Phytoplankton Community Assemblage of Upper Stretches of Nethravati Estuary Dakshina Kannada, Karnataka

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

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Abstract

To gain a more comprehensive understanding of ecosystem health, it is necessary to assess the diversity and density of its phytoplankton communities, considering changes due to freshwater discharge and tidal influx, since phytoplankton community is highly sensitive and more susceptible to disturbances compared to other organisms, thereby serves as an excellent indicator, hence the present study. Surface water samples and plankton (meso/net plankton) were collected at monthly intervals from upper stretch of Nethravati limb of Nethravati-Gurupur estuary, for a period of 16 months covering post-monsoon, pre-monsoon, monsoon and ensuing post-monsoon. Phytoplankton abundance was in the order of Cyanophyta (0.16% to 93.51%) > Chrysophyta (2.79% to 79.92%) > Chlorophyta (0% to 67.19%) > Pyrophyta (0% to 0.23%). While, generic diversity was in the order of Chrysophyta (24) > Chlorophyta (22) > Cyanophyta (18) > Rhodophyta (1) Pyrophyta (0). Alpha diversity indices of plankton were estimated using Primer software and are as follows: Maegalef’s Richness Index (0.47 to 2.15); Pielou’s Evenness Index (0.30 to 0.64); Shannon’s Diversity Index (0.62 to 2.27). Salinity varied over a wide range from 0.04 psu (monsoon) to 25.62 psu (pre-monsoon), being limnetic during monsoon and early post-monsoon seasons. Chlorophyll-a, the main molecule in charge of photosynthesis, varied between 2.95µg/L and 6.86µg/L, thereby indicated the mesotrophic nature of the water

Keywords

Phytoplankton, Nethravati estuary, salinity, chlorophyll, plankton indices

Conclusion

Salinity played a pivotal role in shaping the temporal variability and distribution of phytoplankton populations, as this estuarine system exhibited distinct seasonal patterns, with a marked influence of monsoonal runoff and tidal activity on phytoplankton community structure. Cyanophytes, Chrysophytes, and Chlorophytes were the dominant groups, with Cyanophytes overwhelmingly dominating during pre-monsoon. The observed mesotrophic nature of the water, indicated by Chlorophyll-a concentrations, suggests that the estuary maintains moderate productivity levels. This finding is significant as it indicates that the estuary is not undergoing eutrophication, instead, it appears to be balanced, with nutrient inputs being moderated by tidal exchanges and monsoonal flushing. But, season’s transition from post-monsoon to pre-monsoon witnessed stressful conditions, indicated by the bloom of Coscinodiscus spp., contributing to 78.26% of total phytoplankton

References

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How to cite this article

K. Madhavi, A. Padmanabha, N. Jesintha and Adnan Amin (2024). Phytoplankton Community Assemblage of Upper Stretches of Nethravati Estuary Dakshina Kannada, Karnataka. Biological Forum – An International Journal, 16(3): 276-280