Temporal Variability in the Mesophytoplankton Dynamics at Confluence of River Nethravati with Arabian Sea, off Mangalore, Karnataka

Author: K. Madhavi, A. Padmanabha, N. Jesintha, N. Chetan and Adnan Amin

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Abstract

Studies on the phytoplankton dynamics gives information on the their qualitative and quantitative distribution in the water body concerned, thereby helps in understanding their community structure, food web dynamics, their potential in supporting fisheries and also gives a clue for developing strategies in view of maintaining biodiversity, improving water quality, and ensuring the sustainability of aquatic resources. A holistic understanding of the plankton community and its role in the aquatic ecosystem, is essential for monitoring, managing, and conserving water bodies, hence the present study. Surface water samples and plankton (meso/net plankton) were collected at monthly intervals from the confluence area of River Nethravati with Arabian Sea, off Mangalore, for a period of 12 months covering pre-monsoon and two consecutive post-monsoon seasons, sampling couldn’t be done during monsoon period due to rough weather conditions. A total of 48 genera encountered in the study area, including 23 genera from centrales, 10 from pennales, 7 from pyrrophyta and 4 each from cyanophyta and chlorophyta. Of the total genera recorded, centrale diatoms contributed nearly to half of the diversity of total phytoplankton. The abundance (cells/m3) of phytoplankton varied from 111220 cells/m3 1768800 cells/m3 and was in the order of Chrysophyta (15.83% to 98.81%) > Cyanophyta (0.21% to 82.72%) > Pyrophyta (0.68% to 9.79%) > Chlorophyta (0% to 4.17%). Alpha diversity indices of plankton were estimated using Primer software and are as follows: Maegalef’s Richness Index (1.18 to 2.48); Pielou’s Evenness Index (0.21 to 0.87); Shannon’s Diversity Index (0.61 to 2.68). The study area exhibited mesohaline nature (with an average salinity of 16.23 ppt) during pre-monsoon, while euhaline (with an average salinity of 32.59 ppt) nature during pre-monsoon season

Keywords

Phytoplankton, confluence point, salinity, chlorophyll

Conclusion

The study highlights significant temporal variations in the mesophytoplankton community at the confluence of River Nethravati with Arabian Sea, influenced by associated shift in the dominance of river/tidal influx with seasons. During the pre-monsoon period, the dominance of Chrysophyta in euhaline waters was evident, while a substantial increase in Cyanophyta was observed during the post-monsoon period under mesohaline conditions. This shift underscores the impact of salinity gradients on phytoplankton distribution and abundance. The results suggest that the phytoplankton community structure serves as a reliable indicator of estuarine water quality, reflecting the estuary's response to freshwater influx and tidal dynamics. The allelopathic effects of Cyanophyta on diatoms further emphasize the competitive interactions within the phytoplankton community, which are crucial for understanding ecosystem health and resilience

References

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How to cite this article

K. Madhavi, A. Padmanabha, N. Jesintha, N. Chetan and Adnan Amin (2024). Temporal Variability in the Mesophytoplankton Dynamics at Confluence of River Nethravati with Arabian Sea, off Mangalore, Karnataka. Biological Forum – An International Journal, 16(2): 166-170