VERTICAL-DISTRIBUTION OF MESOZOOPLANKTON IN THE CENTRAL AND EASTERN ARABIAN SEA DURING THE WINTER MONSOON

The vertical distribution of mesozooplankton in the central and easter n Arabian Sea was investigated during the winter monsoon in 1995. Samp les were analysed from discrete depth zones defined according to oxyge n and temperature profiles of the water column. Zooplankton had higher standing stock in the mixed layer compared to the strata below. The m ixed layer had 78.5% of the total column biomass, while the deepest (5 00-1000 m) layer accounted for only 0.9%. The stratum between 500 and 1000 m had the lowest abundance of copepods as well as other zooplankt on. A notable feature was that zooplankton biomass and density did not show much variations between coastal and offshore regions. Copepoda w ere the dominant group. Herbivores were generally more abundant at all depths. A total of 94 species of calanoid copepods were identified. B ased on vertical distributions, they were assigned to four groups: (i) species restricted to the upper 200 m; (ii) predominantly surface-liv ing species with tails to deeper waters; (iii) sparser deeper-living s pecies generally confined below 300 m; (iv) species occurring througho ut the water column. Diversity was fairly high in all strata with equi tability being higher in the deeper strata.