Wetlands ecosystem


Extensive mangrove forests occur on most islands in Seychelles. 4 Sites of international significance (Port Launay, Mare Aux Cochons, La Plain Hollandaise and Aldabra Atoll) have been declared under the RAMSAR Convention. Aldabra Atoll has extensive systems of mangroves that provide feeding and nesting habitats for many seabirds and waders. In Seychelles, all mangroves species are indigenous, having been brought to the islands by the sea. Some species of mangroves are able to act as pioneer species, colonizing new areas of sand and mud which are still unstable, for example Rhizophora (mangliye rouz) and Avicennia (mangliye blan). Other species are found in sheltered areas or along river edges. Other grows towards the landward side of mangroves where sea water only penetrates at very high tides, for example Lumnitzera (mangliye pti fey) and Xylocarpus (mangliye ponm). At the edges of mangroves, on slightly higher land, it is possible for other plant species to grow, but these are usually adapted to wet or marshy conditions or are tolerant of salt, for example fouzer lanmar and patatran. Algae of various types frequently grow as ephiphytes on the aerial roots of mangrove trees, for example on Sonneratia (mangliye fler).

The mangrove is an intertidal habitat. It is often found where a river meets the sea and where the land is sheltered from strong waves, such as in bays or inside a fringing coral reef. The river brings fresh water to the mangrove but at high tide the trees are surrounded by seawater or brackish water (mixture of salt and fresh water). The trees are adapted to the varying salt content of the water and also to the fluctuating tide.

Although mangroves come from several different plant families, they have all developed similar adaptations to life in this intertidal habitat. Mangrove trees are evergreen. Their leaves are thick, leathery and covered with either a waxy cuticle or minute hairs, which reduces water loss from the leaves.

Special aerial roots called pneumatophores develop on most mangrove trees. These can absorb oxygen from the air when the roots are exposed at low tides. This is necessary because the water-logged soil in which the roots grow does not contain much oxygen.

Importance of mangroves; Provides habitats for fish and other animals; Traps, concentrates and recycles nutrients; Protects the coast from erosion; Supports bird life; Supports recreational activities; Is a source of food; Provides fuel; Provides building materials; Supports scientific research; Source of traditional medicine

Six species of mangroves are described from Seychelles:

Mangliye Rouz (Rhizophora mucronata)

Common species occurring on most islands and can grow up to 15 m with many branched aerial roots.  In the past, the bark was used for tanning leather and as a red dye for wooden floors. Its ashes were sometimes used in soap making and the straight trunk was used for posts. Most of the trees used were brought to Mahé from Aldabra.

Mangliye Lat (Bruguiera gymnorhiza)

Small tree or shrub with knee-like aerial roots and is much less common than Mangliye Rouz. It is not a pioneer species like the Red mangrove as it is usually found in well-established mangrove swamp.

Mangliye zonn (Ceriops tagal)

Small tree with lower trunk and roots spread out to form a pyramid. Sometimes knee-like roots are present. Not common. It is found in well established mangrove, mainly on river edges. The old fruit which is left hanging on the tree is used by some children as a whistle, worked by blowing across the yellow-green section.

Mangliye fler (Sonneratia alba)

Small tree with prominent cone-shaped aerial roots sticking out of the mud and is currently relatively common on most islands. It is probable that fruit bats pollinate the flowers. Children use half-open buds to make earrings and the fruit can be made into a spinning top, usually with the calyx lobes removed.

Mangliye Blan (Avicennia marina)

Small tree with pale bark and slender, pencil-like aerial roots sticking out of the sand and by far the most common and widespread of the mangrove species. It is a pioneer species in many of the new intertidal habitats created by reclamation of land on the east coast of Mahé. It prefers shallow water and a sandier substrate than the other mangrove species

Mangliye pti Fey (Lumnitzera racemosa)

Small tree or shrub with rough bark, small aerial roots and can be found growing at the landward edges of mangrove swamps or at the edges of freshwater marsh/rivers. This mangrove tree prefers brackish water which is less salty.

Mangliye ponm (Xylocarpus molucansis)

Spreading tree with flaking bark at the base of the trunk forming flanges above ground and can be found at the landward edge of the mangrove. The names Mangliye pasyans and puzzle nut arise because the process of rearranging the irregularly shaped seeds into a sphere is like doing a 3-dimensional jigsaw puzzle and requires much patience.