Zooplankton standing stock, community structure and diversity in the northern Arabian Sea

Abstract

The effects of large scale oil spill, which occurred during the Gulf War in 1991 on zooplankton standing stock, community structure and diversity in the northern Arabian Sea were studied. Surface (1-0 m) and vertical zooplankton hauls (200-0 m, 250-0 m and 500-0 m) were taken during taken during FORV Sagar Sampada cruise 94 (12-23 September 1991). The shelf region was rich in zooplankton standing stock than the oceanic waters. Highest standing value (581 ml/100 m sup(3)) was obtained at a coastal station (lat. 22 degrees 07'N and long. 67 degrees 03'E) and was due to swarm of gammarid amphipods and shoal of sergestid shrimp Acetes johni. Herbivores dominated the zooplankton community and copepods were most abundant (36.9 to 71.7%). The other important taxa were siphonophores, euphausiids, chaetognaths and decapod larvae. Copopod population showed distinct coastal and oceanic communities. Niche partitioning among congeners particularly the members of genus Pleuromamma was discernible. Species diversity was higher in the oceanic waters and an inverse relationship between standing stock and species diversity was the general trend. High standing stock, faunal and species diversity values indicated no apparent impact of oil spill on plankton population in the studied area.