Estuaries are regions where fresh water from rivers and salt water from the ocean mix, and they are among the most biologically productive ecosystems on Earth. This astronaut photograph, taken from the International Space Station, highlights two estuaries along the northwestern coastline of Madagascar.
The Mozambique Channel separates the island from the southeastern coast of Africa. Bombetoka Bay (image upper left) is fed by the Betsiboka River, and is a frequent subject of astronaut photography due to its striking red floodplain sediments. Mahajamba Bay (image right) is fed by several rivers, including the Mahajamba and Sofia. Like the Betsiboka, the floodplains of these rivers contain reddish sediments eroded from their basins upstream.
The brackish conditions (a mix of fresh and salt water) in most estuaries invite unique plant and animal species that are adapted to live in such environments. The hardy shrubs and trees of mangroves are common in and around Madagascar’s estuaries, and Bombetoka Bay contains some of the largest remaining stands. Estuaries also host abundant fish and shellfish species, many of which need access to fresh water for a portion of their life cycles. In turn, these species support local and migratory bird species that prey on them.
However, human activities such as urban development, overfishing, and increased sediment loading from erosion of upriver highlands threaten the health of the estuaries. In particular, the silt deposits in Bombetoka Bay at the mouth of the Betsiboka River have been filling in the bay.