¨ Nearly three fourths of the Earth’s surface is covered with
water.
¨ Aquatic ecosystems are determined primarily by the depth, flow,
temperature, and chemistry of the overlying water.
¨ Aquatic ecosystems are grouped according to the abiotic factors
that affect them.
v Depth of the water, or distance from shore determines amount of
light that organisms receive
v Water chemistry refers to the amount of dissolved chemicals-salts,
nutrients, and oxygen.
v Latitude determines temperature-polar, temperate and tropical regions.
Freshwater Ecosystems
¨ Only 3 percent of the surface water on Earth is fresh water.
¨ Freshwater ecosystems are divided into two main types: flowing-water
ecosystems and standing-water ecosystems.
Flowing-Water Ecosystems
¨ Rivers, streams, creeks, and brooks are all freshwater ecosystems that flow over land.
¨ A river originates in the mountains or hills, often springing from an underground water source.
¨ Near the source, the turbulent water has plenty of dissolved oxygen but little plant life.
¨ As water flows downhill, sediments build up and enable plants to establish themselves.
¨ Downstream, the water moves more slowly through flat areas, where turtles, beavers or river otters
make their homes.
Standing-Water Ecosystem
¨ Lakes and ponds are the most common standing-water ecosystems.
¨ Water not only circulates in and out but also within them.
¨ The circulation helps to distribute heat, oxygen, and nutrients
throughout the ecosystem.
¨ The still waters provide habitats for plankton that would be washed
away by flowing water.
¨ Plankton is a general term for the tiny, free-floating or weakly swimming
organisms that live in both fresh and salt-water environments.
¨ Phytoplankton or single celled algae are supported by nutrients in the water and form the base of
many aquatic food webs.
¨ Zooplankton are planktonic animals that feed on the phytoplankton.
Freshwater Wetlands
¨ A wetland is
an ecosystem in which water either covers the soil or is present at or near the surface of the soil for at least part of the
year.
¨ The water may be flowing or standing and fresh, salty, or brackish,
which is a mixture of fresh and salt water.
¨ There are three main types of freshwater wetlands: bogs, marshes
and swamps.
¨ Bogs, which are dominated by sphagnum moss, form in depressions where
water collects.
¨ The water in bogs is very acidic.
¨ Marshes are shallow wetlands along rivers and may be underwater for all
or part of the year.
¨ Marshes contain cattails, rushes, and other tall, grasslike plants.
¨ Swamps are wet all year round and resemble flooded forests.
¨ The presence of trees and shrubs is what distinguishes a swamp from
a marsh.
Estuaries
¨ Estuaries are wetlands formed where rivers meet the sea.
¨ Estuaries contain a mixture of fresh and salt water, and are affected
by the rise and fall of ocean tides.
¨ Estuary food webs differ from other aquatic ecosystems because primary
production is not consumed by herbivores.
¨ Much of the organic material enters the food web as detritus.
¨ Detritus is made up of tiny pieces of organic material that provide food
for organisms at the base of the food web, clams, worms, and sponges.
¨ Estuaries support a large amount of biomass but contain fewer species than freshwater
or marine ecosystems.
¨ Commercially important fish and shellfish such as shrimp and crabs spawn and develop
in estuaries.
¨ Salt marshes are temperate-zone estuaries dominated by salt-tolerant grasses
above the low-tide line and by seagrasses under water.
¨ Salt marshes
are found along the eastern seaboard of North America from Maine to Georgia.
¨ One of the largest surrounds the Chesapeake Bay estuary in Maryland.
¨ Mangrove swamps are coastal wetlands that spread across tropical regions
including southern Florida and Hawaii.
¨ The dominant plants are salt-tolerant trees called mangroves which provide a valuable
nursery for fish and shellfish.
¨ The largest mangrove area in the continental U.S.
is within Florida’s Everglades
National Park.
Marine Ecosystems
¨ Sunlight penetrates only a relatively short distance through the
surface of the water.
¨ The photic zone
is a relatively thin surface layer-typically down to a depth of about 200 meters.
¨ Photosynthesis is limited to this layer allowing algae and other
producers to grow.
¨ The aphotic zone,
which is below the photic zone, is permanently dark.
¨ Chemoautotrophs are the only producers that can survive in the aphotic
zone.
¨ Marine biologists divide the ocean into zones based on the depth
and distance from shore: the intertidal zone, the coastal zone, and the open ocean.
¨ The benthic zone covers the ocean floor and is, therefore, not exclusive
to any of the other marine zones.
Intertidal Zone
¨ Organisms that live in the intertidal zone are exposed to regular
and extreme changes in their surroundings.
¨ Once or twice a day, they are submerged by sea water.
¨ The remainder of the time, they are exposed to air, sunlight, and
temperature changes.
¨ Organisms are also battered by waves and sometimes strong currents.
¨ Zonation is the prominent horizontal banding of organisms that live in a
particular habitat.
¨ In the intertidal zone, each band can be distinguished by differences
in color or shape of the major organisms.
v A band of black algae might grow at the highest hightide lineàfollowed by encrusting barnaclesàclusters of blue mussels might stick
out amid clumps of green algae
¨ This zonation is similar to the pattern that you might observe as
you climb up a mountain.
¨ In the intertidal zone, zonation exists on a smaller vertical scale-just
a few meters compared to kilometers you would ascend on a mountain.
Coastal Ocean
¨ The coastal ocean
extends from the low-tide mark to the outer edge of the continental shelf.
¨ The coastal ocean is rich in plankton because it is entirely within
the photic zone.
¨ One of the most productive coastal ocean communities is the kelp
forest.
¨ Kelp forests are named for their dominant organism: a giant brown alga that
can grow as much as 50 centimeters a day.
¨ Huge forests of this seaweed are found in cold-temperate seas along
the coast of California and the Pacific Northwest.
¨ Kelp forests support a complex food web that includes snails, sea
urchins, sea otters, a variety of fishes, seals, and whales.
Coral Reefs
¨ Coral reefs are found in the warm, shallow water of tropical coastal
oceans.
¨ Coral reefs are named for the coral animals whose hard, calcium carbonate skeletons
make up their primary structure.
¨ Coral animals are tiny relatives of jellyfish that live together
in vast numbers.
¨ Most coral animals are the size of your fingernail, or even smaller.
¨ These animals use their tentacles to capture and eat microscopic
creatures that float by.
¨ Coral animals cannot grow in cold water or water that is low in
salt.
¨ Corals that build reefs grow with the help of algae that live symbiotically
within their tissues.
¨ The algae carry out photosynthesis using the animals’ wastes
as nutrients and the algae provide their coral hosts with certain essential carbon compounds.
Open Oceans
¨ The open ocean begins at the edge of the continental shelf and extends
outward.
¨ It is the largest marine zone, covering more than 90 percent of
the surface area of the world’s oceans.
¨ The open ocean ranges from 500 meters deep to more than 11,000 meters
at the deepest ocean trench.
¨ Organisms in the deep ocean are exposed to high pressure, frigid
temperatures, and total darkness.
¨ It has very low levels of nutrients and supports only the smallest
producers.
¨ Fishes of all shapes and sizes dominate the open ocean.
Benthic Zone
¨ The benthic zone extends horizontally along the ocean floor from
the coastal ocean through the open ocean.
¨ Benthos are the organisms that live attached to or near the bottom such
as sea stars, anemones, and marine worms.
¨ Benthic ecosystems often depend on food from organisms that grow
in the photic zone and drift down from the surface waters.
¨ Near deep-sea vents, chemosynthetic primary producers support life
without light and photosynthesis.
