics. They help stabilize the coastline and provide protection from hurricanes. Many species of fish, shrimp, and other marine animals use the tidally flooded mangrove forests as nurseries and foraging areas.
Less well known is the fact that many species of animals make their homes in the mangrove canopy. Around the world, 69 species and subspecies of animals live almost their entire lives in mangroves.
Mangrove Frog (Haiti)
Mangroves occur in 2 distinct biogeographical regions:
The latter region has more species of mangroves and more species of mangrove specialists. The reason for the disparity between regions is unknown but the explanation may be recent ice ages, when mangroves retreated to equatorial regions and may have expanded in Asia because lower water levels exposed more land.
Living in mangroves is not easy. Animals must cope with regular tidal floods, storms, and a salty environment. Nevertheless, food can be abundant and many specialize on eating crabs.
According to a recently published paper by Russ Greenberg and David Luther,
“Mangroves are threatened by development, pollution, mariculture, and changes in sea level and salinity. The global impact of such threats on mangrove taxa remains poorly understood, as mangrove ecology and conservation are usually approached at a local rather than a global scale.”
This article summarizes the information in this publication:
Mangroves: A Global Perspective on the Evolution and Conservation of their Terrestrial Vertebrates. 2009. Luther, David A. and Greenberg, Russell. Bioscience, 59(7): 602-612.
Mangrove ecosystems are found globally along tropical and subtropical coastlines. They exhibit a steep environmental gradient between inland and marine systems, providing a unique, selective environment that shapes local morphological, physiological, and behavioral adaptations. In the first global assessment of terrestrial vertebrate species that are restricted to mangrove ecosystems, we found 48 bird, 14 reptile, 1 amphibian, and 6 mammal species endemic to mangroves, the majority of which are found in Asia and Australia. We also found that more than 40% of assessed mangrove-endemic vertebrates are globally threatened. Clearly, additional research is needed to better understand mangrove-endemic vertebrates in order to conserve them. Future research should focus on global inventories, intercontinental comparative work, and the ecology of mangroveendemic vertebrates.
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