Spatio-temporal dynamics of tropical phytoplankton communities in the diverse coastal environments of southwestern India: HPLCCHEMTAX approach
Date
2025Author
Anil, P.
Madhu, N. V.
Vishal, C. R.
Arya, K. S.
Sudheesh, P.
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A comprehensive investigation on phytoplankton community composition, utilizing HPLC-derived biomarker pigments and CHEMTAX analysis, was conducted in the Chandragiri Estuary (CGE) and adjacent nearshore waters (<20 m, off Kasaragod) along the southwest coast of India during 2018–2019. The CGE exhibited highly dynamic hydrographic conditions, which were reflected in the pronounced spatio-temporal variability of its phytoplankton communities. During non-monsoon periods, particularly the winter monsoon (WM) and spring-inter monsoon (SIM), the estuary was characterized by warm ( >29 °C), well-mixed, polyhaline to euhaline waters (28–35) and relatively elevated concentrations of key nutrients, including ammonium, nitrate and phosphate, These conditions supported moderately high concentrations of chlorophyll a (Chl a) in the CGE, averaging 2.14 ± 0.65 mgm−3 during WM and 1.78 ± 0.45 mg m−3 during SIM. In contrast, the summer monsoon (SM) period was marked by the influx of cooler (<26 °C), turbid freshwaters, which significantly suppressed phytoplankton biomass, resulting in exceptionally low Chl a levels (<0.2 mg m−3) throughout the estuary. In the adjacent nearshore waters, the Chl a concentrations remained consistently low (<1 mg m−3) across all seasons. CHEMTAX analysis using HPLC derived pigments identified five major phytoplankton functional groups (PFGs) in the CGE: diatoms, dinoflagellates, cryptophytes, green algae (chlorophytes), and cyanobacteria. Among these, diatoms, cyanobacteria, and chlorophytes were the predominant groups throughout the study period. Diatoms constantly dominated the phytoplankton community in the nearshore waters as well, as indicated by the predominance of fucoxanthin, except during the SIM, when the composition temporarily shifted. The dominance of diatoms in the CGE, despite periodic increases in cyanobacteria and cryptophytes, reflected variability in nutrient availability, particularly NO3single bondN and PO4-P, driven by fluctuations in river discharge and tidal influence. Conversely, the nearshore waters exhibited relatively stable hydrographic conditions, which supported a persistent, albeit lower, diatom growth with minimal temporal variability in community structure.
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