Ecosystem Variability along the Estuarine Salinity Gradient: A Case Study of Hooghly River Estuary, West Bengal, India

Abstract

Hooghly River, a ~460 km long distributary of the Ganga River, passes through a highly industrialized Metropolis-Kolkata in West Bengal, India, and eventually empties into the Bay of Bengal at Gangasagar. To determine the patterns and drivers of planktonic community, spatiotemporal variations in water quality and micronutrient content and planktic prokaryotic and microeukaryotic abundance and diversity across the salinity gradient (0.1 to 24.6 PSU) in the Hooghly River estuary (HRE) were studied. Plankton and water samples were collected at six sites during October 2017, February 2018, and June 2018. The biotic parameters—phytoplankton (Chlorophyll a), total bacterial abundance (cfu), and copepods—were significantly higher in the downstream estuarine sites than in the upstream riparian sites; conversely, rotifer and cladoceran abundances were significantly higher at upstream stations. The most culturable bacterial strains were isolated from the two freshwater sites and one at the confluence (estuarine) and are characterized as Bacillus subtilis, Pseudomonas songnenesis, and Exiguobacterium aurantiacum. Among zooplankton, rotifers (0.09 ± 0.14 ind L−1) and cladocerans (5.4 ± 8.87 ind L−1) were recorded in higher abundance and negatively correlated with bacterial concentrations at upstream stations. On the temporal scale, February samples recorded lower proportions of bacterivorous zooplankton at the three upstream stations. Cluster analysis separated samples on the basis of seasons and water mass movement. The February samples showed distinct spatial characteristics, as three freshwater (FW) stations grouped together and segregated at second 2nd hierarchical level, whereas the three estuarine stations formed a separate cluster at the 50% similarity level. Samples collected in October 2017 and June 2018 exhibited mixed attributes. June samples recorded higher influence of freshwater discharge. The zooplankton abundance showed significant negative correlation with Chl a. Our results demonstrate the relative role of river continuum, land-driven lateral discharge, and seawater intrusion in shaping community structure, which needs to be considered in management and conservation planning of aquatic ecosystems, especially in highly productive and overexploited HRE.

Ecology of Marine Zooplankton

“…The spatial and temporal variability of plankton depends on environmental parameters. In their contribution, Prakash et al [14] investigate the role of salinity gradients on bacterioplankton, phytoplankton, and zooplankton abundance and diversity in the highly productive Hooghly River Estuary in West Bengal, India. They find zooplankton distribution strongly affected by water circulation, bacteria, and Chl a content, with higher abundances of rotifers and cladocerans in lower salinity stations and copepod dominance in downstream stations with higher salinity.…”

How are zooplankton’s functional guilds influenced by land use in Amazon streams?

“…Zooplankton plays many functional roles in freshwater ecosystems [ 15 ] and can be used when analyzing the integrity of water bodies because of their fast life cycle and sensitivity to environmental changes [ 16 , 17 ], such as the ones created by land use. This group participates in the matter and energy flow of different compartments inside water bodies and acts as a link inside the food chains [ 18 , 19 ].…”

Assessment of phytoplankton diversity, distribution, and environmental variables along the southeast coast of India

“…Several studies have been conducted along the east coast of India to examine the seasonal and spatial pattern of coastal waters and their impact on phytoplankton productivity (Naqvi et al, 1978;Satpathy et al, 2011;Sahu et al, 2012;Prakash et al, 2023). The nearshore and estuaries, which are impacted by both natural and anthropogenic disturbances (Jarvie et al, 1998), vary significantly depending on the local environmental setup, such as rainfall, amount of freshwater inflow, tidal incursion, and biological activities (Satpathy et al, 2011).…”