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Rise in temperature directly affects the poikilothermic aquatic animals such as fishes influencing their population biomass and recruitment. With this perspective, a study on spatial-temporal distribution of Indian oil sardine along south-west coast of India (SW) was conducted by classifying the study area into three strata namely: southern, central and northern region. The data was collected and segregated into three seasons, i.e. pre-monsoon, monsoon and post-monsoon. The trend for sea surface temperature was analyzed and compared among three strata and seasons. The trend of standardized catch per hour for all strata and season was also analyzed, along with observation on gear-wise catch of Indian oil sardine. This study indicates towards latitudinal extension and seasonal changes of Indian oil sardine population, besides changing its distribution into deeper water for avoiding the adverse impact of rising temperature.

Microplastic pollution and the impacts they generate on the marine ecosystem and its biota is a major global concern of recent decades. The present study was conducted to evaluate the spatio-temporal distribution of microplastics in the surface waters, sediments, and their subsequent ingestion by the commercially important fishes of Alappuzha Mud banks, a transient ecosystem formed in the littoral zones of the southwest coast of India exclusively during the Indian summer monsoon. Sampling conducted over three periods, Pre-mud bank (Pre-MB), Mud bank (MB), and Post mud bank (Post-MB) extending over three depths (2 m, 5 m and 18 m), along the semi-circular patch of mudbanks revealed marked spatio-temporal variability in microplastic distribution. In both surface water and sediments, microplastic concentration was comparatively high during MB than in Pre-MB and Post-MB periods. Spatially, during MB, the microplastic concentration was high at 5 m where the dampening of waves occurred concomitant to the thick fluid mud formation. In contrast, during Post-MB, with the subsequent dissipation of MB's and less wave dampening, the microplastics aggregated at 5 m were transported to both inshore (2 m) and offshore (18 m), thus raising their concentration at these depths. Likewise, the microplastic ingestion was more in fishes caught during MB (41%) than Post-MB (30%) and Pre-MB (29%) periods indicating increased uptake corresponding to the higher incidences in their ambient environment. Microplastic ingestion was more among pelagic planktivores, S. gibbosa (38%), A. chacunda (20%) and R. kanagurta (13%) compared to the demersal fishes. White coloured fragments of size 1–5 mm of polypropylene were the dominant microplastic in the surface waters, sediment and fishes analysed. The present study indicates the critical role of wind speed, rainfall, wave patterns, and the fluid muddy environment in regulating the microplastics distribution in a transient ecosystem formed along the southwest coast of India. • Microplastic distribution in Mudbank showed conspicuous spatio-temporal variability. • Microplastics were high in water, sediment and fishes during Mudbank period. • Microplastics aggregated at 5 m depth due to wave dampening elicited by mud banks. • White coloured polypropylene fragments of size 1–5 mm were the most abundant one. [ABSTRACT FROM AUTHOR]

We investigated the effect of depuration of three naturally contaminated commercially important tropical edible bivalve molluscs by varying temperature, salinity and body-size of animals harvested from Ashtamudi and Vembanad estuaries, India using a static depuration system to ensure microbiological food safety. Before depuration, the levels of faecal indicators and pathogens were above the acceptable limits for live consumption. The depuration water temperature had a significant effect on bacterial elimination. Log reduction of faecal coliforms (FC) and E. coli varied between room-temperature (RTDS) and low-temperature depuration system (LTDS) and it was in the range of 1.39-2.44 and 1.88-2.82 log MPN, respectively under RTDS and LTDS. The elimination of bacterial pathogens such as Vibrio and Salmonella spp. was rapid in RTDS compared to LTDS. The highest elimination of FC and E. coli (2.39 and 2.92 log) was at 35 psμ depuration and the lowest (0.87 and 1.65 log) at 15 psμ depuration. The reduction of FC and E. coli was higher in the medium-sized animals compared to the small animals. Based on the results it is recommended that depuration using the static system under room-temperature (30 ± 1 °C); a salinity range of (25-35 psμ) and using medium-size bivalves (clam>30 mm; mussel >45 mm, and oyster >65 mm length) as optimum conditions for producing microbiologically safe bivalves for live consumption within 36 h., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Health of an ecosystem is very much important as we depend on its goods and services for our existence. Because of this, we need to continuously monitor its health for human benefit and for identifying areas for improvement of our natural systems. The present study tries to assess the condition of a coastal ecosystem within the Vembanad Lake, Kerala, India, using key water quality parameters at micro-level. Principal component analysis identified the minimum required water quality dataset for further analysis and was scored using linear scoring functions. The weighted additive method was used to integrate the individual scores to arrive at a final score representing the ecosystem health. Spline interpolation was applied to develop the ecosystem health map of the study area. Using this method, 35.8% area of the aquatic ecosystem studied was characterized as good, 32.2% as moderate, 26.2% as fair and 5.8% as poor. The assessment results can help the policymakers/managers to make appropriate decisions for the better management of the coastal ecosystems studied. Moreover, this methodology can be replicated for the assessment of coastal regions with similar ecosystem characteristics., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The effect of temperature, salinity and body-size on depuration of naturally accumulated heavy metals in clams, mussels and oysters harvested from Ashtamudi and Vembanad estuaries of Kerala, India were investigated using a static depuration system. Before depuration, the concentrations of heavy metals such as Ni, Co, Fe, Mn, Cu, Pb and Zn were analysed and it was found that the Fe, Zn, Cu and Pb contents in all the three bivalve molluscs were above the prescribed limit which poses a significant health risk to bivalve consumers. To protect consumer food safety, depuration experiments were conducted at varying temperatures, salinities and body-sizes. The clams, mussels and oysters depurated under the room temperature depuration system (RTDS) showed a better reduction of heavy metals compared with low-temperature depuration system (LTDS). ANOVA showed clams and mussels depurated at RTDS significantly (p < 0.05) reduced the heavy metals than LTDS. However, there was no significant (p > 0.05) difference in oysters between RTDS and LTDS. Further, clams and mussels depurated at low salinity (15-psμ) showed high resistance against Pb reduction. But, all the heavy metals, particularly, Pb, Fe, Zn and Cu were effectively removed at higher salinity depuration (25-psμ and 35-psμ). Moreover, irrespective of the body-size of clams, mussels and oysters used for depuration, a significant (p < 0.05) reduction in all metals (Ni, Co, Fe, Mn, Zn, Pb and Cu) was observed. Relatively, the medium-size bivalves showed higher reductions compared to small-size bivalves. Based on the experiments conducted, we recommend 48 h depuration using the static system under room temperature (30 ± 1 °C) with a salinity range of (25-35 psμ) using medium-size bivalves (clam>30 mm; mussel >45 mm, and oyster >65 mm length) as optimum conditions for producing safe bivalves for consumption in the tropics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Recurrent jellyfish blooms and their impacts on ecosystem deliverables of coastal habitats have become a major ecological concern. In view of this, repercussions of a surge in the jellyfish population on the plankton community were studied in Cochin estuary (CE), the largest tropical estuary along the southwest coast of India. Evaluation of hydrographic attributes and plankton community of the CE during early and late pre-monsoon revealed a marked disparity in its hydrography which favoured an increase in jellyfish abundances during late pre-monsoon, eliciting distinct impacts on the plankton community. The escalation in the jellyfish abundance and their subsequent predation on the crustacean plankton released the phytoplankton community from the grazing pressure resulting in a trophic cascade in the planktonic food web. The indiscriminate feeding of jellyfishes on the ichthyoplankton, decapod larvae, and Copepoda, the primary diet component of forage fishes evoked a potent threat to the fishery potential of CE., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Restoration of Rhizophora mucronata stand in the Gurupura Estuary resulted in improved water and sediment quality parameters. Monthly monitoring from 2011 to 2016 indicates that the restored mangroves grew to a height of 61.49 ± 5.76 cm. Principal component analysis (PCA) showed that increased duration of salinity in the estuary aided the growth of barnacles in planted mangroves which reduced survival by 10%. The United States Environmental Protection Agency ratings revealed that natural mangrove site in Shambavi River exhibit the maximum good water quality rating though dissolved inorganic phosphorous was rated highest due to non-point pollution sources. The pH, salinity, dissolved oxygen, silicate, phosphate, ammonia, and rainfall demonstrated significant seasonal differences (P < 0.001). Mangrove roots and biomes aided in accumulation of clay and significant difference (P < 0.001) was observed yearly. Land use management, efficient waste disposal system along with restoration of diverse mangroves can improve the water quality of estuarine ecosystem., (Copyright © 2022. Published by Elsevier Ltd.)

Microzooplankton is an important component in the plankton food web transferring microbial food web carbon to the higher trophic levels, including fishes. This study investigates the role and significance of microzooplankton in the diet of three economically important small pelagic fishes along the southwest coast of India: Indian oil sardine (Sardinella longiceps), Indian mackerel (Rastrelliger kanagurta) and Commerson's anchovy (Stolephorous commersoni). The diet content of oil sardine was dominated by diatoms throughout the year with an increase in the presence of microzooplankton and copepods during the Northeast Monsoon. Phytoplankton, microzooplankton and copepods represented the diet of Indian mackerel throughout the year. Commerson's anchovy differed considerably in their diet composition from both Indian oil sardine and Indian mackerel as they chiefly depended on a carnivorous diet feeding on copepods, fish eggs, ostracods, lucifers and microzooplankton. The present study concludes that organic carbon from the microbial food web also, through microzooplankton, provides nutritional support to small pelagic fishes along the southwest coast of India but in varying degrees depending on the fish species as well the seasons., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Trace metal concentrations were monitored in the yellow clam (Paphia malabarica), green mussel (Perna viridis) and edible oyster (Crassostrea madrasensis) from growing areas in the Ashtamudi and Vembanad estuaries, Kerala. Samples of shellfish (clams n=26, mussels n=18, oysters n=36) and environmental parameters (salinity, temperature, pH and rainfall) were measured in these growing areas from July 2012 to December 2014. Ranges of mean annual concentrations (mg/kg) were Ni (0.46-0.65); Co (2.87-3.49); Fe (80.0-119.4); Mn (3.88-9.38); Zn (40.8-76.2); Pb (1.28-2.00); and Cu (1.59-4.38). In Ashtamudi, clams had higher mean concentrations of Ni, Co, Fe, Mn and Pb than oysters. Mean concentrations of Ni, Pb (in all species), Zn (in clams and mussels) and Cu (in mussels) did not exceed maximum permissible limits mandated by the Food Safety and Standards Authority of India. Mean Mn concentrations exceeded the World Health Organization guideline (1 mg/kg) in the three species while mean Fe concentrations in clams and oysters did not exceed the guideline (100 mg/kg). Target hazard quotients were generally ≤ 1, except for a few Pb results in clams and mussels. Although results suggest no health risk to consumers for the reference doses, daily intakes and elements considered, regular monitoring of trace metals is recommended to maintain consumer protection given increasing anthropogenic and climatic pressures on the shellfish growing areas., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The sources of microbiological contamination in shellfish harvesting areas in the Ashtamudi and Vembanad estuaries were identified through a sanitary survey. Samples of shellfish and waters were tested for faecal indicator bacteria. Both estuaries receive high levels of contamination from septic tank discharges and areas with high numbers of birds and livestock. An assessment to illustrate the classification status of the harvesting areas indicated that 64% of oyster and 58% of clam samples from Ashtamudi and 54% of mussel samples from Vembanad would comply with the lower class B standard of the EU classification system. Most water results would comply with the faecal coliform standard for 'Prohibited' areas under the US classification system. None of the water samples from Ashtamudi were below the standard for 'Approved' areas. Pollution reduction measures and implementation of a sanitation programme according to international best practice would improve consumer health protection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Consequences of a catastrophic flood on the habitat quality and the concurrent responses of the bentho-pelagic community were studied in Cochin estuary, a eutrophic estuary along the southwest coast of India. The episodic flood in 2018 led to a marked decline in the dissolved nutrients and heavy metal concentrations in water and sediments of the estuary. The pre-flood phytoplankton abundance dominated by a bloom-forming species Cerataulina bicornis experienced a significant drop after the flood. Contrarily, zooplankton and macrobenthos responded favorably towards the flood-imposed habitat alterations. Higher susceptibility to heavy metal pollution and increased grazing pressure from gelatinous carnivores restricted the abundance of Copepoda, the dominant zooplankton taxon during pre-flood. The lower heavy metal concentration in the sediment after the flood favored higher macrobenthic abundance and diversity with a conspicuous change in the community structure from opportunistic polychaetes, indicators of pollution to molluscans and crustaceans, indicators of the healthy benthic zones., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Epizootic ulcerative syndrome (EUS), primarily caused by the water mold Aphanomyces invadans, is an OIE-notifiable disease, having potential impacts on fisheries. We report EUS epizootics among estuarine fishes of Kerala, India, during 2018, under post-flood conditions 3 decades after its primary outbreak. Six fish species (Mugil cephalus, Platycephalus sp., Scatophagus argus, Arius sp., Planiliza macrolepis and Epinephelus malabaricus) were infected, including the first confirmed natural case in E. malabaricus and P. macrolepis. Salinity, surface temperature, dissolved oxygen and pH of resident water during the epizootic were <2 ppt, 25°C, 4.1 ppm and 7.0. The presence of zoonotic bacterial pathogens (Aeromonas veronii, Shewanella putrefaciens, Vibrio vulnificus and V. parahaemolyticus) in tissues of affected fish indicates that EUS-infected fish may pose a public health hazard if not handled properly. Lack of clinical evidence in the region during the last 3 decades, a high number of affected fishes, including 2 new fish species, the severity of skin lesions and very low water salinity (<2 ppt) during the outbreak in contrast to historical water salinity records suggest relatively recent invasion by A. invadans. Phylogenetic analysis based on the internal transcribed spacer region of the rRNA gene showed that the same clone of pathogen has spread across different continents regardless of fish species and ecotypes (fresh/estuarine environments). Altogether, the present study provides baseline data which can be applied in EUS management strategies within brackish-water ecosystems. We recommend strict surveillance and development of sound biosecurity measures against the disease.

Monthly litter samples were collected from three major beaches in Mangaluru from 2011-2016. Fishing litter persisted at the beaches, resulting in higher abundances by number (59%) and weight (33.4%) relative to all litter in 2016. In addition to plastics, foam comprised 7.14-11.0% of total litter. Significant positive correlations were observed between the amount of plastic on the beaches and rainy days, rainfall, and river discharge. The maximum river discharge coincided with an increase in plastic items on the beach. Yearly quantities of plastic items (p < 0.01), plastic bags (p < 0.001), and plastic footwear (p < 0.05), on the beaches were significantly different indicating clean-up activities reduced the litter quantity. Changes in total beach litter revealed that Panambur Beach, a fishing boat landing centre was the least changed, and thus appropriate incentive-based management options for the resident fishermen could result in collection and elimination of litter., (Copyright © 2019. Published by Elsevier Ltd.)

Polyaromatic hydrocarbons are a group of chemical pollutants which cause a significant threat to the living organisms in estuaries and marine ecosystems. We report the effect of chrysene, a major PAH pollutant found in Cochin Estuary along the southwest coast of India, on the neuroendocrine and immune gene expression of the post larvae (PL-25) of Penaeus monodon. The PL- 25 of P. monodon were administered with feed coated with increasing concentrations of chrysene (1, 2 and 3 µg/g) for 10 days and the gene expression was studied on 7th, 11th and 15th day. The PL exposed to chrysene showed moulting stress and changes in the levels of moult-inhibiting hormone I (MIH I) indicated by irregular moulting in the experimental tanks. At the molecular level, the higher concentration of chrysene induced two-fold upregulation of neuroendocrine (MIH I) and downregulation of immune (ProPO and crustin) gene on the 7th day of exposure. The expression of MIH I gene reduced on withdrawing the experimental feed (on 11th day), while continued downregulation of ProPO and crustin were observed on the 11th day. The results of the present study indicate that the microgram levels of PAH can impinge the neuroendocrine and immune system of the P. monodon, which may induce morbidity and mortality to the larvae in polluted coastal ecosystems. Therefore, more attention may be given to avoid PAH pollution in the estuaries to maintain a healthy ecosystem and to protect the animals from extinction.

A detailed pathological survey was carried out on the commercially important edible oyster, Crassostrea madrasensis (Preston), from two distinct coastal/brackish water ecosystems of south India. Samples were collected twice a year during wet and dry seasons from 2009 to 2012. Bacterial colonies in the form of prokaryotic inclusions, protozoans (Perkinsus beihaiensis, Nematopsis sp. and ciliates Sphenophrya sp. and Stegotricha sp.), metazoans (trematodes, turbellaria, cestodes and crustaceans) and shell parasites (Polydora spp. and Cliona spp.) along with various pathological conditions (digestive tubule atrophy, ceroid bodies, haemocytic infiltration, tissue necrosis and neoplastic disorders) were observed in C. madrasensis collected from two sites. Intensity, spatial and seasonal variations in infection prevalence and pathological effects on the host were studied. The protozoan parasite, P. beihaiensis; shell parasite, Polydora spp. and pathological condition, digestive gland atrophy were most prevalent in occurrence. High-intensity infections with P. beihaiensis, larval trematodes and Polydora spp. were found to cause significant impact on host physiology. All other parasites were observed with low mean prevalence and intensity. Karapad in Tuticorin bay, the site reported with marked pollution levels, exhibited higher number of parasitic taxa and high mean prevalence and intensity for pathological conditions.