The inter-tidal zones, where mangroves flourish, receive regular tidal flushing from the sea and freshwater streams and rivers from inland. A distinctive mix of conditions characterises these areas: high temperature, fluctuating salinity, alternating aerobic and anaerobic conditions, periodically wet and dry, and unstable and shifting substratum. This is a tough habitat for any tree to grow. Mangrove trees, therefore, have many special features for adapting to such stressful coastal environment. These amazing structures make them different from the other terrestrial plants. They not only survive themselves but also provide food and shelter to a variety of animals.
Mangrove communities are made up of taxonomically diverse groups of plants and animals, and each community has its own distinctive flora and fauna species. There are many species of Mangrove trees; about 110 have been identified. They are all adapted in various ways to overcome the problems of anoxia, salinity and frequent tidal inundations.
These trees can grow in the unstable and salty soil that is flooded by the sea when the tide comes in twice in a day. Their trunk and even their canopy may be covered by tidal water during high tide period. The mangroves also face the risk of being washed away by tides due to the unstable substratum. To anchor themselves firmly in the soil some mangrove trees develop prop roots – long roots that grow down from the trunks and branches of the trees and get anchored in the mud. These stilt-like roots trap leaves, detritus and other floating debris making the trees footing firmer.
The mud here is very sticky, closely packed and does not have much oxygen. To counter this prop roots have tiny pores called lenticles. These help the mangrove trees breathe in air since the soil has a low level of oxygen. There are other trees that send up small stick-like “breathing roots” from the mud called pneumatophores. The roots of some other mangrove species form into "knees" that project above the mud surface to facilitate gaseous exchange.
To handle the problem of salinity the roots of mangrove develop filters that keep the salt out; some plants have salt glands on the leaves through which the extra salt exits; or the leaves themselves store salt and become fleshy. Some mangrove trees have droppers – germinated seeds that attach to the parent plant of mangroves after germination. This increases the survival rate of the mangroves in the unstable environment.
Mangroves and ecology
Mangroves play an indispensable role in the protection of the coasts and in maintaining their bio-diversity. Mangroves slow down the tidal waters and help dissipate the tidal energy, thus acting as storm breakers. The rainwater that flows from land to sea contains fine mud called silt and leaves. Mangroves trap these and they are used as nutrients by plants and animals. Mangroves also create more land area by slowly inching their way towards the sea, colonising a tiny bit of sea each year. Mangrove leaves are the beginning of an important food chain called the detritus food chain, one starting with the dead and decaying matter.
Mangroves are home to a variety of animals: Periwinkle, prawn, eel, fiddler crab, oyster, frogs, herons, kingfishers, sandpipers and others.
Mangrove Destruction and Conservation
Unfortunately, however, mangrove forests in the world have been degraded and devastated due to over-cutting, shrimp pond construction and other causes. So habitats of many plants and animals are threatened. Multifarious efforts are going on the world over to save the mangroves. These include planting new mangrove trees, providing alternative land for other uses, educating populations, etc.
Community participation is an important aspect of mangrove conservation. It is necessary to increase the awareness of the important issues involved. Coastal practitioners are also developing innovative and site-specific ways to counter the problem.
http://www.mangrove.or.jp/ http://www.afcd.gov.hk/ ‘Treasured Islands!’, by Kalpavriksh and Andaman & Nicobar Islands Environmental Team