Dynamics of nitrogen genes in intertidal sediments of Darwin Harbour and their connection to N-biogeochemistry.

Microbial mediated nitrogen (N) transformation is subject to multiple controlling factors such as prevailing physical and chemical conditions, and little is known about these processes in sediments of wet-dry tropical macrotidal systems such as Darwin Harbour in North Australia. To understand key transformations, we assessed the association between the relative abundance of nitrogen cycling genes with trophic status, sediment partition and benthic nitrogen fluxes in Darwin Harbour. We analysed nitrogen cycling gene abundance using a functional gene microarray and quantitative PCRs targeting the denitrification gene (nosZ) and archaeal ammonia oxidation (AOA.1). We found a significant negative correlation between archaeal ammonia oxidation and silicate flux (P = 0.004), an indicator for diatom and benthic microalgal activity. It is suggested that the degradation of the diatomaceous organic matter generates localised anoxic conditions and inhibition of nitrification. Abundance of the nosZ gene was negatively correlated with nutrient load. The lowest nosZ gene levels were in hyper-eutrophic tidal creeks with anoxic conditions and increased levels of sulphide limiting the coupling of nitrification-denitrification (P = 0.016). Significantly higher levels of nosZ genes were measured in the surface (top 2 cm) compared to bulk sediment (top 10 cm) and there was a positive association with di-nitrogen flux (N2) in surface (P = 0.024) but not bulk sediment. This suggests that denitrifiers are most active in surficial sediment at the sediment-water interface. Elevated levels of nosZ genes also occurred in the sediments of tidal creek mouths and mudflats with these depositional zones combining the diffuse and seaward supply of nitrogen and carbon supporting denitrifiers. N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique for impact assessment and measuring ecosystem function. This is particularly pertinent for tropical macrotidal systems where systematic monitoring is sparse and in many cases challenged by climatic extremes and remoteness.

Risk Assessment and Sources Apportionment of Toxic Metals in Two Commonly Consumed Fishes from a Subtropical Estuarine Wetland System.

The widespread occurrence of heavy metals in aquatic environments, resulting in their bioaccumulation within aquatic organisms like fish, presents potential hazards to human health. This study investigates the concentrations of five toxic heavy metals (Pb, Hg, Zn, Cu, and Cr) and their potential health implications in two economically important fish species (Otolithoides pama and Labeo bata) from a subtropical estuarine wetland system (Feni estuary, Bangladesh). Muscle and gill samples from 36 individual fish were analyzed using energy dispersive X-ray fluorescence (EDXRF). The results revealed that the average quantities of heavy metals in both fishes' muscle followed the declining order of Zn (109.41-119.93 mg/kg) > Cu (45.52-65.43 mg/kg) > Hg (1.25-1.39 mg/kg) > Pb (0.68-1.12 mg/kg) > Cr (0.31-5.82 mg/kg). Furthermore, Zn was found to be present in the highest concentration within the gills of both species. While the levels of Cu, Zn, and Cr in the fish muscle were deemed acceptable for human consumption, the concentrations of Pb and Hg exceeded the permissible limits (>0.5 mg/kg) for human consumption. Different risk indices, including estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic or target risk (TR), revealed mixed and varying degrees of potential threat to human health. According to the EDI values, individuals consuming these fish may face health risks as the levels of Zn, Cu, and Cr in the muscle are either very close to or exceed the maximum tolerable daily intake (MTDI) threshold. Nevertheless, the THQ and HI values suggested that both species remained suitable for human consumption, as indicated by THQ (<1) and HI (<1) values. Carcinogenic risk values for Pb, Cr, and Zn all remained within permissible limits, with TR values falling below the range of (10-6 to 10-4), except for Zn, which exceeded it (>10-4). The correlation matrix and multivariate principal component analysis (PCA) findings revealed that Pb and Cr primarily stemmed from natural geological backgrounds, whereas Zn, Cu, and Hg were attributed to human-induced sources such as agricultural chemicals, silver nanoparticles, antimicrobial substances, and metallic plating. Given the significance of fish as a crucial and nutritious element of a balanced diet, it is essential to maintain consistent monitoring and regulation of the levels and origins of heavy metals found within it.

Spatial and temporal trends of microplastic contamination in surface sediment of Benoa Bay: An urban estuary in Bali-Indonesia.

This study aims to explore microplastic contamination in the sediments of Benoa Bay. Eight locations were sampled, with four duplications denoting the rainy and dry seasons. Based on observations, the microplastic concentration varied from 9.51 to 90.60 particles/kg with an average of 31.08 ± 21.53 particles/kg. The area near the landfill had the highest abundance, while the inlet and center of Benoa Bay and the Sama River had the lowest concentration. The fragments (52.2 %) and large microplastic sizes (64.7 %) were the most documented particles. We also identified 17 polymers, which dominated (37.5 %) by polyethylene, polypropylene, and polystyrene. There were no appreciable variations in abundance between seasons, although there were substantial variations in shape and size. Comprehensive investigation, adequate policies, continuous monitoring, and reducing waste from land- and sea-based sources that engage various stakeholders must be implemented urgently to prevent the release of microplastic into the aquatic ecosystem.

Assessment of water quality of Netravathi-Gurupur estuary, India through chemometric approach for fisheries sustainability.

The present study aimed to assess the water quality dynamics (physicochemical properties, nutrient and chlorophyll-a) in the Netravathi-Gurupur estuary, India across the space and seasons and to simplify the complex water quality dataset through a chemometric approach. The results indicated that pH, EC, temperature, alkalinity, salinity, TDS, hardness, chloride and intense mixing of suspended solids, driven by the semidiurnal tides, are the major factors affecting water quality. Spatial heterogeneity and monsoon have profound impact on nutrient distribution revealing the following values (mg l-1): phosphate-P (0.015-0.105), nitrate-N (0.016-0.094), nitrite-N (0.001-0.012), and silicate (1.83-14.50). The estuary was evaluated for suitability for brackish water fisheries. The results indicated fair water quality during pre- and post-monsoon but marginal quality in monsoon, primarily due to dilution associated with reduced salinity. The outcome of this study can be suitably utilized for the sustainable development of estuaries and their feasibility for brackish water fisheries.

Distribution of geochemical forms and bioavailability of phosphorus in the surface sediments of Beypore Estuary, southwestern coast of India.

Nutrient management in shallow transitional aquatic systems is very complex due to the sediment-water exchange, especially for phosphorus. The present study tries to get an in-depth understanding of the distribution of geochemical forms of phosphorus in the surface sediments of Beypore Estuary, a tropical estuarine system in southwest India, which has been subjected to immense climate change in recent times. Total phosphorus in the sediments was found to be abysmally lower (76.8 to 889.12 µg/g) than those reported for other tropical estuaries. Organic-bound phosphorus constituted the majority of the total phosphorus in the sediments, and unlike other tropical estuaries, iron-bound and calcium-bound phosphorus were minor fractions in the study region. However, the bioavailable phosphorus was consistent throughout the study period and varied from 16.5 to 51.0% of total phosphorus. This reveals the active phosphorus buffering in the Beypore Estuary even in the absence of an external source. Statistical evaluation of two contrasting seasons (low and high runoff periods) could illustrate the major biogeochemical pathways for phosphorus in the Beypore Estuary. This study highlights the significant role of hydrographical parameters in regulating phosphorus bioavailability in this estuary; therefore, any modifications to the same by climate change could make nutrient management even more challenging.

Estuarine benthic habitats provide an important ecosystem service regulating the nitrogen cycle.

Globally, a key ecosystem service provided by sedimentary estuarine habitats is the regulation of nutrient cycles. The nitrogen (N) cycle is driven by complex biogeochemical transformations within these sediments-including nitrogen fixation, denitrification, assimilation and anaerobic ammonia oxidation-mediated by microorganisms. Evaluating ecosystem processes and their functional value is a knowledge gap for the wet-dry tropics and even more limited for macrotidal estuaries. The capacity of these important environments to withstand and assimilate increasing nitrogenous loads as a consequence of accelerating development pressures in tropical Australia is largely unknown. Because of the critical role nitrogen cycling plays in estuarine ecosystems, identifying important habitats that underpin N cycling, particularly denitrification known to mitigate anthropogenic N inputs, is important. Detailed benthic habitat mapping of the Darwin-Bynoe region of northern Australia has provided a rare opportunity to demarcate its key habitats, such as intertidal mudflats, seagrass, mangroves, reef and saltmarsh. Combined with new measurements of benthic nitrogen fluxes, it has been possible for the first time to map these processes and develop a simple integrated functional value for N cycling across key benthic habitats of a tropical macrotidal estuary. Maps generated in this process have provided broadscale identification of the functional importance of habitats with relevance to N removal processes. The role of intertidal sediments in denitrification has been highlighted. Furthermore, the study emphasises connectivity across benthic seascapes, where multiple services are likely to interact, in supporting overall function and ecosystem health. The distillation of composite processes in this mapping format allows resource managers and scientists to communicate outputs visually with a simple classification scheme which could be superimposed with additional data to support environmental assessment and management.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary.

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Abundance and characteristics of microplastics in the Wanquan River estuary, Hainan Island.

As the nexus where rivers and oceans meet, estuaries are vulnerable to microplastic (MP) pollution derived from rivers. However, few studies have focused on the pollution status of MPs in small estuarine areas. Here, the abundance and characteristics of MPs in surface water and sediment samples from a small estuary, the Wanquan River estuary, were studied. The average abundance of MPs was 6573 ± 2659 n/m3 in surface water and 1065 ± 696 n/kg dw in sediment samples from the Wanquan River estuary. Most of the MPs in water samples and sediments were red (92.9 % and 88.1 %) fragments (87.4 % and 95.5 %) with sizes <1.0 mm (90.8 % and 92.4 %) made up of antifouling paint particles (APPs) (83.5 % and 89.8 %), respectively. A significant positive correlation (p < 0.01) was found between the concentration of Cu2+ and the abundance of APPs in sediment samples from the Wanquan River estuary. The APPs in the sediments can act as a continuous source of toxic chemicals (e.g., Cu2+) to marine environments. The results of this study expand our knowledge about MP pollution in small estuaries, and the ecological risk of APPs in the Wanquan River estuary to aquatic organisms should not be ignored.

Fish assemblage and guild structure in the Ashtamudi Estuary, a tropical Ramsar site in India.

A first hand study on guild structure of fish species (n = 148) in Ashtamudi Estuary, a Ramsar Site of International importance, was carried out from May 2019 to April 2020 based on temporal (monsoon, pre-monsoon and post-monsoon seasons) and spatial (upper, middle and lower zones) data. Guild composition consisted of eight estuarine use guilds (marine estuarine opportunist, marine estuarine dependent, estuarine resident species, anadromous species, freshwater migrants, freshwater stragglers, catadromous and marine stragglers) and eight feeding guilds (zooplanktivore, zoobenthivore, carnivores, herbivores, invertebrate feeders, omnivores, detritus feeders and piscivores). The most dominant estuarine use guilds comprised of marine migrants (marine estuarine opportunist and marine estuarine dependent), whereas carnivore, omnivore and zooplanktivore formed the dominant feeding guilds in Ashtamudi Estuary. The species diversity decreased from upper to lower zone and was highest during the post-monsoon period. The present study has seen a decrease in estuarine resident and freshwater species due to reduced freshwater inflow, saltwater intrusion, unsustainable fishing and inadequate environmental management practices. Hence, we propose a management framework to improve the ecosystem of Ashtamudi Estuary with a special focus on its fish species and their estuarine use.

A multi-metric fish index to measure the ecological quality of tropical predominantly open estuaries along the western coast of India.

Defining the ecological quality of estuaries is challenging because of the inadequacy of available methods and indices to characterise the ecosystem. In Indian estuaries, there are no scientific attempts to establish multi-metric fish index to determine the ecological status. A multi-metric fish index (EMFI) was customised for twelve predominantly open estuaries on India's western coast. The index was established at the individual estuary level to ensure uniformity and contrast from sixteen metrics that designate the fish community and diversity, composition and abundance, estuarine use and trophic integrity from 2016 to 2019. A sensitivity study was followed to measure the responses of the EMFI under different metric varying scenarios. There were seven metrics identified as the most prominent for the EMFI in metric alteration scenarios. We also deduced a composite pressure index (CPI) based on the anthropogenic pressures described for the estuaries. The ecological quality ratios (EQR) defined based on EMFI (EQRE) and the CPI (EQRP) for all the estuaries were positively correlated. The EQRE values calculated based on the regression relationship (EQRE on EQRP) showed the divisions from 0.43 (bad) to 0.71 (high) for the Indian west coast estuaries. Similarly, the standardised CPI (EQRP) values for different estuaries indicated that the values range from 0.37 to 0.61. Our results based on the EMFI suggest four estuarine systems (33%) as 'good', seven (58%) as 'moderate' and one (9%) as 'poor'. Generalised Linear Mixed Model for EQRE showed that EQRP and estuary influenced EQRE; however, the effect of year was not significant. This comprehensive study based on the EMFI is the first record for predominantly open estuaries along the Indian coast. Therefore, the EMFI established in this study could be reliably advocated as a sound, effective and composite tool of ecological quality for tropical open transitional waters.

Fish community structure and functional guild composition in a large tropical estuary (Vembanad Lake, India).

The fish guild structure of 96 fish species inhabiting the Vembanad Lake, an open, large, well-mixed coastal estuary along the south-west coast of India, was studied based on samples from upper (freshwater), middle (estuarine), and lower (saline) zones representing three major seasons (monsoon, post-monsoon, and pre-monsoon). Functional group assessment revealed seven ecological guilds (marine estuarine opportunists, freshwater, marine estuarine dependent, estuarine, catadromous, anadromous, and amphidromous), six feeding guilds (detritivore, zooplanktivore, herbivore, zoobenthivore, omnivore, and carnivore), three vertical distribution guilds (demersal, benthopelagic, and pelagic), five reproductive-mode functional groups (oviparous with pelagic eggs, oviparous with benthic eggs, oviparous guarders, viviparous and ovoviviparous), and five flow-preference guilds (rheophilic A1, eurytopic, rheophilic A2, rheophilic B, and rheophilic C). The estuary was characterized by high species diversity, low individual species abundance, complex guild structure, varying fish diversity from upper to lower estuary and higher proportion of marine rather than 'true' estuarine species. The absence of a significant relationship between season and fish guild structuring could be due to high resource availability in the estuary and low ecological connectivity between upper and lower estuarine zones as a result of anthropogenic interventions in the middle zone. Salinity variations considerably influenced the fish guild formation in the estuary. A drastic change in the hydrography of the estuary over the past sixty years due to topographical alterations has transformed the fish guilds resulting in a considerable increase in freshwater species and a reduction in marine and estuarine-dependant species.

Seasonal and diel modulation of DOM in a mangrove-dominated estuary.

Rivers and estuaries are the main links between continents and oceans. The Paraíba do Sul River is among the most important rivers of the southeastern Brazilian region, carrying an average of 0.08 Tg of dissolved organic matter (DOM) to the ocean but has been facing significant changes in river discharge. In this study, we aimed to provide insights into the sources and transformations of chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) sources across a salinity gradient under changing river discharge scenarios. Three spatial surveys were performed covering the entire salinity gradient of the main estuarine channel and surrounding mangrove waters under contrasting river discharge (178 to 1240 m3 s-1), and diel sampling was conducted in the mangrove tidal creek. The characterization of DOM through the parallel factor analysis (PARAFAC) model identified six components across the river-ocean gradient and mangrove creek: terrestrial origin (C1 - fulvic acid and C2 and C3 - humic-like), protein-like (C4), tryptophan-like (C5), and tyrosine-like (C6). Our results showed a shift in DOM composition and contribution along the salinity gradient, from terrestrial (C3) to autochthonous (C5 and C6) signatures. The October-17 dry campaign was characterized by a higher proportion of microbial protein-like component C4 and a lower contribution of humic-like components compared to February-17 and March-18 across the salinity gradient with an increase in the mixing zone. The DOM compositions of the February 17 dry and March 18 wet campaigns were similar. Additionally, the March-18 wet campaign, marked by the highest river discharge, showed higher inputs of terrestrial DOM (C1-C3 components) compared to February-17 in the estuary, which allowed DOM to be transported rather than transformed. The mangrove diel study showed that tidal fluctuations are also an important driver of carbon input to the mangrove creek with a possible impact on DOM composition in estuarine waters.

Effects of PAHs on meiofauna from three estuaries with different levels of urbanization in the South Atlantic.

Estuarine environments are suggested to be the final receivers of human pollution and are impacted by surrounding urbanization and compounds carried by the river waters that flow from the continent. Polycyclic aromatic hydrocarbons (PAHs) are among the contaminants that can reach estuaries and can directly affect marine conservation, being considered highly deleterious to organisms living in these environments. This research investigated the meiofauna of three estuaries exposed to different levels of urbanization and consequently different levels of PAH concentrations, in order to assess how these compounds and environmental factors affect the distribution, structure and diversity of these interstitial invertebrates. A total of 15 major meiofauna groups were identified, with Nematoda being the dominant taxon (74.64%), followed by Copepoda (9.55%) and Polychaeta (8.56%). It was possible to observe significant differences in all diversity indices studied in the estuaries. With the exception of average density, the diversity indices (richness, Shannon index and evenness) were higher in the reference estuary, Goiana estuarine system (GES). On the other hand, the Timbó estuarine system (TES) had the lowest Shannon index value and richness, while the Capibaribe estuarine system (CES) had the lowest evenness value. The latter two estuaries (TES and CES) presented intermediate and high levels of urbanization, respectively. The ecological quality assessment (EcoQ) in the studied estuaries was classified from Poor to Moderate and the estuary with the lowest demographic density in its surroundings, GES, showed a better ecological quality (Moderate EcoQ). A significant distance-based multivariate linear modelling regression (DistLM) was observed between the environmental variables and the density of the meiobenthic community, where PAHs and pH were the main contributors to organism variation. The sediments were characterized by predominance of very fine sand and silt-clay in the most polluted environments, while the control site environment (GES) was dominated by medium grains. The highest concentrations of PAHs were found in the most urbanized estuaries, and directly affected the structure of the interstitial benthic community. The metrics used in the present study proved to be adequate for assessing the environmental quality of the investigated estuaries.

Influence of environmental variables on the spatiotemporal dynamics of water quality in Buenaventura Bay, Colombian Pacific.

Tropical estuaries are productive dynamic ecosystems where water quality is mediated by physicochemical and biological processes and by fluvial and anthropogenic discharges. The objective of the study was to determine the influence of environmental variables on the spatiotemporal dynamics of water quality in Buenaventura Bay, which is a highly impacted estuary. Sampling was carried out during the dry and rainy season, at three depths, in four stations that represent the environmental gradient of the bay. Temperature, total dissolved solids, salinity, dissolved oxygen, and pH were determined for each sample. In addition, alkalinity, phosphates, nitrites, and nitrates as indicators of water quality were also measured. The estuary was classified as meso- and polyhaline, with appropriate oxygen and pH conditions and spatiotemporal gradients of temperature and solids mediated by river discharges. Significant variations were found in the physicochemical variables by season, with maximum salinity, pH, and solids in the dry season and oxygen and temperature in the rainy season. Likewise, most of these environmental variables were higher in the outer zone of the estuary and lower in the inner stations. Alkalinity and nitrite values were within the permitted ranges, while phosphates and nitrates indicated low water quality. There was a significant direct influence of temperature and oxygen on alkalinity and nitrites. However, for phosphates, no significant influence of environmental variables was found, suggesting a greater influence by fluvial and anthropogenic discharges, which produce a decrease in the environmental quality of the estuary.

Metal enrichment and toxicity assessment through total and speciation of metals in lower and middle regions of tropical (Mandovi) Estuary, western coast of India.

The study aimed to understand the metal enrichment and toxicity in lower and middle regions of a tropical Mandovi Estuary, revealed metals dilution by coarser intertidal mudflat sediments in the lower estuary (downstream of the fishing jetty-core S). A relatively calm depositional environment prevailed at the middle estuary (core M) and also at the upstream of the jetty of the lower estuary (core L) facilitating deposition and enrichment of Mn and Zn in cores M and Mn, Cu and Co in core L. The distribution of trace metals in sediments was regulated by grain size, total organic carbon and Fe-Mn oxides. The potential contamination index indicated a moderate degree of metal contamination in sediments while the anthropogenic factor showed the signatures of human-induced activities in the enrichment of metals. The sequential extraction of metals showed bioavailability of Mn, Cu, Zn and Co. Fe-Mn oxide and organic/sulphide were key phases for the retention of bioavailable metals. The elevated level of these metals suggested possible toxicity to benthic biota, particularly from Mn (cores L and M) and Co (core L) according to the screening quick reference table.

Occurrence of microplastics in bivalve molluscs Anomalocardia flexuosa captured in Pernambuco, Northeast Brazil.

Microplastics (MPs) are widely distributed in marine ecosystems, and their ubiquitous presence is raising concern, particularly about possible impacts on fisheries resources. In tropical regions, shellfish fisheries represent an essential source of income and subsistence for traditional communities, and adverse effects on these resources may have severe consequences on human health. In the present study, bivalve molluscs of the species Anomalocardia flexuosa, captured in the region of the Itapessoca estuary in Pernambuco, Brazil, were analysed. A total of 90% of the individuals presented MP particles in their tissue. We observed an average of 5.15 ± 3.80 MP particles per individual, and for each gram of soft tissue, 3.66 ± 2.59 MP particles were found. Our results showed that MPs are present in clams captured on the Pernambuco coast and that the species studied proved to be suitable for monitoring the levels of microplastic pollution.

Metals Bioaccumulation in 15 Commonly Consumed Fishes from the Lower Meghna River and Adjacent Areas of Bangladesh and Associated Human Health Hazards.

The lower Meghna River, the easternmost part of the Ganges Delta, faces severe anthropogenic perturbations as it receives a huge discharge and industrial effluents. To measure the metal concentrations and human health hazards, edible tissues of 15 commercially important fish species were collected from the local fish markets and the lower Meghna River, Bangladesh. Trace and heavy metals such as Pb, Cr, Cu, Zn, Mn, Fe, Hg, Ni, Ca, Co, Se, Rb, Sr, and As were detected using the Energy Dispersive X-ray Fluorescence (EDXRF) method. The hierarchy of mean metal concentrations obtained was: Fe (162.198 mg/kg) > Zn (113.326 mg/kg) > Ca (87.828 mg/kg) > Sr (75.139 mg/kg) > Cu (36.438 mg/kg) > Se (9.087 mg/kg) > Cr (7.336 mg/kg) > Mn (6.637 mg/kg) > Co (3.474 mg/kg) > Rb (1.912 mg/kg) > Hg (1.657 mg/kg) > Ni (1.467 mg/kg) > Pb (0.521 mg/kg) > As (BDL). Based on the metal concentration obtained, the carnivorous species contained more metals than omnivores and herbivores. Similarly, the euryhaline and benthic feeder fishes had more metals than the stenohalines and demersal fishes. The metal pollution index (MPI) suggested that the highly consumed fish species Tilapia (Oreochromis mossambicus) and Rui (Labeo rohita) accumulated higher metals than other fishes. Both the Targeted Hazard Quotient (THQ) and Hazard Index (HI) values for adult and child consumers were <1, indicating that consumers would not experience the non-carcinogenic health effects. Although children were more susceptible than adults, carcinogenic risk (CR) exposure of Cr for all the consumers was found in the acceptable range (10−6 to 10−4), but the CR exposure of Pb was negligible for all the consumers. The correlation, principal component analysis (PCA), and cluster analysis were conducted to identify the sources of metals identified from the fish tissue. The results indicated that the probable sources of the pollutants were anthropogenic, arising from agricultural activities, electroplating materials, and lubricants used near the study area. However, the present study showed a different metal concentration in the samples at different levels but within the threshold levels non-carcinogenic and carcinogenic health risks; hence, the fishes of the area, in general, are safe for human consumption.

Variable Freshwater Influences on the Abundance of Vibrio vulnificus in a Tropical Urban Estuary.

To better understand the controls on the opportunistic human pathogen Vibrio vulnificus in warm tropical waters, we conducted a year-long investigation in the Ala Wai Canal, a channelized estuary in Honolulu, HI. The abundance of V. vulnificus, as determined by quantitative PCR (qPCR) of the hemolysin gene (vvhA), varied spatially and temporally by nearly 4 orders of magnitude (≤3 to 14,000 mL-1). Unlike in temperate and subtropical systems, temperatures were persistently warm (19 to 31°C) and explained little of the variability in V. vulnificus abundance. Salinity (1 to 36 ppt) had a significant, but nonlinear, relationship with V. vulnificus abundance with the highest vvhA concentrations (>2,500 mL-1) observed only at salinities from 7 to 22 ppt. V. vulnificus abundances were lower on average during the summer dry season, when waters were warmer but more saline. The highest canal-wide average abundances were observed during a time of modest rainfall, when moderate salinities and elevated concentrations of reduced nitrogen species and silica suggested a groundwater influence. Parallel quantification of the vcgC gene suggested that C-type strains, which are responsible for most human infections, comprised 25% of the total V. vulnificus on average, but their relative contribution was greater at higher salinities, suggesting a broader salinity tolerance. Generalized regression models suggested that up to 67% of sample-to-sample variation (n = 202) in log-transformed V. vulnificus abundance was explained using the measured environmental variables, and up to 97% of the monthly variation in canal-wide average concentrations (n = 13) was explained with the best subset of four variables. IMPORTANCE Our data illustrate that, in the absence of strong seasonal variation in water temperature in the tropics, variation in salinity driven by rainfall becomes a primary controlling variable on V. vulnificus abundance. There is thus a tendency for a rainfall-driven seasonal cycle in V. vulnificus abundance which is inverted from the temperature-driven seasonal cycle at higher latitudes. However, stochasticity in rainfall and its nonlinear, indirect effects on V. vulnificus concentration means that high abundances can occur at any location in the canal at any time of year, making it challenging to predict concentrations of this pathogen at a high temporal or spatial resolution. Much of the variability in canal-wide average concentrations, on the other hand, was explained by a few variables that reflect the magnitude of freshwater input to the system, suggesting that relative risk of exposure to this pathogen could be predicted as an average for the system.

Environmental influences on the ichthyoplankton in hypersaline estuaries located in a Semiarid Northeastern Brazilian coast

Hypersaline estuaries are commonly found in the Semiarid Northeast Brazilian coast. However, the utilization of these estuaries by early life stages of fishes is less well documented. This study aimed to evaluate the effects of environmental factors on the ichthyoplankton, and to describe their spatial and temporal variation in two estuaries (Tubarão and Casqueira). The sampling were diurnally in four excursions carried out during two dry-season months (November and December 2017) and two rainy-season months (May and July 2018). A total of 423 larvae representing 30 species (14 families) and 2,762 eggs (five families) were collected. Although the community structures were similar in both estuaries, there was strong seasonal variation, with higher abundances observed during the dry season. Low rainfall was the primary environmental driver affecting ichthyoplankton in both estuaries. Other environmental factors, such as depth, water temperature, and channel width, were also predictor variables for the distribution of eggs and larvae. The ichthyoplankton was dominated by marine estuarine-dependent species in both estuaries, accounting for 76% of individuals. The presence of the early life stages of typically marine species suggests that hypersaline environments provide important nursery areas and play an essential role for some coastal fish species.(AU)

Os estuários hipersalinos são comumente encontrados na região semiárida da costa nordestina brasileira. No entanto, a utilização desses estuários pelos primeiros estágios de vida dos peixes é pouco documentada. O objetivo deste estudo foi avaliar os efeitos de fatores ambientais sobre o ictioplâncton e descrever sua variação espacial e temporal em dois estuários (Tubarão e Casqueira). As amostragens foram diurnas em quatro excursões realizadas em dois meses da estação seca (novembro e dezembro de 2017) e dois meses da estação chuvosa (maio e julho de 2018). Um total de 423 larvas representando 30 espécies (14 famílias) e 2.762 ovos (cinco famílias) foram coletadas. Embora as estruturas das comunidades fossem semelhantes em ambos os estuários, houve fortes diferenças de variação sazonal, com maiores abundâncias observadas durante a estação seca. A baixa precipitação foi o principal fator ambiental que afetou o ictioplâncton em ambos os estuários. Outros fatores, como profundidade, temperatura da água e largura do canal, também foram preditoras para a distribuição de ovos e larvas. O ictioplâncton foi dominado por espécies marinhas dependentes em ambos os estuários, representando 76% dos indivíduos. A presença de estágios iniciais de espécies tipicamente marinhas sugere que ambientes hipersalinos fornecem áreas de berçário importantes e desempenham um papel essencial para algumas espécies de peixes costeiros.(AU)

Large-scale differences in diversity and functional adaptations of prokaryotic communities from conserved and anthropogenically impacted mangrove sediments in a tropical estuary.

Mangroves are tropical ecosystems with strategic importance for climate change mitigation on local and global scales. They are also under considerable threat due to fragmentation degradation and urbanization. However, a complete understanding of how anthropogenic actions can affect microbial biodiversity and functional adaptations is still lacking. In this study, we carried out 16S rRNA gene sequencing analysis using sediment samples from two distinct mangrove areas located within the Serinhaém Estuary, Brazil. The first sampling area was located around the urban area of Ituberá, impacted by domestic sewage and urban runoff, while the second was an environmentally conserved site. Our results show significant changes in the structure of the communities between impacted and conserved sites. Biodiversity, along with functional potentials for the cycling of carbon, nitrogen, phosphorus and sulfur, were significantly increased in the urban area. We found that the environmental factors of organic matter, temperature and copper were significantly correlated with the observed shifts in the communities. Contributions of specific taxa to the functional potentials were negatively correlated with biodiversity, such that fewer numbers of taxa in the conserved area contributed to the majority of the metabolic potential. The results suggest that the contamination by urban runoff may have generated a different environment that led to the extinction of some taxa observed at the conserved site. In their place we found that the impacted site is enriched in prokaryotic families that are known human and animal pathogens, a clear negative effect of the urbanization process.