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The study explores phytoplankton diversity and community structure as indicators of Karanja Estuary health. Surface water samples were collected between January 2022 and March 2023, revealing 139 phytoplankton species across three stations and seasons. Cluster and multidimensional scaling analysis delineated three distinct spatiotemporal clusters within the estuary. Peak phytoplankton abundance and diversity during the post-monsoon period contributed to increased salinity, pH and optimal nutrients. The monsoon season witnessed the lowest phytoplankton abundance due to decreased water transparency and light penetration. Biota-environment (BIO-ENV) analysis highlighted water temperature, biochemical oxygen demand, ammonia, silicate and chlorophyll-a (ρ = 0.9084) as significant factors influencing phytoplankton distribution. Canonical correspondence analysis unveiled significant correlations between Skeletonema costatum, Skeletonema sp., Thalassionema frauenfeldii and Thalassionema nitzschioides with nitrate, ammonia, biochemical oxygen demand (BOD) and dissolved oxygen. Diatom species Asterionellopsis glacialis, Chaetoceros sp., Ditylum brightwellii, Ditylum sol and Pseudo-nitzschia pungens were associated with total phosphorus, chlorophyll-a and silicate. High BOD values suggest a significant presence of organic matter, potentially depleting oxygen through decomposition. A high Shannon–Weiner diversity index implies a diverse phytoplankton community with multiple species, indicating ecosystem resilience and stability. This situation may arise when a stressed ecosystem maintains diversity with pollution-tolerant species, which may be temporary and lead to detrimental long-term consequences. The ecological quality status (EcoQS) using six phytoplankton community indices concluded that all the stations ranged from ‘high’ to ‘bad’ condition, with disagreement among the six indices. This study employs a holistic approach, integrating physical, chemical and biological parameters with multivariate analysis techniques to acknowledge the complexity of ecosystem health. [ABSTRACT FROM AUTHOR]

Contextualization: Tumaco Bay in the Colombian Pacific is potentially a recipient of domestic waste, which leads to different contaminants such as microplastics (< 5mm) accumulating in marine sediments. Knowledge gap: In the Tumaco Bay in Colombian Pacific, it has not been researching the patterns of microplastic contamination in marine sediments. Purpose: The purpose of this study was to identify the presence, characteristics, and spatiotemporal variation of microplastic (MP) contamination during the years 2020 and 2021 in the internal and external zone of Tumaco Bay and whether this had any relationship with the proximity to the coastal zone, river mouths and COVID-19. Methodology: MP samples were collected in the internal and external zone of Tumaco Bay, during the rainy and dry seasons in the years 2020 and 2021. Results and conclusions: MP contamination was higher in the internal zone (721,37 ± 175,96 particles/kg). Likewise, the rainy season presented the highest contamination by microplastics (928,73 ± 220,20 particles/kg) while the lowest was observed in the dry season (440,78 ± 101,54 particles/kg). Finally, there was a decrease in MP from one year to another, being March during the rainy season of 2020, the one that presented the highest contamination with an average of 1543,55 ± 362,92 particles/kg, this pattern is possibly due to the decrease of tourism in the Bay of Tumaco due to the sanitary emergency that began in middle of March 2020 in Colombia and that occurred worldwide. [ABSTRACT FROM AUTHOR]

Simple Summary: This study analyzes muscle and gill samples from 36 samples of 2 popular edible fishes from a subtropical wetland ecosystem to determine the amounts of harmful heavy metals, such as Pb, Hg, Zn, Cu, and Cr. The metal concentrations in the muscle and gills fluctuate, with zinc having the greatest concentration. Pb and Hg levels are higher than those that are acceptable for human consumption, while Cu, Zn, and Cr levels are within safe bounds. High amounts of Zn, Cu, and Cr may pose health hazards, according to risk indices. The research also highlights sources of heavy metals that are caused by humans and the natural world, highlighting the necessity of continual control and monitoring to guarantee the safety of fish for human consumption. 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. [ABSTRACT FROM AUTHOR]

This study delves into the nutraceutical potential of microalgae in brackishwater aquaculture, with a focus on a case study conducted in the Muttukadu estuary, Tamil Nadu, India. The research involved the collection, identification, culture standardization, nutrient profiling, antioxidant and antibacterial properties of seven microalgal species in the brackishwater ecosystem, including Thalassiosira weissflogii, Chaetoceros gracilis, Nannochloropsis oculata, Chlorella marina, Tetraselmis sp, Isochrysis galbana and Arthrospira maxima. The growth kinetics analysis highlighted N. oculata and C. marina with an extended log phase and significantly higher growth rates. Proximate analysis revealed the highest protein content (62.46 ± 3.45%) in A. maxima. I. galbana showed significantly higher lipid content (33.08 ± 2.18%), while T. weissflogii had 20.11 ± 1.02%. Fatty acid profiling identified the highest percentage of polyunsaturated fatty acids (69.51%) in A. maxima, followed by Tetraselmis sp (56.32%). Methanolic extracts from C. marina and T. weissflogii displayed notably higher total phenolic content. A. maxima exhibited the highest total antioxidant activity, and C-Phycocyanin (CPC) extracts showed the highest inhibition zones against pathogenic bacteria. This study underscored the diversity of commercially important microalgal species in the tropical estuarine brackishwater ecosystem. The nutrient composition analysis emphasized the abundance of essential macronutrients, micronutrients, vitamins, and bioactive compounds. These findings contribute to understanding microalgae's nutraceutical potential in brackishwater aquaculture, suggesting their suitability for large-scale cultivation and utilization in aquaculture and other food-producing industries. Moreover, the bioactive compounds present in these microalgae offer opportunities for developing novel nutraceutical formulations with potential health benefits. [ABSTRACT FROM AUTHOR]

Estuaries and coastal environment in the Bay of Bengal are affected by wide range of contaminants due to increased anthropogenic activity from a budding population in the coastal region. Sixteen physico-chemical and biological parameters were measured from 14 stations during four seasons like summer, monsoon, post-monsoon and winter along Mahanadi River, creek, estuarine and adjacent coastal ecosystem in 2011 and 2012. The results indicate that average lower value of pH (6.61 ± 0.68) was in winter, and dissolved oxygen (DO; 3.89 ± 2.01 mg L−1) was during monsoon in the ecosystem compared to the other season, whereas average higher concentration of Biochemical Oxygen Demand (BOD; 5.92 ± 2.62 mg L−1), nitrate (68.77 ± 30.35 µM), ammonium (43.50 ± 21.46 µM) and Phosphate (39.73 ± 10.63 µM) were found in the creek during post-monsoon. The ratio between nitrate and phosphate (N:P) declined in entire ecosystem of the study region indicated nutrient limiting due to the inorganic load into the system. The nutrients and phytoplankton biomass (Chlorophyll-a) show a strong positive correlation (r = 0.591) and negative correlation (r = −0.549) with BOD, respectively. Nutrients behaved non-conservatively and played a significant role in the depletion of DO. Factor analysis shows that loading activities of water quality parameters are mainly related to the major organic pollution, inorganic pollution and nutrients load into the ecosystem, whereas the cluster analysis and water quality index (WQI) resulted that the study region ecosystem has triggered alarm, due to various significant levels of contaminants. Hence, proper industrial management along with necessary measures is recommended for estuary and coastal environment ecosystem from socioeconomic disaster and sustainable ecosystem management. [ABSTRACT FROM AUTHOR]

The mangrove oyster (Crassostrea) is one of the most common bivalves found on the Brazilian coast, widely used in artisanal fisheries. Oysters are dioecious with external reproduction, typically found in estuarine environments. The present study aimed to identify the population aspects of Crassostrea in different fishing locations in northeastern Brazil. The study area was the Acaú-Goiana Extractive Reserve, a protected area focused on the development of artisanal fisheries. Oysters were collected during low tide at three sampling points, where their removal from mangrove roots was carried out, during May, July, September, November 2021, and January and March 2022. In the laboratory, biometric measurements were conducted, and for the months of May and November 2021 histological preparations to study the reproductive cells. Biometric measurements were significantly higher in the dry season at all sampling points. The sex ratio was M = 0.38, F = 0.62, for May, and M = 0.30, F = 0.69, for November. The biometric and reproductive data obtained can support the development of management strategies, including a rotation plan between collection sites and the establishment of a minimum size for fishing. Here we recommend a minimum size of 20 mm shell length (SL) or larger for fishing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Land use and land cover (LULC) can significantly alter river water, which can in turn have important impacts on downstream coastal ecosystems by delivering nutrients that promote marine eutrophication and hypoxia. Well-documented in temperate systems, less is known about the way land cover relates to water quality in low-lying coastal zones in the tropics. Here we evaluate the catchment LULC and the physical and chemical characteristics of six rivers that contribute flow into a seasonally hypoxic tropical bay in Bocas del Toro, Panama. From July 2019 to March 2020, we routinely surveyed eight physical and chemical characteristics (temperature, specific conductivity, salinity, pH, dissolved oxygen (DO), nitrate and nitrite, ammonium, and phosphate). Our goals were to determine how these physical and chemical characteristics of the rivers reflect the LULC, to compare the water quality of the focal rivers to rivers across Panama, and to discuss the potential impacts of river discharge in the Bay. Overall, we found that the six focal rivers have significantly different river water characteristics that can be linked to catchment LULC and that water quality of rivers 10 s of kilometers apart could differ drastically. Two focal catchments dominated by pristine peat swamp vegetation in San San Pond Sak, showed characteristics typical of blackwater rivers, with low pH, dissolved oxygen, and nutrients. The remaining four catchments were largely mountainous with >50% forest cover. In these rivers, variation in nutrient concentrations were associated with percent urbanization. Comparisons across Panamanian rivers covered in a national survey to our focal rivers shows that saltwater intrusions and low DO of coastal swamp rivers may result in their classification by a standardized water quality index as having slightly contaminated water quality, despite this being their natural state. Examination of deforestation over the last 20 years, show that changes were

[Display omitted] • The water column showed dominance of absorption with maximum Chl-a concentration. • Scattering was dominated in water with maximum TSM. • CDOM and Chl-a showed non-conservative behavior during the pre and post ISM seasons. • Stratification plays a significant role in determining the bio-optical properties. Using ten years of in-situ data from a shallow optically complex coastal ecosystem, this study unravels the coupling between bio-optical variability and seasonally changing hydrography. The data presented is novel, as these are long-term simultaneous measurements of bio-optical properties and constituents covering a wide range of hydrographic conditions at different sampling stations in riverine, estuarine, and coastal shelf. The data represent all three seasons experienced in the region, i.e., Indian Summer Monsoon (ISM), post-ISM, and pre-ISM. It allowed us to conduct a baseline study to characterize the bio-optical variability (absorption or scattering dominated) coupled with stratification for remote sensing applications on ecological health. Four groups of sampling stations, representing varying hydrography, were identified as riverine, maximum stratification, maximum chlorophyll-a (Chl-a) concentration, and estuarine/shelf. The maximum concentrations of total suspended matter (TSM) were always collocated with the strongest stratification site, while maximum Chl-a was always located downstream of maximum stratification. Surprisingly, colored dissolved organic matter (CDOM) values were negligible in the ISM season and increased manifold in other seasons. The source of CDOM (either land-derived or in situ generated) inferred from the spectral slope revealed the dominance of land-derived CDOM in the post-ISM season. Combining the entire data into the same groups showed that groups with maximum TSM and samples from estuarine locations were scattering-dominated. In contrast, the group with maximum Chl-a was absorption dominated. The analysis revealed that the optical behavior of the sampling locations being either absorption or scattering dominated depended on the state of stratification and contribution of Chl-a to the absorption budget. [ABSTRACT FROM AUTHOR]

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 (−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.

Contextualization: artisanal fishing in the Colombian Pacific is positioned as one of the main sources of income for the communities settled on the coasts; therefore, there is a strong pressure on fishing resources, with non-selective fishing gears such as the trammel netting and the hand linehook, capturing individuals that have not experienced any reproductive events and that belong to incidental and discard fishery. Knowledge gap: in the Colombian Paci fic, the spatiotemporal relationships have not been explored between target and discard fishing, according to the environmental variables. Purpose: evaluate the spatiotemporal dynamics of catch per unit of effort [CPUE] and the sustainability of artisanal fishing associated with environmental variables, in Tumaco Bay [Colombian Pacific], to value their environmental impact. Methodology: four samplings were conducted throughout the year 2020 and 2021, two in the dry season and two in the rainy season, with the trammel and hand hook line fishing gears in the internal and external zone of the Tumaco bay. Samples of physical-chemical variables were carried out. Results and conclusions: within the target catch, the families Ariidae and Sciaenidae were the most representative, Pristigasteridae and Gerreidae in the bycatch and Engraulidae and Cynoglosidae in the discard. With the hand hook line, 94.60% was target catch, 3.90% bycatch and 1.48% belonged to discard; while with trammel netting, 49.07 % was discarded, 41.78 % was target catch and 9.15 % was bycatch. The trammel net caught smaller individuals (17.49 ± 4.26 cm), which may indicate that it is a little selective gear as it does not respect the minimum catch sizes. The total catch per unit of efiort was higher with the hand hook fishing gear (8.84 ± 5.42 kg h-1). The variables of salinity, total dissolved solids and transparency presented a negative correlation with the total catch per unit of effort in the trammel net, while with the hook they presented a positive association. It is recommended to regulate the use of trammel nets in the internal area and in the rainy season due to the fishing gear captures juvenile commercial species that are discarded. [ABSTRACT FROM AUTHOR]

Scientific fishing programmes were carried out between 1979 and 2013 in several West African estuarine, coastal and lagoon ecosystems. Batrachoides liberiensis represented only 5.2% of the occurrences, of which the majority were recorded in the Sine Saloum estuary. This originality makes it possible to use this population to characterise certain features of the biology and ecology of this little described species. B. liberiensis was recorded in waters with a salinity of 25–46, transparency of 1–3.5 m, at depths of 2–10 m. It was particularly abundant in areas at a distance of 15–35 km from the mouth. The water temperature did not appear to be a determining factor for this species. The sex ratio of the population, whose total length ranged from 10 to 371 mm, was in favour of females (87%) with an estimated size at first maturity of 189 mm (total length). The parameters of the length‐weight relationship were estimated at K = 1.0009*10−5 and b = 3.097. The diet of B. liberiensis consisted mainly of molluscs and crabs, present in respectively, 53.6% and 50.7% of the stomach contents analysed. [ABSTRACT FROM AUTHOR]

Biodiversity baselines are essential subsidies to evaluate how environmental changes and human impacts affect the special and temporal patterns of communities. This information is paramount to promote proper conservation and management for historically impacted environments such as Guanabara Bay, in southeastern Brazil. Here, we propose an ichthyofaunal baseline for this bay using gathered past data from 1889 to 2020, including literature records, scientific collections, biological sampling, and fisheries landing monitoring. A total of 220 species (203 teleosts and 17 elasmobranchs), distributed in 149 genera (136 teleosts and 13 elasmobranchs) and 72 families (61 teleosts and 11 elasmobranchs) were recorded, including the first record of a tiger-shark, Galeocerdo cuvier, in Guanabara Bay. Although the employed sampling effort was sufficient to represent the ichthyofauna in the middle and upper estuary, the Chao2 estimator indicates an even greater richness regarding the bay as a whole. Evidence of reduced abundance and probable local extinction over the decades was found, supporting the importance of implementing management and conservation strategies in the area. The ichthyofaunal distribution analyses revealed that areas close to conservation units are richer compared to their surroundings, indicating that this is an effective strategy to mitigate human impacts in the bay. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Aim This work proposes the application and development of environmental quality indexes for the evaluation of tropical estuarine streams in different spatial scales. The main goal was to understand the biological responses of the ichthyofauna in relation to different spatial indices in each group of streams, according to their predominant land use. Our hypothesis is that the impact on the stream riparian zones and in the land use in adjacent areas to the stream interfere in the structure of the fish assembly. Methods The Physical Habitat Integrity Index (PHI) on the local scale (80.0 m) and the Microbasin Integrity Index (MII) on catchment scale (1.6 km radius) was applied in all streams. In parallel, fish collections with electric fishing equipment were carried out in the 80.0 m reach. With the data from the PHI, MII and ecological estimators (species richness and percentage of Poecilia reticulata), the Kruskal-Wallis non-parametric test and Dunn’s post hoc test were carried out to verify the differences between the groups of land use, followed by a linear and polynomial regression analysis with trend line to show a relationship among indexes used and the biological responses. Results We observed that all streams’ groups presented a high positive correlation among PHI and MII. However, ecological estimators did not respond to changes in land use linearly, but in the form of a parable in a polynomial regression. Conclusions Our main conclusion is that the use of indexes and estimators as tools for environmental assessment is an efficient way to assess the health of the streams. The results also show that the integration of local and spatial indexes reduces the distortions observed in the indexes in isolation.

Abstract Biodiversity baselines are essential subsidies to evaluate how environmental changes and human impacts affect the special and temporal patterns of communities. This information is paramount to promote proper conservation and management for historically impacted environments such as Guanabara Bay, in southeastern Brazil. Here, we propose an ichthyofaunal baseline for this bay using gathered past data from 1889 to 2020, including literature records, scientific collections, biological sampling, and fisheries landing monitoring. A total of 220 species (203 teleosts and 17 elasmobranchs), distributed in 149 genera (136 teleosts and 13 elasmobranchs) and 72 families (61 teleosts and 11 elasmobranchs) were recorded, including the first record of a tiger-shark, Galeocerdo cuvier, in Guanabara Bay. Although the employed sampling effort was sufficient to represent the ichthyofauna in the middle and upper estuary, the Chao2 estimator indicates an even greater richness regarding the bay as a whole. Evidence of reduced abundance and probable local extinction over the decades was found, supporting the importance of implementing management and conservation strategies in the area. The ichthyofaunal distribution analyses revealed that areas close to conservation units are richer compared to their surroundings, indicating that this is an effective strategy to mitigate human impacts in the bay.

Estuaries are highly diverse ecosystems that occur at the interface between land and sea and thus possess a high degree of environmental variation over short spatial and temporal scales. The Gulf of Urabá (1800 km 2; mean depth ~ 40 m) is a semiclosed estuarine area located in the southwestern part of the Caribbean Sea (South America). This large coastal–estuarine ecosystem operates as a biogeochemical reactor due to it featuring examples of high nutrient concentrations on the surface (NO 3- = 1619 μM; NO 2- = 0.505 μM; NH 4+ = 2.938 μM; PO 4 3- = 7.603 μM), high Chl α (max = 30.17; min = 0.02; mean = 9 mg m−3), as well as blooms of toxic algae, mostly Pseudo-nitzschia pseudodelicatissima. An outbreak of Triposfusus causes bioluminescence and about 20 events of hypoxia (< 2–4 mg O 2 L−1) within a time series of 10 years. Despite this, information regarding the biological and biogeochemical oceanography (chlorophyll α, biomass, planktonic composition, nutrient cycling, mass balance of elements, and interannual variability) remains non-existent. Therefore, elucidating an ecosystem's thresholds for various features is necessary for managing marine ecosystems, and especially for climate change projections. We here present a review of the functioning of this estuary, evaluating and reviewing each aspect of oceanographic variability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Living benthic foraminifera have been widely used as ecological indicators in coastal ecosystems. There is, however, a lack of studies on their response to trace element pollution in tropical estuarine systems. Here we analyze the living assemblages of benthic foraminifera, collected in 2016, in the Cachoeira River Estuary (CRE) in northeastern Brazil, to understand their response to natural and anthropogenic stressors, including trace element pollution. Some species were good bioindicators of specific environmental conditions, such as the agglutinant Paratrochammina clossi which preferred mangrove areas and anoxic conditions. In addition, the calcareous Ammonia tepida and Cribroelphidium excavatum, dominant within the whole system disregarding organic or trace element pollution, seem to resist even in the areas most polluted by trace elements. Interestingly, C. excavatum showed a particular positive relationship with trace element pollution (specifically by Cu and Pb), outnumbering the opportunistic A. tepida in the areas with higher pollution of these metals. However, for other species, it is still difficult to constrain to which parameters they respond (i.e., Haynesina germanica and Elphidium gunteri, which in the present study seem to respond to natural conditions, whereas in the literature they are regarded as indicators of trace element and organic pollution, respectively). Therefore, our findings shed light on the response of benthic foraminiferal species in a highly polluted and highly mixed tropical estuarine system and highlight the need to understand the complexity of these environments when applying foraminiferal biological indexes to avoid imprecise conclusions. [ABSTRACT FROM AUTHOR]

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.

Darwin Harbour is a working port and the most populated city in the Northern Territory of Australia. This macrotidal estuary is located in the wet–dry tropics of Northern Australia and notwithstanding mounting development pressures in the region, is largely unmodified. The prevailing oligotrophic condition of estuarine waters suggest that biogeochemical cycling in sediments remain active, buffering the influence of anthropogenic inputs. We tested the hypothesis that nutrient hotspots exist in depositional low-velocity zones, with a gradient of high to low nitrogen processing from the upper to outer reaches of the estuary. A number of factors were examined for their influence on the effectiveness of denitrification in these depositional zones, a putative key process driving nitrogen removal, with particular emphasis on carbon-loading extremes in tidal creeks, spatial gradients along the estuary and the influence of seasonality. There were significant differences in process rates between hypereutrophic/eutrophic tidal creeks that receive the largest proportion of treated sewage loads in the region and the mesotrophic/oligotrophic tidal creeks that were comparatively undisturbed. Net benthic nutrient fluxes and dinitrogen efflux rates were more than an order of magnitude higher and lower, respectively, in degraded (hypereutrophic/eutrophic) tidal creek systems where denitrification efficiency (DE%) was < 40%. Denitrification (Dinitrogen efflux) rates in tidal creeks (mesotrophic/oligotrophic) and broader estuarine sites were high (~ 8 mmol N m−2 day−1) and denitrification efficiency remained > 65%, particularly during the wet season. On a whole-of-estuary basis, denitrification in conjunction with mechanisms such as burial could feasibly make a substantial impact, abating the influence of anthropogenic inputs. Although considerable variability was encountered, particularly across seasons, the hypothesis of elevated denitrification rates as nutrient hotspots in depositional zones along the estuary was not convincing. More influential are tidal creeks as potential 'reactors' for N cycling and removal, but their capacity can be degraded by overloading with nutrients. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The relationships between fish size, weight and otolith morphometry are useful for fisheries management, predator–prey studies and feeding habits. Accordingly, the main purpose of the present study was to determine the relationships between body length, body weight and otolith dimensions, and to calculate the length‐weight relationship and condition factor for a Sciaenid fish Pama croaker, Otolithoides pama (Hamilton, 1822) from the Lower Meghna estuary, Bangladesh. Field sampling was conducted from September 2019 to March 2020. The length, breadth and weight were measured for each pair of sagittae, as well as the total length (TL), standard length (SL) and body weight (BW) for each specimen. A total of 246 fish samples were collected. The TL and BW of collected individuals ranged from 14.40 to 27.40‐cm and 21 to 175‐g, respectively. The calculated growth coefficient (b = 3.018 for males; 3.052 for females) were >3, indicating the fish follow a positive allometric growth. The mean Fulton's condition (Kn) values ranged from 0.674 ± 0.06 to 0.776 ± 0.07, exhibiting similar trends for all size classes. The relationships for fish size and otolith morphometry were described by linear regression models as TL = 0.048OL – 0.308 (r2 = 0.921); BW = 0.047OL + 6.252 (r2 = 0.929); TL = 0.003OW – 0.414 (r2 = 0.836); BW = 0.003OW + 0.039 (r2 = 0.81). The otolith length and weight exhibited a strong correlation (0.929 > r2 > 0.805) with total length and body weight, while the otolith breadth exhibited a weak correlation. No significant differences between left and right otolith were observed (p >.05). Because the results of the present study indicated fish length and otolith growth have a positive relationship, this finding can be a valuable tool to evaluate fish growth by back‐calculating the length of a fish from its otolith characteristics. [ABSTRACT FROM AUTHOR]

Long-term monitoring is required to assess the current state and trend of water quality in anthropogenic-influenced estuarine systems. In this study, we evaluated 1581 samples from a 27-year time series (1990–2016) of physicochemical parameters, microbiological, and heavy metals in the surface waters of the Santa Cruz estuarine channel, Brazil. The results showed that the salinity in the estuarine channel is classified as euhaline (salinity: 30.7) during the dry period and polyhaline (salinity: 26.5) during the rainy season. Statistical analysis showed a significant negative trend for dissolved oxygen (DO) (Mann–Kendall tau; p < 0.05; α: 0.05) with a decrease in DO of − 0.012 mg O2 l−1 year−1. Total phosphorus (TP) showed a significant positive trend in the period 2006–2016 (Kendall tau test; p = 0.0007; α = 0.05). In the last decade, TP showed an increased rate of + 0.007 mg P l−1 year−1. Additionally, the bacterial load (most probable number-MPN method) reached an average value of 55,000 MPN 100 ml, which is 22 times the allowable value for brackish water. Heavy metals (cadmium and manganese) showed a significant increase rate, induced by factors such as industrial growth in the adjacent region and changes in TP, pH, and oxygenation in the water, which changed the accumulation of Fe and Mn in the aquatic medium. The trophic state varied between unpolluted and eutrophic. Comparisons with other systems revealed high fluxes of TP (> 4 mol km−2 year−1). Demographic factors (28% average growth rate) and inadequate public sanitation policies (70% untreated sewage) appear to be the main causes of negative variations in some parameters, such as DO, TP, and pH. [ABSTRACT FROM AUTHOR]

The evaluation of potential ecological risk of aquatic sediments associated with the presence of potentially toxic elements (PTE) determines its degree of danger on native biota. In this work, the potential ecological risk of V, Ti, Cr, Ni, Cu, Zn, As, Se, Cd, Sn, Hg and Pb in superficial sediments is explained in three different areas of Lake Maracaibo: El Tablazo Bay, Strait of Maracaibo and the lake itself, through a multi-guideline approach (elemental enrichment (enrichment factor, contamination degree, pollutant load index and geo-accumulation index), sediment quality guidelines and risk assessment code). The PTE levels ranged from < 0.025 to 176.722 mg·kg−1 DW, with an overall proportion of V > Ti > Pb > Zn > Cr > Cu > Ni > As > Cd > Se > Hg > Sn. The PTE concurrent effect on biota was El Tablazo Bay > lake > Strait of Maracaibo. The superficial sediments of Lake Maracaibo constitute a medium with a high potential ecological risk on estuarine biota. This is mainly due to the levels of As in El Tablazo Bay, Cd in the Strait of Maracaibo and Pb in the lake area. This represents a latent toxicity hazard for native biological communities and other associated organisms. [ABSTRACT FROM AUTHOR]

Tidal flats are inhabited by benthic microalgae (microphytobenthos, MPB) supporting important ecosystem functions and services. Studies on MPB have been conducted mainly in temperate systems, despite that the majority of tidal flats on Earth are found in the tropical zone (∼55%). To fill this gap of knowledge and evaluate the contribution of tidal flat MPB in one of the most productive estuaries worldwide, sediment cores were collected from 14 stations along the inner Gulf of Nicoya (Costa Rica) at different tidal heights or sea levels (SL) from October 2013 to April 2014. MPB abundance, using chlorophyll a (Chla) biomass as a proxy, and net primary production (P N ) and dark respiration (R D ), using O 2 microsensors, were measured together with other sediment biogeochemical variables in muddy and sandy sediments. Landsat-8 satellite images were used to map the extension of tidal flats and the abundance of MPB using Normalized Difference Vegetation Index (NDVI) as a proxy. Chla ranged from 0.45 to 7.45 μg cm -2 , with higher concentrations observed closer to the river mouth. There was no significant correlation between Chla and SL nor with any other sediment physicochemical variable. MPB abundance estimated by remote sensing displayed considerable spatial heterogeneity, both within and among tidal flats, and clear seasonal differences with higher abundance during the rainy season. P N ranged between 0.8 and 8.6 mmol O 2 m -2 h -1 , being positively correlated to SL and to the accumulated rain during 30 days prior to the sampling date and inversely to the mean irradiance at noon during the previous month. Daily net community metabolism estimated from P N and R D data and converted to carbon fixation rates indicates that the unvegetated tidal flats of the gulf contribute as much as the total input of allochthonous C from the Tempisque River. However, the results presented here have to be confirmed with direct measurements of C transfer, including the contribution of the adjacent mangrove system. Such studies are crucial to assess the local, regional and global importance of production and other ecosystem services by MPB in tropical areas., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Alfonso Corzo reports financial support was provided by Spanish Ministry of Economy and Competitiveness. Alfonso Corzo reports financial support was provided by Spanish International Development Cooperation Agency. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Estuaries provide life support to aquatic biota and livelihood support to fishermen and local inhabitants. However, the ecosystem function of estuaries is impaired due to anthropogenic stressors and hence, the assessment of ecosystem health using ecological indicators will deliver the status of stability, maturity, and integrity of an estuary. In this paper, we compiled comprehensive ecological data into an Ecopath model from 2018 to 2019 for a tropical Indian estuary, Mandovi (ME) located along the western coast of India. The functional groups (22) identified in the food web ranged from primary producers (trophic level (TL) = 1) to dolphins (TL 4.4). The indices: biomass/total system throughput (0.01), primary production/respiration (11.04), and primary production/ biomass (35.7) showed that the estuary is a developing ecosystem far from maturity. The ME food web is an immature, complex and organized trophic network with a medium rate of recycling (Finn’s Cycling Index = 9.75%), high total system throughput (17,132.33 tons km−2 year−1), low ascendency (19,610 tons km−2 year−1), high relative ascendency (47.8%), moderate connectance (0.36), and omnivory indices (0.26). The health indices: eco-exergy index (21,471.33 gm detritus equivalent m−2) and system robustness (0.153) showed that the ecosystem is immature but resilient to unexpected perturbations in the ecosystem. The ecological indicators were compared with other global estuaries, and the environmental indices were developed for the ME. Based on the ecological indices, the estuarine system is immature, moderately developed, and not well organized in terms of its ecological components. The study also indicates that an ecological approach would be more appropriate and essential in analyzing tropical transitional waters' health and sustainability. [ABSTRACT FROM AUTHOR]

In the present study, it was analyzed the structure of mesozooplankton community, and their spatio-temporal variations along the Caeté River estuary (northeast of Pará, Brazil). Samples were collected during spring tides conducted in nychthemeral cycles, in three fixed sectors located along the studied estuary (inner-S1, middle-S2 and outer-S3), using conical plankton nets of 200 μm mesh size. Samplings were performed in September 2014 (dry season) and March 2015 (rainy season), totaling 54 samples. A total of 25 mesozooplankton species were recorded, being the copepods the most diversified group (21 species), mostly dominated by estuarine and coastal species. The most abundant mesozooplankton species presented significantly higher densities (p <0.0001) between the middle (Pseudodiaptomus richardi , 583.8±956.5 ind m−3, Paracalanus quasimodo, 108.9±181.4 ind m−3 and Pseudodiaptomus acutus, 23.4±66.6 ind m−3) and outer (Acartia tonsa, 476.9±1,298.8 ind m−3 and Acartia lilljeborgii (407.9±1,038.1 ind m−3 and Parasagitta tenuis , 59.9±117.1 ind m−3) sectors. The non-metric multidimensional ordination analysis highlighted that the average density of the main species varied mainly at a spatial scale, with density increasing toward the mouth of the estuary (except for P. richardi). Spearman's correlation (rs) demonstrated that the salinity, turbidity, dissolved nutrients and chlorophyll a concentrations were the prevailing environmental variables associated with significant spatial changes of mesozooplankton distribution in this area. Overall, the results showed that spatial variation in the water physicochemical characteristics of the Caeté Estuary have significant effects on the structure and succession of the mesozooplankton, which may potentially affect the functioning and biodiversity of this coastal ecosystem. [ABSTRACT FROM AUTHOR]

The mouths of the rivers on the 1500-km-long Guianas coast, South America, are strongly influenced by large mud banks migrating alongshore from the Amazon River. To probe this influence, a river-mouth morphological classification scheme was carried out from satellite images, complemented by data from rare previous studies of estuarine hydrodynamics. The classification highlights a variety of morphological and dynamic river-mouth types that are further influenced by both fluvial water discharge and fluvial catchment rock type. Three basic types are identified: (1) river mouths diverted westward by capes and spits built from multi-decadal to multi-millennial accumulation of mud supplied by the Amazon; among these, mouths close to the Amazon are fixed by bedrock surrounded by mud; (2) small river mouths in French Guiana fixed by outcrops of Precambrian rocks that form headlands devoid of Amazon mud; and (3) large river mouths characterized by high water discharge that imparts an orientation normal to the coast; the largest two belonging to this type (the Essequibo in Guyana and the Maroni on the border between French Guiana and Suriname) exhibit infilled mouths that are transitioning towards deltas. These river mouths show a tropical seasonal estuarine circulation regime strongly influenced by Amazon mud. The influence of mud from the distant Amazon constitutes a unique aspect of the river mouths on the Guianas coast. Field and modelling studies in the future will be needed in order to achieve better characterization of the influence of Amazon mud on the estuarine circulation systems and of the distribution of sediment types within these river mouths, including sand supplied by the rivers. [ABSTRACT FROM AUTHOR]

A massive fish mortality of the major species, viz., Mugil cephalus, Chanos chanos , and Oreochromis mossambicus , occurred on November 27, 2017 in the Adyar estuary. This catastrophe followed a spell of heavy rainfall and flash floods. A detailed study of water quality parameters (pH, water temperature, salinity, total suspended matter, dissolved oxygen, biochemical oxygen demand, and nutrients) and heavy metals, i.e., chromium (Cr), copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), and zinc (Zn), in the sediment and fish tissues were analyzed. Pollution indices like the enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), potential ecological risk index (PERI), and biota sediment accumulation factor (BSAF) were used to measure heavy metals. The pollution indices revealed that metals were significantly enriched in the sediments. The Igeo indicates that there was moderate contamination by Cd (2.27–3.25), whereas CF shows high contamination by Cd (7.22–9.72) and moderate contamination by Pb (2.5–3.25). The PLI (1.04–1.13) suggests that heavy metal contamination of sediments has occurred. Results showed that high concentrations of the toxic metals Pb and Cd were found in the sediment as well as in fish tissues. Length and weight of fish are significantly correlated (r2 = 0.98, p < 0.05). The study revealed that the mass fish kill was due to impulsive changes in the water quality and heavy metal pollution from untreated urban sewage discharges in this region. • Factors related to fish kills in the tropical estuary are investigated. • Cd and Pb toxicity found in the sediment and fish tissue. • The proximate cause of fish kills was due to metal pollution. • Monitoring on a seasonal basis is required in coastal waters. [ABSTRACT FROM AUTHOR]

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 (N 2) 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. [Display omitted] • Functional gene array applied to marine sediment and water enables identification of functionally relevant N cycle genes • NosZ qPCRs for surface sediments show promise as a monitoring tool to differentiate the trophic status of sediments • Relative abundance of nitrogen cycling genes are responsive to nutrient status and sediment partition • N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Sediment In Benoa Bay was contaminated by microplastic. • Microplastics at Benoa Bay are dominated by secondary microplastics. • Strong positive correlation between the microplastic in sediment and water. • Landfill, rivers, and mariculture suspected as a source of microplastics. [ABSTRACT FROM AUTHOR]

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 mL21). 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 mL21) 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT 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.

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 [ABSTRACT FROM AUTHOR]

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp‐fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The family Ariidae, sea catfish of the order Siluriformes, is widely distributed throughout the world, particularly in tropical and subtropical areas. The three species of Ariidae found on the coasts and estuaries of West Africa are the smoothmouth catfish Carlarius heudelotii (Valenciennes 1840), the rough‐head catfish Carlarius latiscutatus (Günther 1864) and the Guinean sea catfish Carlarius parkii (Günther 1864). They have been increasingly exploited by artisanal and industrial coastal fisheries in recent decades, but there is still little information available on their ecology and biology. The aim of this study was to deepen our knowledge of these three West African Ariidae species based on a dataset collected between 1980 and 2013 during experimental fishing programmes. They were carried out in Mauritania in the Banc d'Arguin National Park, in Senegal in the Sine Saloum estuary including the Bamboung Marine Protected Area (MPA), in The Gambia in the Gambia estuary, in Guinea‐Bissau in the Urok Islands MPA in the Bijagos archipelago, in Guinea in the Fatala estuary and Dangara inlet, and in Côte d'Ivoire in the Ebrié Lagoon. C. latiscutatus accounted for 65%, C. parkii for 29% and C. heudelotii for 6% of total number of Ariidae sampled. C. latiscutatus was abundant in the Sine Saloum and Gambia estuaries as well as in Guinea and Guinea‐Bissau and was the only species present in the Ebrié Lagoon. C. parkii was in the majority in Mauritania. The three species were recorded in a salinity range of 0 to 50, a temperature range of 19 to 34°C, in areas 1.7 to 15 m depth, and transparency ranging from 0.1 to 4 m (Secchi disk depth). C. heudelotii was present in less saline (25 vs. 32–34), less warm (27 vs. 29°C) and less transparent (0.8 m vs. 1.6 m) waters than the two other species. The maximum sizes (453 mm, 614 mm and 525 mm for, respectively, C. heudelotii, C. latiscutatus and C. parkii) were comparable to those recorded at sea. Length–weight relationships calculated for each species showed b coefficients greater than 3. Sex ratios were always in favour of females. The number of mature individuals and their smallest size at maturity were calculated per species, sex and study area. A size of 27–28 cm at first maturity was estimated for females of C. latiscutatus. A few dozen records made it possible to describe fecundity and cases of oral incubation by females. The diet of the three species was composed of crustaceans, fish and molluscs, confirming their classification as generalist predators. Thanks to their high environmental tolerance, these sea catfish populations are able to occupy both the continental shelf and adjacent estuaries throughout their life cycle, with the exception of spawning, which generally takes place at sea. [ABSTRACT FROM AUTHOR]

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.

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. [Display omitted] • Surface water quality was investigated for Netravathi-Gurupur estuary, India. • Chemometric analysis indicated higher pollution load in Gurupur stretch. • Water quality index suggested fair to marginal quality for brackish water fisheries. • Study is useful to develop sustainable environmental and fisheries management plans. [ABSTRACT FROM AUTHOR]

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 −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.

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Phytoplankton play a fundamental role in marine food webs but are affected by both natural and anthropogenic fluctuations in environmental conditions. Here, to simulate a dynamic coastal environment, we used mesocosms to examine how different salinity levels and suspended solids concentrations (SSCs) impact a natural phytoplankton assemblage collected from a tropical estuary in Singapore. Significant differences in the phytoplankton composition between the baseline and treatments with medium and high SSC were found, but not among the three salinities tested. Differences can be attributed to nutrient limitation (particularly silicate) and the use of kaolinite for the suspended sediment. Silicate limitation is likely to have caused the observed switch in dominant genus from Skeletonema sp. to Chaetoceros sp. and the occurrence of weakly silicified genera such as Cylindrotheca. Kaolinite affected phytoplankton abundance through effects such as shading, flocculation, and nutrient adsorption. These results demonstrated how the combination of various physicochemical effects of suspended solids can influence tropical phytoplankton communities. Furthermore, as suspended solids such as kaolin can be found in the natural environment, this study showed that their potential effects should be evaluated beyond just their concentration. [ABSTRACT FROM AUTHOR]

In tropical estuaries, fish diversity varies spatially and temporally due to behavioral processes such as reproductive migrations, predator avoidance, and foraging, which are affected by water quality. Eutrophication is one of the main factors affecting water quality in estuaries. The objective of this study was to determine variation in fish assemblage explained by fluctuating water quality in the Buenaventura Bay. Fish were captured using artisanal trawl nets during the wet, dry, and transitional seasons at four sampling sites. Additionally, alkalinity; phosphate, nitrite, and nitrate concentrations; dissolved oxygen; pH; temperature; and suspended solids were measured. Multivariate analysis was used to assess the effect of water quality on fish assemblage. In Buenaventura Bay, the assemblage composition of Pseudupeneus grandisquamis, Daector dowi, and Citharichthys gilberti was affected by nitrate concentration. Moreover, large fish biomasses were associated with high nitrite concentration, intermediate salinity, and low dissolved oxygen, suggesting that these estuaries are dominated by species tolerant to poor water quality. Species richness was associated with low nitrate and phosphate concentrations, more suitable water quality indicators, and intermediate temperatures. These results suggest that the deteriorating water quality of estuaries as a result of the anthropogenic impact could increase dominance and decrease richness, resulting in structural changes of fish assemblages. [ABSTRACT FROM AUTHOR]