This study was conduct at two stations of coastal waters of Karachi, St.1 (Manora) and St.2 (Mubarak Village). The main purpose of study was to observe the day night abundance and distribution of different zooplankton groups and find out the productivity of these waters regarding the fish catch. Day and night distribution, composition and abundance of the main zooplankton groups were analyzed during the year of 2008-9. The copepods, comprising 64.95% in day time and 54.97% in night time at St.1 of the whole zooplankton groups and 73.91% in day time and 64.41% in night time at St.2 of the whole zooplankton population were the most abundant followed by the Appendicularia 20.31% in night and 20.44% in day time at St.1, 18.18% in night time and 14.13% in day time at St.2, Cladocera 18.50% in night time and 13.30% in day time at St.1, 15.61% in night time and 10.80% in day time at St.2. Generally, the day and night composition at both stations (St.1 and St.2) showed little different pattern, most of the zooplankton groups were present at a slightly higher abundance at day time. The Copepods abundance was highest during the month of April in day time and during the months of October and November in night time, other zooplankton groups also shows their high abundance during the same months. This study reveals that coastal waters of Karachi are stable and rich in zooplankton communities. The percentage of zooplankton is high in day time as compare to night time. The coastal waters of Karachi at both stations are productive for fishing.
Keywords: Day-night abundance, Karachi coast, zooplankton groups