Variations in biophysical characteristics of mangroves along retreating and advancing shorelines

Mangrove shoreline retreat or advance is a natural process in a mangrove delta. However, due to various natural and anthropogenic stressors, mangrove shoreline retreat is the second largest cause of mangrove loss globally. It is important to understand the scale at which mangrove shoreline changes are causing biophysical changes along the mangrove shorelines and, in turn, understand if certain biophysical characteristics can explain the changes along the shoreline. This will help identify the response of mangroves to shoreline changes. Videography and spatial mapping were used to study temporarily and permanently changing mangrove shorelines in the Sundarbans, the largest mangrove forest in the world (~10,000 km2), located in India and Bangladesh. Data was collected along a ~ 239 km shoreline at 54 sites. 36.4 % of all the studied shorelines were experiencing major retreat, 63.8 % and 27.2 % of all (major and minor) retreating areas had 1-25 % and > 25 % dead trees. The biophysical characteristics statistically (P < 0.0001) associated with retreating mangrove shorelines were - cliff-type shoreline profiles, number of dead trees, and absence of stream and grass, with shoreline profiles as the strongest predictor of shoreline retreat. Moreover, 68.7 % and 73 % of historically retreating shorelines had a cliff-type shoreline profile and Excoecaria agallocha as the dominating species, respectively. Moreover, due to the strong correlation between historical changes and current shoreline types, it was concluded that characteristics along the shoreline are partly a product of historical shoreline transitions. Thus, the present status of the shoreline can not only predict the history of the shoreline but can also give insights into the future biophysical changes in the mangrove forests.

Analysis of Health Ailments and Associated Risk Factors in Small-Scale Fisherfolk Community of Indian Sundarbans: A Cross-Sectional Study

Background

Small-scale fishers of Indian Sundarbans depend on open-water fisheries for their livelihoods. They often face health, occupational, and safety issues in their profession due to environmental, socio-economic, and policy changes. The morbidity pattern and related risk factors are important indicators of well-being for any community, hence applicable to small-scale fishers of Sundarbans. The present study was designed to assess patterns of morbidities, associated risk factors including occupational health hazards, and treatment-seeking behavior of small-scale fishers in the Indian Sundarbans.

Material and Methods

Household surveys, focused group discussions, and personal interviews were conducted through a predesigned pretested structured questionnaire. Associated risk factors and the nature of seeking treatment were considered during the data collection covering 650 individuals from 132 fishers' families.

Results

Morbidities were more frequent in males (39.33%) than in females (28.5%). The fever (31%) was the most dominant reason for morbidities followed by ocular ailments (23%), musculoskeletal disorder (20%), dermatological ailments (17%), and respiratory illness (9%). The highest morbidities (25%) were recorded in the age group of 21-30 years in males while that was 20% in the 11-20 years age group in the case of the females. Physical labor for fishing activities predisposes to health ailments of the studied population.

Conclusions

The prevalence of morbidity among the fishermen community was found to be 28.5%. The understanding of the morbidity profile of a population in general and specific age groups of both sexes in specific sheds light on the vulnerability of working groups that will help for effective healthcare planning and resource allocation.

Source identification and potential health risks from elevated groundwater nitrate contamination in Sundarbans coastal aquifers, India

In recent years groundwater contamination through nitrate contamination has increased rapidly in the managementof water research. In our study, fourteen nitrate conditioning factors were used, and multi-collinearity analysis is done. Among all variables, pH is crucial and ranked one, with a value of 0.77, which controls the nitrate concentration in the coastal aquifer in South 24 Parganas. The second important factor is Cl-, the value of which is 0.71. Other factors like-As, F-, EC and Mg2+ ranked third, fourth and fifth position, and their value are 0.69, 0.69, 0.67 and 0.55, respectively. Due to contaminated water, people of this district are suffering from several diseases like kidney damage (around 60%), liver (about 40%), low pressure due to salinity, fever, and headache. The applied method is for other regions to determine the nitrate concentration predictions and for the justifiable alterationof some management strategies.

Combined impact of elevated temperature and zinc oxide nanoparticles on physiological stress and recovery responses of Scylla serrata

Global climate change is the major cause behind unexpected fluctuations in temperature. In recent years, application of nanotechnology also has become widespread and nanomaterials are constantly being released into aquatic environments, posing a potential risk to various organisms and ecosystems. The lack of detailed understanding of how multiple stressors work, and how they differ from single stressors, impede to assess their combined effect on aquatic organisms and ecosystems. The prime aim of the current investigation is to decipher the toxicity of ZnO-NP after simultaneous exposure to a global environmental stressor, elevated temperature for 14 days, followed by a 7 days recovery period, on the eco-physiological responses of mud crab Scylla serrata collected from Sundarbans. Physiological energetics such as ingestion, assimilation, absorption, respiration, and excretion rates were measured to determine the Scope for growth (SfG). Additionally, we assessed various biomarkers from different levels of biological organisation (antioxidant, detoxification defence mechanisms, and lipid peroxidation levels) of the species. Combined stress attenuated the SfG in crabs which deteriorated further in the recovery phase. Oxidative stress also exacerbated under coalesced stress condition. Recovery was not observed in crabs with increased lipid peroxidation level under combined stress conditions. Elevated temperature disturbed the energy budget of crabs as mirrored by diminished energy left for compensatory actions under added metal stress, ultimately sensitizing the animals to ZnO NP pollutants. The current results advocate future ocean temperature to aggravate the impact of metal NP pollution and induce oxidative damage in S. serrata.

Exploratory modelling of the impacts of sea-level rise on the Sundarbans mangrove forest, West Bengal, India

In this paper we conduct exploratory simulations of the possible evolution of the Indian Sundarbans mangroves to 2100 under a range of future sea-level rise (SLR) scenarios, considering the effects of both inundation and shoreline erosion. The Sea Level Affecting Marshes Model (SLAMM) is used to simulate habitat transitions due to inundation and these outputs are combined with an empirical model of SLR-driven shoreline erosion. A set of plausible climate-induced SLR scenarios are considered, together with delta subsidence and constrained vertical sediment accretion. Significant mangrove decline is found in all cases: the greater the rise in sea level the greater the losses. By the end of the century, the Indian Sundarbans mangroves could lose between 42 % and 80 % of their current area if current management is continued. Managed realignment could offset these losses but at the expense of productive land and the migration of the human population.

In-silico whole-genome sequence analysis of a halotolerant filamentous mangrove cyanobacterium revealed CRISPR-Cas systems with unique properties

Novel CRISPR systems capable of cleaving both DNA and RNA are progressively emerging as attractive tools for genome manipulation of prokaryotic and eukaryotic organisms. We report specific characteristics of CRISPR systems present in Oxynema aestuarii AP17, a halotolerant, filamentous cyanobacterium and the second known member of the Oxynema genus. In-silico analyses of its whole-genome sequence revealed the presence of multiple Type I and Type III CRISPR loci with one Type I-G system previously unreported in cyanobacteria. We further identified the leader sequences at the 5' end of multiple CRISPR loci, many of which were distinct from previously reported cyanobacterial CRISPR leaders. Phylogenetic analyses of the O. aestuarii AP17 Cas1 proteins revealed two protein sequences that were unique and distantly related to other cyanobacterial Cas1 protein sequences. Our findings are significant because novel Class 1 CRISPR systems possess multi-subunit effectors and are highly flexible for repurposing by protein domain fusions made to the effector complex. Additionally, Type III CRISPRs are particularly useful for genome editing in certain extremophiles for which mesophilic Type II CRISPRs are ineffective.

Coastal aquaculture in Bangladesh: Sundarbans's role against climate change

The Sundarbans, a natural shield on earth, is one and only place that has many noteworthy environmental and geographical values with breathtaking natural beauties. Near the Sundarbans area, proliferation of aquaculture in this delta contributes appreciably to the national economy. Although aquaculture has become a means of daily livelihood, this sector is nevertheless threatened by a complex of climate change impacts. Cyclones, rising temperatures, rising sea levels, coastal flooding, and erosion make coastal farming difficult. As a panacea, the Sundarbans can play a critical role in preserving coastal aquaculture. As noticed, forests have high potential to recover from unusual consequences of climate change. Practicing safe aquaculture should be opted to refrain from endangering the Sundarbans. This review addressed various climate change impacts on coastal farming and identified the capabilities of the Sundarbans to protect coastal aquaculture from calamitous impacts. Findings show clues for researchers to analyze problems, consequences, and mitigations.

Distribution, speciation, and bioaccumulation of potentially toxic elements in the grey mangroves at Indian Sundarbans, in relation to vessel movements

Sundarban is the world's largest mangrove wetland and home of 4.6 million people (Indian part), whose principal mode of communication is motorized boats (ferries). This study shed light on the role played by ferry movement in the speciation (following the BCR three-step sequential extraction method), ecological impact and bioaccumulation of potentially toxic elements (PTEs) in plant tissues (root and lamina) of grey mangrove (Avicennia marina) found near the five ferry ghats (ports). One-way ANOVA showed variation in major soil parameters (silt, clay, organic carbon, pH, Electrical conductivity) and PTEs (As, Cd, Cr, Cu, Hg, and Pb) between sites. Sequential extraction revealed that Cd was present in the 'exchangeable' form across the sites, Pb was in the 'reducible' form, and the rest of the PTEs were majorly found in 'residual' phase. Pollution indices revealed moderate to heavy contamination and considerable potential ecological risk due to Cd. Pearson correlation statistics and concentration variations indicate a relation between Pb and ferry movement frequency in the sites. Higher bioconcentration of Pb in the roots of A. marina, indicates phytostabilization action. Translocation factor for Cd in the leaves, indicates phytoextraction by A. marina. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a close association between vehicle movement and Hg, Pb, Silt fraction, electrical conductivity, Cr, and As. This study recommends regular pollution monitoring across Sundarbans, as the PTEs in sediment-plant matrix can impact the higher trophic levels, human health through possible biomagnification in the detritus food chain, and can adversely impact the existing conservation initiatives.

Abiotic factors and heavy metals defining eco-physiological niche in fish

Ecosystem dynamics undergoing alterations in structure and function highlights the need to look into the relations between ecological parameters and organismal fitness and tolerance. Ecophysiological studies are used to understand how organisms adapt to and cope up with environmental stress. Current study uses a process-based approach to model physiochemical parameters regarding seven different fish species. Species respond to climatic variations via acclimation or adaptation through physiological plasticity. Four sites are differentiated into two types based on the water quality parameters and metal contamination. Seven fish species are clustered into two groups, each group depicting separate pattern of response in similar habitat. In this manner, biomarkers from three different physiological axes- stress, reproduction, and neurology were taken to determine the organism's ecological niche. Cortisol, Testosterone, Estradiol, and AChE are the signature molecules estimated for the said physiological axes. The ordination technique, nonmetric multidimensional scaling, has been utilized to visualize the differentiated physiological response to changing environmental conditions. Then, Bayesian Model Averaging (BMA) was used to identify the factors that play a key role in refining the stress physiology and determining the niche. Current study confirms different species belonging to similar habitats respond to various environmental and physiological factors in a different manner as various biomarkers respond in a species-specific pattern that induces the choice of habitat preference controlling its ecophysiological niche. In the present study, it is quite apparent that adaptive mechanism of fish to environmental stress is achieved through modification of physiological mechanisms through a panel of biochemical markers. These markers organize a cascade of physiological event at various levels including reproduction.

Pollution status and ecological risk assessment of metal(loid)s in the sediments of the world's largest mangrove forest: A data synthesis in the Sundarbans

The Sundarbans is the largest single-mass mangrove forest in the world, experiencing environmental and anthropogenic stress from metal(loid) inputs. We undertook a comprehensive assessment of sediment contamination and ecological risks posed by metal(loid)s in the Sundarbans using previously published data. There was a distinct difference in metal(loid) content, pollution level and ecological risk in Bangladeshi and Indian parts of the Sundarbans, with the Indian counterpart experiencing relatively higher metal(loid) pollution. The higher pollution level in India might be attributed to its vicinity to municipal and industrial areas that act the primary source of metal(loid)s in the Sundarbans. The cumulative ecological risks of metal(loid)s pointed out that the south-eastern part of Bangladeshi Sundarbans and north-eastern Indian part are at moderate ecological risk. This research will provide valuable data to inform the responsible authorities and will underpin future policies and management to reduce future metal(loid) inputs in the Sundarbans.

Do global environmental drivers' ocean acidification and warming exacerbate the effects of oil pollution on the physiological energetics of Scylla serrata?

Global climate change-induced ocean warming and acidification have complex reverberations on the physiological functioning of marine ectotherms. The Sundarbans estuarine system has been under threat for the past few decades due to natural and anthropogenic disturbances. In recent years, petroleum products' transportation and their usage have increased manifold, which causes accidental oil spills. The mud crab (Scylla serrata) is one of the most commercially exploited species in the Sundarbans. The key objective of this study was to delineate whether rearing under global environmental drivers (ocean acidification and warming) exacerbates the effect of a local driver (oil pollution) on the physiological energetics of mud crab (Scylla serrata) from the Sundarbans estuarine system. Animals were reared separately for 30 days under (a) the current climatic scenario (pH 8.1, 28°C) and (b) the predicted climate change scenario (pH 7.7, 34°C). After rearing for 30 days, 50% of the animals from each treatment were exposed to 5 mg L^-1 of marine diesel oil for the next 24 h. Physiological energetics (ingestion rate, absorption rate, respiration rate, excretion rate, and scope for growth), thermal performance, thermal critical maxima (CT_max), acclimation response ratio (ARR), Arrhenius activation energy (AAE), temperature coefficient (Q₁₀), warming tolerance (WT), and thermal safety margin (TSM) were evaluated. Ingestion and absorption rates were significantly reduced, whereas respiration and ammonia excretion rates significantly increased in stressful treatments, resulting in a significantly lower scope for growth. A profound impact on thermal performance was also noticed, leading to a downward shift in CT_max value for stress-acclimated treatment. The present results clearly highlighted the detrimental combined effect of global climatic stressors and pollution on the physiological energetics of crabs that might potentially reduce their population and affect coastal aquaculture in forthcoming years.

Trophic transfer of microplastics in the aquatic ecosystem of Sundarbans mangrove forest, Bangladesh

Globally microplastics (MPs) contaminations have been widely reported across the large number of organisms in the marine ecosystem. Consequently, trophic transfer of MPs inferred to occur across the organisms of marine food webs. However, scientific evidence on trophic transfer of MPs across the marine organisms is very limited. Therefore, this study aimed to understand the transfer of MPs across the trophic levels in the marine ecosystem. We sampled individuals of different species of primary consumers, secondary consumers, tertiary consumers and quaternary consumers from the aquatic ecosystem of Sundarbans mangrove forest from June 2021 to December 2021. This study found that marine organisms in the aquatic ecosystem of Sundarbans mangrove forest are contaminated with MPs. The abundance of MPs in collected samples varied between 0.56 ± 0.25 items/individual and 6.06 ± 1.20 items/individual. Maximum MPs was recorded as 5.5 ± 1.21 items/individual in predators followed by 5.1 ± 0.85, 4.5 ± 0.39, 1.2 ± 0.26, 1.1 ± 0.28 and 1.01 ± 0.25 in filter feeders, browsers, deposit feeders, selective planktivores and variable feeders, respectively. Maximum MPs abundance was encountered in quaternary consumers (4.17 items/individual) followed by tertiary consumers (3.17 items/individual), secondary consumers (2.74 items/individual) and primary consumers (0.56 items/individual). We found that MPs abundance increases with the increase of trophic levels (R² = 0.64, p < 0.001) which indicates that transfer of MPs across different trophic levels and also showed the evidence of biomagnification of MPs in successive trophic levels. Our study is the first report of trophic transfer of MPs in sub-tropical mangrove ecosystem and will serve as a guideline to understand the MPs pollution in the coastal ecosystem of Bangladesh.

Polycyclic aromatic hydrocarbon sequestration by intertidal phototrophic biofilms cultivated in hydrophobic and hydrophilic biofilm-promoting culture vessels

Phototrophic biofilms collected from intertidal sediments of the world's largest tidal mangrove forest were cultured in two sets of a biofilm-promoting culture vessel having hydrophilic glass surface and hydrophobic polymethyl methacrylate surface wherein 16 priority polycyclic aromatic hydrocarbons (PAHs) were spiked. Biofilms from three locations of the forest were most active in sequestering 98-100% of the spiked pollutants. PAH challenge did not alter the biofilm phototrophic community composition; rather biofilm biomass production and synthesis of photosynthetic pigments and extracellular polymeric substances (EPS) were enhanced. Photosynthetic pigment and EPS synthesis were sensitive to vessel-surface property. The lowest mean residual amounts of PAHs in the liquid medium as well as inside the biofilm were recorded in the very biofilm cultivated in the hydrophobic flask where highest values of biofilm biomass, total chlorophyll, released polysaccharidic (RPS) carbohydrates, RPS uronic acids, capsular polysaccharidic (CPS) carbohydrates, CPS proteins, CPS uronic acids and EPS hydrophobicity were obtained. Ratios of released RPS proteins: polysaccharides increased during PAH sequestration whereas the ratios of CPS proteins: polysaccharides remained constant. Efficacious PAH removal by the overlying phototrophic biofilm will reduce the entry of these contaminants in the sediments underneath and this strategy could be a model for "monitored natural recovery".

Heavy Metal Accumulation and Phytoremediation Potentiality of Some Selected Mangrove Species from the World's Largest Mangrove Forest

Toxic metal pollution is a global issue, and the use of metal-accumulating plants to clean contaminated ecosystems is one of the most rapidly growing ecologically beneficial and cost-effective technologies. In this study, samples of sediment and three mangrove species (Excoecaria agallocha, Avicennia officinalis, Sonneratia apetala) were collected from the world’s largest mangrove forest (along the Northern Bay of Bengal Coast) with the aim of evaluating metal concentrations, contamination degrees, and phytoremediation potentiality of those plants. Overall, the heavy metals concentration in sediment ranged from Cu: 72.41−95.89 mg/kg; Zn: 51.28−71.20 mg/kg; Fe: 22,760−27,470 mg/kg; Mn: 80.37−116.37 mg/kg; Sr: 167.92−221.44 mg/kg. In mangrove plants, the mean concentrations were in the order of E. agallocha > A. officinalis > S. apetala. The mean (± SD) concentration of each metal in the plant tissue (root) was found following the descending order of Fe (737.37 ± 153.06) > Mn (151.13 ± 34.26) > Sr (20.98 ± 6.97) > Cu (16.12 ± 4.34) > Zn (11.3 ± 2.39) mg/kg, whereas, in the leaf part, the mean concentration (mg/kg) of each metal found in the order of Fe (598.75 ± 410.65) > Mn (297.27 ± 148.11) > Sr (21.40 ± 8.71) > Cu (14.25 ± 2.51) > Zn (12.56 ± 2.13). The contamination factor (CF) values for the studied metals were in the descending order of Cu > Sr > Zn > Fe > Mn. The values of Igeo (Geo-accumulation index) and CF showed that the area was unpolluted to moderately polluted by Zn, Fe, Mn, Cu and Sr. Enrichment factor (EF) values in both sampling stations portrayed moderate to minimum enrichment. Phytoremediation potentiality of the species was assessed by bio-concentration factor (BCF) and translocation factor (TF). BCF values showed less accumulation for most of the heavy metals (<1) except Mn which was highly accumulated in all mangrove plants. The translocation factor (TF) values depicted that most of the heavy metals were strongly accumulated in plant tissues (>1). However, the BCF value depicts that Mn was highly bioconcentrated in E. agallocha, but the translocation on leaves tissue were minimum, which reveals that E. agallocha is phytoextractor for Mn, and accumulated in root tissues. All the examined plants can be used as phytoextractors as they have bioconcentration factors <1 and translocation factors >1. However, A. officinalis is clearly more suitable for metal extraction than S. apetala and E. agallocha in terms of hyper-metabolizing capabilities.

Variability in the zooplankton assemblages in relation to environmental variables in the tidal creeks of Sundarbans estuarine system, India

The present study illustrates a holistic account of zooplankton community dynamics in relation to physicochemical variables in the tidal creeks of Indian Sundarbans estuarine system. Eleven water variables and zooplankton samples were collected in a monthly basis from the six sampling locations between July 2016 and June 2018. Out of the 11 water parameters, seven parameters (temperature, salinity, dissolved oxygen, turbidity, PO₄ - P, NO₃ - N, and NO₂ - N) varied significantly (p ≤ 0.05) among seasons. A total of 63 zooplankton taxa were recorded with the predominance of Copepoda. Permutational multivariate analysis of variance (PERMANOVA) depicted the significant variations of zooplankton population both spatially (F = 2.313; p = 0.001) and temporally (F = 6.107; p = 0.001). Out of the 41 species of Copepoda recorded, 14 species (Paracalanus parvus, Parvocalanus dubia, Bestiolina similis, Acrocalanus gibber, A. gracilis, Acartia erythraea, A. spinicauda, Pseudodiaptomus serricaudatus, P. annandalei, P. aurivilli, Oithona brevicornis, O. similis, Longipedia weberi and Microsetella norvegica) were indicated as "characterizing species" in the creek environment, which highlighted the euryhaline nature as well as broad range of thermal tolerance of these species. Acrocalanus longicornis, Eucalanus crassus, Candacia bradyi, and Acartia sewelli were specifically found in pre-monsoon; Euterpina acutiformis, Clytemnestrata rostrata, Acartia plumosa, and Canthocalanus pauper were specific to post-monsoon season, whereas Mesocyclops leuckarti, Temora turbinata, and Temora discaudata were found only during monsoon. Thus, it explains the limited period of existence, highlighting the temporal shift in species abundance in the creeks. Overall, the calculated mean value of α-diversity (d' = 4.07; H' = 2.31) indicated a "good" zooplankton diversity in the creeks. The biota-environmental relationship following canonical correspondence analysis revealed that variables, viz., water temperature, turbidity, and NO₃ - N, were the explanatory variables during monsoon; pH and DO in post-monsoon; PO₄ - P, SiO₄ - Si, and salinity in pre-monsoon that explained the variations of zooplankton community compositions in the creeks. The variables (PO₄ - P, NO₃ - N, and SiO₄ - Si) that are correlated to the zooplankton community implied their indirect effect on the distribution of zooplankton by supporting the phytoplankton succession and production in the mangrove-dominated creeks.

Metagenomic insights into surface water microbial communities of a South Asian mangrove ecosystem

Estuaries are one of the most productive ecosystems and their productivity is maintained by resident microbial communities. Recent alterations driven by climate change have further escalated these stressors leading to the propagation of traits such as antibiotic resistance and heavy metal resistance in microbial communities. Surface water samples from eleven stations along the Thakuran and Matla estuaries of the Sundarbans Biosphere Reserve (SBR) of Sundarbans mangrove located in South Asia were sampled in monsoon (June) 2019 to elucidate resident microbial communities based on Nanopore sequencing. Metagenomic analyses revealed the widespread dominance of Proteobacteria across all the stations along with a high abundance of Firmicutes. Other phyla, including Euryarchaeota, Thaumarchaeota, Actinobacteria, Bacteroidetes and Cyanobacteria showed site-specific trends in abundance. Further taxonomic affiliations showed Gammaproteobacteria and Alphaproteobacteria to be dominant classes with high abundances of Bacilli in SBR_Stn58 and SBR_Stn113. Among the eukaryotic communities, the most abundant classes included Prasinophyceae, Saccharyomycetes and Sardariomycetes. Functional annotation showed metabolic activities such as carbohydrate, amino acid, nitrogen and phosphorus metabolisms to be uniformly distributed across all the studied stations. Pathways such as stress response, sulphur metabolism and motility-associated genes appeared in low abundances in SBR. Functional traits such as antibiotic resistance showed overwhelming dominance of genes involved in multidrug resistance along with widespread resistance towards commonly used antibiotics including Tetracycline, glycopeptide and aminoglycoside. Metal resistance genes including arsenic, nickel and copper were found in comparable abundances across the studied stations. The prevalence of ARG and MRG might indicate presence of pollutants and hint toward deteriorating ecosystem health status of Sundarbans mangrove.

Falling "fortresses": Unlocking Governance Entanglements and Shifting Knowledge Paradigms to Counter Climate Change Threats in Biodiversity Conservation

Biodiversity conservation is facing unprecedented challenges at the intersection of rapidly changing climates, widespread ecosystem degradation under the influence of global warming and resultant human tragedies over livelihood, habitation, adaptation and coping needs. These challenges are more acute across biodiversity hotspots in the Global South. This study disentangles the complex interplay to propose alternative paradigms of governance and policy thinking necessary for sustainable biodiversity conservation. Climate change impacts are exposing critical deficiencies of 'scientific forest management' pursued for over a century. For example, recurrent disasters and ecological shifts are increasingly obfuscating cognitive and physical boundaries between the reserve forest and human habitations; putting additional stress on livelihoods which in turn escalate pressures on the forest commons and fuel further conflicts between conservation governance and local communities. Instead of assisting in adaptation, the existing conservation governance mechanisms are producing further conflicts between humans and non-humans; livelihoods and conservation; disaster management and development. Conducted in the Sundarbans Biosphere Reserve -world's largest mangrove forest ecosystem and a climate change hotspot located along the Bay of Bengal across India and Bangladesh -the study finds an urgent need of rethinking and recalibrating biodiversity conservation in the times of climate change. However, institutional and market-based approaches such as promoting ecotourism or mangrove plantations may have little impact in this regard, the study finds. Instead, integrating cultural ecosystem services and co-producing knowledge will be critical to tackle the entanglements of climate change and its impacts on local lives, livelihoods and biodiversity conservation.

Impact of global-scale hydroclimatic patterns on surface water-groundwater interactions in the climatically vulnerable Ganges river delta of the Sundarbans

The global climate patterns like El Niño Southern Oscillation (ENSO) cycle and Indian Ocean Dipole (IOD) have impacts on surface water quality and groundwater recharge patterns. But the ENSO and IOD impacts on surface water-groundwater (SW-GW) interaction in terms of quality have not been studied. Therefore, the present study was conducted to delineate the impacts of ENSO and IOD on the SW-GW interaction process-induced groundwater quality of coastal aquifers of Sundarbans, by the application of isotopic signature, salinity content of groundwater and seawater in relation to rainfall variability. Study results revealed that the declining trend of rainfall potentially increases the seawater salinity. The rainfall pattern also positively correlates with the groundwater level (GWL) at a 5% level of significance observed from the wavelet analysis. The deficit in rainfall due to the El Niño is the possible reason for the declining GWL, which is giving rise to groundwater salinity. El Niño also affected the nearshore seawater salinity which was increased from 19 to 24 ppT. The study provides a surrogate understanding of the potential impact of El Niño in one of the most climatically vulnerable parts of the planet, while IOD impacts are not conclusive. In the scenario of depleted rainfall amount, groundwater abstraction practices need to be managed, otherwise, it could create a potential threat to the available drinking water resources in the present and future climate change scenarios.

Storage and recycling of major and trace element in mangroves

The role of mangroves in sequestering metal and nutrients in sediment has been described in the past, but knowledge gaps still exist on storage capacity and recycling fluxes of elements in plant biomass, notably concerning their magnitude in root uptake and loss by litterfall. This study addresses the storage and transport pathways of 16 elements, classified as macro-nutrients (Ca, Mg, Na, K), micro-nutrients (Fe, Mn, Ni, Co, Cu, Cr, Zn, Mo), and potential toxicants (Al, Cd, Sn, Pb) in the world's largest mangroves, the Sundarbans. Elemental concentrations in plant organs were generally lower than in the sediment. The stock of macro and micro-nutrients in plant biomass varied from 60 to 2717 and 0.003 to 37.7 Mg ha^-1 respectively, with highest values observed for Na and lowest for Cd. The Avicennia species exhibited the maximal accumulation of all elements. Translocation of major elements to different plant organs increased with increasing their concentrations in the sediment. Elemental loss via litterfall indicated that Sundarbans mangrove could act as a source, particularly of Mn, to the Bay of Bengal. Moreover, belowground uptake of the 16 elements showed 2-3 fold higher fluxes than their loss via litterfall. There was a significant retention of some trace elements (notably Mo, Cd, and Sn) in plant biomass, which might allow one to use these mangroves for phytoremediation and restoration purposes. We conclude that mangroves efficiently store and remobilize major and trace elements from the sediments by root uptake and recycle back to sediment surface via litterfall.

Solute exchanges between multi-depth groundwater and surface water of climatically vulnerable Gangetic delta front aquifers of Sundarbans

The coastal aquifers of Sundarbans, an UNESCO world biodiversity heritage site, are highly vulnerable due to changing climatic conditions, intensification and increasing frequency of extreme climate events and uncontrolled abstraction of groundwater. The exchange of solutes between hydraulically connective shallow and deep aquifers, the seawater intrusion and the role of growing population are poorly understood in the Sundarbans. This study aims to address the solute exchange (Cl^-, Sr²⁺, and salinity) process between surface water and groundwater (SW-GW) at local to regional scale under variable hydraulic head conditions, where annual rainfall is declining and population density is increasing [population 573 (1991) to 819 (2011)/Km²]. Electrical resistivity tomography (ERT) in combination with salinity and δ¹⁸O data was used to address the exchange of solutes between SW-GW in a hydraulic continuation. The results revealed that regionally, the Cl^- concentration of Sundarbans shows an increasing trend (average 329-351 mg/L) with declining groundwater levels (⁓3 m). Local, depth-dependent study depicting there is a predominant exchange of Sr²⁺ between shallow depth [D1: 14-25 and D2: 30-50 m below ground level (m bgl)] with seawater (Sr²⁺: 30-85 μM), which is possibly absent at greater depths (D3:115 and D4: 333 m bgl). The recorded Sr²⁺ content ranged from 25 to 102 and 16 to 78 μM for shallow depth D1 and D2, respectively, whereas, the Sr²⁺ concentrations ranged from 1.4 to 6.8 and 1.2 to 5.7 μM for D3 and D4, respectively. The ERT data showed progressively increasing resistivity with increasing depth, similar to high salinity and enriched δ¹⁸O at shallow depths and depleted δ¹⁸O with low salinity at higher depth reflects the continuous distribution of solutes, which is possibly a result of local downward migration of contaminated shallow brackish water within this physically disconnected zone. The lateral and vertical transportation of solutes in variable hydraulic head conditions would be a measure of drinking water threat in present-day and in imminent future for millions of inhabitants near the coastal area.

nov., an actinobacterium isolated from mangrove sediment of Sundarbans, India

A new actinobacterial species of the genus Myceligenerans has been isolated from the intertidal sediment of Indian Sundarbans mangrove ecosystem. The isolate has been characterized based on polyphasic approaches. The isolate exhibit well-developed substrate mycelia along with the presence of cocci- and rod-shaped elements. The organism can grow across a wide range of temperature, salinity, and pH as well as on different carbon sources. Phylogenetic analyses based on 16S rRNA showed that this isolate is closely related to Myceligenerans salitolerans XHU 5031 (99% identity; 100% coverage). Presence of ketosynthase domain representing polyketide synthases in the isolate provides evidence of its potential ability to produce secondary metabolites. Multigene phylogeny based on atpD and rpoB gene sequences confirmed it as a new species within the family Promicromonosporaceae (Phylum Actinobacteria). The DNA G + C content of the isolate has been determined as 72 mol%. The peptidoglycan type was A4α and the whole-cell hydrolysates contained glucose, galactose, and mannose. The polar lipids were represented by diphosphatidylglycerol, one unknown phospholipid and one unknown glycolipid. Major fatty acids present in the isolate are anteiso-C₁₅, iso-C₁₅, iso-C₁₆, and anteiso-C_17. Whole-genome sequence indicates the size of genome is ~ 5 Mbp. GGDC (%), orthoANIu (%), and AAI of I2 genome indicated 28.9%, 77.44% and 0.859 identity with the genome of Myceligenerans xiligouense strain DSM 15,700. The isolate I2 has been proposed as a new species, Myceligenerans indicum sp. nov. The genome sequence has been deposited to GenBank/ENA/DDBJ under the accession number JABBYC000000000.

Assessment of polycyclic aromatic hydrocarbon contamination in the Sundarbans, the world's largest tidal mangrove forest and indigenous microbial mixed biofilm-based removal of the contaminants

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the surface water and sediments in five regions of the Indian Sundarbans was assessed. The capability of microbial biofilm communities to sequester PAHs in a biofilm-promoting vessel was evaluated. The total PAH concentration of water and sediments ranged from undetectable to 125 ng ml^-1 and 4880 to 2 × 10⁴ ng g^-1 dry weight respectively. The total PAHs concentration of sediments exceeded the Effects Range-Low value and the recommended Effects Range-Median values, implying the PAHs might adversely affect the biota of the Sundarbans. Pyrogenic and petrogenic sources of PAH contamination were identified in most of the sampling sites. Indigenous biofilms were cultivated in a patented biofilm-promoting culture vessel containing liquid media spiked with 16 priority PAHs. Biofilm-mediated 97-100% removal efficiency of 16 PAHs was attained in all media. There was no significant difference between the mean residual PAH from the liquid media collected from hydrophobic and hydrophilic flasks. Residual amounts of acenaphthene (Ace), anthracene (Ant), benzo(b)fluoranthene [B(b)F], benzo(a)pyrene [B(a)P] and benzo(g,h,i)perylene [B(g,h,i)P] showed differences when cultivated in hydrophobic and hydrophilic flasks. The mean residual amounts of total PAHs extracted from biofilm biomasses were variable. A biofilm obtained from a specific sampling site cultured in the hydrophobic flask showed higher PAH sequestration when compared to the removal attained in the hydrophilic flask. Relative abundances of different microbial communities in PAH-sequestering biofilms revealed bacterial phyla including Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Chloroflexi and Planctomycetes as well as members of Ascomycota phylum of fungi. The dominance of Candida tropicalis, Clostridium butyricum, Sphingobacterium multivorum and Paecilomyces fulvus were established.

Responses of ecosystem services to natural and anthropogenic forcings: A spatial regression based assessment in the world's largest mangrove ecosystem

Most of the Earth's Ecosystem Services (ESs) have experienced a decreasing trend in the last few decades, primarily due to increasing human dominance in the natural environment. Identification and categorization of factors that affect the provision of ESs from global to local scales are challenging. This study makes an effort to identify the key driving factors and examine their effects on different ESs in the Sundarbans region, India. We carry out the analysis following five successive steps: (1) quantifying biophysical and economic values of ESs using three valuation approaches; (2) identifying six major driving forces on ESs; (3) categorizing principal data components with dimensionality reduction; (4) constructing multivariate regression models with variance partitioning; (5) implementing six spatial regression models to examine the causal effects of natural and anthropogenic forcings on ESs. Results show that climatic factors, biophysical factors, and environmental stressors significantly affect the ESs. Among the six driving factors, climate factors are highly associated with the ESs variation and explain the maximum model variances (R² = 0.75-0.81). Socioeconomic (R² = 0.44-0.66) and development (R² = 27-0.44) factors have weak to moderate effects on the ESs. Furthermore, the joint effects of the driving factors are much higher than their individual effects. Among the six spatial regression models, Geographical Weighted Regression (GWR) performs the most accurately and explains the maximum model variances. The proposed hybrid valuation method aggregates biophysical and economic estimates of ESs and addresses methodological biases existing in the valuation process. The presented framework can be generalized and applied to other ecosystems at different scales. The outcome of this study could be a reference for decision-makers, planners, land administrators in formulating a suitable action plan and adopting relevant management practices to improve the overall socio-ecological status of the region.

Ecosystem service value assessment of a natural reserve region for strengthening protection and conservation

Ecosystem Services (ESs) refer to the direct and indirect contributions of ecosystems to human well-being and subsistence. Ecosystem valuation is an approach to assign monetary values to an ecosystem and its key ecosystem goods and services, generally referred to as Ecosystem Service Value (ESV). We have measured spatiotemporal ESV of 17 key ESs of Sundarbans Biosphere Reserve (SBR) in India using temporal remote sensing (RS) data (for years 1973, 1988, 2003, 2013, and 2018). These mangrove ecosystems are crucial for providing valuable supporting, regulatory, provisioning, and cultural ecosystem services. We have adopted supervised machine learning algorithms for classifying the region into different ecosystem units. Among the used machine learning models, Support Vector Machine (SVM) and Random Forest (RF) algorithms performed the most accurate and produced the best classification estimates with maximum kappa and an overall accuracy value. The maximum ESV (derived from both adjusted and non-adjusted units, million US$ year^-1) is produced by mangrove forest, followed by the coastal estuary, cropland, inland wetland, mixed vegetation, and finally urban land. Out of all the ESs, the waste treatment (WT) service is the dominant ecosystem service of SBR. Additionally, the mangrove ecosystem was found to be the most sensitive to land use and land cover changes. The synergy and trade-offs between the ESs are closely associated with the spatial extent. Therefore, accurate estimates of ES valuation and mapping can be a robust tool for assessing the effects of poor decision making and overexploitation of natural resources on ESs.

Combined effects of climate change and sea-level rise project dramatic habitat loss of the globally endangered Bengal tiger in the Bangladesh Sundarbans

The Sundarbans, in southern coastal Bangladesh, is the world's largest surviving mangrove habitat and the last stronghold of tiger adapted to living in a mangrove ecosystem. Using MaxEnt (maximum entropy modeling), current distribution data, land-use/land cover and bioclimatic variables, we modeled the likely future distribution of the globally endangered Bengal tiger (Panthera tigris tigris) in the Bangladesh Sundarbans. We used two climatic scenarios (i.e., RCP6.0 and RCP8.5) developed by the Intergovernmental Panel on Climate Change (IPCC) to provide projections of suitable habitats of Bengal tigers in 2050 and 2070. We also combined projected sea-level rise for the area in our models of future species distributions. Our results suggest that there will be a dramatic decline in suitable Bengal tiger habitats in the Bangladesh Sundarbans. Other than various aspects of local climate, sea-level rise is projected to have a substantial negative impact on Bengal tiger habitats in this low-lying area. Our model predicts that due to the combined effect of climate change and sea-level rise, there will be no suitable Bengal tiger habitat remaining in the Sundarbans by 2070. Enhancing terrestrial protected area coverage, regular monitoring, law enforcement, awareness-building among local residents among the key strategies needed to ensure long-term survival and conservation of the Bengal tiger in the Bangladesh Sundarbans.

Spatio-temporal variability and source identification for metal contamination in the river sediment of Indian Sundarbans, a world heritage site

Metal pollution is a subject of growing concern as it affects the whole food chain of an ecosystem by bioaccumulation. Growing industrialization and anthropogenic intervention have put tremendous pressure on self-sustaining ecosystems worldwide. Sundarbans mangrove estuary, being a UNESCO World Heritage site, suffers severely from anthropogenic stress, urbanization, ecotourism, overexploitation of natural resources and discharges of industrial as well as municipal waste products. Our study unfolds the extent of metal pollution in the sediment of this estuarine mangrove ecosystem and also investigates the source and distribution of these metals. Extensive samplings were performed during three major seasons, namely pre-monsoon, monsoon, and post-monsoon for two consecutive years at ten sampling stations along the major river networks of the mangrove estuary. Seasonal variations of these metals, physicochemical properties, and soil texture studies were performed to explore the sediment quality of the study area. Positive correlation was observed between the pollutants and siltation. Several environmental indices were investigated to explore the degree of metal pollution which revealed contamination of Cd, Cr, and Pb to cross the permitted safe index in the study area. Pollution load index indicates the spatial as well as seasonal variation of eco toxic metal load along the course of the rivers. Statistical analyses such as principal component analysis and correlation matrix identified different sources for metal contamination. Almost 700 tannery industries are located in the upstream region of the rivers, and several small- and large-scale battery industries seem to be the main possible source for Cd, Cr, and Pb pollution. Analysis of the results indicates the alarming condition of this heritage site. The metal concentrations beyond toxicity thresholds are responsible for gradual deterioration of this estuarine mangrove which may only be protected by developing sustainable management planning.

Participatory evaluation guides the development and selection of farmers' preferred rice varieties for salt- and flood-affected coastal deltas of South and Southeast Asia

Rice is the staple food and provides livelihood for smallholder farmers in the coastal delta regions of South and Southeast Asia. However, its productivity is often low because of several abiotic stresses including high soil salinity and waterlogging during the wet (monsoon) season and high soil and water salinity during the dry season. Development and dissemination of suitable rice varieties tolerant of these multiple stresses encountered in coastal zones are of prime importance for increasing and stabilizing rice productivity, however adoption of new varieties has been slow in this region. Here we implemented participatory varietal selection (PVS) processes to identify and understand smallholder farmers' criteria for selection and adoption of new rice varieties in coastal zones. New breeding lines together with released rice varieties were evaluated in on-station and on-farm trials (researcher-managed) during the wet and dry seasons of 2008-2014 in the Indian Sundarbans region. Significant correlations between preferences of male and female farmers in most trials indicated that both groups have similar criteria for selection of rice varieties. However, farmers' preference criteria were different from researchers' criteria. Grain yield was important, but not the sole reason for variety selection by farmers. Several other factors also governed preferences and were strikingly different when compared across wet and dry seasons. For the wet season, farmers preferred tall (140-170 cm), long duration (160-170 d), lodging resistant and high yielding rice varieties because these traits are required in lowlands where water stagnates in the field for about four months (July to October). For the dry season, farmers' preferences were for high yielding, salt tolerant, early maturing (115-130 d) varieties with long slender grains and good quality for better market value. Pest and disease resistance was important in both seasons but did not rank high. When farmers ranked the two most preferred varieties, the ranking order was sometimes variable between locations and years, but when the top four varieties that consistently ranked high were considered, the variability was low. This indicates that at least 3-4 of the best-performing entries should be considered in succeeding multi-location and multi-year trials, thereby increasing the chances that the most stable varieties are selected. These findings will help improve breeding programs by providing information on critical traits. Selected varieties through PVS are also more likely to be adopted by farmers and will ensure higher and more stable productivity in the salt- and flood-affected coastal deltas of South and Southeast Asia.

Exportation of dissolved (inorganic and organic) and particulate carbon from mangroves and its implication to the carbon budget in the Indian Sundarbans

Mangroves are known for exchanging organic and inorganic carbon with estuaries and oceans but studies that have estimated their contribution to the global budget are limited to a few mangrove ecosystems which exclude world's largest the Sundarbans. Here, we worked in the Indian Sundarbans and in the Hooghly river/estuary in May (pre-monsoon) and December (post-monsoon), 2014. Aims were, i) to quantify the riverine export of particulate organic carbon (POC) and dissolved organic and inorganic carbon (DOC, DIC)) of the Hooghly into the Bay of Bengal (BoB), ii) to estimate the C export (DOC, DIC, POC) from the Sundarbans into the BoB by using a simple mixing model, as well as iii) to revise the existing C budget constructed for the mangroves. The riverine exports of POC, DOC and DIC account for 0.07TgCyr^-1, 0.34TgCyr^-1 and 4.14TgCyr^-1, respectively, and were largest during the monsoon period. Results revealed that mangrove plant derived organic matter and its subsequent degradation is the primary source of DIC and DOC in the Hooghly estuary whereas POC is linked to soil erosion. Mangroves are identified as a major source of carbon (POC, DOC, DIC) transported from the Sundarbans into the BoB, with export rates of 0.58 TgCyr^-1, 3.03TgCyr^-1, and 3.69TgCyr^-1 respectively, altogether amounting to 7.3TgCyr^-1. This C export from the Indian Sundarbans exceeds the 'missing C' of the previous budget, thus necessitating further research to finally resolve the mangrove C budget. However, these first baseline data on C exports from the world's largest deltaic mangrove improves limited global data inventory and signifies the need of acquiring more data from different mangrove settings to reduce uncertainties.

Examining the ecosystem health and sustainability of the world's largest mangrove forest using multi-temporal MODIS products

Sweeping across Bangladesh and India, the Sundarbans forest is the world's largest contiguous mangrove forest. Although the human population density is high at the edge, Sundarbans has not encountered significant areal transformation in the last four decades. However, we argue that forest degradation can occur discontinuously within the forest without alteration of the entire forest area. In this paper, we used MODIS land products to compare the spatiotemporal ecological dynamics of the Bangladesh and Indian part of this mangrove forest between 2000 and 2010. We used the following 5 ecological parameters for our analysis: the Percent Tree Cover (PTC), Enhanced Vegetation Index (EVI), Net Primary Productivity (NPP), Leaf Area Index (LAI), and Evapotranspiration (ET). Our pixel-based time-series trend analysis for each MODIS image stack, using an ordinary least square (OLS) regression method, showed that forest degradation is happening in fragmented parcels within the forest. The degradation rate is comparatively higher in the Bangladesh part than in the Indian part of Sundarbans. Compartments 8, 10, 12, and 15 in the Bangladesh part, in particular, show high degradation, while compartment 48 and the southern edge of 45 show slight increases in PTC or EVI. Forest degradation in the Indian part of the forest is evident in the National Park and Reserve Forest blocks; however, no substantial degradation is evident in the western section. We have identified certain anthropogenic stressors (i.e., oil pollution, shrimp farming) and natural stressors (i.e., increased salinity, cyclones, forest fire) which might be responsible for the observed degradation. We have provided sustainable planning options and policy transformation alternatives for those areas under pressure from these stressors. We anticipate that our analysis of forest degradation will help management agencies, conservators, and policy makers achieve better management of this world's largest mangrove forest for a sustainable future.

Measuring spatial equity and access to maternal health services using enhanced two step floating catchment area method (E2SFCA) - a case study of the Indian Sundarbans

INTRODUCTION

Inaccessibility due to terrain and lack of transport leaves mothers travelling for long hours before reaching a facility to deliver a child. In the present article we analyzed the issue of spatial inaccessibility and inequity of maternal health services in the Indian Sundarbans where complex topography and repeated climatic adversities make access to health services very difficult.

METHODS

We based the article on the health-GIS study conducted in the Patharpratima Block of the Sundarbans in the year 2012. The region has 87 villages that are inhabited, of which 54 villages are in the deltaic (river locked) region and 33 villages are located in the non-deltaic region of the block. We mapped all public and private maternal health facilities and road and water transport network. For measuring inaccessibility, we use the enhanced two-step floating catchment area method (E2SFCA). For assessing inequity in spatial access, we developed an area-based socioeconomic score and constructed a concentration curve to depict inequity. We used ARC GIS 10.3.1 and Stata 11 software for our analysis.

RESULTS

The maternal health facilities are primarily located in the non-deltaic region of the block. On an average it takes 33.81 min to reach the closest maternal health facility. Fifty-two villages out of eighty seven villages have access scores less than the score calculated using Indian Primary Health Standards. Ten villages cannot access any maternal health facility; twenty-six villages have access scores of less than one doctor for 1000 pregnant women; fifty-six villages have access scores less than the block average of 3.54. The access scores are lower among villages in the deltaic region compared to the non-deltaic region. The concentration curve is below the line of equality showing that access scores were lower among villages that were socio-economically disadvantaged.

CONCLUSIONS

Maternal health facilities are not equitably accessible to the populations that are disadvantaged and living in the remote pockets of the study region. Provision of a referral transport system along with a resilient infrastructure of roads is critical to improve access in these islands.

RAPD and ISSR marker mediated genetic polymorphism of two mangroves Bruguiera gymnorrhiza and Heritiera fomes from Indian Sundarbans in relation to their sustainability

Increased salinity distresses some key species severely in Indian Sundarbans. Geomorphic characteristics coupled with demographic obligations have proven to be pivotal factor towards the prevalence of elevated salinity in this zone. Better adaptation to rapid changes in microclimate demands wide range of genetic polymorphism as well. RAPD and ISSR molecular markers were used for this genetic diversity study. Degree of polymorphism was found relatively higher in Bruguiera gymnorrhiza (26.43 % in RAPD and 24.36 % in ISSR) than the other taxa, Heritiera fomes (14.43 and 12.76 % respectively) in case of RAPD and ISSR. Dendrogram constructed based on the similarity matrix showed that for H. fomes, least saline and highest saline zones are positioned in the same clade; whereas in B. gymnorrhiza the higher saline areas were clustered together. Nei's gene diversity (h) as revealed from RAPD and ISSR analysis were found to be 0.0821, 0.0785 and 0.0647, 0.0592 in B. gymnorrhiza and H. fomes respectively. The higher degree of polymorphism as revealed from UPGMA Dendrogram and Nei's genetic diversity might be attributed towards the comfortable growth of B. gymnorrhiza all along the Indian Sundarbans. On the other hand the relatively lesser degree of genetic polymorphism of H. fomes might be attributed towards their precarious status in present days elevated salinity in Indian Sundarbans.

Cataloguing the bacterial diversity of the Sundarbans mangrove, India in the light of metagenomics

In this present study we report the profile of bacterial community at variable depth of soil sediment in the world's largest tropical mangrove sediments of Sundarbans, India using 16S rRNA gene amplicon sequencing. Metagenome of three samples consisted of 61301 sequences with 32.0 Mbp and 55.6% G + C content. Metagenome data of this study are available at NCBI under the Biosample data base accession no. SRX883521. The taxonomic analysis of 2746 species belonged to 33 different phyla revealing the dominance of Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Acidobacteria, Nitrospirae and Actinobacteria respectively. Remarkably less than 5.0% sequences belong to a poorly characterized group. Our pyrosequencing data report unfolds the bacterial community profile at different depth of soil sediment indicating the changing community pattern, in the light of specific chronology.

ISOLATION AND CHARACTERIZATION OF CYANOBACTERIA POSSESSING ANTIMICROBIAL ACTIVITY FROM THE SUNDARBANS, THE WORLD'S LARGEST TIDAL MANGROVE FOREST(1)

Eight obligately halophilic, euryhaline cyanobacteria from intertidal soil were isolated in artificial seawater nutrients III (ASN-III) medium. Antimicrobial activity, 16S rRNA gene sequences, phenotypic characters as well as growth and antibiosis in response to variable salinity, temperature, phosphate concentration, and pH were studied. Minimum inhibitory concentrations (MIC) of the extracts against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and multiple drug-resistant clinical isolates ranged between 0.25 and 0.5 mg · mL(-1) . Cytotoxicity tests showed 73%-84% human colon adenocarcinoma (HT-29/C1) cell survival at MIC values, indicating that the extracts were nontoxic. Morphologically, six cyanobacteria were assigned to the Lyngbya-Phormidium-Plectonema (LPP) group B, and one each was assigned to Oscillatoria and Synechocystis genera. Glycerol, mannitol, and starch supported better photoheterotrophic growth than simpler mono- and disaccharides. No heterocyst formation was observed when grown under nitrogen-starved conditions. All isolates survived 7‰ salinity, grew at minimum 32‰ salinity, and showed sustained growth throughout 32‰-82‰ salinity but matured poorly in freshwater medium supplemented with 30.0 g · L(-1) NaCl. Antimicrobial production occurred only at 32‰ salinity. While four of the eight isolates demonstrated sustained growth at 37°C, maximum antimicrobial activity was obtained at 25°C. All strains showed maximum growth and antimicrobial elaboration at 0.04 g · L(-1) phosphate. All isolates thrived at pH 9.5; six grew at pH 4.5, though antimicrobial production occurred only at pH 7.5. Molecular phylogenetic analysis based on 16S rRNA gene sequences of the filamentous isolates validated the previous taxonomic affiliations established on morphological characteristics. This is the first study of antimicrobial-producing halophilic cyanobacteria from the mangroves.

First record of a parasitic septate gregarines (Apicomplexa: Sporozoea) in the shrimp Peneaus monodon in Sundarbans of West Bengal

Investigations on the incidence of septate gregarines in shrimp have immense importance because of severe pathogenicity of the parasite. The septate gregarines infect the midgut of shrimp Peneaus monodon and severe infection disturbs the intestinal tissues. Mostly gregarines of the genus Nematopsis have been identified from cultured peneaid shrimp. It has worldwide in distribution. In India, gregarine parasites have so far been reported from penaeid shrimps of Bombay and Kerala. The species which was isolated from the midgut of shrimp Peneaus monodon collected from Kharibari area of Sunderbans. 9 out of 20 i.e. 45% of the randomly sampled hosts were found to be infected with a species of the genus Nematopsis. Different developmental stages including trophozoites, sporadins, and gametocysts of the Nematopsis sp. infecting the shrimp have been isolated. No correlations have been established between incidence of infection and environmental parameters.