River Habitats

Rivers and streams are variable ecosystems. All streams appear to be identical but from one extreme to the other many changes are observable, in general no two streams have exactly the same species distribution, organization or chemical conditions.
Why streams are an unique habitat?

A watershed is an area of land that drains into a water body.  The water body, stream, river or lake, is at a lower elevation than the surrounding land. When rain falls it run(s) downhill into the waterbody; topography determines where and how water flows. This area that drains the water into the stream/river/lake is the watersheds. The quality of water within a watershed depends on how the land is used. The trees on the watershed provides the organic matter and food for many of the species that live in the waterbody. For example Cecropia leaves are the main source of energy for Xiphocaris elongata and juveniles of Epilobocera sinuatifrons.


A tributary is a small stream or rivulet that merges or flows into a larger river or stream. A river is typically has several tributaries.


Pools are one of the most common mesohabitat in a stream. Pools often hold fish, snails, crabs and adult shrimps.The pool provides depth (protection from predators or shelter for predator/preys) and still water (a nice place to swim or look for food). This section of the stream is preferred by eels, adult crabs, Atya lanipes, bigmouth sleepers, mountain mullet, river gobies, and giant Macrobrachium (M.carcinus and M.heterochirus).


Riffles are a short, relatively shallow and coarse-bedded length of stream over which the stream flows at higher velocity and higher turbulence than it normally does in comparison to a pool. Riffles are usually caused by an increase in a stream bed's slope or an obstruction in the water. They are at once a food source, a shelter from predators, a hedge against oxygen depletion, and a conveyor belt that brings food to the animals. Many species of insects reproduce or grow to maturity in riffles. The current removes nymphs or snails from the rocks and move these organisms downstream. Riffles also oxygenate the water. The riffles are the mesohabitat for small shrimps such as Micratya, Potimirim and juveniles of Macrobrachium faustinum and Epilobocera sinuatiforns. It's the perfect location for Atya scabra and Atya innocous; these species are habitat restricted. Small eels, Eleotris and juveniles of the river gobies look for shelter or food on this habitat.


Waterfalls are formed when a stream flows over a precipice and plunges downward. Larger waterfalls work as geographical or natural barriers, because they impede the migration of migratory organisms such as shrimps, and fishes to the upper parts of the stream. The effect of a large waterfall on an stream community can be observed clearly in the Espiritu Santo stream; where the waterfall is similar to a concrete wall. This waterfall prevents the upstream migration of eels, mountain mullets, and sleepers to the upper part, but allow the movement of shrimps and river gobies. In addition this waterfall separates predators and preys: carnivorous fishes stay downstream while shrimps stay up the waterfall.


A lake is a body of fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes contrast with rivers or streams, which are usually flowing; and lakes are fed and drained by rivers or streams. This habitat is ideal for fishes: eels, mountain mullets, bigmouth sleepers, Awaous, and many exotics that are released on it. 


Estuaries are the transition zones between river and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. The inflow of both environments provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats. In Puerto Rico the estuaries are the nurseries of freshwater shrimps, freshwater and marine fishes, and some insects.

Omar Pérez,
Oct 3, 2011, 10:19 PM