Cover Image
close this book Biodiversity in the Western Ghats: An information kit
close this folder 4. Fresh- and brackishwater
View the document 4.1 Estuarine ecosystems
View the document 4.2 Mangroves
View the document 4.3 Mangrove communities
View the document 4.4 Wetlands
View the document 4.5 Freshwater wetlands: Carambolim Lake
View the document 4.6 Freshwater algae

4. Fresh- and brackishwater


4.1 Estuarine ecosystems

Estuaries are where rivers discharge into the sea. They are semi-enclosed bodies of water, connected to the open sea, but where the sea water is diluted by fresh water from the land.

Both land and sea affect estuaries, and their influence varies throughout the day and from season to season. These factors pose serious challenges for living organisms, and estuaries have developed unique ecosystems in response.


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. The Mandovi-Zuari estuary in Goa and Cochin backwaters in Kerala are typical estuaries in which surface salinity ranges from 0.65% at the peak of the monsoon in August to 33.64% in the hot pre-monsoon period in April.

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 monsson 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. For instance, to avoid unfavourable salinity, barnacles shut their valves, mussels close their shells, eupogebia burrow into the substrate, and other creatures migrate up and down the estuary.

Many estuaries in India were formed when the sea level rose, submerging parts of the coast and drowning river valleys. The Mandovi and Zuari estuaries in Goa were formed in this way.

Estuarine ecosystems

Estuaries can also be formed when shingle and sand bars form parallel to the coast, enclosing a shallow area and partly blocking a river's exit to the sea. One example of this is the Vellar Estuary in Tamil Nadu.

Vellar Estuary in Tamil Nadu

Most estuarine animals have effective osmoregulatory adaptations (methods of controlling the amount of salt in their bodies). Some regulate their salt content higher than the surroundings when the surrounding water has low salinity (this is called hyperosmotic regulation). The shore crab Carcinus, amphipod Gammarus, the crab Sarsama erythrodactyla certain prawns and the bivalve Mercenaria mercenaria all show hypertonicity in blood in diluted sea water.

Mytilus edulis and Arenicola marina have no osmoregulatory mechanism. They adjust as their tissues are able to function under low salt content. However they are unable to survive in salinity below their threshold concentration.


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.


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.



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 therefoore the most important photosynthesisers of organic matter. Salt-marsh plants such as spartina and zoostera and mangrove forest assume great importance as primary producers.

Typical estuarine habitats and brackish water lakes in India

Nutrient flows

The fertility of the estuary depends on the flow of nutrients from the river and on tidal currents. The Mandovi-Zuari rivers are rich in nutrients, especially nitrates and phosphates. Drainage from the land is the major source of nutrient inputs into the estuary. In addition, industrial effluents and city waters also find their way into the estuary. Some estuaries in Gujarat are subject to heavy industrial pollution, making it difficult for fish to survive.

The overall productivity of most Indian estuaries is low because of their high turbidity. In Cochin backwaters, the gross primary productivity measure of ranges from 270 to 298 g C/m²/yr, while net production is 124 g C/m²/yr. In Cochin backwaters, only 25% of the total phytoplankton production is estimated to be used by the herbivore population. The unconsumed food sinks to the bottom as detritus.

Even though the estuarine phytoplankton production is low, it is well compensated by the productivity of plants such as marsh grass, reeds and mangroves. More than 50% of production is available to estuaries in the form of detritus. Land drainage also supplies abundant detritus.

The abundant detritus means that it is the basis for most of the estuarine food chain. Several animals, or zooplankton, feed on the detritus and thus are primary consumers.

Gross primary productivity: the rate at which energy from light is absorbed and used with carbon dioxide to produce organic matter through photoosynthesis. It is measured in grammes of carbon per square metre per year (9 C/m²/yr).

Net productivity: The amount of organic matter formed in excess of that use in respiration.

Prepared by Dr. X. N. Verlencar


4.2 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 founnd 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 have developed various ways of surviving in this challenging environment. They have an unusual root system of prop and knee roots and aerial breathing roots. The seeds germinate while still attached to the mother plant. The leaf surface has glands that exude excess salt.

Ecological and economic value

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.

Ecological and economic value

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.

Causes of degradation

Various abiotic and biotic factors are responsible for the degradation of mangroves. Direct or indirect interference by humans has affected mangroves all along the west coast of India. Deforestation, reclamation and pollution are three major problems.

Deforestation. Firewood collection in mangrove areas is an age=old practice. This causes acute deforestation around metropolitan cities like Bombay. Urban expansion has also cleared large areas.

Reclamation. Mangroves are being reclaimed for agriculture, aquaculture and industrial development.

Pollution. Pollution by toxic and non-toxic effluents from various sources has created a range of complex problems. Raw sewage discharge in these swamps increases the eutrophication rate. This is most severe near big cities.

Mangrove ecosystems are overexploited and misused. Often the short term economic gains from conversion or exploitation result in long term ecological problems.

Environmental impact of degradation

Continuous overexploitation of mangroves along the west coast of India has had several serious negative impacts.

• It has resulted in the degradation or loss of biodiversity in the region.

• Removal of the mangroves and their root systems has increased coastal erosion.

• Fish yields have suffered because of the loss of a vital food source and breeding and nursery grounds.


It is necessary to identify the available mangrove areas with good forest cover for conservation. Possible approaches include:

• Identify luxuriant mangrove areas and protect them from exploitation.

• Plant mangroves on currently barren intertidal mudflats.

• Allow degraded mangroves to regenerate.

• Prepare land use plans for coastal and estuarine areas and pass the necessary legislation to conserve mangroves.

• Create awareness through the media at all levels.

Prepared by Dr. A. G. Untawale


4.3 Mangrove communities

Mangrove ecosystems are forests uniquely adapted to salty water. They produce large quantities of vegetative matter which, in turn, provides food for other organisms. They are located along the shores of estuaries where fresh water meets the sea. Mangrove forests provide food, fuel, timber and medicines either directly or indirectly. However, these renewable, ecologically and economically important habitats have been largely degraded, severely damaging the coastal environment.

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.

Mangrove communities

Distribution of mangrove species in West Coast estuaries

Extent and composition

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. Large areas with many mangrove species occur in the polyhaline and mesohaline zones (salinity 5-30 percent). The oligohaline (salinity 0.05 to 5 percent) zone supports limited species such as Kandelia candal, Sonneratia caseolaris and Acrostichum aureum.

Mangrove flora of west coast is comprised of 22 species belonging to 15 genera. Maharashtra has the most species (19), whereas only 9 species occur along the Gujarat coast. Avicennia alba, A. marina, A. officinalis, Rhizophora mucronata, Sonneratia alba and S. apetala, are dominant. Scrubby vegetation, mainly of A. marina, Salicornia brachiata and Sueda sp. occurs just above the high tide level. The largest area is in Gujarat, with 37,000 ha, but better formations with greater species diversity occur in Goa and Maharashtra.

Biodiversity of Indian mangroves

Taxonomic group

Number of species



































Wood borers



1 85








Associate flora and fauna

Associate flora and fauna are important components of the mangrove ecosystem as they enhance the productivity and recycling in the system.

Floral components

Clerodendron inermae, Hibiscus tiliaceus, Thespesia populnea, Sessuvium portulacastrum, Porteresia coarctata and Myriostichya waghitiana are commonly found in the mangroves. Another 29 species dominated by Aeluropus lagopoides, Cressa cratica, Fimbristylis cymosa and Heliotropium curassavicum are found just inland of the mangroves, elevated above the spring tide mark.


Seagrasses are often associated with mangroves. Halophila beccarii and H. ovalis, H. ovata and Halodule uninervis occur in the mangrove-influenced regions. Halophila ovalis occurs in sheltered parts (salinity > 30%) of estuaries. H. ovata and Halodule uninervis; have been seen in the vicinity of mangroves in the Gulf of Kutch, Gujarat.


Marine algae in the mangrove environment are either floating or attached to the sea floor. Very little is known of the marine algae associated with mangrove regions of India. The seasonal occurrence of 48 species of marine algae from the mangrove ecosystems of the central west coast of India has been reported.

Caloglossa lepriurii, Catnella impudica and Enteromorpha clathrata form the characteristic flora and commonly occur throughout the year. Economically important algae such as Monostroma spp and Gracilaria verrucosa grow in mangrove areas with high salinity.

The poor distribution and low diversity of marine algae in mangrove environments could be due to unstable soils and wide fluctuations in salinity, temperature, turbidity and nutrients. The maximum number of marine algae occurs during October to April, when the salinity gradually increases. Microscopic blue-green algae (Cyanophyceae) dominate the mangrove environments during the monsoon (June-September).

Manglicolous fungi

Higher marine fungi play significant role in the formation of mangrove detritus. Seventy-six species of higher fungi have been reported from the mangroves of the west coast.


Microbial flora (yeast, bacteria and fungi) play a significant role in the degradation of mangrove litter. Mangrove environments harbour 50 bacterial strains, mostly grampositive. Micrococus, Brevibacterium and Kurthia have been reported as predominant. Other species of bacterial genera such as Lactobacillus, Corynebacterium, Listeria, Bacillus and Clostridium have also been found.


Mangrove environments, though fairly high in primary production, have very few phytoplankton species. These include Pleurosigma, Navicula and Nitzchia, followed by Bacillaria, Coscinoidiscus and Cymbella. Other forms like Biddulphia, Diploneis, Mastogloia and Thalassiothrix occur only rarely.

Manglicolous fungi


Didymosphaeria enalia Lophiostoma sp. Swampomyces aremeniacus Hypoxylon oceanicus Dactyospora haliotrapa Massarina thalassia Aquialus grandis Acrocordiopsis patilie Lulworthia grandispora Helicascus sp.


Trichocladium archarasporum

Cirennalia pygmea


Periconica prolitica

Floral components of mangrove environs in the west coast



No. of species


65,000 ha











Small patches seasonal



Seasonal; less diversity



0-30 mg/m³


Terrestial fungi














General status: moderately known



Zooplankton biomass in mangrove waters has been reported in the range of 6-1 13 mg/m³ per day. Crustaceans and copepod species dominate. The annual mean count of copepods ranges from 570 to 1270/m³, and their diversity is low compared- to estuarine and open ocean waters in the west coast.

Benthic macrofauna

111 species of macrofauna have been reported from the mangrove regions of Goal Segmented worms (Polychaetes) and bivalves contribute over 70% of the macrofaunal component by number and weight. Dominant species are Modiolus metcalfel, Mytilus viridis, Diapatra neapolitanea, Meretrix casta, Paphia malabarica, Cerithidea fluviatilis, Diogenes custus and Golycera alba.

Benthic macrofauna

Benthic meiofauna

Meiofaunal density in the mangrove environments have been reported to range from 3538-111.000/m². It is higher during the premonsoon and postmonsoon periods. Nematodes, especially Chromadoidae and Desmodoridae, account for 80% of the density, followed by copepods with 7%. Almost 60% of the meiofauna occur in the top 2 cm layer of sediment.

Wood borers in mangroves

Dictyathiefer manni

Lyrodus pedicellatus

L. masse

Bankia rochi

B. campanellata

B. carinata

Nausitord hedleyi

N. dunlopei

Bactronophorus thoraciles

Martesic striate

M. nairi

Lignopholas chengi

Sphaeroma terebrans

S. annandalci

S. annandalci var


Faunal components of mangrove environs in the west coast



No. of species


6-113 mg/m³/day






54.17/m²(wet weight)





Wood borers


2 6



















General status: poorly known

Wood borers

Biodeterioration of mangrove wood is quite severe along the Indian coast. The destruction is caused by 14 species and one variety of borers belonging to the molluscan and crustacean family.

Fishes, shellfishes and crustaceans

105 species of fish, 20 species of shellfish and 229 species of crustaceans have been reported in mangroves of the west coast. Commercially important species include Meretrix sp., Crassostrea sp., Peneaus sp., Scylla serrata and Mugil cephalic. The commonly cultivated species are Penaeus monodon, P. indicus, Metapenaeus monoceros, Mugil cephalus, M persica, Chanos chanos, Etroplus suratensis, and Lates calarifer.


Crocodylus palustris, Varanus sp., different kinds of monkeys, otters, deers, fishing cats snakes and wild pigs are very commonly found in the mangroves. Common birds are flamingos, herons, storks, sea eagles, kites, kingfishers, sandpipers, fits, bulbuls and whistlers. About 119 species of birds have been recorded from the mangrove regions of the Gulf of Kutch.

Crocodylus palustris


Rising population, urbanization and industrialization put continuous, intensive pressure on coastal regions. As a result, the mangrove habitats have suffered a reduction in the biota or total loss of some species. The degradation of coastal ecosystems is resulting in severe ecological imbalance in the coastal environments. The conservation and management of mangrove resources is needed immediately to mitigate the further deterioration of coastal environments.

Though mangrove ecosystems are poor in biodiversity, they have a characteristic biota of significant ecological and socioeconomic importance. During the last three decades, almost 40% of the mangrove area along the west coast has been "reclaimed", mainly for agriculture and urbanization. Thoughtful conservation and management of the mangrove environment for sustainable development could prevent further deterioration.

Prepared by T. G. Jagtap

The physical environment

The tidal amplitude along the west coast of India ranges from 0 to 11.5 m. The air temperature ranges from 11° to 39.6°C. Rainfall varies from 600 too 3000 mm a year, falling mainly in May to August. Humidity varies from 71 to 89%. In general, the climate remains relatively dry along the Gujarat coast, but is warm and humid along the other coastal states to the south. The west coast is characterized by steep slopes, rises, and drowned estuaries. The Gulf of Kutch to some extent represents a deltaic environment to a little extent. The west coast plain is very narrow and has alluvial soils.


4.4 Wetlands

Wetlands are unique transient ecosystems, falling between true aquatic systems on one hand and terrestrial systems on the other. The water table is usually at or near surface, or the land is covered by shallow water. 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.


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

• They support extensive freshwater and marine fisheries.

• They are natural sewage treatment plants. An 8-ha marsh or pond can clean 4.54 million litres of raw sewage every day.

• 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 floodor cyclone-prone areas. In estuaries, mangrove forests shield the coast against storms.

• Wetlands help maintain the water table by recharging ground water.

Wetlands and birds

Many species of birds use wetlands for breeding, feeding and roosting. In India, 26.5 percent of the total 1200 species are found in wetlands (this figure includes migratory winter visitors). Because many birds occupy higher trophic levels in the food chain, they can be considered as biological indicators of a healthy wetland.

Wetlands and birds


Cattle grazing

Though large-scale grazing has detrimental effects on wetlands, natural grazing by stray cattle is not a threat. Stray cattle are an integral part of the ecosystem; as they graze, they loosen the soil, allow vegetation to be recycled, add to fertility through their dung, and open passages for free-swimming water fowl.

Wetland types

Wetlands are basically of two types-natural and man-made. Natural wetlands can be formed in many ways: a landslide blocks a mountain valley, dissolved limestone rock forms depressions, shifting sand in arid areas forms a hollow, or a meandering river leaves behind an oxbow lake. People also make wetlands, for instance irrigation canals, reservoirs and irrigated fields.


The silt brought in by surface runoff during torrential tropical rains is a natural phenomenon. Siltation helps transform wetlands into land, and forms shallow wetlands from deeper water. But excessive siltation due to excessive soil erosion, opencast mining and other activities is of serious concern.

Fishing and aquaculture

Many wetlands are rich fisheries. But large-scale, indiscriminate fishing will affect wildlife, especially fish-eaters such as kingfishers, cormorants and oyster catchers. Aquaculture may be commercially profitable but can upset the chemical balance in the wetland, natural gene pools and biodiversity.

Large irrigation and hydroelectricity projects

Large dams across rivers form deep reservoirs and destroy shallow wetlands.


Indiscriminate use of pesticides and chemical fertilizers pollutes wetlands. Industrial and domestic effluents add to the load. Though wetlands are natural purifiers, they cannot withstand excessive pollution. Pollutants may also get into the food web. Petroleum products interfere with the reproductive process of water fowl, reducing the eggshell thickness and hatchability.


Rising demand for land for housing, industries and agriculture is having its toll on wetlands-especially near urban areas. In addition, wetlands are often used as municipal garbage dumps.

Remedial measures

• Phase out the indiscriminate use of pesticides and chemical fertilizers.

• Ban release of raw sewage.

• Implement afforestation programmes that are effective rather than cosmetic. Successful afforestation would minimize siltation.

• Control the reclamation of wetlands.


Defining waterfowl is as difficult as defining the wetland itself. Like other birds, wetland birds can be:

• Residents

• Local migrants, or

• Long distance migrants


These birds are also classified as:

• Completely dependent on wetlands

• Less dependent, or

• Opportunistic users.

Asian mid-winter waterfowl census

An annual census of waterfowl is conducted under the auspices of the Asian Wetland Research Bureau and the International Waterfowl and Wetland Research Bureau. The census aims to:

• Collect data on waterfowl at individual sites and flyways to facilitate conservation of waterfowls and wetlands.

• Monitor threats to waterfowl populations so solutions can be foound before the species and their habitats are irreversibly affected.

• Enhance awareness on the utility of waterfowl and wetlands to promote their conservation.

Prepared by Dr. A. B. Shanbhag and Ajay Gramopadhye


4.5 Freshwater wetlands: Carambolim Lake

Carambolim Lake is a man-made wetland covering about 70 hectares in the coastal area of central Goal

The wetland is flooded for about five months from October to March. The water level is raised to about 2m by closing a sluice-gate, enabling farmers to grow rabi (dry season) rice on the low-lying land around the wetland. In January, the water reaches its maximum depth. In April, the sluice is opened and the water drains out to the rice fields and eventually to the sea.

Surrounding land use changes are affecting the lake, especially its depth.

Location of Carambolim


Between November and March, around 15,000 birds can be seen in Carambolim. The best time to see them is in the early morning or early evening.

The birds feed on algae, grasses, insects, crustaceans, molluscs, and fish. It is this rich food source that attracts both local and migratory species. Egrets are commonly seen foraging for insects in the neighbouring fields while the rice is being transplanted.

About 120 species of birds are known to use the wetland during the year. Half of these are migratory, including around 30 winter visitors from as far away as NE Siberia and the Caspian Sea. Mallard and wigeon, normally found only in Northern India, have been sighted in Carambolim.

The rich bird life also attracts an increasing number of human visitors. Bird watchers and nature lovers, including foreign tourists, visit the wetland.

Other uses of Carambolim

Tourism: must be carefully controlled so that it does not harm the ecosystem.

Education: field visits by students.

Research: Research is needed on why there are no mosquitoes in the wetland, and on the role of Carambolim as a habitat for beneficial insects for the surrounding rice fields.

World travellers

Studies by the Bombay Natural History Society show that some migratory birds travel great distances between their breeding grounds and wintering sites

Distances (in a straight line) travelled by some migratory birds seen in Carambolim:





Spotted sandpiper




Glossy ibis


White wagtail






Common teal


Marsh sandpiper





Some ideas for conserving birds

• Enforce existing measures against hunting.

• Conduct awareness programmes for local people on the importance of the wetland ecosystem.

• Publish a booklet on the wetland.

• Arrange field trips for nature clubs, bird watchers, journalists, students and tourists.

• Erect signs telling the public not to harm the birds.

• Start nature clubs in schools around the wetland.

• Require trains to reduce speed near the wetland.

• Culture fish at appropriate times of the year to attract birds.

• Control erosion of the railway embankment.

• Plant trees of different heights along the track to absorb train noise.

• Erect a few barren trees around the wetland edges as roosts for cormorants, storks and eagles. The one-third reduction in the wetland area due to the railway can be partly compensated for by increasing the roosting sites.

• Ring migrating ducks to determine the role Carambolim plays on migration routes.

• Track the feeding, roosting and nesting grounds of birds outside Carambolim.

Some ideas for conserving birds

Birds of special interest in Carambolim

Birds seen in Carambolim

Lesser Adjutant


Crimsonthroated Barbet

Large Green Barbet

Small Green Barbet


Bluetailed Bee-eater

Small Green Bee-eater


Redwhiskered Bulbul

Redvented Bulbul

Whitebrowed Bulbul

Crested Honey Buzzard


Little Cormorant

House Crow

Jungle Crow



Large Darter or Snake Bird

Indian Spotted Dove

Black Drongo

Comb Duck

Spotbill Duck

Greater Spotted Eagle

Steppe Eagle

Tawny Eagle

Whitebellied Sea Eagle

Cattle Egret

Large Egret

Little Egret

Median or Small Egret



Little Grebe or Dabchick

Blackheaded Gull

Marsh Harrier

Montagis Harrier

Grey Heron

Night Heron

Pond Heron

Purple Heron

Reef Heron


Glossy Ibis

White Ibis

Bronzewinged Jaçana

Pheasant-tailed Jaçana

Blackcapped Kingfisher.

Lesser Pied Kingfisher

Small Blue Kingfisher

Storkbilled Kingfisher

Whitebreasted Kingfisher

Blackwinged Kite

Brahminy Kite

Pariah Kite

Indian Koel

Redwattled Lapwing

Indian Lorikeet


Scarlet Minivet

Small Minivet

Indian Moorhen

Purple Moorhen

Blackheaded Munia

Whitebacked Munia

Common Myna

Jungle Myna

Golden Oriole


Blossomheaded Parakeet

Roseringed Parakeet

Blue Rock Pigeon


Tawny Pipit

Golden Plover

Kentish Plover

Little Ring Plover


Indian Robin

Indian Roller

Common Sandpiper

Marsh Sandpiper

Spotted Sandpiper

Ruddy Shelduck


Indian Baybacked Shrike

Rufousbacked Shrike

Indian Skimmer or Scissorbill

Common or Fantail


Jack Snipe

House Sparrow

Yellowthroated Sparrow


Blackwinged Stilt

Little Stilt

Openbilled Stork

Painted Stork

Whitenecked Stork

Loten's Sunbird

Purple Sunbird

Wiretailed Swallow


Common Teal

Cotton Teal

Lesser Whistling Teal

Gullbilled Tern

Indian River Tern

Whiskered Tern

Grey Wagtail

White Wagtail

Large Pied Wagtail

Blyth's Reed Warbler



Birds seen in Carambolim

Fish and crustaceans

Carambolim has six species of freshwater fish and various species of crabs and shrimps.

In April, an auction is held and the fish are harvested and sold. The auction coincides with the departure of the birds. People thus harvest only what the birds leave behind-the human population has adapted to the needs of the birds.

The number of fish caught is declining apparently because Carambolim is attracting more and more birds-perhaps because other overwintering sites are being degraded.


In the past, Carambolim was home to crocodiles. The Cumbarjua Canal and Banastari, where muggers (marsh crocodiles) still live, are within 5 km of the wetland. A mugger was seen in the wetland in 1991. Snakes such as the Checkered Keelback, Ratsnake and Dog-faced Snake have also been spotted in and around the wetland.


Carambolim abounds in insects, including ladybirds, butterflies and moths, cicadas, flies, beetles, dragonflies and many other insect species and spiders. Many parasites live on these insects, such as parasitic Trichogramma wasps. Coccinellids hibernate around the wetland, ready to move to nearby rice fields to prey on insect pests in the rabi season.

Researchers have found no mosquito eggs or larvae in the wetland-maybe because Chara algae thrive in the water.

Researchers observation

The wetland and its immediate surroundings are a very stable ecosystem, where the predator and prey populations are held in a balance during the winter months.


Wild varieties of rice grow in and around the wetland; 25 varieties have so far been identified. They are a valuable potential resource for plant breeders.

Many of the algae and other plants help break down pesticides.

The wetland is a permanent source of water for a large area of rabi rice. This is one of the best rice-producing areas in Goal

The Konkan railway

The Konkan railway was originally designed to pass through the middle of the wetland. But pressure from environmentalists groups succeeded in changing the route to along one side of the wetland. The Konkan P airway Corporation has undertaken to monitor how the railway activities affect the wetland's ecosystem.

Impact of degradation on birds

• Some migratory and residential species may be disturbed.

• The total population of birds will decline.

• The tracks pass through the western part of the wetland where Storks feed. These birds may have to adapt to some other feeding ground.

• Erosion from the railway embankment into the wetland will disturb the food chain and lead to further shallowing of the lake.

A stable ecosystem

Threats to wetlands

Like other wetlands, Carambolim is threatened by several factors.


Rising numbers of people living in and around wetlands encroach on these areas. Vast areas have been drained for agriculture and buildings.


People in villages around Carambolim are aware of the need to conserve the wetland wildlife, although hunting of wild ducks still takes place.


Deforestation causes erosion, washing soil down rivers and into wetlands. The silt overwhelms the fragile ecosystem, making the wetland shallower and smaller.


Weeds can choke wetlands, covering the open water surface and making the area less attractive for birds.


Sewage, solid waste, industrial effluents, fertilizers and excessive use of pesticides increase the total level of nutrients in the water, leading to algal blooms. When the algae die, they decompose. This decomposition process uses up oxygen in the water, killing fish.


Many wetlands have been converted into aquaculture ponds for prawns and fish.

Symptoms of strain on wetlands

• Lower biological diversity, particularly endangering endemic and endangered species.

• Poorer water quality.

• Sedimentation and shrinkage in size.

• Fewer migratory birds; fewer fish and other animals.

• Prolific growth of obnoxious aquatic weeds.

For more information, see Dilip K. Biswas and C.

L. Trisal. Initiatives for conservation of wetlands of

in India. Ministry of Environment and Forests:

Prepared by V. Gowthaman and Dr J. B. Sardessa.


4.6 Freshwater algae

Like all plants, algae contain chlorophyll. Unlike plants, however, they have no roots, stems or leaves. They range in size from 0.5 microns to huge seaweeds. Algae can be found in many conditions worldwide. As many as 450 species have been recorded.

Algae as food

Algae are efficient photosynthetic "machines" which convert solar energy into biomass. In fact, it has been suggested that some algae be used as a new weapon to fight worldwide protein shortages. Algae can produce 55-110 tonnes of dry matter/hectare/year, of which up to 50% is protein. The blue-green algae Spirulina has received much attention from nutrition researchers. Chlorotea, a green algae, has been proposed as an organism that could absorb CO2 and regenerate oxygen in space stations.

Treating sewage

Algae are important in treating sewage. They help in oxygenating waste water and reduce the number of fecal coliform bacteria in the water by 99%. The algal biomass produced from treating sewage contains toxic substances but can be used to make biogas.

Blue-green algae

Blue-green algae, or cyanophyceae, are highly adaptive and can colonize even polluted water. This means they can be used as an "indicator species": large numbers of blue-green algae show that water is polluted. Some rivers in Goa contain large quantities of iron because of mining. This encourages the growth of blue-green algae.

Monitoring water quality

Nature clubs, schools and non-government organizations can help monitor rivers and lakes for dangerous levels of pollution. They can do this by regularly measuring the water pH, CO2 content, oxygen content and hardness. They should also watch for algal blooms. Any unusual changes should be reported to the local pollution control board. These groups can also mobilize public support ro prevent pollution.

Toxic algae

Many algae are toxic to animals and humans.



Species affected


Anabaena, Microcystis,


Coelosphaerium, Rivularia

Sheep, cattle, dogs, gulls

Weakness, jaundice, diarrhoea, convulsion

Oscillatoria intestini





Gastro-intestinal disorders



Crampy stomach pains, nausea, vomiting



Abdominal pain, nausea, vomiting, diarrhoea

Monitoring water quality