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Port environments are highly dynamic and hotspots for marine bioinvasion. This study investigated the bacterial diversity at two geographically distant ports (Mangalore-marine port; and Haldia-riverine port) using next-generation sequencing during southwest monsoon and non-monsoon (Pre-monsoon) seasons. During southwest monsoon, at both marine and riverine ports, operational taxonomic units (OTUs) affiliated to bacteria reported to have hydrocarbon degrading ability were observed. Whereas during pre-monsoon, a significant increase in benthic bacterial OTUs was evident at the marine port, and the riverine port was characterized by oceanic species OTUs. Results suggest that the dynamics of prevalent environmental conditions, driven by seasons, led to emergence of ecologically relevant bacteria, many of which have been observed for the first time in Indian coastal waters. Their presence could be used as indicators of prevailing environmental conditions and nature of anthropogenic influence in port ecosystems. Unravelling functional roles of such ecologically relevant species is a way forward., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Increasing coastal urbanization and shipping activity-related environmental pollution advocate the importance of assessment of port ecosystems. Fatty acid biomarkers, elemental components, and biopolymers were used to evaluate the composition of sedimentary organic matter and benthic trophic status of Kolkata (freshwater, enclosed docks) and Kandla (seawater, macrotidal) ports of India. The sediment fatty acid composition indicated relatively fresh and energy-rich organic matter of phytoplankton and bacterial origin inside Kolkata port than the outside riverine station and Kandla port. Biopolymeric carbon (BPC), used as an indicator of trophic status, revealed eutrophic condition in Kolkata port with high accumulation of organic matter of autochthonous origin, attributed to poor water flushing and input of anthropogenic wastes. In contrast, Kandla port was meso-oligotrophic, rich in bacteria, and terrestrial plant-derived materials. Such an assessment of ports' trophic status helps to evaluate the health of the ecosystem and in management practices., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The influence of changing salinity on community composition and functional activity (Bacterial Production (BP) and ectoenzyme activity) of major bacterial taxa was evaluated using microcosm experiments in a tropical monsoon influenced estuary. Natural bacterial inocula at different salinities, representing marine, brackish, and freshwater, were inter-transferred and elucidated their response with an emphasis on community composition and β-Glucosidase (BGase) activity. The results revealed a significant decrease in the total bacterial count (TBC) and BP on the translocation of bacterial inocula to different salinity conditions in the case of freshwater bacteria. However, a significant increase in BGase activity coupled with shifts in the studied bacterial groups was evident in the case of marine as well as freshwater bacteria. Quantitative PCR (qPCR) revealed a shift in major bacterial taxa upon translocation to different waters, which was dependent on salinity and the source of inocula. Redundancy and qPCR analyses showed that members belonging to Gammaproteobacteria and Betaproteobacteria were higher, and possibly influenced BGase activity in marine and freshwater, respectively. Translocation of marine inocula to brackish and freshwater resulted in an emergence of Bacteroidetes, Actinobacteria, and Betaproteobacteria, respectively. Whereas, when freshwater inocula were translocated to marine or brackish water, Alphaproteobacteria and Gammaproteobacteria taxa emerged, and this was coupled with increased BGase activity. In contrast, brackish water bacteria showed a strong persistence in bacterial community composition when translocated to different salinities within this estuary. Such phylogenetic persistence or changes suggests species level shifts in specific bacterial taxa, and unravelling the same using different functional gene markers would ascertain their role in organic matter processing and is way forward., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Understanding the variability in organism's immunological response is crucial for predicting changes at population or community level. The present study investigated the immunoecology of a commercially valuable clam Paphia malabarica in a tropical monsoon-influenced estuary. Clams were collected monthly during a year cycle, which coincided with pre-monsoon (February-May), monsoon (June-September) and post-monsoon seasons (October-January). For assessment of immune functioning, selected hemocyte parameters (total hemocyte concentration, hemocyte mortality, lysosomal content, esterase activity, reactive oxygen species production, and phagocytic activity) were analyzed using flow cytometry. Simultaneously, clam's condition index, nutrients, chlorophyll a, dissolved oxygen, pH, temperature and bacterial density were also measured at the sampling site. Our results exhibited seasonal patterns in hemocyte functioning with the highest activity during the pre-monsoon season (suggestive of a suitable harvesting period) and lowest during monsoon (suggestive of a critical biological period). The critical biological period for P. malabarica was marked with compromised immune parameters inflicted by low salinity, food availability, and possibly high bacterial abundance. Also, the involvement of reproductive stress altering the hematological functioning in P. malabarica cannot be ruled out. Nutrients, dissolved oxygen, pH and temperature could not explain much of the hemocyte variability. The present study has further validated the usefulness of hemocyte as a suitable marker for understanding immunoecology of P. malabarica which is of prime importance, especially in a monsoon-influenced tropical estuarine environment. The findings of our research will be constructive in monitoring natural as well as cultivated bivalve populations of economic and ecological relevance., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Paphia malabarica is a predominant and commercially important bivalve in India, persistently challenged by wavering salinity in a monsoon-influenced estuary. To examine the organism's immunological response under such a condition we challenged P. malabarica with different salinities (0, 5, 15, 25 and 35) for varied periods using a two-way experimental approach (in vitro and in vivo). This is the first study to report the response of P. malabarica hemocytes to salinity stress from a monsoon-influenced estuary on the southwest coast of India. Evaluation of total hemocytes count, mortality, lysosomal content, reactive oxygen species production, phagocytic and esterase activity was carried out using flow cytometric analysis. In both the experimental conditions, hemocyte parameters were significantly compromised at lower salinities (0 and 5) with an evident immuno-salinity tolerance range of 15-35. The damaging impact of 0 and 5 salinities on hemocyte function intensified with a longer exposure period, indicating that prolonged exposure to low salinity could be detrimental to bivalve wellness if they are pushed beyond their tolerance range which is usually observed during the monsoon. Further studies should focus on the interactive effect of salinity tagged with different stressors influencing biology of P. malabarica., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Changing climatic conditions have influenced the monsoon pattern in recent years. Variations in bacterial population in one such tropical environment were observed everyday over two years and point out intra and inter annual changes driven by the intensity of rainfall. Vibrio spp. were abundant during the monsoon and so were faecal coliforms. Vibrio alginolyticus were negatively influenced by nitrate, whereas, silicate and rainfall positively influenced Vibrio parahaemolyticus numbers. It is also known that pathogenic bacteria are associated with the plankton. Changes in the abundance of plankton, which are governed mainly by environmental changes, could be responsible for variation in pathogenic bacterial abundance during monsoon, other than the land runoff due to precipitation and influx of fresh water., (Copyright © 2015 Elsevier Ltd. All rights reserved.)