Animals - Rapidly Flowing Waters
In the exposed rock surface habitats only those organisms are found which have efficient mechanisms for staying in one place. In fact despite adaptations for staying put, many individuals of species do get swept away Animals found here include fresh water limpet, larvae or water penny (riffle beetles), fresh water sponges and caddis flies, all specially adapted to this environment. The microhabitat formed in the spaces between rock fragments is slightly sheltered. Here occur the stone fly and dragonfly both of which are flattened and have behavioural adaptations to hold them in place (i.e. clinging by instinct to hard surface and orienting themselves along the current).
In addition to these, the larvae of insect hellgrammite is found here, which avoid being swept away by being large and covered with spines. In the Microhabitat beneath rocks, where current is weak, occur animals which though they have basic adaptations for staying in the rapidly flowing water, are not as highly adapted as members of the two other microhabitats. Animals found here are annelids, flatworms, clams, some snail species and other insect larvae In the rapidly flowing habitat, nekton occur only in areas where current is not too strong and include cold water fish species such as trout or salmon. In areas where the current is very strong nekton are absent and in such cases, the benthos may be many and varied and may form the entire community.