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| Abstract Submission No. | ABS-2022-05-0313 |
| Title of Abstract | Nutrient stoichiometry drives the phytoplankton community structure during the progression of upwelling along the eastern Arabian Sea |
| Authors | B Bikram Reddy*, Anil Kumar Vijayan, Sherin C.K, Sudheesh V, G.V.M. Gupta |
| Organisation | Centre for Marine Living Resources and Ecology, MoES & SOST,KUFOS |
| Address | Centre for Marine Living Resources and Ecology, Ministry of Earth Sciences Kochi, Kerala, India Pincode: 682508 Mobile: 7787021785 E-mail: bikramreddy17@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Phytoplankton community structure during different phases (early, peak and late) of summer monsoon (SM) nutrient enrichment event (upwelling) of 2018 was studied along the eastern Arabian Sea (EAS). The three consecutive observations during the early (June-July), peak (August), and late (September-October) phases of SM covered the entire EAS basin between 6 and 22⁰N. The High Performance Liquid Chromatography (HPLC) and CHEMTAX techniques were used to determine the phytoplankton pigment distribution and relative abundance of phytoplankton group to total chlorophyll a (Chl a). The early phase of upwelling was characterised by a moderate phytoplankton production (column Chl a: 39.62±35.86 mg m-2) dominated by diatom species (60-70%) in the coastal EAS. In contrast, the offshore waters, where the nutricline was below 50 m, were dominated by pico-phytoplankton species (cyanobacteria 30% and prochlorophytes 20%) while diatom contributed to <20% due to low N/P condition (2.6±1.31). During peak SM, the shoaling of thermocline leading to high N/P conditions (8.4±5.25) have significantly enhanced the phytoplankton biomass (90.42±69.94mg m-2) with diatoms as major contributor (>90%) along the coastal EAS. Parallelly, the shallow nutricline in the offshore waters also supported the dominance of diatoms, especially in the south EAS (up to 75 %) relative to north EAS (up to 35 %), where the upwelling intensity was relatively less compared to the former region. The lowering of N/P ratios with the withdrawal of upwelling during the late SM was conducive for the reoccurrence of cyanobacteria and diatoms population sharply decreased (~50%) and succeeded to dinoflagellates. Noticeably, upwelling in the EAS brings the nitrogen deficit (denitrified) waters, the available nitrogen gets immediately consumed by the diatom community and the resultant low N/P conditions favour the dominance of the cyanobacterial population towards the late SM. Thus, the present study indicates that the changes in nutrient stoichiometry during various phases of upwelling control the phytoplankton community structure of the EAS during SM. Keywords: Eastern Arabian Sea, Upwelling, Phytoplankton pigment, HPLC, CHEMTAX, Nutrient stoichiometry |