Coastal and Marine
Sumatra and Associated Islands -
Biodiversity and Tropical Forests in Indonesia

Coastal ecosystems commonly encountered in Sumatra are mangroves, beach vegetation on accreting coasts, beach vegetation on abrading coasts, brackish water forests, rocky shores and coral reefs. Mangroves are located along the coast of all provinces in Sumatra and are common also on the adjoining islands. In the 1980s, Sumatra had more than 850,000 ha of mangroves, the third largest area of the islands in Indonesia. By the late 1990s, only a little more than 480,000 ha (53%) remained. However, the loss of mangroves on other islands moved Sumatra to now having the second largest area of mangroves among the other islands (BAPPENAS, 2003). Mangroves are well developed on the inshore and offshore islands due to the many large rivers that flow into the sea bringing in high sediment and decreasing salinity. Similar to Kalimantan, mangroves are a key ecosystem for coastal stability and for the conservation of a wide range of plants and animals that are dependent on the habitat of and nutrient flow from mangal and to the economy of Indonesia.

Whitten et al. (1996) document dramatic changes in the accretion of parts of the Sumatran coastline, indicating that both Jambi and Palembang had been ports at the end of promontories about 1000 years ago, and speculate on the crucial role of mangroves in coastal accretion.

The most commercially valuable mangrove related species is the paenaeid prawns, which supports an export market worth $150 million annually (Anon 1979). Conversion of mangroves to tambak fish ponds is the major factor in the destruction of the mangrove communities, particularly in eastern Sumatra. Turner (1977) also observed that the conversion of mangroves to tambak is commercially unprofitable and would lead to a loss of jobs. To indicate this, Turner (op. cit.) showed that the average coastal tambak produces 287 kg of fish/ha/yr, which is more than the offshore shrimp yield, but the loss of one hectare of tambak actually leads to an approximate net loss of 480 kg/ha/yr of offshore fish and shrimp per year.

On accreting coasts, there are a wide variety of sand binding, salt tolerant, hardy herbs, grasses and sedges (Whitmore 1984), inhabited by adapted assemblages of crabs and crustaceans. These coasts are also used as nesting sites for Green Turtles, the eggs of which are commonly sold in Padang; Hawksbill Turtles in the region of Sibolga; and the rarer Leatherback Turtle at scattered sites. Most concentrations of turtles are on the offshore islands and the west coast of the mainland (Soegiarto and Polunin 1980), but there is little recent confirmation of turtle nesting sites.

Brackishwater forests or Nipa (Nypa fructicans) forests are scattered along the inner boundaries of mangroves. It has only the date palm (Phoenix paludosa) restricted to it.

The coastal environment of West Sumatra consists of a chain of islands and shallow water reefs, separated from the mainland of Sumatra by deep water. The islands extend from Simuelue Island in the north to the Enggano Islands in the southeast. The eastern sides of these islands are, in some places, covered by mangrove. Some coral species are adjacent to the mangrove roots. Further eastward, more corals appear and among the most abundant are massive Porites, which can form minor atolls. They are mostly dominated by coral boulders of Porites and big columns of Goniastea corals. The reef flats are wide, and they slope down gently to 5-10 m depth. The soft bottom substrate coral communities are dominated by various species of Acropora, Seriatopora and Pocillopora.

There are two chains of small islands running parallel to the east coast of Sumatra at a distance of approx 10 km and 30 km, respectively. The inshore chain is located on the continental shelf with a depth around 50-100 m while the outer chain is in the 200 m isobath on the continental slope. The reef flats are narrow and gently sloping down to 10 m depth.