is believed that life began in the ocean, possibly around deep
volcanic vents in the ocean floor, or perhaps in warm, shallow
seas. The chemicals of life move easily in water, and water
environments support many forms of animals and plants.
life is dependent on access to sunlight and nourishing
chemicals that are dissolved in the water. Living things need
phosphorus, nitrogen, oxygen, carbon (dissolved as carbon
dioxide), sulfur, calcium, and hydrogen. Some of these
chemicals are carried into the ocean from the land, some are
reclaimed from the decaying bodies of dead animals and plants.
The availability of these elements limits the numbers of life
forms that live in different areas.
is an important factor in determining the makeup of aquatic
populations. In some waters, such as muddy rivers, light may
barely penetrate below the surface of the water: in
the deep, clear waters of the ocean, it may go down to 100
meters. However, the light (and the nutrients) are most
abundant in the first meter of water below the surface. Plants
can only grow where they have light.
of limitations in the supply of nourishing chemicals and
light, some parts of the ocean are almost lifeless, while
other parts are thickly populated with life forms. There are
many varieties of life forms near the land, especially where
parts of the ocean are shallow, and where nutrients are being
washed off the land into the water.
Aquatic environments share certain characteristics.
Nutrients in the water come from the decomposition of existing
life forms or are washed into the water from the land.
- Temperatures in water change slowly and are not so extreme
as temperature changes on land.
- Water supports the bodies of living things. Water life forms
do not need to be as concerned about supporting their bodies
as land life forms.
- Living things that live in water are not in danger of dehydration.
- Water is more dense than air. Creatures that need to move
swiftly in water develop streamlined shapes.
- Light does not penetrate far into water.
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Some Types of
|| Between the high
and low tide levels. Alternately wet and dry. Challenging!
barnacles, snails -- exoskeletons protect from predators
Water is mixture of fresh and saline.
|| Where a river flows
into the ocean.
Lots of nutrients in water
productive: a nursery for many life forms
| Oceanic Shallow
Water Mud Flats
water, gentle tides
flounders, burrowing worms, sea grass
| Oceanic Shallow
have strong waves, tide pools
fish, anemones, crustaceans, small plants
Plants and many animals cling to rocks
Water Over Sand
is easily moved by the water. It may be hard for plants
to anchor in
--life forms may dig down into the sand or hide by
clear, deep water
|| Very diverse community:
fishes, corals, sea anemones, eels, octopus
water but still receiving light
plants shelter small fish, snails, sea urchins, abalone
(deep bottom) Zone
|| Cold, dark, enormous
pressures, very little food, life forms few in number, but very
fish, nemotodes, occasional fish: no plants
|| Volcanic eruptions
in sea floor: hot water and sulphur, dissolved minerals.
worms, bacteria, clams
water: cold in the mountains
crayfish, water plants
water: zones similar to ocean
water lilies, rushes, insect larvae