Mangroves are salt-tolerant plants of tropical and subtropical intertidal regions of the world. The specific regions where these plants occur are termed as 'mangrove ecosystem'. These are highly productive but extremely sensitive and fragile. A mangrove ecosystem is the interface between terrestrial forests and aquatic marine ecosystems. The ecosystem includes diversified habitats like mangrove-dominant forests, litter-laden forest floors, mudflats, coral reefs and contiguous water resources such as river estuaries, bays, inter-tidal waters, channels and backwaters. The structural complexities of mangrove vegetation create unique environments which provide ecological niches for a wide variety of organisms. Mangroves serve as breeding, feeding and nursery grounds for most of the commercial fishes and crustaceans on which thousands of people depend for their livelihood.Mangroves give protection to the coastline and minimise disasters due to cyclones and tsunami.
Mangroves acts a buffer Zone between the land and sea and stabilize the coastline, reducing erosion from storm surges, currents, waves, and tides. It acts as nature’s shield against cyclones, ecological disasters and as protector of shorelines. The intricate root system of mangroves also makes these forests attractive to fish and other organisms seeking food and shelter from predators. It acts as a breeding and nursery ground for various marine species and harbours a variety of life forms like invertebrates. Fish, amphibians, reptiles, birds and even mammals like tigers, boar etc., Mangroves purify the water by absorbing impurities and harmful heavy metals and absorb pollutants in the air. Mangroves are a potential source for recreation, tourism and contribute towards the revenue of the country.
Pichavaram mangrove forest is located about 200 km south of Chennai (Madras) city in the southeast coast of India. This mangrove lies between two prominent estuaries, the Vellar estuary in the north and Coleroon estuary in the south. The Vellar - Coleroon estuarine complex forms the Killai backwater and Pichavaram mangrove. Pichavaram mangrove is present in the higher land of Vellar-Coleroon estuarine complex. The mangrove extends to an area of 1,100 hectares, representing a heterogeneous mixture of mangrove elements. The source of freshwater to this mangrove is from both the estuaries and that of seawater is Bay of Bengal.
The mangrove soil usually consists of alluvium derived from the mangrove plants. About 40% of the total area is covered by water ways, 50% by forest and the rest by mud flats, sandy and salty soils. There are numerous creeks, gullies and canals traversing the mangroves with a depth ranging from 0.5 to 1.5 m and discharging freshwater into the system. A major irrigation channel is mainly discharging agricultural waste water from the entire upper reaches to this mangrove.
Pichavaram mangrove is one of the rare mangrove forests in India and it represents 14 exclusive mangrove species Avicennia marina alone constitutes nearly 30% of the total population followed by Bruguiera cylindrica (17%) and Avicennia officianalis (16%).
The organic plant is produced by the withered mangrove leaves in Pichavaram mangrove and these leaves are colonized by bacteria and fungi, which in turn is eaten by protozoans. All these give rise to rich particulate organic matter, forming the source of food the several animals like crabs, worms, shrimps, small fishes which in turn form prey to more than 60 species of larger fish living here. Several species of small organisms live inside the proproot system, which form the food for post larvae, juvenile and adult fishes and prawns like Penaeus indicus, P. monodon, P. semisulcatus, Metapenaeus dobsoni and M. monoceros.