Types of Ecosystem

Terrestrial Ecosystem

A terrestrial ecosystem is a land-based community of organisms and the interactions of biotic and abiotic components in a given area. The terrestrial ecosystems can be found anywhere apart from heavily saturated places.

As the anime suggests, the terrestrial type of ecosystem is all about those environments that don’t involve water bodies. One of the best examples of terrestrial ecosystems would be the forest. The terrestrial part of the biosphere is divisible into enormous regions called biomes. The climate determines the boundaries of a biome and abundance of plants and animals found in each one of them.

• Tundra Ecosystem :

Winters are long with little daylight, Summers are short, with long daylight hours. Precipitation is less than 250 mm per year. It is a zone of permafrost. The tundra ecosystem is found both bordering boreal forests in the Northern Hemisphere and in far southern regions like Antarctica.

The abiotic factors found in tundras make it very difficult for plants to grow, and the plants that do survive are small and adapted to short growing seasons.In fact, tundra comes from the Finnish word tunturia, which means treeless hill.

Tundra wildlife includes small mammals that are adapted to cold weather like lemmings, arctic hares, and arctic ground squirrels. Top predators in the tundra ecosystem include arctic foxes, arctic wolves, polar bears, and snowy owls. Because of the severe winters, many of the animals are migratory. For example, the many shorebirds and waterfowl such as ducks and geese, nest in the Tundra during the summer and migrate south for the winter.

All fauna or animal species found in the tundra use a combination of thick coats of fur and fat stores to survive the winter. Some tundra animals hibernate in the winter as well to survive a season with minimal food. Most of the animals have long life, e.g. arctic willow has a life span of 150 to 300 years.

FORESTS :

Forests represent the largest and most ecologically complex systems. They contain a wide assortment of trees, plants, mammals, reptiles, amphibians, invertebrates, insects and microorganisms which vary depending on the zone’s climate.

• Taiga or Boreal Ecosystem :

The Taiga is a 1300-1450 km wide zone south of the Tundra. This area has long and cold winters. Summer temperature ranges from 10⁰ C to 21⁰ C. Precipitation ranges about 380-1000 mm annually. The Taiga ecosystem includes forests in the subarctic region of the Northern Hemisphere. Found just south of the Arctic Circle, the taiga experiences low temperatures all year long with long winters and very short summers. The boreal forest is therefore made mostly of coniferous or evergreen trees that have adapted to these cold temperatures. It is absent in the southern hemisphere because of the narrowness of the southern continents in the high latitudes.

Moose, caribou, and other large mammals are most abundant in the taiga. Bears, lynx, and Siberian tigers can be found in boreal forests as well, but most birds and smaller mammals are unable to live in this ecosystem year-round due to the extreme temperatures.

• Temperate Forest Ecosystem:

These forests occur in eastern North America, northeastern Asia and western and central Europe. Have well-defined seasons with a distinct winter. Moderate climate and a growing season of 140-200 days during 4-6 frost free months distinguish temperate forests. Annual temperature varies from -30° C to 30° C. Precipitation (750-1500 mm) is distributed evenly throughout the year. Soil is fertile, enriched with decaying litter. Canopy is moderately dense and allows light to penetrate, resulting in well-developed and richly diversified understorey vegetation and stratification of animals. 

Trees have broad leaves that are lost annually such as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs. Fauna consists of squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and black bear. The temperate forest ecosystem is characterised by high levels of precipitation as both rain and snow and temperatures change with the seasons.

Depending on where they’re found in the world, temperate forests can be composed mostly of deciduous trees that lose their leaves in the fall or coniferous forests that are evergreens. There are even temperate rainforests, which are more commonly found closer to a coast where the humidity is higher. Temperate forests have a high diversity of flora and fauna supported by rich soils and abundant precipitation. In addition to trees, lichen and mosses are commonly found in temperate forest ecosystems.

• Tropical Rainforest Ecosystem:

They occur near the equator (between latitudes 23.5⁰ at north and 23.5⁰ at south). The major characteristic of tropical forests is their distinct seasons. Only two seasons are present (rainy and dry). Winter is absent. The length of daylight is about 12 hours and varies little. The average annual temperature ranges between 20° C and 25° C. Precipitation is evenly distributed throughout the year with annual rainfall exceeding 2000 mm. Soil is nutrient-poor and acidic.  Decomposition is rapid and soils are subject to heavy leaching.Tree canopy is multilayered and continuous, allowing little light penetration.

Flora is highly diverse: one square kilometre may contain as many as 100 different tree species.Trees are 25-35 m tall, with buttressed trunks and shallow roots, mostly evergreen, with large dark green leaves. Common vegetation are orchids, bromeliads, vines (lianas), ferns, mosses, and palms. They are characterised by the greatest diversity of fauna which includes birds, bats, small mammals, and insects.

The tropical rainforest ecosystem is characterised by high temperatures and humidity throughout the year, with up to 400 inches(10.16 m) of rainfall annually. The high temperatures and humidity are caused by their location in the tropics, where the sun’s rays are most intense. In fact, tropical rainforests are one of the most diverse ecosystems in the world, with roughly half of the world’s species found in tropical rainforests.

The tropical rainforest ecosystem can be found in Central and South America, western and central  Africa, western India, Southeast Asia, New Guinea, and Australia. The Amazon rainforest in South America is the largest tropical rainforest in the world, with estimates of 2.5 million different insects, 40,000 plant species, 1,300 bird species, 3,000 fish species, and 427 mammal species.

TYPES OF INDIAN FORESTS :

• Tropical Evergreen and Semi Evergreen Forests

Location: Found in the western slope of the Western Ghats, hills of the northeastern region and the Andaman and Nicobar Islands in.

Climatic condition: Warm and humid conditions with an annual precipitation of over 200 cm and mean annual temperature above 22oC.

Characteristics: Stratified with layers closer to the ground and are covered with shrubs and creepers, with short-structured trees followed by a tall variety of trees. Trees reach great heights up to 60 m or above. There is no definite time for trees to shed their leaves, flowering and fruition and these forests appear green all the year round.

Floral composition: Rosewood, mahogany, ebony, etc. The under growing climbers provide an evergreen character to these forests. Main species are white cedar, and kail. The semi evergreen forests are found in the less rainy parts of these regions. Such forests have a mixture of evergreen and moist deciduous trees.

Faunal composition: Elephants, monkey, lemur and deer, one-horned rhinoceros are found in jungles of Assam and West Bengal along with plenty of birds, bats, sloth, scorpions and snails etc.

• Tropical Deciduous Forests : Most widespread forests in India, also called the monsoon forests.

Climatic condition: They spread over regions which receive rainfall between 70-200 cm. Based on the availability of water and rainfall, they are divided into:

1. Tropical Moist Deciduous Forests :

Location: Northeastern states along the foothills of Himalayas, eastern slopes of the Western Ghats and Odisha.

Climatic condition: Rainfall between 100-200 cm.

Floral Composition: Teak, sal, shisham, hurra, mahua, amla, semul, kusum, and sandalwood etc. Faunal Composition: Mammals include the predators Indian tiger, wolf, dhole, and sloth bear, and the herbivores gaur, chousingha, blackbuck, and chinkara.

2. Dry Deciduous Forest :

Location: Rainier areas of the Peninsula and the plains of Uttar Pradesh and Bihar. In the higher rainfall regions of the Peninsular plateau and the Northern Indian plain. Climatic Condition: Rainfall ranges between 70 -100 cm.

Characteristics: On the wetter margins, it has a transition to the moist deciduous, while on the drier margins to thorn forests. Forests have a parkland landscape with open stretches in which teak and other trees interspersed with patches of grass are common. As the dry season begins, the trees shed their leaves completely and the forest appears like a vast grassland with naked trees all around.

Floral Composition: Tendu, palas, amaltas, bel, khair, axlewood, etc.

• Tropical Thorn Forests :

Location: It includes semi-arid areas of south west Punjab, Haryana, Rajasthan, Gujarat, Madhya Pradesh and Uttar Pradesh.

Climatic condition: Tropical thorn forests occur in the areas which receive rainfall less than 50 cm.

Characteristics: Variety of grasses and shrub, plants remain leafless for most part of the year and give an expression of scrub vegetation.

Floral composition: Babool, ber, and wild date palm, khair, neem, khejri, palas, etc.

• Montane Forests :

In mountainous areas, decrease in temperature with increasing altitude leads to a corresponding change in natural vegetation. Mountain forests can be classified into two types, the northern mountain forests and the southern mountain forests.

Location: The southern mountain forests include the forests found in three distinct areas of Peninsular India viz; the Western Ghats, the Vindhyas and the Nilgiris and northern montane forests include mountain ranges in Kashmir, Uttarakhand, Himachal Pradesh, Sikkim and Darjeeling are covered by Himalayan temperate forests.

Climatic condition: The mean annual rainfall here is 150 cm to 300 cm, the mean annual temperature is about 11°C to 14°C and the average relative humidity is over 80 per cent.

Characteristics: Deciduous forests are found in the foothills of the Himalayas. It is succeeded by the wet temperate type of forests between an altitude of 1,000- 2,000 m. The temperate forests are called Sholas in the Nilgiris, Anaimalai and Palani hills. Such forests are also found in the Satpura and the Maikal ranges.

Floral composition: At higher altitudes, mosses and lichens form part of the tundra vegetation. Some of the other trees of this forest of economic significance include, Magnolia, Laurel, Cinchona and Wattle. Faunal Composition: Hangul or Kashmir Stag, Shou or Sikkim Stag, Red Panda, Elephants, Sambhar, Swamp deer etc.

• Littoral and Swamp Forests :

Littoral forests are forests along the coast featuring salt-tolerant vegetation. They occur in patches and narrow strips along the mainland coast. Swamp forests are found on peat-poor soils that are permanently waterlogged. They may be created and maintained by land topography (basin swamps), hydrological barriers, and/or high-water tables.

Aquatic habitats in swamp forests may be sporadic,seasonal, or permanent.

Location: Along the coast and of the islands and to the deltas of the Ganga, the Mahanadi, the Godavari,,the Krishna and the Cauvery.

SHRUBLAND ECOSYSTEM :

Like the name suggests, the shrubland ecosystem is characterised by their large amount of shrubs and similar plants. Also known as scrubland, the bush, or heath, this ecosystem is influenced by mild weather that is wet during the winter and dry during the summer.

Shrubland ecosystems can be found all over the world, with unique biodiversity found in each part of the world. Each shrubland ecosystem is home to a wide diversity of plants, which in turn can support several animal, bird, and insect species. The milder temperatures make shrublands hospitable for insects and birds throughout the whole year.

GRASSLAND ECOSYSTEM :

The grassland ecosystem is found all over the world and is characterised by their open spaces where grasses are the dominant plant species,Grasslands occur in temperate and in the tropical regions.Also known as prairies or steppes, grasslands receive ten to thirty-five inches (25.4 cm to 88.9 cm) of rainfall a year and usually experience hot summer temperatures. Some trees may be found, but the open space and lower amounts of rainfall make it difficult for trees to thrive in grasslands. Grazing animals are commonly found in grasslands and can include large species like buffalo and elephants. Many bird and insect species also thrive in grasslands.

• Steppe or Temperate Grassland Biome:

They are practically treeless, and the grasses are much shorter. Grasses are fresh and nutritious. Poleward, an increase in precipitation gives rise to a transitional zone of wooded steppes where some conifers gradually appear. Do not have much animal diversity.

• Savanna or Tropical Wet and Dry Biome:

The savanna landscape is typified by tall grass and short trees. The trees are deciduous, shedding their leaves in the cool, dry season to prevent excessive loss of water through transpiration, e.g. acacias. Trees usually have broad trunks, with water-storing devices to survive through the prolonged drought. Many trees are umbrella shaped, exposing only a narrow edge to the strong winds. Savanna biome is rich in mammal, bird and reptile diversity.

DESERT ECOSYSTEM :

Deserts cover about one fifth of the earth’s surface. While you may picture a desert as one of the hottest places in the world, desert ecosystems can also be found in cold regions.

The main characteristic of a desert ecosystem is a very low moisture level, with less than ten inches of rain (25.4 cm) annually and very dry air throughout the year, Evaporation rates regularly exceed rainfall rates.

Soils are coarse-textured, shallow, rocky or gravely with good drainage and have no subsurface water. The finer dust and sand particles are blown elsewhere, leaving heavier pieces behind. Sand dunes are common. Mean annual temperatures range from 20-25° C. The extreme maximum ranges from 43.5 – 49° C. Minimum temperatures sometimes drop to -18° C.

Based on the temperature range, deserts can be Hot deserts and Cold deserts. Whether hot or cold, desert ecosystems have abiotic factors like a lack of moisture and poor soil or sand that make it difficult for biotic components to survive. Hot deserts such as the Sahara of North Africa and the deserts of the south western U.S., Mexico, Australia and India (Thar Desert) occur at low latitudes.

The dominant animals of warm deserts are reptiles and small mammals. The Indian Spiny-tailed lizard, the blackbuck, the white-footed fox are the common fauna of the Thar deserts. There are also insects, arachnids and birds. Cold deserts occur in the Antarctic, Greenland and the Nearctic realm, parts of USA and in parts of western Asia and the Ladakh region in India. Widely distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice, grasshopper mice, antelope and ground squirrels.

In cold desert ecosystems like Antarctica, animals have adapted by adding layers of fat and finding ways to conserve energy since food can be scarce. In hot desert ecosystems like the Sahara Desert, animals have adapted by becoming nocturnal and sleeping during the day in order to protect themselves from the extreme heat.

Aquatic Ecosystem

Ecosystems consisting of water as the main habitat are known as aquatic ecosystems. Based on their salt content, aquatic ecosystems are categorised into following three types:

• Freshwater Ecosystems with less than 5 ppt (parts per thousands) such as lakes, ponds, springs, rivers etc.
• Marine Ecosystems with 35 ppt or above such as Seas and Oceans.
• Brackish Water Ecosystems with 5 to 35 ppt such as estuaries, mangroves.

Aquatic Organisms:

The aquatic organisms are classified on the basis of their zone of occurrence.

• Neuston : These organisms live at the air-water interface, e.g. floating plants.
• Periphyton : These are organisms which remain attached to stems and leaves of rooted plants or substances emerging above the bottom mud such as sessile algae.
• Plankton : Microscopic floating organisms such as algae, diatoms, protozoans and larval forms are called plankton. This group includes both microscopic plants like algae (phytoplankton) and animals like crustaceans and protozoans (zooplankton).The locomotory power of the planktons is limited so that their distribution is controlled, largely, by currents in the aquatic ecosystems.
• Nekton: This group contains powerful swimmers that can overcome the water currents.
• Benthos: The benthic organisms are those found living at the bottom of the water mass.

Factors Limiting the Productivity of Aquatic Habitats.:

• Sunlight : Sunlight penetration rapidly diminishes as it passes down the column of water. The depth to which light penetrates a lake determines the extent of plant distribution. Suspended particulate matters such as clay, silt, phytoplankton, etc. make the water turbid. Turbidity limits the extent of light penetration and photosynthetic activity in a significant way. Based on light penetration and plant distribution they are classified as photic and aphotic zones.

Photic zone : Photic (or “euphotic”) zone is the portion that extends from the lake surface down to where the light level is 1% of that at the surface. The depth of this zone depends on the transparency of water. Photosynthetic activity is confined to the photic zone. Both photosynthesis and respiration activity takes place.

Aphotic zone : The lower layers of the aquatic ecosystems, where light penetration and plant growth are restricted forms the aphotic zone (profundal zone). Only respiration activity takes place in this zone. The aphotic zone extends from the end of the photic zones to bottom of the lake.

• Dissolved oxygen : In freshwater the average concentration of dissolved oxygen is 10 parts per million by weight. This is 150 times lower than the concentration of oxygen in an equivalent volume of air. Oxygen enters the aquatic ecosystem through the air-water interface and by the photosynthetic activities of aquatic plants. Dissolved oxygen escapes the water body through the air-water interface and respiration of organisms (fish, decomposers, zooplankton, etc.) The amount of dissolved oxygen retained in water is also influenced by temperature. Oxygen is less soluble in warm water. Warm water also enhances decomposer activity.

Therefore, increasing the temperature of a water body increases the rate at which oxygen is depleted from the water. When the dissolved oxygen level falls below 3-5 ppm, many aquatic organisms are likely to die.

• Winterkill : An ice layer on the top of a water body can effectively cut off light. Photosynthesis stops but respiration continues in such water body. If the water body is shallow, the oxygen gets depleted, and the fish die. This condition is known as winterkill.
• Temperature : Since water temperatures are less subject to change, the aquatic organisms have a narrow temperature tolerance limit. As a result, even small changes in water temperature are a great threat to the survival of aquatic organisms when compared to the changes in air temperatures in the terrestrial organisms.

Freshwater Ecosystems

It emphasises mainly the study of the relationship between organisms and the freshwater environment. Limnology is the study of all aspects (physical, chemical, geological and biological) of freshwater. Freshwater habitats occupy a relatively small portion of the earth’s surface as compared to marine and terrestrial habitats.

• Lentic Ecosystem : Lentic ecosystems are solely found in still, fresh waters like lakes, ponds, marshes, and even ditches and seeps. Freshwater makes up only 1.8% of the Earth’s total surface, making lentic ecosystems one of the least common ecosystems. Depending on the depth of the water, lentic ecosystems can be found in layers. These layers differ from each other by the amount of light and oxygen found in the water.

The abiotic factors found throughout the layers of lentic ecosystems determine which biotic species can be found, with some species found only at the bottom of the waterbody and other species found only at the top. Lentic ecosystems are often nutrient-rich and are home to many species of plants and animals.

• Lotic Ecosystem : All ecosystems found in moving water are classified as lotic ecosystems. Lotic ecosystems are found in springs and rivers of all sizes, whether water moves in one direction like a river or has a more inconsistent flow like a spring. Lotic ecosystems are broken into areas with fast-moving water and areas with pools and slower currents. Like other ecosystems, these different zones allow different plants and animals to thrive throughout the ecosystem.

Wetland Ecosystem

Wetlands are areas of marsh or peatland with water that is static or flowing, fresh, brackish or saline, including areas of marine water the depth of which at low tide does not exceed 6 m. Wetlands are transition zones (ecotone) between terrestrial and aquatic ecosystems.

E.g. Mangroves, lake littorals (marginal areas between highest and lowest water level of the lakes), floodplains (areas lying adjacent to the river channels beyond the natural levees and periodically flooded during high discharge in the river) and other marshy or swampy areas. These habitats experience periodic flooding from adjacent deepwater habitats and therefore supports plants and animals specifically adapted to such shallow flooding or waterlogging. Waterlogged soil adapted to plant life (hydrophytes), and hydric soils (not enough O2) are the chief characteristics of wetlands.

India has over 27,000 wetlands, of which 23,000+ are inland wetlands, and around 4000 are coastal wetlands. Wetlands occupy 18.4% of the country’s area of which 70% are under paddy cultivation. Natural wetlands in India range from high altitude wetlands in the Himalayas; flood plains of the major river systems; saline and temporary wetlands of the arid and semi-arid regions; coastal wetlands such as lagoons, backwaters, estuaries, mangroves, swamps and coral reefs, and so on.

India became a party to the ‘Convention on Wetlands’, also known as the Ramsar Convention

on 1st February 1982 and has since then designated about 75 wetlands under the List of Wetlands of International Importance. World Wetland Day is observed on 2nd February

Ramsar Criteria for Wetland Identification :

• Contains a representative, rare, or unique example of a natural or near-natural wetland type.
• Supports vulnerable, endangered, or critically endangered species; or threatened ecological communities.
• Supports populations of plant and/or animal species important for maintaining the biological diversity of a particular biogeographic region.
• Supports plant and/or animal species at a critical stage in their life cycles or provides refuge during adverse conditions.
• Regularly supports 20,000 or more water birds.
• Regularly supports 1% of the individuals in a population of one species or subspecies of water birds.
• Supports a significant proportion of indigenous fish subspecies.
• Is an important source of food for fishes, spawning ground, nursery and/or migration path.
• Is an important source of food and water resources, increased possibilities for recreation and ecotourism, etc.

Importance of Wetlands :

1. Wetlands are indispensable for the countless benefits or “ecosystem services” that they provide humanity, ranging from freshwater supply, food and building materials, and biodiversity, to flood control, groundwater recharge, and climate change mitigation.
2. Wetlands are habitat to aquatic flora and fauna, numerous species of native and migratory birds.
3. Wetlands are an important resource for sustainable tourism.
4. They carry out water purification, filtration of sediments and nutrients from surface water.
5. They help in nutrient recycling, groundwater recharging and stabilisation of local climate.
6. Play an important role in flood mitigation by controlling the rate of runoff.
7. Buffer (act as a riparian buffer) shorelines against erosion and pollutants.
8. They act as a genetic reservoir for various species of plants (especially rice).

Reasons for Depletion:

1. Excessive pollutants (Industrial effluents, domestic waste, agricultural runoff etc.) are dumped into wetlands beyond the recycling capacity.
2. Habitat destruction and deforestation create ecological imbalance by altering the population of wetland species.
3. Conversion of wetlands for agriculture and encroachment by the public and mafia.
4. Overfishing and fish farming (Aquaculture).
5. Overgrazing in marshy soils.
6. Removal of sand from beds near seas makes the wetland vulnerable to wave action and tidal bore.

Mitigation:

1. Demarcation of wetlands using the latest technology, proper enforcement of laws and stringent punishments for violators.
2. Preventing unsustainable aquaculture and cultivation of shellfish.
3. Treating industrial effluents and water from farmlands before discharging into wetlands.
4.  Artificial regeneration for a quick recovery.
5. Utilising wetlands on a sustainable basis by giving enough time for natural regeneration.
6. Afforestation, weed control, and preventing invasive species is the key to wetland conservation. Preventive measures to stop the introduction of exotic invasive species like water hyacinth. Soil conservation measures & afforestation.
7. Preventing grazing in the peripherals of wetlands.
8. Wildlife conservation, sustainable tourism, eco-tourism and sensitising the local populace.
9. Eutrophication abatement by processing nutrient rich discharge into the water body.
10.  Involving the local population in the conservation of wetlands.

Wetlands (Conservation and Management) Rules, 2017

• Nodal Authority : Wetlands Authority within a state is the nodal authority for all wetland-specific authorities in a state/UT for the enforcement of the rules. 
• Prohibited Activities : Setting up any industry and expansion of existing industries, dumping solid waste or discharge of untreated wastes and effluents from industries and any human settlements. Encroachment or conversion for non-wetlands uses. 
• Integrated Management Plan : The guidelines recommend that the state/UT administration prepare a plan for the management of each notified wetland by the respective governments. 
• Penalties : As per the Environment (Protection) Act, 1986.

Lake Ecosystem

Lake (hollow) is created from geological or geomorphic processes. It then receives surface run-off water or ground discharge. In the next stage chemicals and minerals mix up and finally the lake starts to age. Lake is surrounded by land. Algae, bacteria, fungi, aquatic phanerogams, crustaceans, aquatic insects,molluscs and fish make its flora and fauna. Extent to which and number of times the water is mixed during the year is known as turn-over cycle of the lake.

Deep water abstraction, Flushing, Algae skimming, plants to suck nutrients, Harvest fish & macrophytes,Sludge removal, Filters for algae removal are different mechanisms for cleaning lakes.

Physiographic categorisation gives 4 types of lakes namely, Natural Lakes, Artificial Lakes, Oxbow Lake (Formed by river deposits) and Crater Lake (due to volcanic activity). Classification based on salt content gives Freshwater, Brackish, Saline Lakes.

EUTROPHICATION :

Due to addition of domestic waste (sewage), phosphates, nitrates etc, from wastes or their decomposition products in water bodies, from point and nonpoint sources, they become rich in nutrients, especially phosphate and nitrate ions.

• Point sources are attributable to one influence, therefore easy to regulate.
• Non-point sources having multiple unknown influences become very difficult to regulate.

With the passage of these nutrients through such organic wastes, the water bodies become highly productive or eutrophic.

Toxicity, new species invasion, decreased biodiversity, decrease in species richness and diversity, Toxic Aerosols in microenvironment are its effects.

Restoration and preservation of ecosystems, creating buffer zones for sediments to collect, nitrogen testing, Industrial waste treatment and efficiency, reducing livestock densities and nonpoint pollution are required for effective mitigation.

 Distinction ( Lakes v/s Wetland )

Lakes are generally less important when compared to wetland from the viewpoint of ecosystem and biodiversity conservation. There is no clear distinction between lakes and wetlands. Wetlands are shallow water bodies whereas lakes can be deep or shallow.

The National Lake Conservation Programme (NLCP) considers lakes as standing water bodies which have a minimum water depth of 3 m, generally cover a water spread of more than ten hectares and have no or very little aquatic vegetation.

Wetlands (generally less than 3 m deep over most of their area) are usually rich in nutrients (derived from surroundings and their sediments) and have abundant growth of aquatic macrophytes (an aquatic plant large enough to be seen by the naked eye). They support high densities and diverse fauna, particularly birds, fish and macroinvertebrates, and therefore, have high value for biodiversity conservation. Excessive growth of macrophytes (both submerged and free-floating) in wetlands affects the water quality adversely and interferes with the utilisation of the water body. However, marginal aquatic vegetation is desirable as it checks erosion, serves habitat for wildlife and helps improve water quality.

Oceanic Ecosystem

Oceanic ecosystems include almost all of the saltwater ecosystems in the world. About 71% of the Earth’s surface is covered by the ocean, making oceanic ecosystems the most common in the world. Oceanic ecosystems are split into four zones based on depth of water.

The intertidal ocean ecosystem is found in coastal areas where the ocean interacts with both land and freshwater ecosystems. The neritic ocean ecosystem is found in shallow areas of the ocean. The abyssal ocean ecosystem is found in deep water on the ocean floor, where sunlight is unable to penetrate the water. This ecosystem is the least explored ecosystem in the world. The oceanic ecosystem covers the rest of the ocean.

Estuarine Ecosystem:

 An estuary is a place where a river or a stream opens into the sea (mouth of the river). It is a partially enclosed coastal area of brackish water (salinity varies between 0-35 ppt) with one or more rivers or streams flowing into it, and with a free connection to the open sea. At the estuaries, freshwater carrying fertile silt and runoff from the land mixes with the salty sea water.

Estuaries form a transition zone (ecotone) between river environments and maritime environments. Examples of estuaries are river mouths, coastal bays, tidal marshes, lagoons and deltas. Estuaries are formed due to rise in sea level, movement of sand and sandbars, glacial processes and tectonic processes.

All the plants and animals in the estuaries are subjected to variations in salinity to which they are adapted (osmoregulation). Estuaries are greatly influenced by tidal action. They are periodically washed by sea water once or twice a day based on the number of tides. In some narrow estuaries, tidal bores are significant. Tidal bores cause great damage to the estuarine ecology.

Importance of Estuaries :

They are the most productive (more productive than wetlands) water bodies in the world because of the mixing of freshwater and saline water zones where marine organisms of both ecosystems meet.

Ecotone regions (transitional zones) like mangroves, wetlands, estuaries, grasslands etc. have far greater productivity compared to natural ecosystems like a forest ecosystem, ocean ecosystem, pond ecosystem, riverine ecosystem, desert ecosystem etc. This is because of the wide-ranging species from the adjacent ecosystems being present in the ecotone. Also, an estuary has very little wave action, so it provides a calm refuge from the open sea and hence becomes ideal for the survival of numerous aquatic species.

Estuaries are the most heavily populated areas throughout the world, with about 60% of the world’s population living along estuaries and the coast. The vast mangrove forests on the seaward side of an estuary act as a barrier for the coastal habitat to check the wind speed during cyclones and high velocity landward winds.

Mangroves act as a filter trapping suspended mud and sand carried by rivers which leads to delta formations around estuaries. Precipitation of clay and alluvium particles in the estuarine region is high because of the exposure to saline water (saline water precipitates fine alluvium).

Estuaries store and recycle nutrients, traps sediment and forms a buffer between coastal catchments and the marine environment. They also absorb, trap and detoxify pollutants, acting as a natural water filter.

Estuaries with their wetlands, creeks, lagoons, mangroves and sea-grass beds are rich in natural resources including fisheries. They are deep and well protected from marine transgressions, and hence they are ideal locations for the construction of ports and harbours.

The banks of estuarine channels form a favoured location for human settlements, which use the estuaries for fishing and commerce but nowadays also for dumping civic and industrial waste.

Differences between Lagoon and Estuary:

A lagoon is a stretch of salt water separated from the sea by a low sandbank or coral reef.

Backwaters in Kerala are mostly lagoons where seawater flows inwards through a small inlet that is open towards the sea.

In estuaries, the water flows fast and strong, while in lagoons the water is shallower and flows sluggishly.

Estuaries are usually deeper than lagoons. Also, lagoons mostly don’t have any fresh water source while the estuaries have at least one. Lagoons are more saline than estuaries.

Lagoons are formed due to falling sea levels (coastline of emergence. E.g. Kerala Coast) whereas estuaries are mostly formed due to rise in sea levels (coastline of submergence. E.g. Konkan coast)

India Estuarine Ecosystem :

The Country has 14 major, 44 medium and 162 minor rivers drains into the sea through various estuaries. Major estuaries occur in the Bay of Bengal. Many estuaries are locations of some of the major seaports. Most of India’s major estuaries occur on the east coast. In contrast, the estuaries on the west coast are smaller (in environmental studies, deltas are considered as subsections of estuaries). Two typical examples of estuaries on the west coast are the Mandovi and Zuari estuaries.

Issues of Indian Estuarine Ecosystem :

1. Modifications of the estuarine catchments result in changes in water flow in various estuaries, either far in excess or much lower than required (E.g. Hooghly, Godavari, Pulicat etc.)
2. Pollution through industries and combined city sewage discharge.
3. Recreational boating and fishing.
4. Navigation, dredging and shipping (e.g. Hooghly).
5. Expansion of urban and rural settlements, mining & industries, agriculture and dumping of solid wastes.
6. Overexploitation of target fish stock due to increased demand.
7. Reclaiming the fringed areas for intensive aquaculture in pens.
8. Obstructing the migratory routes of fish and prawn recruitment (e.g., Chilka, Pulicat).
9. Polluting the environment through feeding of stocked fish and prawn in pens (Chilka).
10. Destruction of biodiversity through prawn seed collection and operation of small-meshed nets (e.g., Hooghly, Chilka, Pulicat).
11.  Submergence of catchment areas due to rising water level.

Mangroves

Mangroves represent a characteristic littoral (near the seashore) forest ecosystem. These are mostly evergreen forests that grow in sheltered low lying coasts, estuaries, mudflats, tidal creeks, backwaters (coastal waters held back on land), marshes and lagoons of tropical and subtropical regions.

Mangroves grow below the high water level of spring tides. The best locations are where abundant silt is brought down by rivers or on the backshore of accreting sandy beaches.Mangroves are highly productive ecosystems, and the trees may vary in height from 8 to 20 m. They protect the shoreline from the effect of cyclones and tsunamis. They are breeding and spawning ground for many commercially important fishes.

Since mangroves are located between the land and sea, they represent the best example of ecotone. Mangroves are shrubs or small trees that grow in coastal saline or brackish water.Mangroves are salt tolerant trees, also called halophytes, and are adapted to harsh coastal conditions. Mangrove vegetation facilitates more water loss. Leaves are thick and contain salt-secreting glands. Some block absorption of salt at their roots itself.

They contain a complex salt filtration system and complex root system to cope with salt water immersion and wave action. They are adapted to the low oxygen (anoxic) conditions of waterlogged mud. They produce pneumatophores (blind roots) to overcome the respiration problem in the anaerobic soil conditions.

Mangroves occur worldwide in the tropics and subtropics, mainly between latitudes 25° N and 25° S. They require high solar radiation to filter saline water through their roots. This explains why mangroves are confined to only tropical and subtropical coastal waters.

Mangroves occur in a variety of configurations. Some species (e.g. Rhizophora) send arching prop roots down into the water. While other (e.g. Avicennia) send vertical “Pneumatophores” or air roots up from the mud. Adventitious roots which emerged from the main trunk of a tree above ground level are called stilt roots.

Mangroves exhibit Viviparity mode of reproduction. i.e. seeds germinate in the tree itself (before falling to the ground). This is an adaptive mechanism to overcome the problem of germination in saline water.

Mangroves in India

The mangroves of Sundarbans are the largest single block of tidal halophytic mangroves of the world. This mangrove forest is famous for the Royal Bengal Tiger and crocodiles. Mangrove areas here are being cleared for agricultural use. The mangroves of Bhitarkanika (Orissa), which is the second largest in the Indian subcontinent, harbour high concentration of typical mangrove species and high genetic diversity.

Mangrove swamps occur in profusion in the intertidal mudflats on both side of the creeks in the Godavari-Krishna deltaic regions of Andhra Pradesh. Mangroves of Pichavaram and Vedaranyam are degraded mainly due to the construction of aquaculture ponds and salt pans.

On the west coast of India, mangroves, mostly scrubby and degraded, occur along the intertidal region of estuaries and creeks in Maharashtra, Goa and Karnataka. The mangrove vegetation in the coastal zone of Kerala is very sparse and thin. In Gujarat (north-west coast) mangroves Avicennia marine, Avicennia officinalis and Rhizophora mucronata are found mainly in the Gulf of Kutch and the Kori creek.

Mangroves are of scrubby type with stunted growth, forming narrow, discontinuous patches on soft clayey mud. The condition of the mangroves is improving especially in the Kori creek region, which is a paleodelta of the Indus river (once upon a time it was part of the Indus delta). In size, mangroves range from bushy stands of dwarf mangroves found in Gulf of Kutch, to taller stands found in the Sunderbans.

On the Andaman & Nicobar Islands, the small tidal estuaries and the lagoons support a dense and diverse undisturbed mangrove flora.

Importance of Mangroves:

1. Mangrove plants have (additional) special roots such as prop roots, pneumatophores which help to impede water flow and thereby enhance the deposition of sediment in areas (where it is already occurring), stabilise the coastal shores, provide a breeding ground for fishes.
2. Mangroves moderate monsoonal tidal floods and reduce inundation of coastal lowlands.
3. They prevent coastal soil erosion.
4. They protect coastal lands from tsunamis, hurricanes and floods.
5. Mangroves enhance the natural recycling of nutrients.
6. Mangrove supports numerous florae, avifauna and wildlife.
7. Provide a safe and favourable environment for breeding, spawning, rearing of several fishes.
8. They supply woods, firewood, medicinal plants and edible plants to local people.
9. They provide numerous employment opportunities to local communities and augment their livelihood.

 Coral Reefs:

Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral. Corals are of two types: Hard coral and Soft coral. The coral species that build reefs are known as hermatypic, or “hard,” corals because they extract  calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like  bodies.

Other species of corals that are not involved in reef building are known as “soft” corals. Soft corals, such as sea fingers and sea whips, are soft and bendable and often resemble plants or trees. These corals do not have stony skeletons, but instead grow wood-like cores for support and fleshy rinds for protection.

Deep-sea corals live in much deeper or colder oceanic waters and lack zooxanthellae. Unlike their shallow water relatives, which rely heavily on photosynthesis to produce food, deep sea corals take in plankton and organic matter for much of their energy needs. Coral reef ecosystems are the most diverse oceanic ecosystem. The shallow water allows more sunlight to be available, creating more nutrients that lead to increased plant and animal species.

Coral reef ecosystems cover about one percent of the ocean floor but about 25% of fish species depend on coral reef ecosystems for survival. This is because coral reefs often serve as protection, breeding grounds, and food sources for many different fish and other marine species.

How are they formed?

Coral polyps are tiny and fleshy sea anemones that live in tropical and subtropical oceans and seas. They live in shallow waters along with microscopic algae called Zooxanthellae, with which they share a symbiotic relationship. This algae has photosynthesis abilities that feed the coral polyps with carbon compounds which give them energy. In return, the polyps provide protection to Zooxanthellae.

Coral reefs are formed when the freely moving larvae of corals attach themselves to sedimentary rocks or hard surfaces near the coastlines. This process is undertaken with the help of several other processes like sedimentation, compaction, cementation and solidification of the skeletons of coral polyps.

Where are coral reefs found in India?

India is recorded to have around 7,517 km of coastline but only 6,100 km represents the mainland coastline. The three major types of coral reefs found in India are fringing, barrier and atolls.

Coral reefs in India are found in a lot of areas including the Gulf of Kutch, Gulf of Mannar, Palk Bay, Andaman & Nicobar and Lakshadweep Islands. The Gulf of Kutch in the northwest has some of the most northerly reefs in the world. Patches of coral reefs are also found in Ratnagiri, Malvan and Redi, south Bombay and at the Gaveshana Bank located in the west of Mangalore. Corals running parallel to the shore are found at Quilon near the Kerala coast to Enayem in Tamil Nadu. On the east coast, between Parangipettai (south of Cuddalore) and Pondicherry, corals are found in abundance. When it comes to island corals, the Andaman and Nicobar Islands, and Lakshadweep Islands are rich with flourishing corals.

Types of coral reefs in India :  India has three major prevailing types of coral reefs:

1. Fringing Reefs – Fringing reefs evolve and develop near the continent and remain close to the coastline. These reefs are separated from the coastline by small, shallow lagoons. They are the most commonly found reefs in the world. 
2. Barrier Reefs – Barrier reefs are found offshore on the continental shelf. They usually run parallel to the coastline at some distance. A deep and wide lagoon is located between the coastline and the barrier reef. 
3. Atolls – Atolls are formed on mid-oceanic ridges. They are shaped circularly or elliptically and are surrounded by seas on all four sides and have shallow waters in the centre are called a lagoon.

What are the ideal environmental conditions for corals to grow?

Coral reefs have certain conditions that must be met for them to grow in full bloom.

• Shallow water : Coral reefs need to grow in shallow parts of the water. The surface of the reef shouldn’t be more than 80m from the water surface. The Zooxanthellae need adequate sunlight for their photosynthesis processes. 
• Semi-hard or hard surface : The semi-hard or hard surface is a precondition for compaction, cementation and solidification of the coral polyps skeletons. 
• Clear water : The beautiful coral polyps perish in areas filled with sediment-filled waters. Moreover, they cease to exist in opaque waters. This is because the presence of sediments and opaque water limits the passage of sunlight to the algae that sustains their life. 
• Warm water :  Coral reefs are directly connected with the warm oceanic waters. The temperature of the water must be around 20 degrees. Hence, coral reefs generally prevail on the eastern coasts of continents. However, this is not true in the case of India as the eastern waters are filled with high amounts of sediment matter. 
• Saline-filled waters : The slight salt in ocean waters is extremely important for the development of coral polyps. The polyps extract calcium from the waters to protect their skeletons. Hence, mild salinity is a necessity for coral reefs to flourish. 
• Rich supply of nutrients : Coral reefs flourish in sea waters because ocean waves support the constant supply of rich nutrients. Coral polyps multiply faster when supplied with nutrients.

Why is the survival of corals and coral reefs important to human and marine life? Corals are important to marine life because of the following reasons:

1. The health of the marine ecosystem is dependent on corals.
2. They support a wide range of ecosystems and hence, are called the rainforests of the ocean.
3. Corals provide a place to live for a huge variety of fish.
4. Corals are a primary source of food in the marine ecosystem.

Coral reefs act as a barrier and protect the coastal areas from strong ocean currents and waves. They provide protection from ocean storms and cyclones. With the increasing amount of cyclones in India due to climate change, these natural barriers have become excessively important.

Fish that live in and around coral reefs are a healthy source of protein for billions of people, mainly living on coastlines. Some fishing industries are entirely dependent on the coral reefs and the wildlife that it attracts.

Coral reefs are said to be the medicine chests of the sea. Some fish that the corals attract, leave behind some chemical compounds that are similar to the ones used in human hospitals.

A new study by the Indian Institute of Meteorology has stated that corals along the north-western coast provided insights on the patterns of the onset and withdrawal of Indian monsoons.

Most of the gross national product of countries with coral reef industries comes from the tourism sector due to these beautiful corals. A study had estimated that the value of coral reefs was $10 billion and the direct economic benefits were approximately $360 million per year.

What are the threats that push corals to the brink of extinction?

Coral reefs are facing a large number of threats, directly or indirectly, by human actions. Scientists believe that all coral reefs will face threats by 2050, 75% of them facing high-risk threats. Some of these threats are :

1. Global warming : Due to global warming, the waters are getting more acidic and posing threats to the coral ecosystem. Moreover, the glaciers across the world are melting due to which sea levels are rising. Rising sea levels lead to the coral reefs drowning and not getting enough sunlight which leads to their slow growth.
2. Coral Bleaching : Coral bleaching takes place when the oceans get warmer. Since corals have a narrow temperature tolerance, they get stressed and release a symbiotic algae in response. When they run out of the algae, they run out of their life source and hence, cease to exist.
3. Marine pollution : Marine pollution in the form of plastic pollution and other activities has led to the corals being suffocated. Coral reefs need air and space to breathe. With the rising levels of sea pollution, we might lose them sooner than we thought.
4. Stronger storms and ocean acidification : The upsurge of stronger storms has led to oceanic waves that break and damage the coral reefs. They might even break colonies and make them unsafe for living. As the sea absorbs more and more CO2, the pH levels continue to increase. High pH levels lead to weaker coral skeletons, their vulnerability to diseases and destruction by storms.
5. Ozone depletion : Coral polyps have in-built UV rays protection. However, now that the radiation is increasing, the corals in shallow waters can get damaged and destroyed.