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AQUATIC ECO-SYSTEM
In this lecture we are going to learn about an ecosystem.To understand the factors that influence the life in
an aquatic eco system. To understand about the various zones of marine and fresh water eco system. Marine
means ocean and sea, fresh water means rivers ponds, lakes etc.
Ecosystem, what is an eco-system?
An ecosystem is a biological system consisting of all the living organisms or biotic components in a particular
area and the non-living or abiotic components with which the organisms interact, such as air, mineral soil,
water, and sunlight. Here in eco system biotic, meaning living organisms like plants and animals, they interact
with abiotic factors i.e. light, air, water, soil, minerals etc. So in an ecosystem the biotic factors and the abiotic
factors are very essential, they interact with each other .That is how the eco system exists.
The key processes in ecosystems include the capture of light energy and carbon through photosynthesis, the
transfer of carbon and energy through food webs, and the release of nutrients and carbon through
decomposition. See the eco system is balanced because of some processes .This process is known as food
chain. The autotorphs, the plants are the autotrophs they produce food through the process called
photosynthesis with the help of sunlight, carbon-di-oxide, chlorophyll etc. These plants are eaten up by the
hetertrophs i.e. animals. Once the animals die they are decomposed by the micro-organisms, so again the
micro-organism are acted upon by the degradable organic substances, they become manure. So this process
keeps going on in a cycle. So that is how an ecosystem is maintained in this entire universe.
Ecosystems provide a variety of goods and services upon which people depend, i.e. everyone is depending on
the eco system .Different types of eco systems in a large area is known as a biome. So without that it is highly
impossible for our existence. The principles of ecosystem management suggest that rather than managing
individual species, natural resources should be managed at the level of the ecosystem itself. So any organism
is very comfortable in its own eco system. So it is easier to maintain an ecosystem rather than maintaining a
single organism in a separate locality. In this lecture we are going to see about aquatic eco system.An aquatic
ecosystem is an eco-system in a body of water aquatic Eco system .An aquatic ecosystem nothing but the
ecosystem related with water. Communities of organisms that are dependent on each other and on their
environment live in aquatic ecosystems.Aquatic Eco system has two main types of aquatic ecosystems one is
Marine ecosystems and another one is Freshwater ecosystems. Marine eco systems nothing but the living
organisms that live in the seas and oceans i.e. the water is rich in salt or the water contains more salinity. And
fresh water eco system is nothing but the plants and animals living in the ponds, rivers, lakes etc.
The environmental factors for maintain an aquatic ecosystem is composed of biotic communities i.e. plants
and animals ranging from small algae to huge water animals like whale and shark and abiotic environment is
nothing but all the physical features like light, air water et. It forms a self-regulating and self-sustaining unit
.Water itself, any river or any ocean for that matter it has the quality of cleaning itself. It can self-regulate and
the self-cleansing process is very much common in the water bodies, of they are not polluted. If they are
polluted that becomes very badly affected. The abiotic environmental factors of aquatic ecosystems include
temperature, salinity, flow and the amount of dissolved oxygen in a water body .For the aquatic eco system to
sustain or to retain to have a proper balance we need some physical qualities i.e. temperature of the water is
very important, i.e. the water should be neither too cold nor too warm.
Then salinity, salinity means the amount of salt dissolved in the water body. In general the salinity of sea of
ocean water is 35 parts per million. If it exceed the quality of water changes and it affects the aquatic life. For
example the Dead Sea in Israel has salinity 45 parts per million so a swimmer cannot swim he/she can float on
the water. Then flow, flow of water is also very important. It should be in a balanced manner otherwise it will
definitely affect the planktons and zooplanktons and phytoplankton. Then amount of dissolved oxygen in
water is also very important, because of that dissolved oxygen only the aquatic animals like fish and other
insects take the oxygen for their survival. The salinity of the water body is also a determining factor in the
kinds of species found in the water bodies. Organisms in marine ecosystems tolerate salinity while many
freshwater organisms are intolerant of salt. The organisms like fish which are from sea and ocean can tolerate
the salinity, whereas the fresh water animals cannot tolerate the salinity, they will die if they are replaced or
displace. Freshwater used for irrigation purposes often absorb levels of salt that are harmful to freshwater
organisms .The fresh water used for irrigation purpose mainly dissolve the salts which are applied in the form
of fertilizers and pesticides etc. So the salt content or the dissolved substances which are present in the fresh
water are going to be very harmful for the aquatic life of the water bodies close to the agricultural field.
Biotic Characteristics, The organisms found in aquatic ecosystems are either Autotrophs or
Heterotrophs.Autotrophs are plants. They produce their own food, they are the producer’s .Whereas the
heterotrphs are animals which are depending on the plants and they always feed on autotrophs. Autotrophic
organisms are producers that generate organic compounds from inorganic material. Algae use solar energy to
generate biomass from carbon dioxide and are the most important autotrophic organisms in aquatic
environment. Algae play a very important role in the aquatic they are the major producers of food for the
major aquatic life in that particular water body, because most of the worms and small fish depend on this
algae for their food. Heterotrophic organisms consume autotrophic organisms and use the organic compounds
in their bodies as energy sources and as raw materials to create their own biomass e.g. Worms that feed on
algae and small fish feeds on worms and like that it keeps on going. There is a food chain to maintain this
balance and so many food chains form a food web. Now let us see about the marine eco system. Marine
ecosystems cover approximately 71% of the Earth's surface i.e. our earth is covered by 71% of water i.e. sea
water and ocean water which is saline in nature, i.e. Salt content is very high .It contains approximately 97%
of the planet's water is our sea water or the ocean water. We have distinguished this water body as fresh
water as well as salt water. The marine water is mainly saline due to the presence of dissolved compounds.
Approximately 85% of the dissolved materials in seawater are sodium and chlorine; simply we can call it as
sodium chloride used as a common salt. We get this common salt by evaporating sea water. Seawater has an
average salinity of 35 parts per thousand. Fishes caught in marine ecosystems are the biggest source of
commercial foods obtained from wild populations. See this marine water serves multipurpose. Such a huge
water body we have surrounded our earth. Based on the sea and the coast lie the country’s economy also
depends on it .For example India has got a very huge and long coastline it stays at 19th place in the world for
its coastline around 7500kms of coastline we have including our two island groups and a long stretch of
coastline .Which plays very important role in our economic growth for example commercial activated like
trading , transporting etc and fishing is a very important industry in our country and it brings in lots of foreign
money into our country.
Marine ecosystems can be divided into oceanic, profundal and benthic. Let me explain one by one. Ocenanic is
the open part of the ocean where animals such as whales, sharks, and tuna live. This is only oceanic, i.e. the
upper surface of the water body is known as oceanic, here we can find big water animals like whale, shark,
tuna etc. The profundal i.e. bottom or deep water is an area that does not get much sunlight and it is colder
also the profundal zone is a very cold and ordinary zone, such as an ocean or a lake, located below the range
of effective light penetration. And it is a dark zone and also known as aphotic zone. That means it does not get
much light, it is dark and cold zone.
The lack of light in the profundal zone determines the type of biological community that can live in this region.
Let us discuss about the benthic zone or the bottom substrate. Benthic zone is the ecological region at the
lowest level of a body of water, including the sediment surface and some sub-surface layers. Organisms living
in this zone are called benthos. They generally live in close relationship with the substrate bottom and many
such organisms are permanently attached to the bottom. Many organisms adapted to deep-water pressure
cannot survive in the upper parts of the water column .For example it is like the bottom layer of the ocean.
Here the organism are attached with the sol or the bottom layer of the water body and organism that live in
this layer cannot survive on the top layer of the water because of the cannot withstand the force of the water.
Intertidal Zone, Intertidal zone is nothing but the area between high and low tides. The intertidal zone is also
known as the foreshore or the seashore, i.e. the area close to the sea shore. The area that is
above water at low tide and under water at high tide. This area can include many different types of habitats,
with many types of animals like starfish, sea urchins, and some species of coral. And this area is very much
familiar to us because most of us would have visited seashore and we must have seen different types of
animals floating and coming to the sea shore, especially the children collect the shells, different types of shells
and from that itself we can know what kind of animals are living there. Organisms in the intertidal zone are
adapted to an environment of harsh extremes, because they are exposed to the different climatic changes as
well as the environmental changes because they live on the surface of the water.
Water is available regularly with the tides but varies from fresh with rain to highly saline and dry salt with
drying between tidal inundations. See it is obvious that during rainy time, rainy season the water may not have
the usual salinity. But in the summer season the density of water also increases the salinity and the salinity
increases , water evaporates , the rate of evaporation will be very high, so the animals are able to withstand
these kinds of surroundings. With the intertidal zone's high exposure to the sun the temperature range can be
anything from very hot with full sun to near freezing in colder climates, again with the temperature same thing
happens with the temperature during summer they are exposed to the high temperature during winter they
are exposed to the cold weather , so this animals which are living on the intertidal tidal zone are exposed to
extremes of climatic condition.
Marine eco system also has estuaries, one of the characteristic features of marine eco system is coral reefs,
estuaries, mangrove forest etc. So let us discuss about estuaries .What are estuaries? Usually any fresh water
source like a river or a lake when it gets into an ocean or a sea they bring lot of alluvial soil and they form
alluvial fan or a deltaic land by accumulating silt. This land is usually fertile; it is a pyramid shape land. In case
of estuaries the rivers directly get into the sea to form any deltaic land. An estuary is a partly
enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection
to the open sea. The inflow of both seawater and freshwater provide high levels of nutrients in both the water
column and sediment, making estuaries among the most productive natural habitats in the world. See in our
country the best example for estuaries is formed by river Namarada and Tapi. They get into Arabian sea
without forming any deltaic land , where as you come to the eastern coastal plains we have many delta lands
formed by the river Godavari, Krishna, Kaveri etc. In marine eco systems estuaries play very important role.
They provide habitats for many fish nurseries, depending upon their locations in the world, such
as salmon and sea trout.
Also, migratory bird populations make essential use of estuaries. Phytoplanktons are key primary producers in
estuaries. They may not form a deltaic land it doesn’t mean they are not useful. They are very much useful by
providing habitat to number of aquatic life as well as migratory birds .They are also a source of
phytoplankton , which are micro organic plants floating in the water body. They are the main food for the
aquatic life. Let me tell you something about phytoplankton and how important they are. They move with the
water bodies and can be flushed in and out with the tides because they are very small in nature and they are
micro organic along with the water body and they give green colour to the water also. Their productivity is
largely dependent upon the turbidity of the water. They increase the turbidity in the water. Phytoplanktons
are photosynthesizing microscopic organisms that inhabit the upper sunlit layer of almost all oceans and
bodies of fresh water. Fresh water and oceans sometimes look green in colour, this is nothing, it is only
because of the presence of the presence of phytoplanktons.
They are agents for "primary production" that means they are the primary food producers. The creation
of organic compounds from carbon dioxide dissolved in the water, a process that sustains the aquatic food
web, so they play a very major role in maintaining the food chain as well as food web.
Salt marshes, what are salt marshes?
A salt marsh is an environment in the upper coastal intertidal zone between land and the salt water or
brackish water; it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs.
Simply they can be called as mangroves. When I want to talk about the salt marshes I would like to share some
of my points here. These last marshes accommodate the kind of forest known as mangrove forest. The trees
which are found here are suitable for this particular environmental condition. The world’s largest delta is the
Ganga, Bhramaputra delta or the Sunderban delta. The name for this Sunderban delta is derived from the
name of the tree called Sundari. The Sundari tree is abundant in large number here so, that place got the
name Sunderban delta. The Sundari trees are very hard and durable. This is also the main shelter for the royal
Bengal tiger. Apart from this place we have number of mangrove forest all over our coast line especially the
Krishna-Godavari delta and Kaveri delta also we have our coastline. In Kaveri delta we have our coastline
called Pichavaram. They also have mangrove forest and the trees are also bushy and dense. Is serves as a
recreational centre and an interesting tourist spot. In Sunderban delta we have the royal Bengal tiger and
Gangatic Gharials, snakes then crocodiles etc.
The plants which live in the salt marshes are terrestrial in origin and are essential to the stability of the
salt marsh in trapping and binding sediments .some of the places in salt marshes , the trees will develop aerial
root, that means , the roots growing upwards which will have pores known as Pneumatophores which will
trap oxygen form the atmosphere , because the roots may not get sufficient oxygen in the slushy soil. When
I’m talking about these mangrove forests I would like to share some information about how these mangrove
forests are affected by human activities, because we have a huge coastal area it is overused and salinity
increases because of the unwanted deposition of pollutants in the water and mangrove forest serves a
purpose. During 2004 Tsunami where ever the mangrove forest was there that particular area was protected
from the Tsunami. So that is how it is protecting people from these natural calamities. Nowadays the
government is also insisting on developing shelter belts i.e. growing trees along the sea shore. Because of the
human activities we are destroying the mangrove forests moreover, greenhouse effect that means our earth’s
temperature is increasing day by day because of the industrial and other human activities, because of the this
the ice caps or glaciers start melting they will cause floods in the areas the river floes and the water level
increases in the sea and countries like India and Maldives have the danger of submerging into the sea.
Another important aspect of our marine eco systems is our coral reefs.Coral reefs are underwater structures
made from calcium carbonate secreted by corals. Corals are small living organisms, they secrete calcium
carbonate as shells, and they live in that .After the coral dies the coral shells are used by the other animals for
their shelter. So the accumulated coral reefs form a huge area, form a shelter for the other animals.
Coral reefs are colonies of tiny living animals found in marine waters and contain few nutrients .Often called
“rainforests of the sea”, coral reefs form some of the most diverse ecosystems on Earth. They occupy less than
0.1% of the world's ocean surface, about half the area of France, yet they provide a home for 25% of all
marine species. They are most commonly found at shallow depths in tropical waters. Coral reefs are dying
around the world. Coral mining, agricultural and urban runoff, pollution, overfishing, blast fishing, disease, and
the digging of canals and access into islands and bays are localized threats to coral ecosystems. Our
Lakshadweep islands are mainly made out of coral reefs only .We have the great barrier coral reefs in
Australia .There are three types of coral reefs, one is barrier reefs, another is fringing reefs and the third one
is atolls. Atolls are nothing but the horse shoe shaped or the circular coral reefs. Great barrier coral reefs are
found in Australia. These coral reefs are disappearing very fast because of human activities , form that there
are great threats for these coral reefs one is the sea temperature is increasing, sea level is rising
and pH changes i.e. acidity and the basic nature of the sea water is also changing and then greenhouse gas
emission , naturally causes greenhouse effect which increases the rise in water level in ocean. Another
important feature of marine eco system is hydro thermal vents. A hydrothermal vent is a fissure in a planet's
surface from which geothermal heated water issues.
Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are
moving apart and ocean basins .Basically below our earth, the earth has three layers crust, mantle and core.
So as we go down deeper and deeper the earth’s temperature is very high because of the core so where ever
the tectonic plates movement is available, below the earth we have volcanoes, even in the oceans we have
volcanoes and dormant volcanoes so from there the water comes out through the vent so they are also
providing a very important role in our marine eco system. They form the base of the food chain, supporting
diverse organisms, including giant tube worms, clams, limpets and shrimp. So these kinds of palaces where the
hydro thermal vents are there we can find the organisms like worms and clams these are the living organisms
found near the hydro thermal vents.
Environmental problems concerning Marine ecosystems .So we have to discuss about this
topic.Overfishing and other destructive fishing practices that deplete our nation's ocean fish populations,
reduce the diversity of underwater life and lower the resilience of marine systems. See as I already told you
we have very huge coastline and it exhibits many geo morphological features .People are overusing our
coastal line and this has negative effect on our marine life. Nutrient pollution from farm and yard fertilizer
runoff, sewage, and other land-based sources that contributes to harmful blooms of algae, which in turn lead
to fish kills and swimmer illness, and ocean "dead zones “places devoid of marine life. The human activities,
the human development leads to lot of water pollution so even in the ocean, even after 100 meters also we
could find the ill effects of these pollutants. They kill lot of marine life, i.e. lots of fish are killed because of the
poisonous and toxic pollutants emitted by the industries as well as the algae. They cause illness in the
swimmers and they also produce dead zones. Coastal development that destroys ecologically sensitive areas
and critical habitat for valuable fish species, and also creates a network of paved surfaces that convey oil,
grease, and toxic pollutants into coastal waters. Invasive species taking root in marine waters, crowding out
native species, damaging ecosystems, destroying the food chain, diluting gene pools and more. Invasive
species are exotic species which are introduced by human beings, they also come along with other ships or
other travellers which eat up our indigenous species and they are also causing damage to our indigenous
species. Climate change, will profoundly impact coastal and marine ecosystems through rising sea levels,
damage to habitat-rich coral reefs from increased temperatures and threats to shell-forming creatures from
ocean acidification, which could have impacts throughout the entire marine food chain. Climate change plays
very important role because the temperature of the water changes most of the species which are living in the
marine water is into able to survive.
What is fresh water? Fresh water is mainly the water we get from the surface i.e. lakes, river, ponds, tanks
etc. as well as the ground water i.e. wells and tube wells. Freshwater ecosystems cover 0.80% of the Earth's
surface. Inhabit 0.009% of its total water. Freshwater ecosystems contain 41% of the world's known fish
species. Before going in detail about the fresh water I would like to some information. Mostly for our water we
depend on rivers and lakes .Almost all the cities are towns are depending on rivers and lakes which is situated
close to the towns .In our country we are blessed with a number of rivers but most of them are in the north
India. They are known as perennial rives. They always carry water throughout the year. They originate from
the Himalayas i.e. most of them are originating from the glaciers. They carry more water an d in summer they
flood because of the melting of glaciers. Whereas the south Indian rivers like Krishna , Godavari, Mahanadi etc
are seasonal .They originate from the western Ghats or from the central highlands. Now they are the major
source of our drinking water. Apart from that we have some lakes contain fresh water they also provide us
water. Rivers and lakes play a major role in our economy. I would like to say in what way they are useful? They
provide drinking water we are also able to take hydroelectricity from them , they provide shelter for various
animals and plants , they also serve as a recreational centre and good tourist spots They also balance the
temperature of the surrounding area ,regulating the water flow. During summer season they provide water
and during winter they stop flooding .They also enhance natural beauty they also balance the aquatic eco
system. So they are very much useful in our economy. Rivers play an important role even in our religious
activities. Almost all the religions in our country believe in holy bath or dipping in Holy River. There are
different types of freshwater eco systems. The major two types we are going to discuss. Lentic, this is the first
type of fresh water eco system. Lentic refers to standing or relatively still water. Lentic water ranges from
ponds to pools to wetlands. Lentic water has two regions, the pelagic open water zone and the benthic zone
or the lower surface of the water. In the upper surface of the water we have a number of fish and other
animals whereas in the lower surface of the water animals which are attached or plants which are attached to
the substrata are commonly found. Since lakes have deep bottom regions not exposed to sunlight these
systems have additional zone, the profundal these three areas can very different abiotic conditions and hence
host species that are specially adopted to live here. Species which are belonging to profundal zone cannot be
comfortable in the pelagic zone or the other zones
Lotic type of fresh water eco system mean s here the fresh water is flowing water. Lotic refers to flowing
water. Lotic water range from springs only. Rapidly-moving water, for example streams which are only a few
centimetres wide to major rivers on the earth. Environmental threats to the fresh water eco system, in what
way the freshwater eco system is disturbed? One is loss of water, then construction of dams, introduction of
new species etc.
Loss of water is nothing but overusing the river water or a lake water or even ground water. When ground
water is overused it leads to the intrusion of seawater into the ground water. Same way when the river water
is overused aquatic life which is found there will disappear. Then dams, construction of dams may be a
multipurpose project or it may be very helpful in so many ways but it also has got its negative impacts people
will lose their habitat , while constructing the dams people are displaced and most of the animals and the
plants which live in that particular area also will be displaced or they may be disappearing from that
environment .Then chemical pollution, then chemical pollution is a major cause of accumulation of pollutant
substance from the industries and other fields .When we talk about chemical pollution it is not only a single
reason , it is accompanied by so many other causes , the pollution can be from industries , the pollution can be
from agricultural field or from commercial areas or urban area etc. So all these things are things put together
becoming a great threat for the aquatic life .The introduced species, when a new species, i.e. Exotic species in
aquatic system for the economic purpose it is becoming a great threat to our indigenous species because the
guest will be dominating our host .That is how our indigenous species are affected. They may be eating our
indigenous species and our planktons which cause lack of food and other facilities for our indigenous species.
The major functions is that, aquatic eco systems help in recycling nutrients ,Purify water, attenuate floods,
recharge ground water, provide habitats for wildlife, generate electricity, source of food, important to the
tourism industry especially in coastal regions. This we have already discussed when we were talking about
lakes and rivers , I mentioned about the economical uses of lakes and rivers , same points only we are again
going to discuss .They recycle nutrients, It means they provide food i.e. fish becoming a major food all over the
country. They purify water because they accommodate lots of phytoplanktons and zooplanktons, the dirt is
eaten up by the fish and other aquatic animal’s. They also stop flooding. Especially lakes regulate the flow of
water during the flood. Then they are also recharging agents for ground water and they provide shelter for
number of animals and plants especially the migratory birds come from different countries take shelter here,
i.e. The birds which come from the polar region take shelter and they lay eggs, they incubate here example
Vedanthangal bird sanctuary then they generate electricity, the rivers and the waterfalls are only providing.
Then source of food, naturally the aquatic eco system we get good fish ,Then importance to tourism industry,
for that matter people come and see Mettur dam, Brindavan dam and different types of dams, they attract
tourists from different parts of the country and they also serve as a recreational centre. The great stress on
aquatic eco system is physical alteration, chemical alterations and biological alterations. Let us see what is
physical alterations. The change in the water temperature, the water temperature may increase or it may
decrease. The increased water temperature is due to the release of water from the industries with high
temperature, were water serves as a coolant. The decreased water temperature is due to the opening of
water from reservoirs’ and dams, so definitely they affect the aquatic life in the water body. Then excessive
use water, not the water flow, or flooding also affects the water flow. That too also causes a lot of damage the
aquatic eco system. Then light availability, in some places the phytoplankton or the weeds or the algal bloom
occupies the upper surface of the water, the penetration of light to the bottom of water is impossible. That
also affects the water quality and the aquatic eco system. Chemical alterations, loading rates of bio
stimulatory nutrients means the nitrates, phosphates, ammonia which increase the algal or the growth of
weeds in the water so that leads to eutrophication. And oxygen and presence of bacteria, this eutrophication
leads to increased bacterial population .Then toxins, accumulation of toxic substances in water bodies affects
our eco system. Biological alterations are nothing but the introduction of a new species to an existing aquatic
system which will be a threat for the indigenous species .In this entire lecture you must have understood the
basics of aquatic eco system ,What is aquatic eco system, food web, chain, how the coastal plains are useful ,
economically useful for the developing countries commercial value , then we have also understood the effects
of all these things and how they are affecting the eco system. As we all know our earth is surrounded by
water, 3/4th of earth is surrounded by water that means the aquatic ecosystem plays a very important role. So
protecting this eco system is very important and essential. Without that it is going to be very difficult. So we
need to protect this eco system.