Transcript Aquatic Ecosystems make up most of the Biosphere

Aquatic Ecosystems make up
most of the Biosphere
34.4
Ponds and Lakes
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Freshwater ecosystems include water bodies
with very little dissolved salt, such as most
ponds, lakes, streams, and rivers.
Ponds and lakes are standing (not flowing)
bodies of water.
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Lakes and large ponds are divided into
zones based on water depth and distance
from shore.
The shallow water close to shore and the
upper zone of water away from shore make
up the photic zone, so named because light
is available for photosynthesis.
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Phytoplankton, microscopic algae and
cyanobacteria that carry out photosynthesis,
live in the photic zone, along with water
plants.
The deep, murky areas of a lake, where light
levels are too low to support photosynthesis,
are called the aphotic zone.
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The bottom of any aquatic ecosystem is
called the benthic zone.
The benthic zone consists of rock, sand, and
sediment.
The organisms of deep (aphotic) benthic
areas feed on wastes that sink down from the
photic zone.
Streams and Rivers
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A body of flowing fresh water is known as a
stream or a river.
A river changes greatly between its source
and the point at which it empties into a lake
or the ocean.
Near the source, the water is usually cold,
low in nutrients, and clear.
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Few phytoplankton inhabit this part of a river.
Instead, the major producers near a river's
source are algae attached to rocks on the
river bed.
Many species of arthropods live in the
benthic zone, feeding on algae, fallen leaves,
and one another.
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Downstream from its source, a river
generally becomes wider and deeper.
Marshes and other wetlands are common in
these downstream areas.
The water is usually warmer and murkier
than it is upstream.
More phytoplankton live in this part of a river.
Estuaries
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Streams and rivers merge with ocean water
in areas known as estuaries.
Estuary organisms experience changes in
salt concentration and temperature as the
fresh water and salt water mix.
Estuaries serve as breeding grounds for
many invertebrate and fish species, and as
nesting and feeding areas for a great
diversity of birds.
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Along most of the east coast of the United
States, the major ecosystems found in
estuaries are salt marshes.
In tropical areas, the typical estuary
ecosystems are mangrove swamps.
These swamps are dominated by mangrove
trees, which are anchored by tangled
networks of arching roots.
Ocean Zones
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Zones of depth include the benthic zone, or ocean
floor, and the pelagic zone, or open water above the
ocean floor.
Also as in freshwater ecosystems, the ocean has a
photic zone, which receives enough sunlight to
support photosynthesis, and a dark aphotic zone.
Zones of distance from shore include the intertidal
zone, neritic zone, and oceanic zone.
Intertidal Zone
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The area of shore between the high-tide and
low-tide lines is called the intertidal zone.
Pounded by waves during high tide and
exposed to the sun and drying winds during
low tide, benthic organisms in this zone must
be well-adapted to survive these harsh
conditions
Neritic Zone
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The area of the ocean from the low-tide line
out to the edge of the continental shelf is the
neritic zone.
Since the ocean here is fairly shallow, some
sunlight reaches the bottom in most of the
neritic zone.
As a result, many organisms that require light
for photosynthesis can live in this zone,
including seaweeds and phytoplankton.
Oceanic Zone
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The vast open ocean from the edge of the
continental shelf outward is called the
oceanic zone.
Phytoplankton drifting in the photic layer are
the major producers in this zone.
Microscopic animals called zooplankton also
inhabit the photic zone and in turn are a
source of food for other animals.
Coral Reefs
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All the invertebrate phyla are found on coral
reefs, including sponges, sea anemones,
worms, sea stars, and mollusks.
Vertebrates such as sea turtles and fishes
also roam the reefs.
Most reefs are formed by colonies of coral
polyps, animals in the phylum Cnidaria that
secrete hard external skeletons.
Deep-sea Vents
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Imagine the surprise of biologists when they
first glimpsed giant tube worms living at
depths of 2,500 meters.
These unfamiliar organisms live around
deep-sea hydrothermal vents, spots on the
ocean floor where hot gases and minerals
escape from Earth's interior into the water.
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No sunlight reaches this deep, dark zone.
The vent communities use the chemical
energy from Earth's interior as their energy
source.
The producers in these ecosystems are
prokaryotes that, instead of carrying out
photosynthesis, can extract energy from
sulfur compounds spewing from the vents
and use this energy to make carbohydrates.