Sea grasses and mangroves of Estuarine and coastal ecosystems are the most efficient in carbon sequestration. Hence, these ecosystems are called as "Blue carbon ecosystems".

The movement of energy from producers upto top carnivores is known as food chain, i.e., in any food chain, energy flows from producers to primary consumers, then from primary consumers to secondary consumers, and finally secondary consumers to tertiary consumers. Hence, it shows linear network links.

The transfer of energy in an ecosystem between trophic levels can be termed as energy flow. It is the key function in an ecosystem. Energy flow is always unidirectional in an ecosystem.

Producers (autotrophs) occupy the first tropic level (T₁) whereas the fourth tropic level (T₄) is occupied by Tertiary Consumers (Secondary carnivore).

The amount of living materials present in a population at any given time is known as standing crop.

Biotic (living) components includes all living organisms like plants, animals, fungi and bacteria. They form the trophic structures of any ecosystem.

The total inorganic substances present in any ecosystem at a given time is called standing quality (or) standing state.

(a) Climatic factors: Light and Air.
(b) Edaphic factors: Soil and pH of soil.

There is a gradual decrease in energy transfer at successive tropic levels from producers to higher levels, hence the pyramid of energy is always upright.

Because there is no effective light penetration & predominance of heterotrophs.

Significance of food web
(I) Food web is constructed to describe species interaction called direct interaction.
(II) It can be used to illustrate indirect interactions among different species .
(III) It can be used to study bottom-up or top-down control of community structure.
(IV) It can be used to reveal different patterns of energy transfer in terrestrial and aquatic ecosystems.

Pyramid of number
(i) In a forest ecosystem the pyramid of number is different in shape, it is because the base (T ₁) of the pyramid occupies large sized trees (producer) which are lesser in number.
(ii) Herbivores (T₂) occupying second trophic level, are more in number than the producers (T₁).
(iii) In final trophic level (T₄) tertiary consumers (lion) are lesser in number than the secondary consumers (T₃).
(iv) Therefore, the pyramid of numbers in forest ecosystem looks spindle-shaped.
Pyramid of biomass
(i) In forest ecosystem, there is a gradual decrease in biomass of organisms at successive trophic levels from producers to top carnivores (Tertiary consumer). Therefore, the pyramid of biomass looks upright.

Detritus food chain
(i) This type of food chain begins with dead organic matter which is an important source of energy.
(ii) A large amount of organic matter is derived from the dead plants, animals and their excreta.
(iii) This type of food chain is present in all ecosystems
(iv) The transfer of energy from the dead organic matter is transferred through a series of organisms called detritus consumers. (detrivores)-Small carnivores -large (top) carnivores with repeated eating and being eaten respectively.

Characteristics of ecological succession
(I) It is a systematic process which causes changes in specific structure of plant community.
(II) It is resultant of changes of abiotic and biotic factors.
(III) It transforms unstable community into a stable community.
(IV) Gradual progression in species diversity, total biomass, niche specialisation, and humus content of soil takes place.
(V) It progresses from simple food chain to complex food web.
(VI) It modifies the lower and simple life form to the higher life forms.
(VII) It creates inter-dependence of plants and animals.

Mechanism of decomposition
Decomposition is a step wise process of degradation mediated by enzymatic reactions.
Detritus acts as a raw material for decomposition.
It occurs in the following steps.
(a) Fragmentation - The breaking down of detritus into smaller particles by detritivores like bacteria, fungi and earth worm is known as fragmentation. These detritivores secrete certain substances to enhance the fragmentation process and increase the surface area of detritus particles.
(b) Catabolism - The decomposers produce some extracellular enzymes in their surroundings to break down complex organic and inorganic compounds in to simpler ones. This is called catabolism.
(c) Leaching or Eluviation - The movement of decomposed, water soluble organic and inorganic compounds from the surface to the lower layer of soil or the carrying away of the same by water is called leaching or eluviation.
(d) Humification - It is a process by which simplified detritus is changed into dark coloured amorphous substance called humus. It is highly resistant to microbial action, therefore decomposition is very slow. It is the reservoir of nutrients.
(e) Mineralisation - Some microbes are involved in the release of inorganic nutrients from the humus of the soil, such process is called mineralisation.