Amazon Estuary #2: General Info, Vertebrates, and Aquatic Plants

The Amazon Estuary has by far the largest water output of any estuary in the world, discharging an average of 46 million gallons (175 million liters) per second into the Atlantic. The sheer magnitude of this discharge means that, almost uniquely among estuaries, there is very little saltwater intrusion into it. Instead, nearly all of the mixing between the river’s discharge and seawater occurs outside the estuary, on an area of continental shelf. Despite the relative lack of seawater intrusion, the whole estuary is significantly affected by twice-daily tides, which cause inundation (by river water) of most of the islands in the estuary.

 Water plants play a key role in Amazon ecology. Many animals, such as the manatee, feed upon the plants. Their underwater roots are used for shelter and spawning by small fish, amphibians and crustaceans. The vegetation above water is home to a host of insect and spider species. Mats of water plants provide nesting sites for water birds such as the Jacana. The habitat also supports large water dwelling reptiles, such as caiman, monitor lizards and snakes, especially constrictors: the boas and the Anaconda.

There are many distinctive water plants but only a few are especially abundant and common. These play and especially important part in the dynamics of the forest and river. The water hyacinth and water lettuce are the two most common fully aquatic species. These can quickly block water ways, especially if their main consumer, the manatee, is absent, as it is in many places. Cane species then take over. If floods are insufficient to dislodge the mass of vegetation, it will remain and eventually undergo the succession process. During heavy floods, plant mats are broken up and passively float around the ecosystem, moved by river currents. This is undoubtedly important in distributing animals to places they may not otherwise reach (commensalism).

Of the water plants, the Giant Water Lily is the most famous for being by far the world's largest water lily. The pads measure up to six feet across, compared with most other species that reach at most one or two feet across.  Other important species are water hyacinth, water lettuce, water fern and various aquatic grasses.


  0°55'38.21"S
 48°27'46.58"W