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

Abstract The surface waters of the northeastern Arabian Sea sustained relatively high chlorophyll a (average 0.81±0.80 mg m–3) and primary production (average 29.5±23.6 mgC m–3 d–1) during the early spring intermonsoon 2000. This was caused primarily by a thick algal bloom spread over a vast area between 17–21°N and 66–70°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–1) over an extensive area, making the northeastern Arabian Sea highly productive (average 607±338 mgC m–2 d–1) even during an oligotrophic period such as spring intermonsoon.