· Life in Isolation
· Special Features
· Did You Know?
· Wild Side
· Cause for Concern
· Looking Ahead

Global 200 Snapshot

Madagascar has one of the most distinctive freshwater ecosystems in the world, with many endemic species.  

Life in Isolation

Two thousand years seems like a long time to us, but it’s barely a blink when considering the natural wonders of Madagascar. Although people began to move there about 2,000 years ago, the island itself broke off from the tip of Africa almost 100 million years earlier. This geographical isolation helped diverse and unusual species to evolve. Many live in Madagascar's rivers and streams and nowhere else on Earth.

Special Features

Several large mountains occur on the island, including the Ankaratra Massif, which towers almost 9,000 feet (2,700 m) above central Madagascar and is the source of several rivers. The freshwater systems of the east side of the island contrast greatly with those of the west. The island has an elevated plateau from which short, swift rivers flow over waterfalls and rapids as they descend to the Indian Ocean to the east. But to the west, long, slow rivers flow down gradual slopes and carry fertile soil to the plains. These waterways create wide sandbanks before they pass into the Mozambique Channel.

	Volcanoes may die, but they are slow to disappear. When ancient volcanoes on Madagascar exploded or collapsed, they left behind many craters. These then filled with water to create lakes, some of which still provide habitat for birds and fish. One crater lake named Tsimanampetsotsa lies so close to the coast that it contains saltwater.

Wild Side

A large proportion of the freshwater species of Madagascar are found only on this island. All aquatic frogs, many freshwater reptiles, and a high proportion of freshwater fish are endemic. An aquatic mammal, the web-footed tenrec, lives along the banks of streams and the shores of marshes and lakes, at altitudes of 1,980 to 6,600 feet (600 to 2,000 m). It eats small frogs and fish, freshwater shrimp, crayfish, and aquatic insect larvae. The freshwater turtle, Eretmochelys madagascariensis, is declining in numbers as its habitat disappears. In the diverse freshwater habitats of Madagascar, water birds such as the nearly extinct Alaotra little grebe and the Madagascar pochard, nest, breed, and hunt. A blind fish that lives in Ankarana caves was recently discovered. Many freshwater species have yet to be identified. Unfortunately, many of these may become extinct before they are ever known.

Cause for Concern

Madagascar’s rivers and streams have historically been preserved by surrounding forests, but much of these forests have been cut in recent years. This has caused siltation, temperature increases, and increases in flow from rapid runoff. Rice cultivation and overfishing, hunting, and trapping also threaten the ecoregion. But exotic species may be the greatest threat to native species. Introduced fish species have already replaced many native species in inland lakes and streams.

Looking Ahead

If current rates of deforestation continue, little of Madagascar’s forests will survive the next century. With the loss of more protective forests along the rivers and streams, water quality will further decline, and a total loss of forest cover would certainly mean the loss of many native freshwater species. Introductions of exotic species should be eliminated to prevent the loss of natives.