Protecting mangrove forests

by Vishaka Senadhira

Mangrove forests or mangals are truly a beautiful gift of mother nature. The word mangroves means the 'tropical seashore trees with many tangled roots above ground.'

Mangroves are tropical communities. They could be found along the coast and is usually exposed to the high and low tides. The height of the tidal water level, as well as the salinity of the water constantly maintain the surroundings of the mangrove communities. Mangroves or mangals develop where the wave action is absent and the sediments accumulate.

Mangrove communities could be found in lagoons, river estuaries and also in the shores of deeper lagoons. Mangroves are scattered into about 15 districts of Sri Lanka.

The largest mangroves are seen in the Jaffna peninsula, Mulative, Trincomalee, Potuvil, Ratgama, Maduganga, Chilaw, Wantavilluwa, Mannar etc.

There are small mangal communities along the coastline from Panadura to Bundala. In mangrove communities you can find two kinds of species viz. true mangroves and mangrove associates.

True mangroves are specifically adopted to mangrove conditions. Some of the species of this category are Rhizophora (maha kadol), Avecennia, Ceriops, Luminitzera, Bruguiera (mal kadol) etc. Mangrove associates usually arise in coastal and in inland habitats. Acanthus, Calophylun, Acrostichum, Tamarix etc. are some of the species in this category.

Mangroves are found in the low lying muddy areas. The soil in the mangrove forests always come in contact with the sea water. Hence the waters in these communities are always high in salinity. The soil is muddy. It is water logged and poorly aerated.

Mangrove forests are strongly influenced by the tides. the nutrients are brought to the ecosystem by the incoming tides. Zonation is one of the features of tidal fluctuation; which means the changes in vegetation from seaward edge to true terrestrial environment.

The red mangroves (Rhizophora mangle) experience the deepest tidal action so they occupy the seaward edge. The black mangroves (Avicennia germinanas) which are next, are familiar with shallow floods caused by the high tides. White mangroves (Lagncularia racemosa) dominate the edge landward.

Since the water in the mangrove communities is high in salinity the water absorption by the plants may be difficult. The mangrove species have adopted to such conditions of high salinity. The botanists have proved scientifically that the osmotic pressure of the cells of these plants is high. That's why these plant species absorb water from the hyper-saline water.

The mangrove plants are adopted to retain the absorbed water. Many plants have shiny, thick, fleshy leaves. E.g. Rhizophora, Ceriops, Soneratia, Aegicerus etc.

The leaves of some plants are also adopted to reduce the water loss from the plants. The soil of the mangroves are usually water logged and is poorly aerated. Certain mangrove species like Sonneratia (Kirala) have special, kind of roots called 'pneumatophores' or 'pencil roots'.

They grow against the gravity, so they could be seen clearly protruding above water. They can absorb the atmospheric oxygen.

In Bruguiera (mal kadol) the 'knee roots' could be seen above water. They are like loops and absorb the air from the atmosphere.

In the mangroves the soil is loose and muddy. The trees of the mangroves usually grow up to a certain height, and some kind of anchorage is necessary for these plants.

There are two kinds of roots that help in anchoring the mangrove plants to the soil.

Prop roots

These arise from the main trunk of the plant and grow into the soil. Thus extra strength is provided to the plant. E.g. Rhizophora

Stilt roots

They emerge from the branches of the mangrove plants and grow into the soil. E.g. Ceriops

Both these roots prevent the plants being uprooted due to the action of the tides. Many plants of this community germinate while being attached to the parent plant. After germination they fall out. This way the seeds do not come in contact with the saline water which could be harmful for the germination of the seeds.

Fauna in mangroves

Mangroves are usually rich in fauna. A variety of animals which are a mixture of terrestrial and marine life live within them. Fiddler crabs, (Uca spp) and some other land crabs make borrows in the soil.

Some major carnivores like alligators, crocodiles, bears, big cats (like tigers) exist in the inner portions of these forests. Some aquatic birds like herons and bitterns live on the branches of many mangrove species. Littorina snails could be seen attached to the prop roots or the large trunks of the plants of the mangrove forests.

These ecosystems serve as excellent breeding grounds for fish, shrimp, crab or prawns. The fruit and bark of certain mangrove species have a medicinal value. They have been used to cure boils, rheumatism, eye infections etc. The pulp of some species are used to make tannin, rayon, lacquer, etc. The mangroves play a huge role of protecting our coasts from erosion.

Human impact

Statistics show that mangroves of the Pacific and Persian Gulf regions have been exploited by men. It also says that some have never been recovered. In Vietnam, large areas of mangroves have been completely damaged due to the Vietnam war.

In Sri Lanka these forests have been utilised in imbalanced ways by humans. The tsunami, which we experienced two years ago was violent on our island due to the lack of a barrier such as the mangroves along the costal belt. These forest areas are polluted with numerous toxic material, like various types of polythene and plastic. This will become lethal to the fauna and flora of our mangroves.

It's time to take action. The concerned authorities should implement projects on a large-scale to restore and protect our mangroves. At the same time the public should be made aware of the importance and protection of mangroves.

Many awareness programmes which also includes active participation, should be held at school level to educate our future generations.