Pakistan Journal of Marine Sciences, Vol. 25(1&2), 173-186, 2016. PRELIMINARY STUDIES ON ZOOPLANKTON BIOMASS IN KORANGI – PHITTI CREEK SYSTEMS, KARACHI (NORTHERN ARABIAN SEA) Qadeer Mohammad Ali, Quratulan Ahmed and Sumera Farooq The Marine Reference Collection and Resource Centre, University of Karachi, Karachi - 75270, Pakistan (QMA); Marine Science Division, Department of Zoology, University of Karachi (SF). email: taxonomist@hotmail.com ABSTRACT: A research study was conducted on hydro-biological features including zooplankton, salinity temperature, dissolved oxygen, pH and turbidity in the Korangi-Phitti creek system at two stations during January to December 1998. Three commonly used techniques wet weight, dry weight and settled volume were adopted for the estimation of zooplankton biomass. From (Korangi creek) the highest wet weight (65.80 gms/100m 3 ), dry weight (3.20 gms/100m 3 ) and settled volume (82.30 ml/100m 3 ) were recorded in southwest monsoon season. From (Phitti creek) highest wet weight (49.50 gms/100m 3 ), dry weight (1.90 gms/100m 3 ) and settled volume (58.50 ml/100m 3 ) were also estimated in southwest monsoon season. Statistical analysis (P>0.05) shows statistically significant difference between wet weights, dry weight and settled volume with seasons and stations. KEYWORDS: Zooplankton biomass, Korangi - Phitti creek system, Indus delta. INTRODUCTION The Korangi-Phitti creek system constitutes about one tenth of the Indus deltaic area. It is recognized as significant mangrove area, a vital natural resource for the coastal communities and for the sustenance of fisheries and coastal protection. The Korangi-Phitti creek system can be referred as the most threatened mangrove area in the Indus delta due to ever increasing population pressure and unabated flow of untreated pollution (domestic sewerage and industrial effluents). The study of zooplankton biomass is helpful in determining the fertility of an aquatic system and fishery potentials. Zooplankton play a vital role in sustaining aquatic systems, constituting the basic link in food chain as grazers (primary and secondary consumers) and serve as food for fishes directly or indirectly. Thus, acquire a crucial position in the export of carbon from the surface to the intermediate and deepest part of an aquatic ecosystem. Zooplankton has become a significant tool in monitoring water bodies and is being widely studied due to their use as ecological indicators. The study of quantitative distribution of zooplankton is an important step in understating the dynamic relationships between trophic level in the Sea. Settling volume, displacement volume, wet weight, dry weight, ash-free dry weight and the organic weight of the samples are the most popular techniques for the presenting zooplankton biomass (Omori and Ikeda, 1984). The four commonly used techniques involve measurement of displacement volume (Yentsch and Hebard 1957; Frolander 1957; Sutcliffe 1957; Tranter 1960; Ahlstrom and Thrailkill 1963), wet weight (Nakai and Honjo1962), dry weight