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Characterization of phytoplankton size-structure based productivity, pigment complexes (HPLC/CHEMTAX) and species composition in the Cochin estuary (southwest coast of India) : special emphasis on diatoms

Paul Meenu, Velappan Madhu Nikathithara, Nanappan Ullas, Gopinath Vineetha, Velloth Rehitha Thekkendavida, Rajendran Ashwini, Nair Maheswari, Peariya Anil

Oceanologia

2021

No. 63 (4)

463--481

Seasonal studies on size-fractionated phytoplankton productivity (biomass and primary production), marker pigments, and species composition and abundance were carried out in the Cochin estuary (CE), located on the southwest coast of India, to identify the critical environmental factors that control the consistent preponderance of diatoms. The overall results of the study showed a significant contribution of small-sized phytoplankton, specifically nanophytoplankton (2-20 µm), to the total chlorophyll a and primary production in the estuary, regardless of seasons. Diatoms constituted the major phytoplankton taxa, showed an exceptional seasonal scale increase in numerical abundance during the post-southwest monsoon. The relative increase in fucoxanthin (biomarker of diatoms) over other marker pigments substantiated the numerical dominance of diatoms throughout the sampling periods. This is the first study in the CE in which phytoplankton marker pigments have been detected and elucidated the seasonality of functional groups based on HPLC/chemotaxonomy analytical approaches. The prevalence of high DiatDP and diatom chlorophyll a equivalent (estimated by CHEMTAX), further confirmed the preponderance of diatoms in the CE, despite the intermittent dominance of cyanophytes and cryptophytes (monsoon period). The consistent increase in SPM levels (> 25 mg L–1), established at all sampling stations, indicated that the water column turbidity might be one of the significant environmental factors hindering the growth of large-sized phytoplankton (ca. >20 µm) in the CE even if the system invariably holds high inorganic nutrients, irrespective of seasons.

First recorded bloom of Akashiwo sanguinea (Dinophyceae) from the Cochin backwaters, a tropical estuarine system along the South Eastern Arabian Sea

Sathish Twinkle, Thomas Lathika Cicily, Aishwarya, Benny Niya, Padmakumar K. B.

Oceanological and Hydrobiological Studies

2020

Vol. 49, No. 4

391--397

Akashiwo sanguinea, a cosmopolitan red tide-forming dinoflagellate, is reported for the first time as a bloom from the Cochin estuary along the South Eastern Arabian Sea. Monthly sampling showed the continuous presence of A. sanguinea with occasional blooms. Blooms of A. sanguinea with the highest abundance of 2.8 × 105 cells l-1 were observed during the monsoon season (June 2019) with chlorophyll a of 17.2 mg m-3. The bloom period was characterized by higher concentrations of nitrate (26 µmol l-1) and phosphate (3.8 µmol l-1). Routine monitoring of the bloom region showed the survival of the Akashiwo sanguinea population in the temperature (26 to 30°C) and salinity (22 to 24 PSU) range indicating its eurythermal and euryhaline characteristics.