LONG-TERM CHANGES IN HYDROGRAPHY, NUTRIENTS AND PHYTOPLANKTON IN TOLOHARBOR, HONG-KONG

This paper presents the results of a long-term survey of the hydrograp hy, nutrients and phytoplankton in Tolo Harbour carried out between 19 82 and 1992. Some nutrients such as total inorganic nitrogen, ammonia and total phosphorus increased during the 10 year period, but chloroph yll a, which indicated algal biomass, did not show an increasing trend . The phytoplankton of Tolo Harbour consisted largely of diatoms. Dino flagellates and minor algal groups such as cryptomonads and small flag ellates constituted a smaller fraction of the phytoplankton population . Densities of diatoms and minor algal groups increased in some statio ns, but the density of dinoflagellates remained relatively unchanged d uring the study period. Most nutrient variables were negatively correl ated with densities of diatom and total phytoplankton, and positively correlated with densities of minor algal groups. While dinoflagellate densities were positively correlated with total nitrogen in some stati ons, no correlation existed between dinoflagellate density and most of the nutrient variables. Our results show that there is a gradual chan ge in phytoplankton community in Tolo Harbour, most notably in the nut rient-rich inner harbour waters, with the smaller algae assuming incre asing abundance. Thus there was a net increase in density of total phy toplankton even though chlorophyll a concentrations did not increase. No evidence was found in this study to show that increased nutrient lo ading would inevitably lead to increase in densities of dinoflagellate s in Tolo Harbour. Instead, dinoflagellate densities showed stronger c orrelations with physical variables such as temperature, pH and salini ty.