Search

Eutrophication of marine ecosystems is a global problem, particularly in a changing climate and the spreading of Oxygen Minimum Zones (OMZs). The eastern Arabian Sea has both seasonal and permanent/perennial OMZs, but our understanding of the fauna there is extremely poor. So, this study investigated the composition and physiological status (alive or dead) of zooplankton (copepods) in the two OMZs. The study was accomplished by employing a Multiple Plankton Net and vital staining method. Our results showed for the first time that the oxygen deficiency adversely impacted the physiological status of copepods in OMZs which was reflected as (a) a two-fold decrease in zooplankton in the more intense oceanic OMZ compared to the coastal OMZ, (b) a marked increase of dead copepods in both OMZs (50 to 60 %) compared to normoxic waters (35 %) observed in previous studies and (c) higher copepod carcasses (50-70 %) and lower copepods larvae in the intense oceanic OMZ., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest with this manuscript., (Copyright © 2024. Published by Elsevier Ltd.)

The largest continental shelf Oxygen Minimum Zone (OMZ) in the world is formed along the Indian western shelf in the eastern Arabian Sea during the Southwest Monsoon [(SWM); June-September], which is a natural pollution event associated with the coastal upwelling. This study examines the composition, abundance, and distribution of copepods during the Northeast Monsoon [(NEM); November to February] and SWM in 50 m depth zones along the Indian western shelf in the eastern Arabian Sea. The NEM was characterised by warm, stratified, and low-salinity waters in the southeast Arabian Sea and cold, high-salinity, and well-mixed waters in the northeastern Arabian Sea. During the SWM, cold and Dissolved Oxygen (DO) deficient waters (<22 μM/0.5 ml L -1 ), which are the signs of coastal upwelling, were evident all along the study zone, but with more intensity off Kochi, Mangalore, and Goa in the south than off Mumbai and Okha in the north. The zooplankton total biomass and abundance showed seasonality with a general decrease during the SWM (av. 3.68 ± 1.29 ml m -3 and av. 5711 ± 3096 Ind. m -3 , respectively) compared to the NEM (av. 7.37 ± 2.17 ml m -3 and av. 14,473 ± 4966 Ind. m -3 , respectively). At the same time, the abundance of Polychaeta and Siphonophora showed an increase during the SWM (av. 1187 ± 1055 Ind. m -3 and av. 169 ± 119 Ind. m -3 , respectively), probably a result of the DO deficient waters associated with upwelling. Two striking seasonal features in Copepoda community were evident in this study: (a) a compositional shift from Cyclopoida dominant during the NEM to Calanoida dominant during the SWM, and (b) the coastal OMZ along the Indian western shelf during the SWM was dominated by Calanoida, which include oceanic OMZ species such as Pleuromamma indica, Lucicutia flavicornis, L.paraclausii, Eucalanus elongatus, Subeucalanus pileatus, S.subcrassus, and Clausocalanus furcatus. This forms a clear imprint for the extension of the oceanic OMZ into nearshore waters during the SWM due to coastal upwelling., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest with this manuscript., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This baseline study on microplastics (MPs) in calanoid copepods in the Kochi backwaters (KBW), India's largest estuary system on the west coast, focuses on (a) the spatiotemporal variations of MPs with the seasonal hydrography setting, and (b) how man-made flow restrictions of a large saltwater barrage contribute to MPs in copepods and their potential to transfer to higher trophic levels. This study found that MPs in copepods in the KBW ranged from av. 0.01 ± 0.014 to 0.11 ± 0.03 no./ind. seasonally. When the saltwater barrage shutters were fully/partially closed during the Pre-monsoon/Northeast Monsoon, MPs in copepods were considerably larger (av. 0.11 ± 0.03 no./ind., and av. 0.075 ± 0.02 no./ind., respectively) as compared to the Southwest Monsoon (av. 0.03 ± 0.01 no./ind.), when the barrage shutters were fully open. This shows the potential of man-made flow restrictions to increase the bioconcentration of MPs in copepods and their possible transfer to higher trophic levels through the food chain, adding to the region's previous discovery that much higher trophic level resources are polluted with a high concentration of MPs., (Copyright © 2022. Published by Elsevier Ltd.)

Eichhornia crassipes and Monochoria vaginalis are waterweeds, and their uncontrolled proliferation in fresh and brackish water habitats is a serious ecological problem in many parts of the world. These weeds are quite common in the Vembanad Lake System (VLS), India's second-largest Ramsar wetland. During the non-monsoon season, the Thannermukkom saltwater barrage divides the VLS into two zones: saline water downstream and freshwater upstream. The field sampling of the current study was carried out in the upstream zone of the VLS during the Pre-Monsoon (March 2017). Fresh Eichhornia and Monochoria samples were collected, transported to the lab, and experiments were conducted under natural light conditions to determine how much extra water they transpire into the atmosphere. The results showed that the water loss in experimental tanks with Eichhornia (evapotranspiration) is roughly twice that in control tanks without them (only evaporation). Monochoria transpires fairly more water to the atmosphere than Eichhornia. These results reveal that the proliferation of waterweeds has a significant adverse effect in conserving water in all freshwater bodies infested with them. The current study also points out that the expansion of waterweeds has the potential to worsen drought conditions as they cause excess water loss into the atmosphere and a faster drying up of freshwater reservoirs. Two possible approaches for managing the waterweeds in the VLS include reducing nutrient loading upstream and more frequent opening of the Thannermukkom saltwater barrage to allow saltwater intrusion, which could inhibit the growing waterweeds., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The baseline study of Microplastics (MPs) in zooplankton (copepods, chaetognaths, decapods, and fish larvae) from six different zones along India's west coast (off Kanyakumari/Cape Comorin, Kochi, Mangalore, Goa, Mumbai, and Okha) in the Eastern Arabian Sea (EAS) is presented here with their vast ecosystem impacts. This investigation revealed that zooplankton in all six zones accumulated MPs pellets (52.14%), fibres (28.40%), films (10.51%), and fragments (8.95%). The highest average retention of MPs (MPs/individual) was found in fish larvae (av. 0.57 ± 0.18) while copepods had the lowest (av. 0.03 ± 0.01). The presence of low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate was confirmed by Raman Spectra of MPs. The MPs in zooplankton found in this study (av. 22 ± 7 pieces/m 3 ) were nearly 2-fold greater than those found in some of the world's most densely populated areas. It is shown that the strong southerly coastal currents could advect the MPs contaminated water mass too far away, having the potential to affect the fish and corals., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This study in the Kochi backwaters (KBW) presents the distribution of 9 trace metals (Fe, Zn, Cu, Mn, Ni, Co, Cr, Cd, Pb) in different parts (root, stolon and leaf) of the common water hyacinth Eichhornia crassipes during three different seasons [Pre-Monsoon (PRM), Southwest Monsoon (SWM), and Northeast Monsoon (NEM)]. The hyacinth was collected from 4 sections upstream of the KBW where a saltwater barrage [Thannermukkom Barrage (TB)] prevents saltwater intrusion. Results showed that regardless of seasons, all the trace metals concentration in different parts of Eichhornia varied in the following order: roots > stolon > leaves. All the trace metals except Fe showed their highest concentration during the PRM when TB introduces stagnancy of the water upstream through flow restrictions. Instead, Fe was high during the SWM associated with increased river influx at that time. Overall results showed that the hydrographical alterations of TB upstream of KBW have clear imprints on the trace metals concentrated in the hyacinth Eichhornia crassipes., (Copyright © 2021. Published by Elsevier Ltd.)

Coccolithophores are unique primary producers in the ocean with the ability to calcify. They are known to produce calcareous scales, which form the significant part of calcite oozes or chalk deposits on the seafloor. Coccolithophores are very noteworthy and they are explored to a great extent as nannofossils to reconstruct the past climate. Calcite plates in coccolithophores make them a vital tool in global climate change studies specifically with ocean acidification. These microscopic plants are the major contributor of the carbonate rain that controls the inorganic carbon pump in the ocean, which in turn influences both carbon and carbonate cycles. The emergence of advanced techniques enables us to study the biological aspects of this pelagic calcifier with improved precision. But still, they are understudied world over compared to any other phytoplankton groups. The northern Indian Ocean, being landlocked in three sides and vulnerable to climate change and ocean acidification, severely lacks focused studies on coccolithophores, though the US JGOFS in the 1990s have outlined the ecological significance of coccolithophores in the Arabian Sea. This paper reviews and outlines our understanding of coccolithophores as well as the nix in the northern Indian Ocean.