PHOTOTROPHIC PICOPLANKTON COMMUNITY STRUCTURE IN 3 DIFFERENT PELAGIC REGIMES IN THE ARABIAN SEA

Cell numbers and vertical distribution of Synechococcus, eucaryotic phototrophic picoplankton and prochlorophytes as determined by epifluorescence microscopy are presented from 3 different epipelagic systems (the mesotrophic coast off Oman, the oligotrophic central Arabian Sea and the shelf edge off Pakistan) in the Arabian Sea during the inter-monsoon period 1987. The vertical distribution patterns are described in relation to the epipelagic structure of the respective study sites. Synechococcus dominated phytoplankton in the upper mixed layer and prochlorophytes at the bottom of the euphotic zone in the lower part of and below the deep chlorophyll maximum. High pressure liquid chromatography analysis confirmed the presence of prochlorophytes and revealed vertical profiles of characteristic pigments of picoplankton organisms, chlorophyll (chl) a and b, divinyl chl a (chl a(2)) and zeaxanthin. Cellular pigment concentrations of Synechococcus and prochlorophytes are presented.