Specialized Flowing Water Habitats

The hyporheic region is the area below the bed of a stream where interstitial water moves by percolation. In gravelly substrates or glacial outwash areas, it may also extend laterally from the banks. In some situations an extensive fauna occurs down to one meter in such substrates. Most orders are represented, especially taxa with slender flexible bodies or small organisms with hard protective exoskeletons. Some stoneflies in the Flathead River of Montana spend most of their larval period in this extensive subterranean region of flow adjacent to the river. Stonefly larvae have been collected in wells over 4 m deep, located many meters from the river. Rivers draining glaciated regions where there are large boulders and cobble appear to have an exceptionally well-developed hyphoreic fauna.

Other specialized flowing water habitats include the madicolous (or hygropetric) habitats, which are areas in which thin sheets of water flow over rock. These often approach vertical conditions (e.g., in waterfalls) and have a characteristic fauna. Among common animals in these habitats are caddisflies, including several microcaddisflies (Hydroptilidae), Lepidostomatidae, beetles such as Psephenidae, and a number of Diptera larvae belonging to the Chironomidae, Ceratopogoniidae, Thaumaleidae, Tipulidae, Psychodidae, and some Stratiomyiidae.

Thermal (hot) springs often have a characteristic fauna, which is fueled by algae and bacteria adapted to high temperatures. The common inhabitants include a number of dipteran families such as Chironomidae, Stratiomyiidae, Dolochopodidae, and Ephydridae, as well as some coleopter-ans. A number of these survive within rather narrow zones between the thermal spring and cooler downstream areas.

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