Life of a River - Biology
Adaptations (pg 1 of
Among ecosystems, rivers are unique for the
continual flow of water, sediment, nutrients,
and organisms (see Spiraling).
Stream organisms of all kinds have
physical and behavioral adaptations to
varying water velocities. Consequently, the
plants and animals found in riffles differ
from those in pools, even within the same
stretch of a river.
For example, fish that are adapted to fast
water can have a streamlined shape like
darters to minimize the force of the current,
or fins like a sculpin that anchor them to
Trout tuck behind a rock or other shelter when
feeding to conserve energy. When prey appears, the
trout quickly move out into the current to capture
it. Smallmouth bass, less streamlined than trout,
generally occupy slower water, moving to riffles
only when actively feeding. Northern pike, though
built for quick acceleration, cannot swim
continuously against a strong current. They occupy
slack eddies and backwaters in wait of prey.
Flathead catfish have been observed
overwintering in slack water on the downstream side
of rocks in the Mississippi River. A conspicuous
film of sediment that had settled around the fish
suggested a motionless state of torpor and the
protection that these rocks afforded (Hawkinson
and Grunwald, 1979).
Map turtles and softshell turtles are uniquely
adapted to larger swift-moving rivers. Softshells
have snorkel-like nostrils that allow them to
breathe in shallow water while their flat,
pancake-shaped shell is nestled in the sand.
Birds and mammals have also adapted to exploit
the aquatic habitats. Long-legged herons and egrets
effortlessly stalk the backwaters to spear fish and
frogs. Mergansers and scaup dive in main channels
after fish and fingernail clams. The body profiles
and thick fur of otter and beaver allow them to
comfortably navigate swift currents and withstand
cold water temperatures.
Brook trout, flathead catfish, smooth softshell
turtle, spiny softshell turtle, great blue heron,