Zooplankton study of Tolo harbour, Hong Kong

Abstract

Zooplankton abundance and composition were collected at fortnightly intervals together with the measurements of water temperature and salinity from 4 stations of Tolo Harbour. These stations were chosen because of their distinctive geographical location. The physical conditions were those expected for the subtropical climatic factors on shallow inshore water. Surface water temperature closely followed weather changes. Surface water salinities were closely related to the monsoon and heavy rainfall periods. Bottom water temperatures and salinities were stable. The numerical abundance and composition of zooplankton communities followed the variabilities of the physical parameters. Copepods were always the most abundant group at all stations. Calanoida and Cyclopoida were in high numbers in summer and late autumn/early winter. Temora was more abundant in winter. Harpacticoida occurred mainly in late winter and spring. Ostracods, ranked second most abundant in the zooplankton and occurred in summer. Large numbers of female ostracods carrying eggs were found in autumn suggesting that this is their spawning season. Chaetognatha, ranked third in the total zooplankton,and occurred mainly from summer till early winter. Cladocera were found mostly at stations I and II. Their high concentrations were recorded after the long period of heavy rainfall in summer 1975. Small scale patchiness of zooplankton was found moving inwards and outwards of the harbour in the 24-hour samples in March and June 1975. Medusae, Larvacea, Appendicularia were found more in warm water temperature but occurred in low numbers in the 24-hour samples which were taken in June 1975 coincident with the heavy rainfall days of the month. Zooplankton of Tolo Harbour are clearly subtropical and warm water temperate communities.