Water Ecosystems: Who Lives There?
There are many kinds of water ecosystems on Earth. Rivers,
streams, lakes, ponds, and oceans are some examples. Many water
ecosystems have differences in water movement, temperature, and
amount of salt. For example, oceans have salt water, and streams
have freshwater. Rivers have flowing water, and ponds have still
water. These characteristics determine the types of organisms that
live in a water ecosystem.
In an ocean ecosystem, waves wash over the area near the shore.
Organisms that live there must be able to survive in the waves.
Clams burrow into the sand to escape the waves. Barnacles and
seaweed attach to rocks along the shore so they are not swept away.
Starfish have special feet that allow them to cling to rocks.
Rivers and streams have water that flows in one direction. Animals
in streams and rivers must be able to survive in the moving water.
Tadpoles use suckers to attach to rocks so they will not be swept
away. Crayfish live under rocks, away from the water current. Fish
have streamlined bodies so they can swim in the moving water.
Plants in rivers and streams have strong roots
to keep them in the soil. However, some
rivers do not have many plants because the
current is too fast for them to stay rooted in
the soil.
The water in a pond does not flow. Water
lilies are plants that often live in ponds. They
float on the water, and their roots do not
reach into the soil. Water lilies would be
swept away in a stream or river, but they are
able to survive in a pond ecosystem.
Water lilies float on top of pond
water. They would not survive in
the moving water of a river or
stream.
The amount of light in a water ecosystem also affects the types of
organisms that live there. The open ocean gets plenty of sunlight.
Plankton lives here. Plankton is a collection of small organisms
that are carried along by the water. They use sunlight to make food.
Fish and whales live in the open ocean and feed on plankton.
However, sunlight does not reach deep in the ocean. Because there
is no sunlight, there are no plants or plankton here. Few animals
live in the deep ocean. Most of the animals that do live there can
feed on dead organisms. These animals include flounders, skates,
crabs, and octopuses.
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Water Ecosystems: Who Lives There?
The amount of salt in water also determines what kinds of
organisms live in a water ecosystem. Oceans have salt water.
Ponds, lakes, rivers, and streams have freshwater. Ocean fish
can pump extra salt out of their bodies. Because of this, they
can survive in salty ocean water. However, they cannot
survive in freshwater. Fish that live in freshwater would die
in salt water because they cannot pump extra salt out of their
bodies.
Whales live in salt water. Their
body parts help them remove extra
salt.
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