Skip to page content

Back to: Projects

Coastal Biodiversity in Ranong

The Mangrove

Mangrove Creek

Mangrove Creek on the Kampaun River.

What are mangroves?

Along the coasts of many tropical and subtropical zones forests appear to grow out of the sea. They are mangroves; trees which have adapted to live in the zone between low and high tide. On first examination mangrove forests appear to be uninviting, characterised by sticky mud, biting insects and thickets of trees with dense sometimes impenetrable aerial roots. However, mangrove forests are complex ecosystems which harbour rich biodiversity and have an important role in coastal waters. They are nursery grounds for commercially important fish and prawns that live in surrounding habitats. The forests act as a buffer between the sea and the land mitigating all but the worst effects of storm surges. In less severe weather they slow down erosion. Mangroves also effectively act as a giant filter trapping sediment and sometimes pollutants draining from

Mangroves

The mangrove tree Rhizophora apiculata

Mangroves are found along many stretches of the Thai coast, although forests are in decline in many provinces. One of the most extensive areas of mangrove forest is found in Ranong, approximately 19,500 ha. The Royal Forestry Department established a research centre near Ranong City which has now become a world reserve in the UN Man and the Biosphere Programme. Within Coastal Biodiversity in Ranong's study area, mangroves are widely distributed along the estuaries of rivers, such as the Kampaun, and fringing many of the more sheltered areas of off-shore islands.

One of the main objectives of the project is mapping the distribution of mangroves in this area.

Thalassina spp

Mud shrimp Thalassina

Within the study area there are 17 species of trees that contribute significantly to the mangrove forest. In addition, there are 30 or more other plants species recorded. The forests also have a diverse marine fauna. Crabs are the most obvious component, with colourful fiddler crabs living in burrows along the creeks and grapsids foraging within the forest and up into the trees. Mud shrimps, Thalassina spp. build huge mounds, processing large amounts of mud and sediment.

Molluscs are common; oysters attach onto the aerial roots of the trees edging the creeks (sometimes: rare in our area) and channels, while gastropods of many species are found on the mud and in the trees. Polychaete worms are also found in tubes in the mud, but they are not as abundant or diverse as in the muddy sediments at the mouth of the rivers like the Kampaun. The mangrove also has a transient population of the youngest stages of many marine species.

Fish larvae

Larval fish from the mangrove

The larvae and juveniles of prawns and shrimps develop among the relative shelter of the mangrove roots and, on maturity, migrate into surrounding off-shore habitats. These larvae, in turn, are preyed on by larger fish, like Lates calcarifer, which enter the lower reaches of the mangroves at high tide.

Finally, mangrove forests have a rich bird-life. The forest canopy is home to many small and seldom seen species. Far more noticeable are the egrets and herons that stalk the muddy banks and the colourful kingfisher species that are often seen perched on branches at the water's edge.


Find out more about mangroves at these websites:

Mangroves in Thailand
Tropical coastal sites
Wetland International
Australian Institute for Marine Studies:
The Mangrove Replenishment Initiative
Mangrove Action Project