Research professor for the coastal environment Otto S.R. Ongkosongo said the seven were Nyamuk Kecil, Damar Kecil, Kelor, Air Besar (Ayer), Sakit, Kapal Onrust and Bidadari.

"The sea continuously bombards the islands causing erosion. The problem is worsened by illegal sand and soil removal in the islands, with the material being used for the construction of buildings in Jakarta," he told The Jakarta Post at the LIPI Oceanology office, located in Ancol, North Jakarta.

Of the seven islands, four are large and have only suffered minor erosion, said Otto, who received his doctoral degree from the School of Geology of the University of Bordeaux I, France.

"However, the erosion has reached far into the remaining three islands, namely Nyamuk Kecil, Damar Kecil and Kelor island.

"I am afraid that those islands will disappear before the year 2020 if nopreventive measures are taken," he predicted.

Otto added that 10 islands had disappeared since 1983, including Van Der Smith, Ubi Besar, Air Sedang, Air Kecil, Nyamuk Besar, Dapur, Jong, and Telegraf islands.

Otto said that Ubi Besar island, for example, disappeared in the 1980's because the city administration removed the soil and sand from the island and used them in the construction of Soekarno-Hatta International Airport between 1983 and 1987.

Otto said the destruction of the islands had negative consequences both for people living on the islands and on the mainland.

"The islands cannot be used for earning a living anymore. The number of fish will decrease if the islands disappear as the fish won't have protective rocks to live in and shelter them from the tide," he explained.

He said that the government could build sea defenses around the islands to prevent erosion.

"The city administration should also prevent the removal of sand and soilfrom the islands and seek other ways of carrying out land reclamation on the Jakarta mainland," he said.

He lamented the government's slow response in having only built sea defenses on a few islands, including Kelor island.

"Ideally, however, such defenses should be built on all of the islands," he said.

Otto proposed a mutually beneficial plan under which the city administration could earn revenue while the islands could be saved from theravages of erosion.

He said the city administration should try to entice the wealthy to live part of the time on the islands, by turning them into resorts.

"The city administration could build housing complexes on the islands, with the profits from these complexes being used to finance the maintenanceof the islands.

"As long as the city administration can keep the islands from becoming overpopulated, both aims could be achieved," he said.

The seven islands are part of 106 islands in the Seribu Islands, which cover an area of some 69,976 square kilometers.