Introduction Water Quality in the Tropical

Like many other developing countries in the world, Indonesia faces enormous aquatic

environmental degradation. One of the main problems is related to the load of organic waste from coastal fish farms into coastal waters or estuaries, so there is an urgent need for recuperative actions. This environmental degradation is predicted to be apprehensively aggravated in the coming period due to the rapid increase in mariculture. In case of coastal aquaculture in Indonesia, marine fish culture with cages has been growing since 1999.

The production of aquaculture industry in Indonesian waters grew fast in the past 4 years, from 135 thousand tons in 1999 to 220 thousand tons in 2001. It contributes more than 24% of the total fish production of Indonesia’s fisheries sector (Directorate General of Fisheries Indonesia, 2002). Associated with this profitable development are risks of negative environmental impact, such as pollution, landscape modification, or biodiversity change.

Intensive fish farming generates large amounts of organic waste in the form of unconsumed feed, fecal and excretory matters that were released to the environment. The scale of environmental impact would depend not only on the intensity of fish culture operations, such as stocking density and feed input, but also on the hydrographic conditions of the culture site (Pawar et al., 2001). It has been well known that the major area of impact on the marine environment from organic wastes produced by fish farms is the sea floor directly underneath and some distance away from the cages (Yokohama, 2003).

The waste from marine fish cage operations which include uneaten food and faeces settled on the bottom may develop anoxic water and produce toxic gases (e.g. ammonia, methane and hydrogen sulfide (Wu, et al., 1995). A decrease in DO and increases in BOD, nutrients (phosphate and nitrate) have been generally found in water column around fish farm (Pawar, et al, 2001). In addition, potentially toxic decay products such as methane and hydrogen sulfide can outgas into the water from the bottom. These conditions may cause

physiological stress, disease, reduced growth, or death of cultured species.

But in Indonesia, not only the study about the environmental impact caused by the marine fish culture but also the basic knowledge of the coastal sea besides, the mangrove estuary and coral reef are lacking. The coastal waters studies on hydrography, water quality and their relations to marine culture activity are very limited in Indonesia. Moreover, generally the study on hydrology and its ecological consequences in tropical coastal waters is not as extensive as in temperate areas (Damar, 2003). Therefore this study was made for describing the basic characteristics of the tropical coastal water where the fish culture is operating