Enhanced chlorophyll a and primary production in the northern Arabian Sea during the spring intermonsoon due to green Noctiluca scintillans bloom

Abstract

The surface waters of the northeastern Arabian Sea sustained relatively high chlorophyll a (average 0.81+ or -0.80 mg m sup(-3)) and primary production (average 29.5+ or -23.6 mgC m sup(-3)d sup(-1)) during the early spring intermonsoon 2000. This was caused primarily by a thick algal bloom spread over a vast area between 17-21 degrees N and 66-70 degrees E. Satellite images showed exceptionally high concentration of chlorophyll a in the bloom area, representing the annually occurring 'spring blooms' during February-March. The causative organism of the bloom was the dinoflagellate, Noctiluca scintillans (Dinophyceae: Noctilucidea), symbiotically associated with an autotrophic prasinophyte Pedinomonas noctilucae. The symbiosis between N. scintillans and P. noctilucae is most likely responsible for their explosive growth (average 3 million cells l sup(-1)) over an extensive area, making the northeastern Arabian Sea highly productive (average 607+ or -338 mgC m sup(-2) d sup(-1)) even during an oligotrophic period such as spring intermonsoon.