Aquatic Ecosystem
Intended
Learning Outcomes
At the end of this Lecture, students will
be able to
• Explain Aquatic ecosystem
• Discuss the characteristic features of
Aquatic ecosystem
• Discuss the structure and functional of
the Aquatic ecosystem
Content
• Introduction to Aquatic ecosystem
• Characteristic features of Aquatic
ecosystem
• Structure and functional of the Aquatic
ecosystem
Aquatic
Ecosystem
• Aquatic ecosystems constitute the marine
environments of the seas and the fresh water systems in lakes, rivers, ponds
and wetlands
• Provide human beings with a wealth of
natural resources (food such as fish and crustaceans)
• Natural aquatic systems such as rivers
and seas break down chemical and organic wastes created by man
• If aquatic ecosystems are misused or over
utilized, their ability to provide resources suffers in the long term
• Over-fishing leads to a fall in the fish
catch
What is an
aquatic ecosystem?
• In aquatic ecosystems, plants and animals
live in water
• These species are adapted to live in
different types of aquatic habitats
• Aquatic ecosystems may be classified as
being stagnant ecosystems or running water ecosystems
• The mud gravel or rocks that form the bed
of the aquatic ecosystem alter its characteristic and influence its plant and
animal species composition
• The aquatic ecosystems are classified
into freshwater, brackish and marine ecosystems, which are based on the
salinity levels
• The fresh water ecosystems that have
running water are streams and rivers
• Ponds, tanks and lakes are ecosystems
where water does not flow
• Wetlands are special ecosystems in which
the water level fluctuates dramatically in different seasons
• They have expanses of shallow water with
aquatic vegetation, which forms an ideal habitat for fish, crustacea and water
birds
• Marine ecosystems are highly saline,
while brackish areas have less saline water such as in river deltas
• Coral reefs are very rich in species and
are found in only a few shallow tropical seas
• Richest coral reefs in India are around
the Andaman and Nicobar islands and in the Gulf of Kutch
• Brackish water ecosystems in river deltas
are covered by mangrove forests and are among the world’s most productive
ecosystems in terms of biomass production
• The largest mangrove swamps are in the
Sunderbans in the delta of the Ganges
Pond
Ecosystem
• Pond is the simplest aquatic ecosystem to
observe
• There are differences in a pond that is
temporary and has water only in the monsoon and a larger tank or lake that is
an aquatic ecosystem throughout the year
• Most
ponds become dry
after the rains
are over and
are covered by terrestrial plants for the rest of the
year
• When a pond begins to fill during the
rains, its life forms such as the algae and microscopic animals, aquatic
insects, snails, and worms come out of the floor of the pond where they have
remained dormant in the dry phase
• Gradually more complex animals such as
crabs frogs and fish return to the pond
• As the pond fills in the monsoon a large
number of food chains are formed
• Algae is eaten by microscopic animals,
which are in turn eaten by small fish on which larger carnivorous fish depend,
these are in turn eaten by birds such as kingfishers, herons and birds of prey
• Aquatic insects, worms and snails feed on
the waste material excreted by animals and the dead or decaying plant and
animal matter
• They act on the detritus, which is broken
down into nutrients which aquatic plants can absorb, thus completing the
nutrient cycle in the pond
• The temporary ponds begin to dry after
the rains and the surrounding grasses and terrestrial plants spread into the
moist mud that is exposed
• Animals such as frogs, snails and worms
remain dormant in the mud, awaiting the next monsoon
Lake
Ecosystem
• Lake Ecosystem functions like a giant
permanent pond
• Large amount of its plant material is the
algae, which derives energy from the sun, which transferred to the microscopic
animals and feed on the algae
• Fish that are herbivorous and are
dependent on algae and aquatic weeds
• Small animals such as snails are used as
food by small carnivorous fish, which in turn are eaten by larger carnivorous
fish
• Specialised fish, such as catfish, feed
on the detritus on the muddy bed of the lake
• Energy cycles through the lake ecosystem
from the sunlight that penetrates the water surface to the plants
• From plants energy is transferred to
herbivorous animals and carnivores
• Animals excrete waste products, which
settle on the bottom of the lake
• This acts as the nutrient material that
is used by aquatic plants for their growth
• During this process plants use Carbon
from CO2 for their growth and in the process release Oxygen
• This Oxygen is then used by aquatic
animals, which filter water through
Streams and
Rivers Ecosystem
• Streams and rivers are flowing water
ecosystems in which all the living forms are specially adapted to different
rates of flow
• Some plants and animals such as snails
and other burrowing animals can withstand the rapid flow of the hill streams
• Other species of plants and animals such
as water beetles and skaters can live only in slower moving water
• Some species of fish, such as Mahseer, go
upstream from rivers to hill streams for breeding, they need crystal clear
water to be able to breed
• As deforestation occurs in the hills the
water in the streams that once flowed throughout the year become seasonal
• This leads to flash floods in the rains
and a shortage of water once the streams dry up after the monsoon
• The community of flora and fauna of
streams and rivers depends on the clarity, flow and oxygen content as well as
the nature of their beds
• Stream or river can have a sandy, rocky
or muddy bed, each type having its own species of plants and animals
Marine
Ecosystem
• Indian Ocean, Arabian Sea and Bay of
Bengal constitute the marine ecosystems
• The
producers in this
ecosystem vary from
microscopic algae to
large seaweeds
• Millions of zooplankton and a large
variety of invertebrates and marine mammals are available
• Shallow areas near Kutch and around the
Andaman and Nicobar Islands are some of the most incredible coral reefs in the
world
• Coral reefs are only second to tropical
evergreen forests in their richness of species
• Fish, crustacea, starfish, jellyfish and
polyps that deposit the coral are a few of the thousands of species that form
this incredible world under the shallow sea
• Deforestation of adjacent mangroves leads
to silt being carried out to sea where it is deposited on the coral which then
dies
• Marine ecosystem is used by coastal
fisherfolk for fishing which forms their livelihood
• Marine ecosystem continued to maintain
its abundant supply of fish over many generations
Seashore
Ecosystem
• Beaches can be sandy, rocky, shell
covered or muddy
• On each of these different types, there
are several specific species which have evolved to occupy a separate niche
• There are different crustacea such as
crabs that make holes in the sand
• Various shore birds feed on their prey by
probing into the sand or mud on the sea shore
• Several different species of fish are
caught by fishermen
• In many areas the fish catch has
decreased during the last decade or two
How are
aquatic ecosystems used?
• Man uses aquatic ecosystems for the clean
freshwater on which his life is completely dependent (water to drink and for
other domestic uses)
• Water is essential for agriculture
• Fisher folk use the aquatic ecosystems to
earn a livelihood
• People catch fish and crabs
• They also collect edible plants (used
locally as food or for sale in the market)
• Over fishing leads to a serious decline
in the catch and a long-term loss of income for fisher folk
• Marshes and wetlands are of great economic
importance for people who live on their fish, crustacea, reeds, grasses and
other produce
• Agriculture and industry are highly
dependent on large quantities of water
• These dams make rich people richer in the
farmland and supports people in large urban centres that use enormous quantities
of water
• The poor tribal folk become even poorer
as the natural resources they depend on are taken away as their lands are
submerged under the water of the dam
• Dams are built across rivers to generate
electricity
• Large proportion of this energy is used
by urban people, by agriculturists in irrigated farmlands and in enormous
quantities for industry
• Large dams have serious ill effects on
natural river ecosystems
• This makes such lands gradually more and
more saline and unproductive
What are
the threats to aquatic ecosystems?
• Water pollution occurs from sewage and
poorly managed solid waste in urban areas when it enters the aquatic ecosystem
of lakes and rivers
• Sewage leads to a process called
eutrophication, which destroys life in the water as the oxygen content is
severely reduced
• Fish and crustacea cannot breathe and are
killed (foul odour is produced)
• Gradually
the natural flora
and fauna of
the aquatic ecosystem
is destroyed
• In rural areas the excessive use of fertilisers
causes an increase in nutrients, which leads to eutrophication
• Pesticides used in adjacent fields
pollute water and kills off its aquatic animals
• Chemical
pollution from industry
kills a large
number of life
forms in adjacent aquatic
ecosystems
• Contamination by heavy metals and other
toxic chemicals affects the health of people who live near these areas as they
depend on this water
How can aquatic
ecosystems be conserved?
• For sustainable use of an aquatic
ecosystem, water pollution must be prevented
• It does not make sense to allow water to
be polluted and then try to clean it up
• Changing
the nature of
the aquatic ecosystem
from a flowing
water ecosystem to a static ecosystem destroys its natural biological
diversity
• Thus dams across rivers decrease the population
of species that require running water, while favouring those that need standing
water
• Aquatic ecosystems, especially wetlands,
need protection by including them in Sanctuaries or National Parks in the same
way in which we protect natural forests
• These sanctuaries in aquatic ecosystems
protect a variety of forms of life as well as rare fish which are now highly
endangered such as the Mahseer
• Wetland Sanctuaries and National Parks
are of greatest importance as this is one of the most threatened of our
ecosystems
• As the proportion of the earth’s surface
that is naturally covered by wetlands is very small compared to forests or
grasslands, the wetland ecosystems are very highly threatened
Summary
• Aquatic ecosystems constitute the marine
environments of the fresh water systems in lakes, rivers, ponds and wetlands
the seas and
• In aquatic ecosystems, plants and animals
live in water
• Pond is the simplest aquatic ecosystem to
observe
• Lake Ecosystem functions like a giant
permanent pond
• Streams and rivers are flowing water
ecosystems
• Indian Ocean, Arabian Sea and Bay of
Bengal constitute the marine ecosystems
• Man uses aquatic ecosystems for the clean
freshwater, agriculture etc.,
• Water pollution occurs from sewage and
poorly managed solid waste in
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