Microplastics ingestion in zooplankton in tropical estuarine fronts of Terengganu, Malaysia.

Tracing multi-anthropogenic inputs in intertidal mudflat sediments using lead and zinc isotopes.

Latitudinal patterns of food source assimilation and food-chain length in estuarine food webs.

A decade-long (2013-2023) study of the tropical Amba estuary revealed that abiotic parameters exhibited both spatial and temporal variability across the study period. A total of 134 taxa were identified, with polychaetes dominating the assemblage (> 65%). The numerically dominant species varied annually, with taxa such as Nephtys paradoxa, Capitella capitata, Namalycastis senegalensis showing temporal shifts in dominance, indicating species turnover. Multivariate analyses indicated pronounced spatio-temporal structuring, with salinity as the key driver of benthic distribution, consistent with other tropical estuaries. Although year-to-year shifts in dominating species were noted, the relatively stable long-term physico-chemical conditions from 2013 to 2023 clearly led to little temporal differences in species compositions, with most intermediate years remaining comparable. The estuarine ecological quality status using AZTI Marine Biotic Index (AMBI) was largely similar from 2013 to 2023, while it varied throughout the estuary, indicating spatial variability. This study provides the first long-term ecological analyses for any Indian estuary, emphasizing the role of salinity gradient and anthropogenic stressors in shaping macrobenthic communities. These findings underscore the need for sustained biomonitoring for pertinent conservation and management policies.

Zooplankton community structure and environmental responses revealed by in situ observations in the Ningyuan River estuary, Hainan Island.

Oil ingestion and genotoxic biomarkers in three swimming crab species (Decapoda, Portunidae) from tropical estuaries affected by oil spills.

Background: Estuarine and mangrove ecosystems are dynamic zones where microbial processes regulate nutrient cycling and water quality but are increasingly impacted by pollution and seasonal changes. An integrated assessment of physicochemical and microbial indicators is essential to understand water quality dynamics, especially in tropical estuaries like Can Gio. Aims: To assess organic pollution, microbial indicators, and surface water quality in the Can Gio estuary, Vietnam, and to compare their seasonal and spatial variation using previously published monitoring data. Study Design: Secondary analysis of an existing surface water quality dataset. Place and Duration of Study: Can Gio estuary, Ho Chi Minh City, Vietnam, using monitoring data collected at 14 sampling sites during the dry season (March 2023) and rainy season (September 2023). Methodology: Published numerical data from previous studies were reorganized and interpreted using descriptive statistics, graphical comparison, and a simple regression to examine the five-day biochemical oxygen demand (BOD5) - dissolved oxygen (DO) pattern. The assessed parameters included DO, BOD5, chemical oxygen demand (COD), ammonium (NH4+), nitrite (NO2-), phosphate (PO43-), total coliform, and Escherichia coli. Results: Water quality showed clear seasonal and spatial variation. BOD5 and COD were generally higher in the dry season, whereas DO tended to be slightly higher in the rainy season. Organic pollution was unevenly distributed among sampling sites, with several hotspots likely influenced by aquaculture, domestic wastewater, and other local human activities. Among nutrient variables, NO2- showed the clearest seasonal fluctuation, while NH4+ and PO43- varied less consistently. Microbial indicators remained high in both seasons, and E. coli fluctuated more strongly in the rainy season. The BOD5 - DO relationship at site scale was weak, indicating that DO was influenced not only by organic loading but also by hydrodynamic and environmental conditions. Conclusion: The Can Gio estuary is under pressure from mixed organic and microbial pollution, with the dry season being more sensitive to organic load accumulation. The study provides an integrated basis for water quality monitoring and management in tropical mangrove estuaries.

Introduction Dimethylsulfoniopropionate (DMSP) is a key marine organosulfur compound produced by phytoplankton and macroalgae that functions as an osmolyte, antioxidant, and precursor of dimethylsulfide (DMS)—a climate-relevant gas influencing the global radiation balance. Marine bacteria degrade DMSP through demethylation and cleavage pathways, driving the marine sulfur cycle. This study aimed to quantify DMS(P) concentrations and to isolate, identify, and characterize DMSP-degrading bacteria from the Cochin Estuary (CE), Kerala, India. Methods Surface water and sediment samples were collected from fifteen CE stations across three seasonal regimes (pre-monsoon, monsoon, and post-monsoon) between 2015 and 2018. DMS(P) levels were determined by alkali hydrolysis followed by gas chromatography with headspace sampling. Heterotrophic bacterial abundance was estimated by spread plating on Zobell’s Marine Agar. DMSP-degrading bacteria were isolated on DMSP-enriched minimal medium, and selected isolates were identified by 16S rRNA gene sequencing. PCR amplification was performed to detect DMSP lyase (Ddd) genes, and phylogenetic analyses were conducted using MEGA6. Results DMSP concentrations ranged from BDL to 0.15 ng/µL in water and 0.01 to 2.35 ng/µL in sediments, with higher values recorded during the pre-monsoon season. A total of 112 water and 211 sediment bacterial isolates were obtained, with Gram-negative strains dominating (70% in water and 64% in sediment). Sediments harbored higher bacterial counts than water. Four isolates capable of growing on DMSP-enriched medium were identified: Acinetobacter calcoaceticus, Acinetobacter beijerinckii, Bacillus cereus , and Lysinibacillus fusiformis . Amplification of the dddP gene was observed in A. calcoaceticus . Seasonal variations in salinity, temperature, and nutrient levels influenced DMS(P) distribution, with higher concentrations recorded in sediments. Discussion The findings confirm CE sediments as microbial “hotspots,” dominated by γ-Proteobacteria and Firmicutes—groups known for their significant roles in sulfur cycling. Hydrographic seasonality, particularly salinity fluctuations, shaped bacterial diversity and DMSP transformation patterns. The detection of DddP genes suggests active enzymatic cleavage pathways contributing to atmospheric DMS release. Conclusion This first baseline study on DMSP degradation in the CE highlights the ecological significance of estuarine sediments in sulfur cycling. The results enhance the understanding of microbial mediation of DMSP catabolism in tropical estuaries and its implications for climate regulation. Further research is warranted to elucidate additional catabolic pathways and environmental controls.

Objective – To identify the main aspects of adaptive capacity in relation to vulnerability, considering risks or exposure to environmental and anthropogenic threats in tropical estuaries, while highlighting key challenges and directions for environmental management and democracy in this ecosystem. Methodology – The first methodological stage consisted of a Systematic Literature Review, which enabled the identification, selection, and critical analysis of relevant studies on vulnerability, management, and environmental democracy in tropical estuaries. The second stage involved content analysis in order to categorize and interpret the main findings of the selected publications. Originality/relevance – This research addresses a theoretical gap concerning the integration of environmental democracy and territorial management in tropical estuaries, a topic still underexplored from a systemic and multi-scalar perspective. Furthermore, the articulation between these themes contributes to the advancement of knowledge in environmental public policy and the governance of complex coastal ecosystems such as estuaries. Results – Three main aspects were identified: (I) the importance of involving social actors in the creation of integrated and equitable environmental management; (II) the challenges of protecting estuaries, which require understanding their vulnerabilities at different spatial and temporal scales; and (III) the development of territorial management that incorporates efficient monitoring and modeling tools adapted to local (environmental and social) specificities. Theoretical/methodological contributions – The study highlights the significance of environmental democracy as a central element for socio-ecological resilience in tropical estuaries, emphasizing the need for the active participation of traditional communities in decision-making processes. Social and environmental contributions – Socially, the study promotes the recognition of traditional knowledge and the strengthening of community capacities for engagement in decision-making. Environmentally, the research offers pathways toward a management approach that is more sensitive to the ecological specificities of estuaries, fostering public policies that are more just, effective, and sustainable in the face of environmental vulnerabilities.

Environmental gradients drive the beta diversity of benthic macroinvertebrate communities in tropical estuaries

High-frequency monitoring reveals recurrent extreme events in a tropical estuary

Functional dynamics of fish assemblages in a tropical estuary during different phases of El Niño‒Southern Oscillation.

Population dynamics of Oikopleura dioica (Tunicata: Appendicularia) in a tropical estuary: Spatiotemporal patterns and environmental drivers

Bio-invasion and decadal changes in the trophic dynamics of a temporarily closed estuary: An Ecopath model from Veli-Akkulam Estuary, Kerala, India.

Historical PAHs contamination is well documented in urbanized estuaries; however, their dynamics in tropical ecosystems considered relatively preserved remain poorly investigated. This study reconstructs the historical deposition of PAHs in the Serinhaém Estuary, a tropical Environmental Protection Area in Northeastern Brazil, quantifying their concentrations, distinguishing their sources, and assessing the associated ecological risks. To achieve these objectives, five sediment cores were collected, dated using 210Pb geochronology, and analyzed by gas chromatography. Diagnostic ratios and multivariate statistical analyses were applied to identify contaminant sources and distribution patterns. The sedimentation rate was approximately 2.5±0.1mm·year-1. Results showed that cores C1 to C4 were dominated by high-molecular weight PAHs of predominantly pyrogenic origin, likely associated with regional biomass burning. In contrast, core C5, located downstream, displayed low concentrations with petrogenic signatures, suggesting inputs related to maritime activities. Core C3 exhibited the highest total concentration (Σ16PAHs=1508ng·g-1), with a pronounced peak in the early 2000s. In this layer, compounds such as fluoranthene (154.36ng.g-1), benzo[a]anthracene (138.55ng.g-1), chrysene (138.91ng.g-1), benzo[a]pyrene (153.86ng.g-1), and dibenzo[a,h]anthracene (42.64ng.g-1) exceeded threshold effect levels (TEL), indicating potential ecological risk. Multivariate analyses confirmed both vertical and lateral heterogeneity, highlighting specific episodes of increased contaminant input. Although overall concentrations ranged from low to moderate, distinct contamination events were identified, reflecting contributions from both diffuse and localized sources. These findings demonstrate that even legally protected estuaries remain vulnerable to anthropogenic pressures. Reconstructing sedimentary records proves essential for understanding the history of contamination and underscores the need for continuous monitoring to support effective conservation strategies.

Marine and freshwater pollution is a major environmentalconcern,yet the spatial extent of estuarine contamination in marine food websremains poorly understood. In this study, we sampled blood from piscivorouswaterbirds (15 species, 316 individuals) along a gradient from estuariesin southeastern Brazil to the nearshore and offshore southwesternAtlantic Ocean to assess trace element concentrations and the influenceof habitat and trophic position on the basis of stable isotopes ofcarbon, nitrogen, and sulfur. All nonessential trace elements (arsenic,cadmium, lead, and mercury) were inversely related to sulfur isotopevalues (δ34S) and decreased along the estuarine–openocean gradient. Conversely, most essential elements (chromium, copper,and manganese) were positively correlated with δ34S, suggesting an increase from estuarine to oceanic waters. Nonessentialtrace elements in estuarine birds were above the benchmarks of toxicityestablished for bird species, suggesting potential health impairmentdue to trace element contamination associated with freshwater inputs.In addition, the lower concentrations of essential elements in estuarinebirds may suggest interference in metal homeostasis caused by highconcentrations of nonessential elements. Assessments combining multipletrace elements and stable isotopes, particularly sulfur, remain rareover large spatial scales. Across this broad environmental gradient,stable sulfur isotopes proved to be efficient markers of bird habitatsfor assessing spatial patterns in trace element contamination in aquaticfood webs.

Abstract This study documents an ecotoxicological evaluation of bottom sediments ( n = 21) from a tropical lagoon complex performed in the Itaipu-Piratininga system (Rio de Janeiro State), an impacted urban tropical estuary. To achieve this purpose, three lines of evidence were adopted: sediment characterization, metal contamination and toxicity to tropical species (bioassays with mussels Perna perna , tanaids Kalliapseudes schubartii , amphipods Tiburonella viscana , and microalgae Cylindrotheca closterium) . The sediments from Piratininga lagoon were muddier and more organically enriched than those from Itaipu lagoon, once only the last one is influenced by an active connection with the ocean. Sediment texture and organic matter played a crucial role in metal distribution, but contaminated river mouths and the canal connecting the lagoons presented elevated Zn, Cu, Cd, Cr, Ni and P concentrations, which seem to be linked to domestic sewage discharges and other anthropic wastes. In addition, Pb and Mo hot spots were associated with an embayment area in Piratininga lagoon. Mussel embryo-larval development was 100% abnormal for all the samples. Although almost all the samples were toxic to tanaids and amphipods, tanaid mortality (mean ± SD = 76.4 ± 23.6%) was significantly higher than amphipod one (56.3 ± 20.4%). Inhibition of algae reproduction was the endpoint of lower concern (31.1 ± 26.5%). The toxicity was especially higher in river mouths and in the canal that connects the lagoons, being significantly correlated with sewage-related pollutants (Zn, Cu and P). Finally, although spatial variability of the toxicity has been explained by metal pollution along the lagoons, other toxicants should also be considered as stressors.

This study investigated the distribution, geochemical fractions, bioavailability, mobility, sources, and ecological risks of heavy metals (Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb) in the sediments of the highly urbanized tropical (Netravathi-Gurupur) estuary, India. he estuary sediment pollution was evaluated using enrichment factor (EF), geoaccumulation index (Igeo), sediment quality guidelines, risk assessment code (RAC), individual and global contamination factors (ICF and GCF), bioavailability indices (BI and BIT), mobility index (MI), and potential ecological risk factor of individual heavy metal (MEr). The EF and Igeo results identified Cu as the primary contaminant. Bioavailable metal concentrations of Ni and Cu frequently exceeded threshold effect level, effect range low and probable effect level values. However, Cd contributed the most to the overall ecological risk due to the dominance of the acid-soluble fraction of Cd and its enrichment in surface sediments. The potential ecological toxicity of Cd was further supported by multiple ecological risk indices (RAC, IFC, BI, MI and MEr). Source identification using dual hierarchical cluster analysis clearly separated the Gurupur stretch from Netravathi stretch and indicated common anthropogenic sources for the labile fractions of Zn, Cu, Cr, Cd, and Pb. Overall, the study suggests that metal fractionation and bioavailability provide a more realistic assessment of ecological risk than total metal concentrations alone. The findings emphasize the need for targeted pollution control and continuous monitoring programs to ensure sustainable management and ecological protection of the estuarine system.

Abstract. Takarina ND, Azzahrah RM, Budianto LW, Soelias NJ, Anwar MZ, Samudra YR, Akhmad AAA. 2026. Seasonal impacts of microplastic contamination on benthic species using CMPI and PLI indices at Karangsong Estuary, West Java, Indonesia. Biodiversitas 27 (1): d270125. https://doi.org/10.13057/biodiv/d270125. Benthic species play a crucial role in estuarine environments. While there is ongoing research on microplastics, information regarding the seasonal variation of microplastics in benthic species remains limited. This study explores the impact of seasonal variation (wet and dry seasons) on microplastic contamination in two representative benthic species at the Karangsong Estuary in West Java, Indonesia. The samples were collected from nine sampling sites in the Karangsong Estuary, with a total of two benthic species and 27 individuals sampled. After a microplastic extraction procedure, Raman Spectroscopy was utilized to identify the microplastic polymers. During the wet season, the predominant types of microplastics found in both Telescopium telescopium and Metaplax longipes are fragments, pellets, and fibers, in that order. The results showed that total microplastic abundance was significantly higher during the wet season than the dry season (χ² = 9.108, p = 0.002), with M. longipes consistently accumulating more microplastics than T. telescopium. During the wet season, microplastic fragments dominated in both species, reaching 0.37 particles g⁻¹ wet mass in T. telescopium (95% CI: 0.06-0.74) and 107.18 particles g⁻¹ wet mass in M. longipes (95% CI: 0-256.00). In contrast, fibers were more prevalent in the dry season, particularly in M. longipes (18.78 particles g⁻¹ wet mass; 95% CI: 6.60-32.80). According to the Comprehensive Microplastics Pollution Index (CMPI), fragments were extremely dominant in M. longipes during the wet season (CMPI = 0.984), while fibers were dominant in T. telescopium during the dry season (CMPI = 0.638). Pollution Load Index (PLI) values for all shapes remained within the low contamination category. Polymer analysis indicated that polyethylene terephthalate (PET) and polyethersulfone (PES) were the dominant polymers in T. telescopium, whereas polypropylene (PP) was most frequently associated with M. longipes. Differences likely influence seasonal variation in microplastic contamination in rainfall, tidal dynamics, surface runoff, and fishing activity between seasons. Although this study is limited by sample size, estuarine coverage, and the use of Raman spectroscopy for polymer identification, the findings highlight clear seasonal patterns in microplastic contamination. These results underscore the importance of season-specific management strategies and support the potential use of M. longipes as a sensitive bioindicator for microplastic pollution in tropical estuaries.

We conducted a high-resolution analysis of diatom populations in the microphytoplankton size range using data collected at 30-min intervals over a 20-month period by an automated imaging system deployed near the mouth of Baía de Todos os Santos (BTS), Brazil. Seven diatom taxa were identified and quantified through automated classification using a Convolutional Neural Network (CNN). Frequency-domain analysis revealed distinct environmental drivers acting across different temporal scales. At high-frequency scales (<53h), solar radiation was the predominant factor influencing diatom abundances. At intermediate to monthly scales (53h-13 days, neap-spring cycles of 13-15 days, and monthly scales), canonical correspondence analysis (CCA) indicated that dissolved oxygen, temperature, and salinity were the primary environmental drivers. Multiple linear regression (MLR) models highlighted colored dissolved organic matter (CDOM) and the north-south wind component as key predictors for Coscinodiscus wailesii abundances. K-strategist marine taxa, including Rhizosolenia robusta and the Rhizosolenia-Proboscia complex, exhibited peak densities during neap tides, coinciding with stronger intrusion events of oligotrophic oceanic waters into the bay. Conversely, r-strategist coastal and estuarine taxa, including C. wailesii, Bacteriastrum-Chaetoceros complex, and Guinardia striata, reached maximum abundances during spring tides, associated with enhanced river discharge and pronounced ebb flow conditions. These taxon-specific distribution patterns demonstrate the influence of environmental forcing across multiple temporal scales on diatom populations. Our findings show the effectiveness of frequency-domain analytical approaches in resolving the complex interactions between environmental variability and phytoplankton dynamics, enhancing understanding of bottom-up regulatory processes and inter-taxa ecological interactions in coastal tropical ecosystems.