A first report on a bloom of the marine prymnesiophycean, Phaeocystis globosa from the Arabian Sea

A thick bloom of the marine prymnesiophycean, Phaeocystis globosa was observed in the central Arabian Sea during the summer monsoon period (July-August, 1996). The cells were mostly in colonial form, embedded in gelatinous matrices. The cell diameter was approximately 7 mu m and showed a distinct double feature form. The intensity of the bloom was as high as 3750 x 10(6) cells m(-2) and the carbon content ranged between 33 and 550 mu g L-1. Almost 90% of the phytoplankton population was composed of P. globosa in the bloom area. Other common forms were chain-forming diatoms like Rhizosolenia spp., Nitzschia spp. and Chaetoreros spp. The photosynthetic pigment chlorophyll a, however did not show any concomitant rise with the bloom intensity probably because the bloom was sampled during a senescent phase. The carbon chlorophyll ratio varied between 112 and 810. This is the first report on the occurrence of Phaeocystis from the Arabian Sea. It seems pertinent to ask whether this is a result of the genus being introduced and adapted to new environments due to human influence and whether it will influence food chains in the future. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.