STUDIES ON PLANKTON, PRIMARY PRODUCTION AND FISH IN THE INNER BRUNEI BAY

The Brunei Bay is a relatively shallow enclosed water area (Figure 1), approx. 45 x 45 km in size. Depth figures normally range between 30 and 40 meters. The bay is influenced by a number of rivers which discharge into the area, the largest being Padas in the north and Limbang in the south. The annual mean flow of Padas is estimated at 200 m per sec and the maximum over 1550. The rivers contribute with large quantities of sediment into the bay, and this sediment is covering the seabed and cause turbidity of the water. The total amounts of suspended solids brought to Brunei Bay from the river Padas has been measured at 2000—3000 tos per day or about 1 million ton per year. The vegetation in the area north, east and south of Brunei Bay consists'of primary and secondary rain forest, rubber plantations and other crop, and mangrove swamps. In 1982-1983 large areas of tropical forest on Borneo was affected by fire. It has been estimated that, in East Kalimantan only, some 3,5 million hectares of forest were destroyed. The fires also affected close to 1 million hectares of tropical vegetation in western Sabah (MALINGREAU et al 1985) and it seems probable that there have been indirect effects also in the marine environment due to thess fires. An area in the eastern central portion, the Gunong Lumako Forest Reserve, is since the last 5 years subject to extensive forestry operations involving systematic clear-cutting and plantation. This area is also being industrialized, involving for example the construction of a wood—, pulpand papermill complex, the construction of an ocean harbor and various other infrastructures. The study reported here was carried out in 1984 and 1985 to provide some basic information on the marine ecosystems of the inner Brunei Bay. The present results cover studies of the diversity and abundance of the plankton, primary production, and fish fauna of the inner Brunei Bay. A separate report covers the state of the coral reefs in the area (LINDEN et al, 1988), and another report various physico-chemical parameters of the water and sediment (in preparation). The only plankton study available from Brunei Bay is the result of a preliminary study of the species composition of zooplankton carried out by MOHAMED et al (1984). Also with regard to the South China Sea in general, few studies have been reported. However, some baseline work has been carried out in the Straits of Malacca and along the east coast of Peninsular Malaysia (CHUA & CHONG 1973, CHU A1984).