Many but not all marine animals live in seas and oceans.
Plenty of others inhabiting the sweet waters of rivers, streams, lakes, and
marshes. Some sea creatures make an annual visit to fresh water rivers as part of their reproductive cycle.
Likewise the sea, food chain from phytoplankton and zooplankton to big fishes is
found here as well.
Let us start with rivers:
Between the source and the sea, rivers hold five kinds of habitat. First comes the narrow
headstream where algae and willow moss, cling to the boulders and shelter small flattened,
crawling creatures like the smidges, mayflies, stone flies and caddis flies.
The downstream holds a broader stretch known as the trout back. Here the current
pours over boulders and gouges out deep pools. Few plants can root. But small, aquatic
insect larvae feed on morsels washed downstream. They themselves form food for trout.
Dippers are tubby birds that swim under water with their wigs to seize young caddis flies.
Next comes the minnow reach. The river has at last slowed down enough to dump sand
and shingle banks between the pools. Plants grow under water here. Apart from the larvae
inhabiting the trout beck This is reach with dragonfly nymphs, freshwater shrimps and
crayfishes. Minnows, trout, eels and other fishes find food and shelter in this gentler
stretch. Some fishes like salmon comes up this far from downstream.
On its path toward the sea the river next enters its lowland reach. No other
stretch contains so many kinds of animal. The slow pace of water flow and soft mud floor
formed by the siltation and deposition of particles from the upstream goes to this level.
Worms, insects, mollusks and crustaceans abound. Many help to feed fishes of the carp
family - the barbell, bream, Rudd and roach. Such fishes in turn are snapped up by the
predatory perch and pike.
In the few kinds of freshwater or saltwater animal can stand its brackish waters.
But those that can are plentiful. A square of mud one pace across may house 10000 worms,
or, 20,000 little snails that browse upon green, slimy algae. Fishes that swim here are
most prone to fall prey of ducks, geese, wading birds and gulls those flock here in
In Australia, on the banks freshwater stream, there lives
a rare species of egg-laying mammal. Called platypus, these are very good swimmers, even
under water. Their bills are also like those of ducks and the webbed feet and a flat tail.
While the beak grubs for food on river beds
These apart there are some inhabiting the typical tropical waters. The year round food
supply and warmth help support a wealth of marine life - from insects and fishes to
reptiles and amphibians. The strange variety of frogs include the goliath frog. Found in
West Africa these are the largest variety of known frogs. Also strange is flat-bodied
Surinam toad from South America. It never leaves the water. The female carries her eggs on
her back in skin 'blisters'.
The upside down catfish from Africa guzzles food from the surface film on water. An
elephant trunk fish has a long, trunk like lower lip that probes mud for the
invertebrates. The Chinese algae eater has a vacuum cleaner mouth for browsing on under
water leaves an stones. South Africa's hatchet fish has deep but knife-thin bodies. These
thumb length creatures can take off and glide 5 meters(16 ft) through the air after insect
prey or away from predators. The tiny looking piranha is one of the most ferocious
freshwater fishes. These hard jawed saw teethed fishes with a sharp smelling sense attack
their prey always in a large group. They start nibbling casually. The biting picks up as
the nibbling continues until the prey is fully consumed leaving the
The fresh water turtles with flattened shells streamlined for swimming inhabit all warm
continents. Soft shelled turtles lack a hard protective shell, but make up for it by biting savagely.
Some fishes can give off electric impulses from nerves inside the body. Like South
America's electric eel that produces an electric shock strong enough to stun a horse or
scare predatory crocodiles.
Crocodiles and alligators are the real ferocious amphibians of this habitat. Crocodiles
are the largest of all living reptiles. Equipped with hard jaws lined with grinding teeth
these mighty monsters float log-like on the surface. They swim fast by lashing their long,
deep, flattened tails. Some can drag cattle into water from quite afar.
The big monitor lizard include species almost as aquatic as a crocodile. Other reptiles
include snakes that can swim well and prey on fish.
Ponds and streams:
As water travels overland it gathers chemicals - for instance, mineral salts and the
gases, oxygen and carbon dioxide. Water plants make food and grow with these. Living and
dead water plants themselves form food for many animals that live in water. Other
creatures prey on some of these. Body waste and dead animals in turn yield nourishment to
fertilize the water plants. Thus sets off a fresh water food chain. Unlike the running
waters the still water of a pool has its own special group of creatures. Yet their variety
is no less amazing!
Around the soft, gently sloping edge of a pool with reeds, arrowheads, bulrushes and other
tall plants. And
it is because of these plants at the pool animal life here grows richest. The plants
shelter and feed thousands of tiny crustaceans, insect larvae, mollusks and worms.
Between the water weeds the water spiders spin their underwater home filled with
air bubbles that it brings down from the surface.
Newts, frogs and toads also make their
habitat at the pool side rim. Frog and toad tadpoles browse on soft vegetation. Newts
larvae feed on worms and water fleas. Daphnia in turn eat minute green plants, mostly
algae that drift about in water. Again the larvae and tadpoles may
fall prey to big beetles that dive and hunt under water. Young dragonflies are
Farther out, in deeper water, lurk larger fishes. Most kinds eat water plants and worms or
other small invertebrates.
Trench and bream forage among underwater plants near the bottom. Not everywhere the
same species of these still water creatures are found. It depends on the climatic zones.