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| Abstract Submission No. | ABS-2022-09-0320 |
| Title of Abstract | Upwelling induced phytoplankton size-fractionated productivity and community responses in the Alappuzha mud banks and nearby waters |
| Authors | Anil.P*, Madhu N V, Sajeev R, Gireesh Kumar.T.R, Gopika.P |
| Organisation | CSIR National Institute of Oceanography, Regional Centre, Kochi |
| Address | CSIR National Institute of Oceanography, Regional Centre, Dr.Salim Ali Road Kochi, Kerala, India Pincode: 682018 Mobile: 9605575987 E-mail: anilnassa@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Mud banks or ⿿chakara⿿ are unique coastal oceanographic phenomena that usually occur in the nearshore waters of the southwest coast of India, particularly on the Kerala coast. The seasonal formation of fragmented stretches of calm turbid waters, especially during the southwest monsoon period (SWM), along with considerably high suspended sediments, are the characteristic physical indications of this phenomenon. Among the mud banks on the Kerala coast, the Alappuzha mud bank (AMB) is unique for its diverse reasons. Since the AMB is highly influenced by the prevailing SWM induced coastal upwelling process, the whole physico-chemical and biological (mainly phytoplankton) properties of waters in and around the AMB exhibit pronounced temporal variations. Therefore, the present study has attempted to elucidate the phytoplankton size-structure-based productivity (chlorophyll a and primary productivity) and community composition and succession patterns in the AMB and nearby coastal waters (<15 m depth) during various seasons (2017). The size-fractionated phytoplankton measurements have shown a distinctive growth pattern with respect to the seasonal hydrographic changes. An exceptional increase in phytoplankton chlorophyll a (3.41-16.87 mg m-3) and primary production (1091-1990 mgC m-3 day-1), found to be mainly derived from microphytoplankton (20-200 µm) community, was evident in the study region during the peak SWM (July). A more or less similar productivity pattern was apparent in the study region during the waning phase of SWM (September) and post SWM (November) periods as well, in which microphytoplankton contributed much to the chl a and primary production. By contrast, during the pre-SWM (April) and onset phase of SWM (June), the whole study region was dominated by a relatively smaller nanophytoplankton (2 - 20 µm) community, in terms of both chl a (47-74 %) and PP (51-86 %). The microscope derived phytoplankton (mostly >20 µm) composition data has revealed the preponderance of diatoms, despite the prevalence of diverse species with variable cell sizes. Nevertheless, during the onset of SWM period, dinoflagellates have outnumbered the diatoms, wherein a marked proliferation of Tripos furca (in stations 1-4) and Prorocentrum micans (in stations 6-7), was encountered. On the other hand, an exceptional numerical dominance (88 ⿿ 99 % of the total abundance) of a centric diatom, Thalassiosira sp. (44.00 - 188.56 x 103 cells L-1), was found to be responsible for the remarkable increase in the chl a and primary production recorded during the peak SWM period. The present study, even though it has evidenced the prevalence of wide temporal scale variability in nutrient levels and water column turbidity, has clearly demonstrated the profound dominance of diverse diatom species, regardless of seasons, in spite of the sporadic abundance of dinoflagellates. In conclusion, it can be stated that although the study region is evident for the drastic increase in phytoplankton growth (mainly due to diatoms) as a result of the upwelling induced nutrient enrichments, the clear cut dominance of diatoms even before and after the coastal upwelling process, has revealed the survival capacity of diatoms in low nutrient waters as well. |