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Ecosystem and its functions


To prepare for ENVIRONMENT for any competitive exam, aspirants have to know Ecosystem and its functions. Here we will study the Ecosystem and its functions in details. It gives an idea of all the important topics for the IAS Exam and the Governance syllabus (GS-II.). Ecosystem and its functions terms are important from Environmental perspectives in the UPSC exam. IAS aspirants should thoroughly understand their meaning and application, as questions can be asked from this static portion of the IAS Syllabus in both the UPSC Prelims and the UPSC Mains exams. Even these topics are also highly linked with current affairs. Almost every question asked from them is related to current events. So, apart from standard textbooks, you should rely on newspapers and news analyses as well for these sections.


Definition of an Ecosystem:

  • The term ecosystem was coined by Sir Arthur Tansley in 1935. The ecosystems are parts of nature where living organisms interact amongst themselves and with their physical environment.
  • An ecosystem is composed of a biotic community, integrated with its physical environment through the exchange of energy and recycling of the nutrients.
  • An ecosystem has two basic components:

Abiotic (non-living), and Biotic (living organisms).


Components of an Ecosystem:

  • Ecosystem
  • Biotic Components
  • Producers
  • Consumers
    1. Primary Consumer
    2. Secondary Consumer
    3. Tertiary Consumers
  • Decomposers
  • Abiotic Components Examples
    1. Air
    2. Water
    3. Wind
    4. Soil
    5. Temperature
    6. Rainfall




  • Abiotic components (or inorganic components) are the physical/chemical factors that act on the living organisms at some or the other part of their life.
  • They are also known as ecological factors.
  • Air, light, soil, nutrients, temperature and rainfall form the abiotic components of an ecosystem.
  • Abiotic factors vary from ecosystem to ecosystem.
  • In an aquatic ecosystem, the abiotic factors may include water pH, sunlight, turbidity, water depth, salinity, available nutrients and dissolved oxygen. Similarly, abiotic factors in terrestrial ecosystems can include soil, soil types, temperature, rain, altitude, wind, nutrients, sunlight etc.

Various important abiotic factors have been classified as follows:

  • Climatic factors: These include light, temperature, precipitation, atmospheric humidity and wind.
  • Topographic factors: These include altitude, surface slope and exposure, etc.
  • Edaphic factors: These include soil and substratum.
  • Air: Air is the invisible mixture of gases that surrounds the Earth.
  • Air contains important substances, such as oxygen and nitrogen that most species need to survive.
  • Nitrogen and oxygen make up about 99 percent of Earth’s air. People and other animals need oxygen to live.
  • Carbon dioxide, a gas that plants depend on, makes up less than .04 percent.
  • Humidity: Humidity is the amount of water vapor in the air. If there is a lot of water vapor in the air, the humidity will be high. The higher the humidity, the wetter it feels outside.
  • Relative humidity: It is the amount of water vapor actually in the air, expressed as a percentage of the maximum amount of water vapor the air can hold at the same temperature.
  • Weather and Climate: The term “weather” refers to the temporary conditions of the atmosphere, the layer of air that surrounds the Earth.
  • Weather doesn’t just stay in one place. It moves, and changes from hour to hour or day to day.
  • Over many years, certain conditions become familiar weather in an area.
  • The average weather in a specific region, as well as its variations and extremes over many years, is called climate.
  • Temperature: Temperature is the degree of hotness or coldness of an
  • Precipitation: Precipitation is any type of water that forms in the Earth’s atmosphere and then drops onto the surface of the Earth.
  • Water vapor, droplets of water suspended in the air, builds up in the Earth’s atmosphere. Water vapor in the atmosphere is visible as clouds and fog.
  • Water vapor collects with other materials, such as dust, in clouds.
  • Precipitation condenses, or forms, around these tiny pieces of material, called cloud condensation nuclei (CCN).
  • Clouds eventually get too full of water vapor, and the precipitation turns into a liquid (rain) or a solid (snow).
  • Altitude: Altitude, like elevation, is the distance above sea level. As altitude rises, air pressure drops.


  • The living components (or Organic Components) of an ecosystem are called the biotic components.
  • The biotic components of the ecosystem both live on and interact with the abiotic components. Some of the biotic factors include plants, animals, fungi and bacteria.
  • The biotic components can be further classified into three broad categories, based on the energy requirement source.


Producers (Autotrophs):

  • They are the producers of food for all other organisms of the ecosystem.
  • In terrestrial ecosystem, producers are basically green plants, while in aquatic ecosystem, producers are microscopic algae.
  • The total rate at which the radiant energy is stored by the process of photosynthesis in the green plants is called Gross Primary Production (GPP).
  • This is also known as total photosynthesis or total assimilation. From the gross primary productivity a part is utilized by the plants for its own metabolism.
  • The remaining amount is stored by the plant as Net Primary Production (NPP) which is available to consumers.


Types of producers:

There are two major types of producers:

  1. Phototrophs: They use the energy from the sun to convert carbon dioxide into carbohydrates.
  2. Chemotrophs: They obtain energy mainly from carbon dioxide and from other inorganic chemicals through a process called chemosynthesis.


Consumers (Heterotrophs):

  • They are not capable of producing their own food.
  • They are directly or indirectly dependent on producers for their food. Consumers are further categorized as herbivores, carnivores, omnivores.
  • The herbivores are the living organisms that feed on plants.
  • Carnivores eat other living organisms.
  • Omnivores are animals that can eat both plant and animal tissue.

Decomposers (Saprotrophs/Micro Consumers):

  • Decomposers are the living component of the ecosystem that breaks down waste material and dead organisms.
  • Examples of decomposers include earthworms, dung beetles and many species of fungi and bacteria.
  • They feed on the decaying organic matter and convert this matter into nitrogen and carbon dioxide.
  • The saprophytes play a vital role in recycling the nutrients so that the producers i.e. plants can use them once again.



Functions of an Ecosystem:

Ecosystem functions are natural processes or exchange of energy that take place in various plant and animal communities of different biomes of the world. The following are 3 broad functions of an ecosystem:

  1. Energy Flow
  2. Nutrient Cycling
  3. Ecological Succession.



  • Energy moves life. The cycle of energy is based on the flow of energy through different trophic levels in an ecosystem. Our ecosystem is maintained by cycling energy and nutrients obtained from different external sources.
  • At the first trophic level, primary producers use solar energy to produce organic material through photosynthesis.
  • The herbivores at the second trophic level, uses the plants as food which gives them energy. A large part of this energy is used up for the metabolic functions of these animals such as breathing, digesting food, supporting growth of tissues, maintaining blood circulation and body temperature.
  • The carnivores at the third trophic level, feeds on the herbivores and derive energy for their sustenance and growth. If large predators are present, they represent still higher trophic level and they feed on carnivores to get energy. Thus, the different plants and animal species are linked to one another through food chains.
  • Decomposers which include bacteria, fungi, molds, worms, and insects break down wastes and dead organisms, and return the nutrients to the soil, which is then taken up by the producers. Energy is not recycled during decomposition, but it is released.
  • The trophic level interaction involves three concepts namely:
    1. Food chain
    2. Food web
    3. Ecological Pyramids.

Previous year Question:

Q. In the context of ecosystem productivity, marine upwelling zones are important as they increase marine productivity by bringing the

1) Decomposer microorganisms to the surface.

2) Nutrients to the surface.

3) Bottom-dwelling organisms to the surface.

Which of the statements given above is/are correct?

  1. 1 and 2
  2. 2 only
  3. 2 and 3
  4. 3 only

Answer: B

Q. Which one of the following is the best description of the term ‘Ecosystem’?

  1. A community of organisms interacting with one another
  2. That part of the Earth which is inhabited by living organisms
  3. A community of organisms together with the environment in which they live
  4. The flora and fauna of a geographical area

Answer: C

Q.Which one of the following terms describes not only the physical space occupied by an organism, but also its functional role in the community of organisms?

  1. Ecotone
  2. Ecological niche
  3. Habitat
  4. Home range

Answer: B



  • The sun is the ultimate source of energy on earth. A food chain is an energy transfer link between living organisms.
  • Food chain starts with the producers, then moves to the consumers and finishes with the decomposers. Each step in the food chain is called trophic level.
  • Organisms in the ecosystem are related to each other through feeding mechanism or trophic levels. Small insects feed on green plants (Producers), and bigger animals feed on smaller ones and so on. This feeding relationship in an ecosystem is called a food chain.
  • During this process of transfer of energy some energy is lost into the system as heat energy and is not available to the next trophic level. Therefore, the number of steps are limited in a chain to 4 or 5.

Types of food chain:

In nature, the food chains have been distinguished into two types:

  • Grazing food chain: This food chain start with green plants at the base and the primary consumer is herbivore.


  • Grasses → Grasshopper → Frog → Snake → Eagle (on land);

  • Phytoplankton → zooplankton → fish → seal → great white shark (on water);

  • Detritus food chain: It starts from dead organic matter of decaying plants and animal bodies consumed by the micro-organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.



  • Litter → Earthworms → Snake → Eagle.
  • Mangroves leaves→ Detritus→ Micro organisms→ Crab→ Small fishes→ Large fishes.
  • Dead organic matter→ Worms→ Frog→ Snake→ Hawk.

Previous year Question:


Q. What would happen if phytoplankton of an ocean is completely destroyed for some reason?

1) The ocean as a carbon sink would be adversely affected.

2) The food chains in the ocean would be adversely affected.

3) The density of ocean water would drastically decrease.


Select the correct answer using the codes given below:

  1. 1 and 2 only
  2. 2 only
  3. 3 only
  4. 1, 2 and 3

Answer: A


Q. With reference to food chains in ecosystems, consider the following statements:

1) A food chain illustrates the order in which a chain of organisms feed upon each other

2) Food chains are found within the populations of a species

3) A food chain illustrates the number of each organism which are eaten by others


Which of the statements given above is/are correct?

  1. l only
  2. 1 and 2 only
  3. 1,2 and 3
  4. None

Answer: A


Q. With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms?

1) Virus

2) Fungi

3) Bacteria


Select the correct answer using the codes given below.

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Answer: B


Q. A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop.

The food chain is: Food crop-Rat- Snake- Hawk.

In this food chain, the highest concentration of the pesticide would accumulate in which one of the following?

  1. Food crop
  2. Rat
  3. Snake
  4. Hawk

Answer: D



  • Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight or energy. The rate of biomass production is called productivity.

It can be divided into gross primary productivity (GPP) and net primary productivity (NPP).

§ Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP

§ Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).


  • Secondary productivity is defined as the rate of formation of new organic matter by consumers.


Homeostasis in Ecosystem:

  • Homeostasis is the ability of ecological systems to maintain stable system properties despite perturbations.
  • Organisms try to maintain the constancy of its internal environment despite varying external environmental conditions that tend to upset their homeostasis in ecosystem.
  • Ecosystem homeostasis is all about equilibrium. When something is in equilibrium, it’s in balance. In the real world of ecosystems, nothing is ever perfectly balanced. So an ecosystem in equilibrium is said to be in a relatively stable state. This means that the populations of various animals in the ecosystem are generally staying within a similar range. Populations can go up and down in cycles, as long as there isn’t a general upwards or downwards trend.

Ecological Efficiency:

  • The amount of energy decreases at each subsequent trophic level because:

1. At each trophic a part of the available energy is lost in respiration or used up in metabolism.

2. A part of energy is lost at each transformation, i.e. when it moves from lower to higer trophic level as heat.

§ It is the ratio between the amount of energy acquired from the lower trophic level and the amount of energy transferred from higher trophic level is called ecological efficiency.

§ Lindman in 1942 defined these ecological efficiencies for the 1st time and proposed 10% rule

§ e.g. if autotrophs produce 100 cal, herbivores will be able to store 10 cal. and carnivores 1cal. However, there may be slight variations in different ecosystems and ecological efficiencies may range from 5 to 35%.


  • The word ‘web’ means network. Food web can be defined as ‘a network of interconnected food chains so as to form a number of feeding relationships amongst different organism of a biotic community.’
  • The same food resource may be a part of more than one chain. This is possible when the resource is at the lower tropic level. A food web comprises of all the food chains in a single ecosystem.
  • If any of the intermediate food chain is removed, the succeeding links of the chain will be affected largely.
  • The food web provides more than one alternative for food to most of the organisms in an ecosystem and therefore increases their chance of survival.


  • An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem.
  • The concept was first introduced by Charles Elton, the pioneer British Ecologist.
  • The basis of an ecological pyramid is biomass, energy, and number. Just as the name suggests, ecological pyramids are in the shape of a pyramid.
  • The ecological pyramid consists of a number of horizontal bars representing specific trophic levels which are arranged sequentially from producer to top level consumers.
  • The length of each horizontal bar depicts the total number of individuals at each trophic level in an ecosystem.
  • The bottom of an ecological pyramid is the broadest and is occupied by the producers. They form the first trophic level. Just as in a food chain, in the ecological pyramid also, primary consumers occupy the next level. This is because primary consumers consume producers. Similarly, secondary consumers occupy the third level. And then the tertiary consumers that occupy the next level and so on.
  • The ecological pyramids are of three types:
    1. Pyramid of numbers
    2. Pyramid of biomass
    3. Pyramid of energy.

  1. Pyramid of Numbers:
  • A pyramid of numbers shows the relative number of organisms at each stage of a food chain. Pyramids of numbers can be either upright or inverted, depending on the ecosystem.
  • This type of pyramid can be convenient, as counting is often a simple task and can be done over the years to observe the changes in a particular ecosystem. However, some types of organisms are difficult to count, especially when it comes to some juvenile forms.


a. Pyramid of Numbers (Upright):

  • The typical grassland during the summer season has an upright shape since it has a base of many plants, with the numbers of organisms decreasing at each trophic level.
  • However, during the summer in a temperate forest, the base of the pyramid consists of few trees compared with the number of primary consumers, mostly insects.
  • As trees are large, they have great photosynthetic capability and dominate other plants in this ecosystem to obtain sunlight. Even in smaller numbers, primary producers in forests are still capable of supporting other trophic levels.


v Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.

b. Pyramid of Numbers (Inverted):

  • A pyramid of numbers does not always have a regular pyramid shape because it does not take into account the biomass of the organisms. An inverted pyramid of numbers can be found in an ecosystem where the community contains a few producers with a very large biomass that support a larger number of smaller consumers.
  • An inverted pyramid of numbers can also be found in an ecosystem where the community contains parasites. There can be many more parasites than the hosts they feed on because each individual parasite has a very small biomass.
  • In these food chains, there’s normally one producer supporting numerous parasites. The parasites, in turn, support more hyper-parasites. In short, in this pyramid, number of individuals at each level is increased from lower level to higher level.


c. Pyramid of Biomass:

  • The pyramid of biomass indicates the total mass of organisms at each trophic level. Usually, this type of pyramid is largest at the bottom and gets smaller going up, but exceptions do exist.
  • The biomass of one trophic level is calculated by multiplying the number of individuals in the trophic level by the average mass of one individual in a particular area.
  • This type of ecological pyramid solves some problems of the pyramid of numbers, as it shows a more accurate representation of the amount of energy contained in each trophic level, but it has its own limitations.
  • For example, the time of year when the data are gathered is very important, since different species have different breeding seasons. Also, since it’s usually impossible to measure the mass of every single organism, only a sample is taken, possibly leading to inaccuracies.


d. Pyramid of Biomass – Upright:

  • For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level perched on top.
  • The biomass of producers (autotrophs) is at the maximum. The biomass of next trophic level i.e. primary consumers is less than the producers. The biomass of next higher trophic level i.e. secondary consumers is less than the primary consumers. The top, high trophic level has very less amount of biomass.


e. Pyramid of Biomass – Inverted:

  • The pyramids of biomass are almost always upright in shape, as biomass diminishes along food chains as CO2 and waste is released. An exception to this rule is found in marine ecosystems, where zooplanktons have a large total biomass than phytoplankton (Inverted).
  • Here, the pyramid of biomass has a small base, with the consumer biomass at any instant exceeding the producer biomass and the pyramid assumes an inverted shape.
  • This is because, phytoplankton replace their biomass at such a rapid rate and so can support a larger biomass of zooplankton.


f. Pyramid of Energy:

  • A pyramid of energy shows the amount of energy trapped per area in a given time period at each stage of a food chain. These pyramids are always upright in shape, as energy is lost along food chains (either used in respiration or lost as heat).
  • Each level in the pyramid will be roughly one tenth the size of the preceding level as energy transformations are ~10% efficient.
  • An energy pyramid reflects the “Law of Thermodynamics”, with conversion of solar energy to chemical energy and heat energy at each tropic level and with loss of energy being depicted at each transfer to another trophic level.


  • Pollutants, especially non-degradable ones move through the various trophic levels in an ecosystem.
  • Non-degradable pollutants mean materials, which cannot be metabolized by the living organisms. Example: Chlorinated Hydrocarbons.
  • Movement of these non-degradable pollutants involves two main processes:
    1. Bioaccumulation
    2. Bio-magnification.

Bioaccumulation and Bio-magnification:

  • Bioaccumulation refers to how pollutants (metals) enter a food chain and relates to the accumulation of contaminants, in biological tissues by aquatic organisms, from sources such as water, food, and particles of suspended sediment.
  • Bioaccumulation is the process by which toxins enter the food web by building up in individual organisms, while biomagnification is the process by which toxins are passed from one trophic level to the next (and thereby increase in concentration) within a food web.
  • Thus in bio-magnification, there is an increase in concentration of a pollutant from one link in a food chain to another.
  • For example, pesticides such as DDT, is non biodegradable. It gets incorporated in the food chain and gets deposited the tissues of the organisms.
  • When DDT enters aquatic bodies, it gets build up in the body of fishes and this is known as When fishes are eaten by animals of higher trophic levels, concentration of DDT is increased at each successive trophic level and this is known as bio-magnification.


Effects of biomagnification:

  1. High concentrations of DDT in some bird species caused failure of eggs by thinning the shells.
  2. PCBs can affect the immune system, fertility, child development and possibly increase the risk of certain cancers.
  3. Mercury poisoning interferes with the nervous system development in fetuses and young children.


Q. With reference to food chains in ecosystems, consider the following statements:

1) A food chain illustrates the order in which a chain of organisms feed upon each other

2) Food chains are found within the populations of a species

3) A food chain illustrates the number of each organism which are eaten by others

Which of the statements given above is/are correct?

  1. l only
  2. 1 and 2 only
  3. 1,2 and 3
  4. None

Answer: A


Q. With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms?

1) Virus

2) Fungi

3) Bacteria

Select the correct answer using the codes given below.

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Answer: B


Q. A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is: Food crop-Rat- Snake- Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following?

  1. Food crop
  2. Rat
  3. Snake
  4. Hawk

Answer: D


  • All elements in the earth are recycled time and again. The major elements such as oxygen, carbon, nitrogen, phosphorous, and sulphur are essential ingredients that make up organisms.
  • (“Bio” – living, “Geo” – rock, “Chemical” – element). The cycling of the nutrients in the biosphere is called biogeochemical or nutrient cycle. It involves movement of nutrient elements through the various components of an ecosystem.
  • As an element moves through this cycle, it often forms compounds with other elements as a result of metabolic processes in living tissues and of natural reactions in the atmosphere, hydrosphere, or lithosphere.
  • Such cyclic exchange of material between the living organisms and their non-living environment is called Biogeochemical Cycle. Thus the nutrients are never lost from the ecosystems.
  • Following are some important biogeochemical cycles:


Carbon Cycle:

  • Carbon is the second most abundant element in organisms, by mass. Carbon enters into the living world in the form of carbon dioxide through the process of photosynthesis as carbohydrates.
  • During photosynthesis, the carbon is converted into organic compounds such as glucose, which are stored within the bodies of these organisms. This carbon can be stored for many hundreds of years within the bodies of plants in areas such as tropical rainforests.
  • When the organic compounds are consumed by heterotrophs, they are passed through the food web, where they are broken down into useful substances using cellular respiration. Cellular respiration produces CO2, which is released back into the atmosphere.
  • The carbon is finally returned to the surrounding medium by the process of respiration or decomposition of plants and animals by the decomposers. Carbon is also recycled during the burning of fossil fuels.
  • The ocean is the second largest carbon sink. As well as dissolved inorganic carbon which is stored at depth, the surface layer holds large amounts of dissolved carbon that is rapidly exchanged with the atmosphere.
  • Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world. The recent increase in amounts of greenhouse gases such as carbon dioxide is having a significant impact on the warming of our planet.


Water Cycle:

  • The biogeochemical cycle of water, or the hydrological cycle describes the way that water (Hydrogen Dioxide or H2O) is circulated and recycled throughout Earth’s systems.
  • The hydrologic cycle is the continuous circulation of water in the earth-atmosphere system which is driven by solar energy.
  • All living organisms, without exception, need water to survive and grow, making it one of the most important substances on Earth.
  • On a geographical level, the biogeochemical cycle of water is responsible for weather patterns.
  • As water in its various forms (vapor, liquid and ice) interacts with its surroundings and it alters the temperature and pressure of the atmosphere, creating wind, rain and currents, and is responsible for changing the structure of earth and rock through weathering.
  • Although there is no real beginning to the water cycle, 97% of the world’s water is stored within the oceans.
  • Of the ocean water, a very small proportion becomes frozen at it reaches the poles, and is stored as ice within glaciers.
  • Some of the surface water is heated by the sun, and evaporation takes place. In this process, the liquid water is converted into water vapor and is taken up in to the atmosphere. As the water rises, it cools and condensation occurs. This results in the water being stored within the atmosphere in the form of clouds.
  • As the clouds are moved around the earth’s atmosphere they collide and grow. Eventually the water droplets grow large enough so that they are heavy enough to fall as precipitation (rain) or as snow, depending on the environmental conditions.
  • Most of the snow that falls is either stored as ice caps, or melts to form streams and rivers.
  • Some of the water that makes it to the ground is affected by gravity and flows back in to the ocean via surface runoff.


Nitrogen Cycle:

  • Most of the nitrogen on Earth is in the atmosphere. Nitrogen is present in the atmosphere in an elemental form so, it cannot be utilized by living organisms.
  • Approximately 80% of the molecules in Earth’s atmosphere are made of two nitrogen atoms bonded together (N2). All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a form that they can use.
  • Nitrogen needs to be ‘fixed’, that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants.
  • Nitrogen fixation on earth is made in three different ways:
  • By microorganisms (bacteria and blue-green algae)
  • By industrial processes (fertilizer factories)
  • By atmospheric phenomenon (thunder and lightning).
  • Plants get the nitrogen they need from the soils or water in which they live mostly in the form of inorganic nitrate (NO3-). Nitrogen is a limiting factor for plant growth.
  • Animals get the nitrogen they need by consuming plants or other animals that contain organic molecules composed partially of nitrogen.
  • Cyanobacteria, Rhizobium and Azotobacter are some examples. Cyanobacteria play a role in nitrogen fixation in aquatic ecosystems. The other two fix nitrogen in a terrestrial ecosystem.
  • When organisms die, their bodies decompose bringing the nitrogen into soil on land or into the oceans. As dead plants and animals decompose, nitrogen is converted into inorganic forms such as ammonium salts (NH4+) by a process called mineralization.
  • The ammonium salts are absorbed onto clay in the soil and then chemically altered by bacteria into nitrite (NO2-) and then nitrate (NO3-).
  • Nitrate is the form commonly used by plants. It is easily dissolved in water and leached from the soil system. Dissolved nitrate can be returned to the atmosphere by certain bacteria through a process called de-nitrification.


Phosphorous Cycle:

  • Phosphorus is an essential nutrient for living processes. It is a major component of nucleic acids and phospholipids, and, as calcium phosphate, it makes up the supportive components of our Phosphorus is often the limiting nutrient (necessary for growth) in aquatic, particularly freshwater, ecosystems.
  • Phosphorus occurs in nature as the phosphate ion (PO43-) and enters the cycle from erosion and mining activities.
  • The phosphate rock has its origins in the ocean. Phosphate-containing ocean sediments form primarily from the bodies of ocean organisms and from their excretions.
  • However, volcanic ash, aerosols, and mineral dust may also be significant phosphate sources. This sediment then is moved to land over geologic time by the uplifting of Earth’s surface.
  • Excess phosphorus and nitrogen that enter the ecosystems from fertilizer runoff and from sewage cause excessive growth of algae. The subsequent death and decay of these organisms depletes dissolved oxygen, which leads to the death of aquatic organisms such as shellfish and fish. This process is responsible for dead zones in lakes.
  • A dead zone is an area in lakes and oceans near the mouths of rivers where large areas are periodically depleted of their normal flora and fauna. These zones are caused by eutrophication coupled with other factors including oil spills, dumping toxic chemicals, and other human activities.


Sulphur Cycle:

  • Sulphur is one of the components that make up proteins and vitamins. Proteins consist of amino acids that contain sulphur atoms.
  • Sulphur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulphur.
  • Plants absorb sulphur when it is dissolved in water. Animals consume these plants, so that they take up enough sulphur to maintain their health.
  • Most of the earth’s sulphur is tied up in rocks and salts or buried deep in the ocean in oceanic sediments.
  • Sulphur can also be found in the atmosphere. It enters the atmosphere through both natural and human sources. Atmospheric sulphur is found in the form of sulfur dioxide (SO2), which enters the atmosphere in three ways: first, from the decomposition of organic molecules; second, from volcanic activity and geothermal vents; and, third, from the burning of fossil fuels by humans.
  • On land, sulphur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents.



Q.Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

1) Volcanic action

2) Respiration

3) Photosynthesis

4) Decay of organic matter

Select the correct answer using the code given below.

  1. 1 and 3 only
  2. 2 only
  3. 1, 2 and 4 only
  4. 1, 2, 3 and 4

Answer: C


Q. Human activities in the recent past have caused the increased concentration of carbon dioxide in the atmosphere, but a lot of it does not remain in the lower atmosphere because of

1) Its escape into the outer stratosphere.

2) The photosynthesis by phytoplankton in the oceans

3) The trapping of air in the polar ice caps.

Which of the statements given above is/ are correct?

  1. 1 and 2
  2. 2 only
  3. 2 and 3
  4. 3 only

Answer: B



  • Succession is a series of progressive changes in the composition of an ecological community over time. Ecological succession is the process by which the structure of a biological community evolves over time.
  • The species living in a particular area gradually change over time as does the physical and chemical environment within that area.
  • Succession takes place because, organisms interact with and affect the environment within an area, through the processes of living, growing and reproducing, gradually changing it.
  • Each species is adapted to thrive and compete best against other species under a very specific set of environmental conditions. If these conditions change, then the existing species will be outcompeted by a different set of species which are better adapted to the new conditions.
  • Change in the plant species present in an area is one of the driving forces behind changes in animal species. This is because each plant species will have associated animal species which feed on it. The presence of these herbivore species will then dictate which particular carnivores are present.
  • The structure or ‘architecture’ of the plant communities will also influence the animal species which can live in the microhabitats provided by the plants.
  • Changes in plant species also alter the fungal species present because many fungi are associated with particular plants.
  • Succession is directional. Different stages in a particular habitat succession can usually be accurately predicted. These stages, characterised by the presence of different communities, are known as ‘seres’.
  • Communities change gradually from one sere to another. The seres are not totally distinct from each other and one will tend to merge gradually into another, finally ending up with a ‘climax’ community.
  • Succession will not go any further than the climax community. This is the final stage.
  • This does not however, imply that there will be no further change. When large organisms in the climax community, such as trees, die and fall down, then new openings are created in which secondary succession will occur.
  • Many thousands of different species might be involved in the community changes taking place over the course of a succession. For example, in the succession from freshwater to climax woodland.
  • The actual species involved in a succession in a particular area are controlled by such factors as the geology and history of the area, the climate, microclimate, weather, soil type and other environmental factors.
  • Succession occurs on many different timescales, ranging from a few days to hundreds of years.
  • It may take hundreds of years for a climax woodland to develop, while the succession of invertebrates and fungi within a single cow pat (cow dung), may be over within as little as 3 months.
  • By this time, the dung has been transformed into humus and nutrients and has been recycled back into the soil. The holes clearly visible in the cow pat (right) have been made by the animals which have colonized it.
  • Two different types of succession—primary and secondary—have been distinguished:


Primary Succession:

  • Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before.
  • Examples of such habitats would include newly exposed or deposited surfaces, such as landslips, volcanic lava and debris, elevated sand banks and dunes, quarried rock faces.
  • A number of seral stages will take place in which an initial or ‘pioneer’ community will gradually develop through a number of different communities into a ‘climax’ community, which is the final stage. If this primary ecosystem is disturbed and wiped out, secondary succession can take place.


Secondary Succession:

  • Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. Examples include areas which have been cleared of existing vegetation (such as after tree-felling in a woodland) and destructive events such as fires (For example: Australian fires most recently).
  • Secondary succession is usually much quicker than primary succession for the following reasons:
    • There is already an existing seed bank of suitable plants in the soil.
    • Root systems undisturbed in the soil, stumps and other plant parts from previously existing plants can rapidly regenerate.
    • The fertility and structure of the soil has also already been substantially modified by previous organisms to make it more suitable for growth and colonization.


Q. In the grasslands, trees do not replace the grasses as a part of an ecological succession because of

  1. Insects and fungi
  2. Limited sunlight and paucity of nutrients
  3. Water limits and fire
  4. None of the above

Answer: C


Q. Lichens, which are capable of initiating ecological succession even on a bare rock, are actually a symbiotic association of

  1. Algae and bacteria
  2. Algae and fungi
  3. Bacteria and fungi
  4. Fungi and mosses

Answer: B


Types of Ecosystem:

An ecosystem is defined as a functional unit wherein all living organisms interact with their surroundings and one another to sustain in the environment. In a broad sense, an ecosystem can be categorized as a land/terrestrial ecosystem or a water/aquatic system.

Difference between Terrestrial and aquatic ecosystem:

  • Terrestrial ecosystems are distinguished from aquatic ecosystems by the lower availability of water.
  • Terrestrial ecosystems are characterized by greater temperature fluctuations on both a diurnal and seasonal basis than occur in aquatic ecosystems in similar climates, because water has a high specific heat, a high heat of vaporization and a high heat of fusion compared with the atmosphere.
  • The availability of light is greater in terrestrial ecosystems than in aquatic ecosystems because the atmosphere is more transparent than water.
  • Gases are more available in terrestrial ecosystems than in aquatic ecosystems. Those gases include carbon dioxide that serves as a substrate for photosynthesis, oxygen that serves as a substrate in aerobic respiration and nitrogen that serves as a substrate for nitrogen fixation.


Terrestrial Ecosystem:
  • A terrestrial ecosystem is a land-based community of organisms and the interactions of biotic and abiotic components in a given area.
  • Terrestrial ecosystems are the third largest global carbon pool only after the ocean and geological carbon pool.
  • Terrestrial ecosystems are characterized by low water availability and greater temperature fluctuations. There is greater availability of gases and light in terrestrial ecosystems as compared to aquatic ecosystem.
  • Examples of terrestrial ecosystems include the tundra, taigas, temperate deciduous forests, tropical rainforests, grasslands, and deserts. The type of terrestrial ecosystem found in a particular place is dependent on the temperature range, the average amount of precipitation received, the soil type, and amount of light it receives.



  • Taiga, also called boreal forest, composed primarily of cone-bearing needle-leaved or scale-leaved evergreen trees, found in northern circumpolar forested regions characterized by long winters and moderate to high annual precipitation.
  • The taiga, “land of the little sticks” in Russia, takes its name from the collective term for the northern forests of Russia, especially Siberia.
  • Taigas are cold-climate forests found in the northern latitudes.
  • Taigas are the world’s largest terrestrial ecosystem and account for about 29% of the Earth’s forests.
  • The largest taiga ecosystems are found in Canada and Russia.
  • Taigas are known for their sub-arctic climate with extremely cold winters and mild summers.
  • They primarily consist of coniferous trees, such as pines, although there are some other deciduous trees, such as spruce and elm that have adapted to live in these areas that receive little direct sunlight for much of the year.
  • Taigas are home to large herbivores, such as moose, elk, and bison, as well as omnivores, such as bears.



  • Soil beneath the taiga often contains permafrost—a layer of permanently frozen soil.
  • In other areas are a layer of bedrock lies just beneath the soil. Both permafrost and rock prevent water from draining from the top layers of soil. This creates shallow bogs known as
  • Muskegs can look like solid ground, because they are covered with moss, short grasses, and sometimes even trees. However, the ground is actually wet and spongy.


Plants and Fungi:

  • Taigas are thick forests. Coniferous trees, such as spruce, pine, and fir, are common.
  • Coniferous trees have needles instead of broad leaves, and their seeds grow inside protective, woody cones. While deciduous trees of temperate forests lose their leaves in winter, conifers never lose their needles. For this reason, conifers are also called “evergreens.”
  • Conifers have adapted to survive the long, cold winters and short summers of the taiga. Their needles contain very little sap, which helps prevent freezing. Their dark colour and triangle-shaped sides help them catch and absorb as much of the sun’s light as possible.
  • In the taiga, tree growth is thickest beside muskegs and lakes formed by glaciers.
  • Taigas have few native plants besides conifers. The soil of the taiga has few nutrients. It can also freeze, making it difficult for many plants to take root. The larch is one of the only deciduous trees able to survive in the freezing northern taiga. Instead of shrubs and flowers, mosses, lichens, and mushrooms cover the floor of a taiga. These organisms can grow directly on the ground, or have very shallow roots. They can survive in the cold, and with little water or sunlight.


Animals of the Taiga:

  • Many kinds of animals live in the taiga. All animals have to be well-adapted to the cold. Birds native to the taiga usually migrate south during the freezing winter Small animals, mostly rodents, live close to the floor. Many birds of prey, such as owls and eagles, hunt these animals from the trees of the taiga.
  • Moose, the largest type of deer in the world, is able to live in the cold taiga. Like all deer, moose are herbivores. They favor the aquatic plants growing on the taiga’s bogs and streams.
  • Few large carnivorous animals live in the taiga. Bears and lynx are fairly common. The largest cat in the world, Siberian tiger, is a native taiga species.
  • Siberian tigers live in a small part of eastern Siberia. They hunt moose and wild boars.


Threats to Taigas:

  • Taiga ecosystems are threatened by direct human activity and climate change. Animals of the taiga, such as foxes or bears, have always been hunted. Their warm fur and tough skin, turned into leather, have helped people survive in harsh climates for thousands of years.
  • Though the most serious threat to taigas does not come from hunting activity, Civilization is dependent on sturdy buildings for homes, industry, and schools. The trees of the taiga are cut down for lumber projects, as well as paper, cardboard, and other supplies. The export of wood and paper products is one of the most economically important industries in Canada, for instance.
  • Clear cutting is the most popular type of logging in taigas. Clear cutting involves cutting down all the trees in a designated area. This destroys habitats for many organisms that live in and around the trees, and makes it difficult for new trees to grow. Clear cutting also increases the risk of erosion and flooding in the taiga. Without a root system to anchor it, a taiga’s soil can be blown away by wind or worn away by rain or snow. This exposes the bedrock and permafrost beneath the taiga, which does not support many forms of life.
  • Climate change puts taigas in danger in different ways. Warming climate contributes to a partial thawing of the permafrost. Since this water has no place to drain, more area of the taiga is taken over by muskegs. Few trees take root.
  • Warming temperature also changes animal habitats. It pushes native species out and attracts non-native species. Animals such as the Siberian tiger are not adapted to warm weather. Its coat is too heavy, and it stores too much body fat to thrive in a temperate habitat.
  • Non-native insects such as the bark beetle can infest trees such as spruce.



  • Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy, and rainfall is scant.
  • Arctic’s permafrost, the literal foundation for much of the region’s unique ecosystem, is deteriorating with the warmer global climate.
  • Permafrost is a layer of frozen soil and dead plants that extends some 1,476 feet (450 meters) below the surface. In much of the Arctic, it is frozen year-round.
  • In the southern regions of the Arctic, the surface layer above the permafrost melts during the summer, and this forms bogs and shallow lakes that invite an explosion of animal life. Insects swarm around the bogs, and millions of migrating birds come to feed on them.
  • With global warming, the fall freeze comes later—in some places recently, not at all—and more of the permafrost is melting in the southern Arctic. Shrubs and spruce that previously couldn’t take root on the permafrost now dot the landscape, potentially altering the habitat of the native animals.
  • Tundra lands are covered with snow for much of the year, but summer brings bursts of wildflowers.

Plants and animals in tundras:

  • Mountain goats, sheep, marmots, and birds live in mountain/alpine tundra and feed on the low-lying plants and insects. Hardy flora like cushion plants survive in the mountain zones by growing in rock depressions, where it is warmer and they are sheltered from the wind.


  • The Arctic tundra, where the average temperature is -30 to 20 degrees Fahrenheit (-34 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese, and musk oxen. The summer growing season is just 50 to 60 days, when the sun shines up to 24 hours a day.
  • The relatively few species of plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.

Climate change impact on tundras:

  • The Arctic tundra is changing dramatically due to global warming, a term that falls within a wider range of trends scientists now prefer to call climate change. The impacts in this region are broad and somewhat unpredictable.
  • Animals that are typically found further south, like the red fox, are moving north onto the tundra. This means the red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.


Forest Ecosystem:

  • It is a functional unit or a system which comprises of soil, trees, insects, animals, birds, and man as its interacting units.
  • Forest ecosystems and the communities and industries that depend on them are vulnerable to changes in the climate worldwide.
  • A forest is a large and complex ecosystem and hence has greater species diversity. Also, it is much more stable and resistant to the detrimental changes as compared to the small ecosystems such as wetlands and grasslands.
  • A forest ecosystem, similar to any other ecosystem, also comprises of abiotic and biotic components.
  • Abiotic components refer to inorganic materials like air, water, and soil. Biotic components include producers, consumers, and decomposers. These components interact with each other in an ecosystem and thus, this interaction among them makes it self-sustainable.
  • Forest ecosystem is a large area of land that’s covered in trees and other woody plants and filled with living animals.


Structural Features of the Forest Ecosystem:

  • The two main structural features of a forest ecosystem are:
  • Species composition: It refers to the identification and enumeration of the plant and animal species of a forest ecosystem.
  • Stratification: It refers to the vertical distribution of different species which occupy different levels in the forest ecosystem. Every organism occupies a place in an ecosystem on the basis of source of nutrition. For example, in a forest ecosystem, trees occupy the top level, shrubs occupy the second and the herbs and grasses occupy the bottom level.


  • Deforestation is the permanent removal of trees to make use the land for agriculture croplands or grazing, or using the timber for fuel, urbanization, or mining activities.
  • Forests cover more than 30% of the Earth’s land surface, according to the World Wildlife Fund. These forested areas can provide food, medicine and fuel for more than a billion people. Worldwide, forests provide 13.4 million people with jobs in the forest sector, and another 41 million people have jobs related to forests.

Causes of deforestation:

  • Multiple factors, either of human or natural origin, cause deforestation.
  • Natural factors include natural forest fires or parasite-caused diseases which can result in deforestation.
  • Human activities are among the main causes of global deforestation.
  • According to the Food and Agriculture Organization (FAO), the expansion of agriculture caused nearly 80% of global deforestation, with the construction of infrastructures such as roads or dams, together with mining activities and urbanization, making up the remaining causes of deforestation.

The Effects of Deforestation on Biodiversity:

  • Deforestation has many consequences for natural ecosystems and it poses serious problems to the resilience of the planet.
  • The most known consequence of deforestation is its threat to biodiversity.
  • By destroying the forests, human activities are putting entire ecosystems in danger, creating natural imbalances, and putting Life at threat.
  • Healthy forests support the livelihoods of 1.6 billion people globally. There are many people depending on forests for survival and using them to hunt and gather raw products for their small-scale agriculture processes. The deforestation affects the livelihood of many.
  • Today, 52% of all the land used for food production is moderately or severely impacted by soil erosion. In the long term, the lack of healthy, nutritious soil can lead to low yields and food insecurity. Deforestation weakens and degrades the soil.
  • Deforestation also has a very strong contribution to climate change. Trees absorb and store CO2 throughout their lives. Firstly, taking down trees means they’ll release back into the atmosphere the CO2 they were keeping. Secondly, fewer trees available meant reducing the planet’s overall ability to capture and store CO2. Both these effects negatively contribute to the greenhouse effect and to climate change.

How can we stop deforestation?

  • According to OECD, the human population is expected to continue to increase and reach over 9 billion people by 2050. At the current rate of consumption, and with more people inhabiting Earth, the need for more space to grow food and extract natural resources is only likely to increase.
  • According to the WWF, livestock-caused deforestation is responsible for the discharge of 4% of current global emissions of carbon to the atmosphere every year. That’s why the 2018 IPCC report said that, reducing meat consumption by 90% is the single biggest way to reduce global warming.
  • Educating local communities and tourists about the need to protect forests and develop and enroll in ecotourism activities.
  • Protecting forested areas by creating laws and policies that ensure forests are kept protected and restored and betting on land practices such as wildfire corridors.
  • Everyone can do their part to curb deforestation. We can buy certified wood products, go paperless whenever possible, limit our consumption of products that use palm oil.
  • Forests can also be restored, through replanting trees in cleared areas or simply allowing the forest ecosystem to regenerate over time.


Grassland Ecosystem:

  • Grasslands are areas where the vegetation is dominated by grasses.
  • Grasslands grow in the area where there is less moisture in the soil. Furthermore, the grassland ecosystem contains plants that do not grow much. They remain shorter in height as they do not receive much rainfall.
  • However, they can survive in areas like these as their roots are deep within the soil. As a result, they can receive moisture from the soil. The vegetation of the grassland ecosystem depends on the amount of precipitation it is receiving.
  • Moreover, the different types of grasslands have different types of animal species. These species adapted the environment of the climate they are living in.
  • Grasslands occur naturally on all continents except Antarctica and are found in most eco-regions of the Earth.
  • Grasslands grow in the area where there is less moisture in the soil. Furthermore, the grassland ecosystem contains plants that do not grow much. They remain shorter in height as they do not receive much rainfall.
  • Grasslands across the globe (have many names)—
  • Prairies in North America, Asian steppes,
  • Savannah’s and veldts in Africa, Australian rangelands, and pampas,
  • llanos and Corrodes in South America.

Types of Grassland Ecosystem:

  • Tropical Grasslands: Grasslands near the equator produce plants that can withstand a hot climate through most of the year as well as drought and fires. The savannas of Africa are probably the best known but tropical grasslands are also located in South America, India and Australia. There are llanos in Colombia and Venezuela, campos of the Brazilian highlands, pantanals of Upper Paraguay, plains in Australia and the Deccan Plateau of India.
  • Temperate Grasslands: Temperate grasslands are areas of open grassy plains that are sparsely populated with trees. Temperate grasslands receive low to moderate precipitation on average per year (20-35 inches). Most of this precipitation is in the form of snow in temperate grasslands of the northern hemisphere. Examples of temperate grasslands include Eurasian steppes, North American prairies, and Argentine pampas.
  • Montane Grasslands: This major habitat type includes high elevation (montane and alpine) grasslands and shrublands, including the puna and paramo in South America, subalpine heath in New Guinea and East Africa, steppes of the Tibetan plateaus, as well as other similar subalpine habitats around the world.
  • Desert Grassland: Grassland is a semiarid biome characterized by warm, humid summers with moderate rain and cold, dry winters. Grass is the dominant life form. Desert grasslands generally occur in valleys and basins at the southern end of North America’s Basin and Range Province. Due to the variable topography of the Basin and Range Province, desert grasslands are distributed in discontinuous patches, forming transitional areas with desert vegetation at lower elevations and woodlands or chaparral at higher elevations.



  • Desert, any large, extremely dry area of land with sparse vegetation. It is one of Earth’s major types of ecosystems, supporting a community of distinctive plants and animals specially adapted to the harsh environment.
  • Deserts cover more than one-fifth of the Earth’s land area, and they are found on every continent. A place that receives less than 10 inches (25 centimeters) of rain per year is considered a desert.
  • Deserts are part of a wider class of regions called drylands. These areas exist under a “moisture deficit,” which means they can frequently lose more moisture through evaporation than they receive from annual precipitation.
  • Desert environments are so dry that they support only extremely sparse vegetation; trees are usually absent and, under normal climatic conditions, shrubs or herbaceous plants provide only very incomplete ground cover.
  • The largest hot desert in the world, northern Africa’s Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day. But some deserts are always cold, like the Gobi desert in Asia and the polar deserts of the Antarctic and Arctic, which are the world’s largest. Others are mountainous.
  • Only about 20 percent of deserts are covered by sand.
  • Some of the world’s semi-arid regions are turning into desert at an alarming rate. This process is known as desertification. It is not caused by drought, but usually arises from deforestation and the demands of human populations that settle on the semi-arid lands.


  • An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems.
  • In general, there are two types of aquatic ecosystem, namely marine ecosystems and fresh water ecosystems.
  • Aquatic ecosystem includes freshwater habitats such as lakes, ponds, rivers, oceans and streams, wetlands, swamp, etc. Whereas marine habitats include oceans, intertidal zone, coral reefs, seabed and so on. Furthermore, the aquatic ecosystem is the habitat for water-dependent species like animals, plants, and microbes.


Types of Aquatic Ecosystem:

Freshwater Ecosystem:

These cover only a small portion of the earth which is nearly 0.8 percent. Freshwater means lakes, ponds, rivers and streams, wetlands, swamp, bog, and temporary pools. The salt content of fresh bodies is very low, always less than 5 ppt (parts per thousand).

  • Lotic Ecosystems:
Photic Zone: This zone is the upper layer of the aquatic ecosystems, up to which light penetrates and within which photosynthetic activity is confined.

Aphotic Zone: The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted forms the aphotic zone. Only respiration activity takes place.

These mainly refer to the rapidly flowing waters that move in a unidirectional way including the rivers and streams. Furthermore, these environments have numerous species such as beetles, mayflies, stoneflies and several species of fishes including trout, eel, minnow, etc.

  • Lentic Ecosystems:

They include all standing water habitats. Moreover, lakes and ponds are the primary examples of the Lentic Ecosystem. Also, these ecosystems contain algae, crabs, shrimps, and amphibians such as frogs and salamanders.

  • Wetlands:

Wetlands are marshy areas and are sometimes covered in water which has a wide variety of plants and animals. Swamps, marshes, bogs, black spruce, and water lilies are the main examples in the plant species. The animal life of this ecosystem consists of dragonflies, damselflies, and various birds and fishes.


Marine Aquatic Ecosystem:

The marine ecosystem covers the largest surface on the earth. Two-thirds of the earth is covered by water which constitutes oceans, seas, intertidal zone, reefs, seabed, etc. They are the water bodies containing salt concentration equal to or above that of sea water (i.e.35 ppt or above).

  • Ocean Ecosystems:

Our earth is having five major oceans. Moreover, these oceans are like a home to more than five lakhs aquatic species. Some species of this ecosystem include shellfish, Shark, Tube Worms, Crab Small, and large ocean fishes.

  • Coastal Systems:

These are the open systems of land and water, joined together to form the coastal ecosystems. A wide variety of species of aquatic plants and algae live at the bottom of it. The diverse fauna consists of crabs, fish, insects, lobsters snails, shrimp, etc.


Aquatic Organisms:

Aquatic organisms generally fall into four broad groups: Planktons, Nektons, Benthos, Periphyton. They vary in how they move and where they live.

  • Planktons: They are tiny aquatic organisms that cannot move on their own. They live in the photic zone. They include phytoplankton and zooplankton. Phytoplanktons are bacteria and algae that use sunlight to make food. Zooplanktons are tiny animals that feed on phytoplankton.
  • Nektons: They are aquatic animals that can move on their own by “swimming” through the water. They may live in the photic or aphotic zone. They feed on plankton or other nekton. Examples of nekton include fish and shrimp.
  • Benthos: They are aquatic organisms that crawl in sediments at the bottom of a body of water. Many are decomposers. Examples of Benthos include sponges, clams, and anglerfish.
  • Periphytons: They are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom Examples such as sessile algae and their associated group of animals.


  • The ocean ecosystem covers most of the earth’s surface and is home to millions of plants and animals.
  • While there are five different named oceans – the Arctic, Atlantic, Indian, Pacific and Southern oceans – they are all actually the same body of water. The oceans cover about 70 percent of the earth’s surface and have an average depth of 2.4 miles.
  • The deepest part of the ocean, the Mariana Trench, is about 36,200 feet deep, which is deeper than Mt. Everest is tall.
  • The ocean ecosystem includes everything in the oceans, as well as the saltwater bays, seas and inlets, the shorelines and salt marshes.
  • It is home to the smallest organisms like plankton and bacteria, as well as the world’s largest living structure – the Great Barrier Reef, which can even be seen from the moon.



  • In addition to the amount of salts, other conditions in ocean water vary from place to place. One is the amount of nutrients in the water. Another is the amount of sunlight that reaches the water.
  • These conditions depend mainly on two factors: distance from shore and depth of water. Oceans are divided into zones based on these two factors.
  • Zones Based on Depth of Water:
  • The vertical extent of ocean water is referred to as the water column. The ocean is divided up into three light zones, or layers, based on how much sunlight they receive.
  • The top layer is called the euphotic zone, which receives lots of sunlight. It starts at the ocean’s surface and goes down to about 230 feet on average.
  • The second layer is the disphotic zone, which receives some sunlight, but not enough for plants to survive.
  • The third layer is the aphotic zone, which gets no light at all. Not only is the aphotic zone completely dark, it is extremely cold and few marine animals can survive here.
  • Zones Based on Distance from Shore:
  • There are three main ocean zones based on distance from shore. They are the intertidal zone, neritic zone, and oceanic zone. Distance from shore influences how many nutrients are in the water.
  • Most nutrients are washed into ocean water from land. Therefore, water closer to shore tends to have more nutrients. Living things need nutrients. So distance from shore also influences how many organisms live in the water.
  • The intertidal zone is closest to shore. At high tide, it is covered with water. At low tide, it is exposed to air. Living things must adapt to changing conditions and moving water in this zone.
  • The neritic zone lies over the continental shelf, where the water is not very deep. There are plenty of nutrients and sunlight, hence so many organisms live in this zone.
  • The oceanic zone is the open ocean out beyond the continental shelf. The water may be very deep. Nutrients may be scarce. Fewer organisms live in this zone.




  • Lakes are inland bodies of water that lack any direct exchange with an ocean. Lake ecosystems are made up of the physical, chemical and biological properties contained within these water bodies. Lakes may contain fresh or saltwater (in arid regions).


  • They may be shallow or deep, permanent or temporary. Lakes of all types share many ecological and biogeochemical processes and their study falls within the discipline of ‘limnology’.
  • Although lakes contain less than 0.01% of all the water on the Earth’s surface, they hold more than 98% of the liquid surface freshwater.
  • Many organisms depend on freshwater for survival, and humans frequently depend on lakes for a great many ‘goods and services’ such as drinking water, waste removal, fisheries, agricultural irrigation, industrial activity, and recreation. For these reasons lakes are important ecosystems.
  • Lakes vary greatly in size. Some measure only a few square meters and are small enough to fit in your backyard. Such small lakes are often referred to as Other lakes are so big that they are called seas. The Caspian Sea, in Europe and Asia, is the world’s largest lake.
  • Lakes are classified based on productivity as follows:
  • Oligotrophic lakes: These have low primary productivity, and low biomass associated with low concentrations of nitrogen and phosphorous (nutrients). They tend to be saturated with oxygen.
  • Mesotrophic lakes: These are lakes in transition from oligotrophic to eutrophic conditions. Some depression of oxygen concentration occurs in hypolimnion during summer stratification.
  • Eutrophic lakes: These display high concentration of nutrients, high biomass productivity and low transparency. Oxygen concentrations can get very low (as low as 1 mg/L) in the hypolimnion during summer.
  • Hypereutrophic lakes: These are lakes at the extreme end of eutrophication with very high concentration of nutrients and associated biomass production. Anoxia or complete loss of oxygen takes place in the hypolimnion during summer.
  • Dystrophic lakes: These are organic rich lakes (humic and fulvic acids) fed by external inputs of the lake (watershed).



  • Although lakes naturally age and die, people have sped up the process by polluting the water. A major problem that threatens many lakes is blue-green algae.
  • Blue-green algae, sometimes referred to as “pond scum” and can be blue-green, blue, green, reddish-purple, or brown. It stays on the surface of the water and forms a sort of mat. When the conditions are just right, the algae multiplies quickly. This is called an algal bloom and is harmful to lakes, animals, plants, and people.
  • Blue-green algae also called cyanobacteria, is not a part of the food web. It uses up important nutrients without contributing to the lake ecosystem.
  • Instead, the algal bloom chokes up a lake and uses up the oxygen that fish and other living things depend on for survival. Plants die more quickly, sinking to the bottom and filling up the lake basin.
  • Blue-green algae also can become so dense that it prevents light from penetrating the water, changing the chemistry and affecting species living below the surface.
  • When an algal bloom happens, water becomes contaminated. The toxic water can kill animals and make humans sick.


  • ‘Eu’ means well or healthy and ‘trophy’ means nutrition. The enrichment of water bodies with nutrients causes eutrophication of the water body
  • when a lake gets too many nutrients, causing blue-green algae growth. Sewage from towns and cities causes explosive growth of blue-green algae, and waste from factories can wash into the lakes and pollute them.
  • Phosphorus-based fertilizers from farms, golf courses, parks, and even neighborhood lawns can wash into lakes and pollute them.
  • The phosphorus seeps into the ground and eventually reaches the lake. Phosphorus is an important nutrient for a lake, but too much of it is not a good thing because it encourages blue-green algae.

How can blue-green algae be prevented or reduced?

  • At home, people can help by using phosphorus-free fertilizer and by fertilizing only where it’s needed.
  • Preventing lawn clippings and leaves from washing into the gutter and maintaining a buffer of native plants help filter water and stop debris from washing away.
  • Making sure septic systems don’t have leaks, safely disposing of household chemicals (like paint), and minimizing activities that erode soil also help prevent the spread of blue-green algae.
  • Controlling phosphorous and chemicals from factories and farms is much more complicated. Citizens need to work with businesses and elected leaders to help reduce the amount of runoff and water pollution.


Invasive Species:

  • When a plant or animal species is moved to a location where it’s not originally from, the species is called an exotic species. When that species harms the natural balance in an ecosystem, the species is called invasive.
  • Invasive species can harm life in a lake by competing for the same resources that native species do. When introduced to new food sources, invasive species multiply quickly, crowding out the helpful native species until there are more invasive than native species.
  • Invasive species can change the natural habitat of the lake and are known as biological pollutants when this happens. Once non-native species have been introduced into a lake, they are almost impossible to get rid of.
  • Non-native plants and animals are almost always introduced by people. As people use waterways more frequently, they may inadvertently move organisms from one area to another.
  • Plants such as Eurasian watermilfoil, an invasive aquatic plant in the U.S., may cling to boats, clothing, pets, equipment, and vehicles.


Acid Rain:

  • Another major threat to lakes today is acid rain. Some acid is natural, even in pure rain. This slightly toxic chemical slowly weathers rocks and soil.
  • Acid rain, however, is caused by human activities and is harmful. It is caused by toxic gases from factories, coal-fired power plants, vehicle exhaust, and home furnaces.
  • Nitrogen and sulfur, the main ingredients of acid rain, rise in the air and may be carried hundreds of kilometers by wind. When these gases mix with the moisture in clouds, they form strong acids, which kill fish, plants, and other organisms when the acids fall as rain or snow on lakes.
  • Acid rain can also affect humans, causing asthma and bronchitis, and damaging lung tissue.
  • Methylmercury, a toxic form of mercury, has been linked to acid rain.



  • An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, the salty ocean mixes with a freshwater river, resulting in brackish water. Brackish water is somewhat salty, but not as salty as the ocean.
  • An estuary may also be called a bay, lagoon, sound, or slough.
  • Water continually circulates into and out of an estuary. Tides create the largest flow of saltwater, while river mouths create the largest flow of freshwater.
  • When dense, salty seawater flows into an estuary, it has an estuarine current. High tides can create estuarine currents. Saltwater is heavier than freshwater, so estuarine currents sink and move near the bottom of the estuary.
  • When less-dense freshwater from a river flows into the estuary, it has an anti-estuarine current. Anti-estuarine currents are strongest near the surface of the water. Heated by the sun, anti-estuarine currents are much warmer than estuarine currents.
  • In estuaries, water level and salinity rise and fall with the tides. These features also rise and fall with the seasons.
  • During the rainy season, rivers may flood the estuary with freshwater. During the dry season, the outflow from rivers may slow to a trickle. The estuary shrinks, and becomes much more saline.
  • During a storm season, storm surges and other ocean waves may flood the estuary with saltwater. Most estuaries, however, are protected from the ocean’s full force. Geographical features such as reefs, islands, mud, and sand act as barriers from ocean waves and wind.


Characteristics of Estuarine Ecosystem:

  • Salinity:
  • Inflow of fresh water from one side and the open sea at the other gives rise to a gradient of increasing salinity from the interior to the estuary mouth. The salinity also changes with the tides and the season.
  • Brackish waters are poorer in species diversity than either the sea or fresh water. Seasonal fluctuations in salinity influence the distribution of organisms in the estuary. Continuous rains during the monsoon harms marine fauna. When salinity returns to normal after few months, the marine animals re-establish themselves. Estuarine animals either adapt to avoid unfavourable salinities or tolerate a range in salinity by using physiological mechanisms.
  • Temperature:
  • Temperatures vary widely in estuaries owing to the mixing of water of different temperatures and shallowness of the water.
  • In shallow estuaries, the water is much cooler in winter and warmer in summer. These temperature fluctuations affect the species composition and eliminate most animals that cannot withstand wide changes.
  • Sediments:
  • The sediment type influences the organisms living in the estuary, especially plants and benthic animals.
  • Mudflats are common. The substrate here is composed of soft, loose mud or a mixture of mud and sand.
  • Characteristic vegetation such as eel grass in temperate areas and mangroves in the tropics develops on mudflats, making estuarine ecosystems very productive and at the same time providing special habitat for animals. Mangroves are found in most estuaries along the Indian coast.
  • Turbidity:
  • Silt suspended in the water in estuaries causes the water to be turbid. The degree of turbidity varies widely throughout the year; it is at a maximum during the rainy season. It also varies from place to place within the estuary.
  • Turbid water prevents light from penetrating even one metre below the water surface. This reduces the level of photosynthesis by phytoplankton in the deeper layers. Shore plants which are not covered by turbid waters are therefore the most important photosynthesisers of organic matter. Salt-marsh plants and mangrove forest assume great importance as primary producers.
  • Nutrient flows: The fertility of the estuary depends on the flow of nutrients from the river and on tidal currents.


Threats to Estuarine Ecosystem:

  • Estuarine ecosystems are usually dominated by stress-tolerant organism, able to withstand a relatively wide range of environmental factors. However, they to face some threats from anthropogenic activities.
  • Estuaries are preferred locations for human settlement due to their high productivity and availability of natural connections between maritime and inland waterways. Estuaries are often challenged by land development; land reclamation is particularly detrimental in this respect as it results in a permanent loss of habitat.
  • Climate change impacts of concern for estuaries are the overall temperature rise and elevation of the sea level.
  • Rivers discharging into their estuaries carry various constituents depending on the land use of the drainage area (catchment). This means that various contaminants introduced at any point in the catchment ultimately end up in the estuary.


  • As per the ‘Ramsar Convention’, Wetlands are defined as the “areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres”.
  • About 6% of the total surface area of the world is covered by wetlands. With almost twice the productivity of tropical rain forests, wetlands are among the earth’s most productive ecosystems.
  • Five major wetland types are generally recognized:
  • marine (coastal wetlands including coastal lagoons, rocky shores, and coral reefs);
  • estuarine (including deltas, tidal marshes, and mangrove swamps);
  • lacustrine (wetlands associated with lakes);
  • riverine (wetlands along rivers and streams); and
  • palustrine (meaning marshy – marshes, swamps and bogs).
  • In addition, there are human-made wetlands such as fish and shrimp ponds, farm ponds, irrigated agricultural land, salt pans, reservoirs, gravel pits, sewage farms and canals.
  • The Ramsar Convention has adopted a Ramsar Classification of Wetland Type which includes 42 types, grouped into three categories: Marine and Coastal Wetlands, Inland Wetlands, and Human-made Wetlands.

Significance of Wetland Ecosystem:

Wetlands have immense value from ecological, economic, biological and aesthetic viewpoints:

  • They support extensive freshwater and marine fisheries.
  • They are natural sewage treatment plants.
  • Wetland plants like water hyacinth act as pollution filters for some heavy metals.
  • Wetlands serve as the breeding and feeding sites for resident and migrating water birds.
  • Wetlands act as an efficient buffer against natural calamities in flood or cyclone-prone areas. In estuaries, mangrove forests shield the coast against storms.
  • Wetlands help maintain the water table by recharging ground water.



  • The Ramsar Convention, signed in 1971 in Ramsar, Iran, is the only global treaty that focuses specifically on wetlands. Today 170 nations are signatories to the Ramsar Convention.
  • The convention is to provide a framework for national action and international cooperation for the conservation and wise use of wetlands and their resources.
  • A contracting party agrees to nominate at least one wetland in its territory to the List of Wetlands of International Importance based on enumerated criteria.
  • The Convention also mandates contracting parties to adopt National Wetland Policies, produce wetland inventories, conduct wetland monitoring and research, raise public awareness of wetlands, and develop integrated management plans for wetlands sites.


SI.No. Name Of Site State Location Date Of Declaration Area
(in Sq. km.)



























Asthamudi Wetland

Bhitarkanika Mangroves

Bhoj Wetlands Chandertal Wetland

Chilka Lake

Deepor Beel

East Calcutta Wetlands

Harike Lake

Hokera Wetland

Kanjli Lake

Keoladeo Ghana NP

Kolleru Lake

Loktak Lake

Nalsarovar Bird Sanctuary Point Calimere

Pong Dam Lake

Renuka Wetland

Ropar Lake

Rudrasagar Lake

Sambhar Lake

Sasthamkotta Lake Sunderbans Wetland

Surinsar-Mansar Lakes Tsomoriri Lake

Upper Ganga River (Brijghat to Narora Stretch)

Vembanad Kol Wetland

Wular Lake



Madhya Pradesh Himachal Pradesh



West Bengal


Jammu and Kashmir



Andhra Pradesh



Tamil Nadu

Himachal Pradesh

Himachal Pradesh





West Bengal

Jammu and Kashmir

Jammu and Kashmir

Uttar Pradesh


Jammu & Kashmir









| 8.11.2005














































Total Area (in Sq. Km.) 11121.31




  • In 2019, India has added 10 more wetlands selected under Ramsar Convention taking total number of Ramsar wetlands in the country to 37 covering about 10,679.39 sq km area across 15 different Indian States and two Union Territories (UTs).
  • A decade after the first meeting at Ramsar in Iran for wetland protection in 1971, India got its first wetlands, Chilika lake (Odisha) and Keoladeo National Park (Rajasthan) registered as Ramsar wetland of global significance in Oct 1981.
  • Out of 37 Ramsar wetlands in India now, 20 are located in three states and two UTs in North India, 13 of them are situated in just two states of Uttar Pradesh (7) and Punjab (6), where the large states of Madhya Pradesh, Maharashtra, Gujarat, Andhra Pradesh and Tamil Nadu have just one Ramsar site each.
  • Major states like Karnataka, Telangana, Bihar, Jharkhand, Chhattisgarh and several states of North East India have none. Only one Ramsar site of India, namely the Upper Ganga River (Brijghat to Narora Stretch) is a river.


The Ramsar Sites Criteria:

  • The nine criteria for identifying Wetlands of International Importance:
  • Criteria 1: A wetland should be considered internationally important if it contains a representative, rare, or unique example of a natural or near natural wetland type found within the appropriate bio-geographic region.
  • Criterion 2: A wetland should be considered internationally important if it supports vulnerable, endangered, or critically endangered species or threatened ecological communities.
  • Criterion 3: A wetland should be considered internationally important if it supports populations of plant and/or animal species important for maintaining the biological diversity of a particular bio-geographic region.
  • Criterion 4: A wetland should be considered internationally important if it supports plant and/or animal species at a critical stage in their life cycles, or provides refuge during adverse conditions.
  • Criterion 5: A wetland should be considered internationally important if it regularly supports 20,000 or more water birds.
  • Criterion 6: A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of water bird.
  • Criterion 7: A wetland should be considered internationally important if it supports a significant proportion of indigenous fish subspecies, species or families, life-history stages, species interactions and/or populations that are representative of wetland benefits and/or values and thereby contributes to global biological diversity.
  • Criterion 8: A wetland should be considered internationally important if it is an important source of food for fishes, spawning ground, nursery and/or migration path on which fish stocks, either within the wetland or elsewhere, depend.
  • Criterion 9: A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of wetland-dependent non-avian animal species.


Previous year Questions

  1. What is wetland? Explain the Ramsar concept of ‘wise use’ in the context of wetland conservation. Cite two examples of Ramsar sites from India. 2018
  2. Discuss the wetlands and their role in ecological conservation in India. 2009


Q1 Consider the following statements:

1) Under Ramsar convention, it is mandatory on the part of the government of India to protect and conserve all the wetlands in the territory of India.

2) The wetlands (conservation and management) rules, 2010 were framed by Government of India based on the recommendations of Ramsar convention.

3) The wetlands (Conservation and Management) Rules, 2010 also encompass the drainage area or catchment regions of the wetlands as determined by the authority

Which of the statements given above is/are correct?

  1. 1 and 2 only
  2. 2 and 3 only
  3. 3 only
  4. 1,2 and 3

Answer: C


Q2. India is a party to the Ramsar Convention and has declared many areas as Ramsar Sites. Which of the following statements best describes as to how we should maintain these sites in the context of this Convention?

  1. Keep all the sites completely inaccessible to man so that they will not be exploited
  2. Conserve all the sites through ecosystem approach and permit tourism and recreation only
  3. Conserve all the sites through ecosystem approach for a period without any exploitation, with specific criteria and specific period for each site, and then allow sustainable use of them by future generations
  4. Conserve all the sites through ecosystem approach and allow their simultaneous sustainable use.

Answer D



  • It is a register of wetland sites on the List of Wetlands of International importance where changes in ecological character have occurred, are occurring/ are likely to occur as a result of technological developments, pollution or other human interference (maintained as part of the Ramsar List).
  • Indian sites included in the Montreux Record are Keoladeo National Park (Rajasthan), Loktak Lake (Manipur).

Previous year Questions

Q1 If a wetland of international importance is brought under the ‘Montreux Record, what does it imply?

a) Changes in ecological character have occurred, are occurring or are likely to occur in the wetland as a result of human interference.

b) The country in which the wetland is located should enact a law to prohibit any human activity within five kilometres from the edge of the wetland

c) The survival of the wetland depends on th cultural practices and traditions of certain communities living in its vicinity, and therefore the cultural diversity therein should not be destroyed

d) It is given the status of ‘World Heritage Site’

Answer: A


Threats to Wetland Ecosystem:

  • One of the important reasons for granting Ramsar recognition to the wetlands is their being safe haven for migratory birds and endangered animal species.
  • Owing to increasing pollution loads, siltation, disturbing human activities there has been marked reduction in number of avian numbers in most Ramsar sites in India.
  • The construction of dams, barrages without credible impact assessments, options assessment or democratic decision making and their faulty operation have become one of the biggest reason behind continual degradation of many Ramsar sites in India.
  • Most of the Ramsar sites are located along the rivers making them the essential part of river eco-system.
  • The impact of dams on aquatic life and dependent communities have been well known. Despite this, the Convention has selected many man-made reservoirs as Ramsar sites.
  • While the increasing human development pressures, destruction of mangroves and deforestation have worsened the crisis, holistic preparatory/remedial action plans are missing.
  • It’s an irony that the central and state government mandated to be guardians of crucial wetlands resources are themselves deliberately pushing destructive developmental projects playing havoc on the Ramsar wetlands.
  • The invasion of exotic plants species in Ramsar wetlands has become serious issue over the years which still largely remains unaddressed.


  • Mangrove forests make up one of the most productive and biologically diverse ecosystems on the planet.
  • They grow in a variety of depths of salt water (also called halophytes) and are adapted harsh coastal conditions.
  • Their roots sticking up out of the mud, with fish, crustaceans and a host of other species living between tree trunks.
  • They contain a complex salt filtration system and complex root system to cope with salt water immersion and wave action. (produce pneumatophores/blind roots for respiration in the anaerobic soil conditions )
  • They occur worldwide in the tropics and subtropics, (mainly between latitudes 25° N and 25° S) and are adapted to the low oxygen (anoxic) conditions of waterlogged mud.
  • Mangroves exhibits Viviparity (seeds germinate in the tree itself before falling to the ground) it is an adaptive mechanism to overcome the problem of germination in saline water.
  • Mangroves have the ability to absorb up to four times more carbon dioxide by area than upland terrestrial forests. The remarkable traits of the mangrove ecosystem translate into a wide variety of goods and services that we benefit from.
  • These play a critical role in supporting human well-being by delivering the necessities of life like food, shelter and livelihoods.
  • At the same time mangroves reduce loss of property and vulnerability of local communities.


Significance of Mangroves:

  • Mangroves are flowering plants which can tolerate salinity and show peculiar ecological adaptations.
  • They are able to tolerate mean temperatures only above 20°C, so are mostly confined to the tropics.
  • Various species have different salinity tolerances and are found in different zones in estuaries.
  • They prefer soft clay, silty, waterlogged substrata in the intertidal region (the area experiencing the daily influence of high and low tides).
  • Mangroves act as a shelter belt to minimize the impact of cyclone winds and waves.
  • The dense roots mean the sedimentation rate in mangrove swamps is very high, helping build up new land, reducing coastal erosion and protecting human habitations.
  • The food chain of the mangrove ecosystem is mainly detritus-based. Protein-rich detritus is broken down by micro-organisms and provides food for various organisms-fishes, crabs and molluscs.
  • The abundance of food and suitable habitat in mangrove swamps attract many nearshore and estuarine organisms.
  • The biodiversity of plants and animals is very rich.
  • Mangrove areas are invaluable feeding, breeding and nursery grounds for many economic species of fish and shellfish.
  • Mangroves have many uses for humans. The trees are widely used for fuel, fibre, tannin, timber, alcohol, paper, charcoal and such byproducts as honey and fodder.
  • Some species have medicinal properties such as anti-fertility and anti-cancer drugs and to treat arthritis. Research on these properties is continuing.
  • Despite their economic value and provision of environmental services, there is a growing trend to reclaim mangrove areas for fishponds or agriculture.


Mangroves in India:

  • India has approximately 315,000 ha of mangrove cover, of which about 65,000 ha occurs along the west coast.
  • Gujarat and Kerala coasts have the most degraded mangroves, while Maharashtra, Goa and Karnataka have occasional luxuriant pockets.
  • Various biotic communities associated with mangroves form a complex food web in these areas.
  • The distribution and extent of mangroves are influenced by topography, tidal height, substratum and salinity.
  • The west coast of India has a narrow intertidal belt which supports fringing mangroves.
  • Sundarbans Mangroves, West Bengal: The Great Sundarbans is the largest Mangroves region in the world and a UNESCO World Heritage Sundarbans region is densely covered by mangroves, its a National Park, Tiger Reserve and a Biosphere Reserve Park of India.
  • Bhitarkanika Mangroves, Odisha: Bhitarkanika Mangroves is India’s second largest forest, located in Odisha. Bhitarkanika is created by the two river delta of Brahmani and Baitarani river and one of the important Ramsar Wetland in India.
  • Godavari – Krishna Mangroves, Andhra Pradesh: The Godavari Krishna mangroves lies in the delta of the Godavari and Krishna rivers in Andhra Pradesh. Mangroves eco-region is under protection for Calimere Wildlife and Pulicat Lake Bird
  • Pichavaram Mangroves, Tamil Nadu: Pichavaram mangrove is one of the largest mangrove in India, situated at Pichavaram near Chidambaram in Tamil Nadu. It ranks among the one of the most exquisite scenic spot in Tamil Nadu and home of many species of Aquatic birds.
  • Baratang Island Mangroves, Andamans: Baratang Island Mangroves is beautiful swamp, located at Great Andaman and Nicobar Islands.
  • Mangrove Swamps of Baratang Island are situated between Middle and South Andamans, capital city Port Blair.


Previous year Questions

  • Prelims
  1. Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?
    1. Oceans, lakes, grasslands, mangroves
    2. Mangroves, oceans, grasslands, lakes
    3. Mangroves, grasslands, lakes, oceans
    4. Oceans, mangroves, lakes, grasslands

Answer: C



Q1 Where do mangrove forests occur in India? Describe their main characteristics. (10m, 1996)




  • Coral reefs are shallow water, tropical marine ecosystems which are characterized by a remarkably high biomass production and a rich fauna and flora diversity, perhaps unequaled by any other habitat.
  • Corals require certain conditions to occur and can flourish only in relatively shallow waters, exposed to direct sunlight, with optimum temperature of 23-25°c and free from suspended sediments.


Coral polyps are short-lived microscopic organisms, which live in colonies. They flourish in shallow, mud free and warm waters. They secrete calcium carbonate. The coral secretion and their skeletons from coral deposits in the form of reefs:. they are mainly of three kinds: barrier reef. fringing reef and atolls. The Great Barrier Reef of Australia Is a good example of the first kind of coral reefs. Atolls are circular or horse shoe shaped coral reefs.

  • The structure of a reef is formed by the calcareous skeleton that houses corals, a type of soft-bodied, radially symmetrical, marine invertebrates of the phylum coelenterat Individuals of a colony are called polyps or hydroids.
  • Millions of coral skeletons cemented together over a period ranging from a few thousand to millions of years give rise to such reefs (WWF1992).


Types of coral reef

  • Reefs can vary in structure and complexity and are roughly divided into three major types.
  • Fringing reefs, reefs that grow close to the shore and extend out into the sea like a submerged platform. Fringing Reefs are the most frequently found coral reefs among the three. For example Sakau Island, South Florida Reef.
  • Barrier reef: it separated from the land by wide expanses of water and follow the coastline. Great Barrier Reef of Australia is one of the examples of barrier reefs.
  • Atolls: a roughly circular ring of reefs surrounding a lagoon, a low lying island, common in the Indian and South pacific oceans. For example Fiji Atolls.


Inventory, distribution and extent coral reefs in India:

  • India with its coastline extending over 7,500 kilometers and subtropical climatic conditions has very few coral reef areas. The absence of reef in the Bay of Bengal is attributed to the immense quantity of freshwater and silt brought by the rivers.
  • Other disincentives to reef growth are the heavy monsoonal rains and the high human presence on the coastline.
  • The mainland coast of India has two widely separated area’s containing reefs: The Gulf of Kutch in the north-west, which has some of the most northerly reefs in the world and Gulf of Mannar and the Palk Bay (with numerous fringing reefs around small islands) in the south east.
  • Important off shore island groups of India with extensive reef growth include the Andaman and Nicobar Islands in the Bay of Bengal and the Lakshadweep group of Islands in the Arabian sea. The
  • Andaman and Nicobar islands have fringing reefs and a 320 km long barrier reef on the west coast. The Lakshadweep Islands are made up of atolls.


Coral Bleaching:

  • Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching.
  • When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.


Causes of Coral Bleaching:

  • Extreme climate conditions: Corals cannot survive if the water temperature is too high. Global warming has already led to increased levels of coral bleaching.
  • Overfishing: It affects the ecological balance of coral reef communities, and alters the food chain.
  • Tourism Activity: Some tourist resorts and infrastructure have been built directly on top of reefs, and some resorts empty their sewage or other wastes directly into water surrounding coral reefs. Over boating and over fishing also affects coral reefs.


Measures taken for Coral Restoration Global Measures

  • Chapter 17 of “Agenda 21” specifically addresses the protection and sustainable development of the marine and coastal environment within the context of the United Nations Convention on the Law of the Sea (UNCLOS).
  • International Coral Reef Initiative (ICRI)- is an informal partnership between Nations and organizations which strives to preserve coral reefs and related ecosystems around the world.
  • ICRI had declared 2018 as the third International Year of the Reef (IYOR) to strengthen awareness globally about the value of, and threats to, coral reefs and associated ecosystems. 1997 was declared the first IYOR, in response to the increasing threats on coral reefs and associated ecosystems, such as mangroves and sea grasses around the world.
  • UN Environment World Conservation Monitoring Centre (UNEP-WCMC)- It works with scientists and policy makers worldwide to place biodiversity at the heart of environment and development decisionmaking to enable enlightened choices for people and the planet.


Measures taken in India

  • Government of India has taken steps to protect its coral reefs under Coastal Ocean Monitoring and Prediction system (COMAPS), Land Ocean Interactions in Coastal zones (LOICZ) and Integrated Coastal and Marine Area Management (ICMAM).
  • Government of India has notified Coastal Regulation Zones (CRZ) and has setup National Coastal Zone Management Authority and State Coastal Zone Management Authority to protect coral reefs.
  • Coral Bleaching Alert System (CBAS)- a service initiated from INCOIS uses the satellite derived Sea Surface Temperature (SST) in order to assess the thermal stress accumulated in the coral environs.
  • Coral Reef Recovery Project– is a joint venture of Wildlife Trust of India and the Gujarat Forest Department, supported by Tata Chemicals Limited (TCL).
  • In Mithapur coast in the Gulf of Kachchh, the project envisions the creation of a model public-private-managed coral ecosystem of international standards using global benchmarks to restore degraded reefs through activities including coral transplantation and natural recruitment.
  • ReefWatch India- An NGO, has taken up two projects —Re(ef)Build and Re(ef)Grow – to conserve the reefs.
  • Re(ef)build involves the restoring and rehabilitation of coral reefs at the Andamans by rescuing naturally broken coral fragments that would otherwise get smothered in the sand and die, and reattaching them to a robust substratum.


Coral in news

  • Fire corals (Millepora boschmai)
  • They are closely related to jellyfish (less related to Corals)
  • Distribution: Panama Pacific Province Indonesia, Gulf of Chiriqui,. Perhaps extinct from Australia, India, Indonesia, Malaysia, Panama, Singapore and Thailand.
  • Threats: Collected for decoration and jewellery trade. It is also sensitive to temperature rise and is thought to have completely disappeared from the majority of marine areas because of growing global warming related bleaching effects.


Previous year Questions

  • Assess the impact of global warming on the coral life system with examples. 10 m (2019)
  • The acidification of oceans is increasing. Why is this phenomenon a cause of concern?


1) The growth and survival of calcareous phytoplankton will be adversely affected.

2) The growth and survival of coral reefs will be adversely affected.

3) The survival of some animals that have phytoplanktonic larvae will be adversely affected.

4) The cloud seeding and formation of clouds will be adversely affected.

Which of the statements given above is/are correct?

  1. 1,2 and 3 only
  2. 2 only
  3. 1 and 3 only
  4. 1,2,3 and 4

Answer: D


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 Career Development Program 2023 Result PDF     Download UPSC Mains 2023 Question Papers PDF  Free Initiative links -1) Download Prahaar 3.0 for Mains Current Affairs PDF both in English and Hindi 2) Daily Main Answer Writing  , 3) Daily Current Affairs , Editorial Analysis and quiz ,  4) PDF Downloads  UPSC 2022 Final Result🔥5 out of Top 10 from PW OnlyIAS Community. UPSC Prelims 2023 Trend Analysis cut-off and answer key