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Description: When the Dutch naturalist J. Umbrove arrived in Jakarta Bay in 1928, he was struck by the beauty of the coral reefs surrounding Nyamuk Besar Island. Nyamuk Besar is part of a chain of approximately 100 small islands, making up the Thousand Islands. One of the key factors in the formation of these islands and their reefs is the reversing monsoonal climate. As a result of monsoonal winds, currents are reversed, helping to shape the structure of coral communities. These conditions were nearly ideal for reef growth in the Java Sea during the early 1900s. Yet even in 1928, the reefs were already under pressure from human influences as the city of Jakarta began to develop.
Threats: Today Jakarta is one of the largest cities in the world, teeming with more than 11.5 million people. Although they are still a popular vacation spot for Jakarta residents, the islands are no longer the healthy, natural systems they once were, and with Jakarta's growth and development, the coral reefs of the Thousand Islands are increasingly stressed. The sea floor and reefs near to the city have been dredged for land fill and materials for road construction. Farther offshore, a major oil refinery is in operation. Destructive fishing practices have stopped, their effects are still being felt. Some of the islands are designated as national wildlife refuges and 50 have been designed as tourist resorts. Approximately 17,900 local people inhabit 11 islands. These people are primarily fishers.
Even high levels of protection have not been enough to reinvigorate the reefs. The largest threat facing them are the sewage, pollution, sediment, and other effluents that are regularly discharged into the bay from thirteen major coastal rivers, whose coastal watersheds have undergone major changes in land use and drainage patterns. Today these rivers transport garbage and industrial effluents, including heavy metals and pesticides into the bay. Waters in Jakarta Bay have high levels of nutrients and nitrogen, which are carried 5-10 km into the Thousand Islands, especially during the rainy season.
The reefs are in poor condition and only small patches of corals remain. The average coral cover is 5 percent, with just 16 species. Reefs nearest to Jakarta have been the most adversely affected by nutrient loads. Overfishing has devastated the outer reefs. The El Nino episodes of 1982 and 1998 further stressed the reefs, causing 90-95 percent mortality. The coral reef communities in Jakarta Bay are an example of coral reefs' continued degradation by rapid urban and industrial development.
References
De.Vantier, L., Suharsono, Yosephine, T., Imanto, P., and Lesdes, R. 1998. "Status of coral communities of Pulau Seribu 1985-1990," Proc. Coral Reef Evaluation Workshop Pulau Seribu - Jakarta, Indonesia : 1-12
Umbgrove, J.H.F. 1928. De koraalriffen in de Baai van Batavia. Dienst v.d. mijnbouw in Ned.Ind.Watensch.Meded; 1 - 62
Umbgrove, J.H.F. 1929. De koraalriffen der Duizen eilanden (Java zee) Dienst.v.d.minjbouw in Ned.Ind.Wetensch.Meded.12.1-47
Umbgrove, J.H.F. 1939. Madeporaria from the Bay of Batavia. Zoologishe Mededeelingen XXIII : 1 - 64
Tomascik T, Suharsono and Mah, A.J. 1993. A Historical Perspective of the Natural and Anthropogenic Impact in the Indonesian Archipelago with a Focus on the Kepulauan Seribu, Java Sea. Rosenstiel School of Marine and Atmospheric Science, University of Miami.
For more information, visit Reefs at Risk in Southeast Asia.
Related WRI report: Reefs at Risk in Southeast Asia
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