A halocline is a cline caused by a strong, vertical salinity gradient within a body of water. As salinity (in concert with temperature) affects the density of seawater, it can play a role in its vertical stratification. Increasing salinity by one kg/m3 results in an increase of seawater density of around 0.7 kg/m3.

Fresh water is naturally occurring water on the Earth's surface in bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids.It is classified as freshwater biome.

 The word ecology was coined in 1866 by the German scientist Ernst Haeckel (1834–1919).

Antarctica is one of eight terrestrial ecozones. The ecosystem includes Antarctica and several island groups in the southern Atlantic and Indian Oceans.

In ecology, a niche is a term describing the relational position of a species or population in an ecosystem.The niche includes how a population responds to the abundance of its resources and enemies.

 Lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.

Limnology is the study of inland waters. This includes the study of lakes and ponds, rivers, springs, streams and wetlands.

Often called “rainforests of the sea”, coral reefs forms the most diverse ecosystems on Earth. Coral reefs are underwater structures made from calcium carbonate secreted by corals. Corals are colonies of tiny living animals found in marine waters that contain few nutrients.

In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g., a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food resources and foraging methods

An ecotone is a transition area between two adjacent but different patches of landscape, such as forest and grassland. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and grassland ecosystems).

A mycotroph is a plant that gets all or part of its carbon, water, and/or nutrient supply through symbiotic association with fungi.

Ethology is the  branch of zoology that studies the behaviour of animals in their natural habitats.

Parasitic nutrition is a mode of nutrition where organism (known as a parasite) lives on the body surface or inside the body of another type of organism and obtains nutrition directly from the body of the other organism (known as a host).

There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organism in the food chains, there is the problem of assigning the decomposers and detritivores to a particular trophic level.

All are the fresh water ecosystems.

Biomagnification, is the increase in concentration of a substance, such as the pesticide DDT, that occurs in a food chain .

Bacterivores are free-living, generally heterotrophic organisms, exclusively microscopic, which obtain energy and nutrients primarily or entirely from the consumption of bacteria. Many species of amoeba are bacterivores, as well as other types of protozoan .e.g., Vorticella and paramuecium.

An ecological network is a representation of the biotic interactions in an ecosystem, in which species (nodes) are connected by pairwise interactions (links). These interactions can be trophic or symbiotic. Ecological networks are used to describe and compare the structures of real ecosystems, while network models are used to investigate the effects of network structure on properties such as ecosystem stability.

When a stable community, which is not the climatic or edaphic climax for the given site, is maintained by man or his domestic animals, it is designated as Disclimax (disturbance climax) or anthropogenic subclimax (man-generated). For example, overgrazing by stock may produce a desert community of bushes and cacti where the local climate actually would allow grassland to maintain itself.

Climax Pattern Theory was proposed by Whittaker (1953). This theory recognizes a variety of climaxes governed by responses of species populations to biotic and abiotic conditions.

The bloat stage provides the first clear visual sign that microbial proliferation is underway. In this stage, anaerobic metabolism takes place, leading to the accumulation of gases, such as hydrogen sulphide, carbon dioxide, and methane.

Temporal resource partitioning is when two species eliminate direct competition by utilizing the same resource at different times.

An ecological pyramid of productivity is often more useful, showing the production or turnover of biomass at each trophic level. Instead of showing a single snapshot in time, productivity pyramids show the flow of energy through the food chain. Typical units would be grams per meter²  per year or calories per meter²  per year. As with the others, this graph begins with producers at the bottom and places higher trophic levels on top.

A psammosere is a seral community, an ecological succession that began life on newly exposed coastal sand. Most common psammoseres are sand dune systems.

Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which new substrate devoid of vegetation and usually lacking soil, such as a lava flow or area left from retreated glacier is deposited. In other words, it is the gradual growth of an ecosystem over a longer period of time.