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Based on the results of survey on estuarine ecosystem conducted from 2021 to 2023, this study analyzed the distribution pattern of invasive alien species. A total of six invasive alien species (Micropterus salmoides [M. salmoides], Lepomis macrochirus [L. macrochirus], Lithobates catesbeianus [L. catesbeianus], Trachemys scripta [T. scripta], Pseudemys concinna [P. concinna], and Pseudemys nelsoni [P. nelsoni]) were identified across 118 estuarine wetlands. The survey revealed 960 individuals of M. salmoides, 2,596 individuals of L. macrochirus, 1,088 individuals of L. catesbeianus, and 44 individuals of T. scripta, while 1 individual of P. concinna and P. nelsoni were found. These invasive species were found to be densely distributed in estuarine wetlands in the Haenam and Goheung regions of the southern coast. Furthermore, the distribution density varied depending on the characteristics and locations of the estuarine wetlands. It was observed that the distribution density was higher in closed type than in open type, in riverine than in lacustrine, and in the south coast than in the east coast. Once the basic survey of estuarine wetlands located on the west coast is completed, a clearer understanding of the nationwide distribution characteristics of invasive alien species in estuarine wetlands can be achieved. This information will be crucial for formulating appropriate management strategies tailored to the characteristics of wetlands or coastal areas in the future.

With global surge in reservoir construction over the past decades, river systems worldwide have been profoundly fragmented. Consequently, flow manipulation by reservoirs has altered the natural hydrological processes, resulting in extensive modifications of fluvial-marine ecosystems. Mitigating the adverse ecological consequences of reservoirs has become a global concern and has garnered increasing attention. The Yellow River, as one of the most extensively manipulated river systems globally, has experienced substantial changes in the amount and timing of water discharge due to the presence of numerous reservoirs scattered throughout its catchment area. These alterations have caused physicochemical changes in the estuary and subsequent modifications to the estuarine ecosystem. In recent years, the Yellow River Conservancy Committee initiated the release of water through the Xiaolangdi Dam during the major spawning period of fisheries, specifically in the spring, with the aim of improving the estuarine ecological environment. From 2011 to 2020, a total of 84.05 km3 of water was discharged from the Xiaolangdi Reservoir during spring seasons, of which 40% (33.16 km3) constituted water impounded within the reservoir during preceding months. Correspondingly, the spring water discharge from the Yellow River to the sea increased significantly from 1.50 km3/yr to 3.46 km3/yr in the past decade, leading to a decrease in estuarine salinity by 1.6 PSU. The estuarine fishery resources, such as fish eggs in the Yellow River estuary, have demonstrated evident improvement. The reservoir regulation in the Yellow River, which has successfully enhanced spring water discharge and subsequently restored estuarine fishery resources, presents an effective attempt for mitigating the adverse ecological effects associated with reservoirs. [ABSTRACT FROM AUTHOR]

A 10‐year monitoring program was developed to quantify the population dynamics of the long‐snouted seahorse population in the Mar Menor coastal lagoon. Based on 985 underwater visual censuses, we estimated the long‐snouted seahorse (Hippocampus guttulatus Cuvier, 1829) population size in the Mar Menor lagoon and its reduction in size in the last decades, as well as the effect of eutrophication crises in 2016 and 2019 on the species. The annual recruitment for the 2013–2020 period was estimated by comparing the relative abundance of early seahorse life stages in the ichthyoplankton. The density ranged from 0.0458 specimens/m3 at the beginning of the sampling period to 0.0004 at the end, showing a statistically significant difference between the three analyzed periods (Hgl=2 = 14.0, p = 0.001). The long‐snouted seahorse population from the Mar Menor lagoon exemplifies the impact of fishing activities and human pressure, especially euxinic episodes and habitat destruction. As a result of this, the Mar Menor population has decreased from several million specimens to a few thousand, in only three decades. This species showed considerable resilience, the seahorse population began to recover once fishing activity stopped. In contrast, the long‐snouted seahorse showed high vulnerability to habitat loss and an episodic flooding event. Adult seahorses showed preferences for highly complex habitats, especially Caulerpa prolifera–Cymodocea nodosa mixed meadows and habitats of high complexity and anthropogenic origin, such as harbors, jetties, or breakwaters. In contrast, juvenile seahorses preferred monotonous seabeds with low complexity, such as the sandy beds that are characteristic of the Mar Menor lagoon littoral. [ABSTRACT FROM AUTHOR]

Abstract Background Archaea are key mediators of estuarine biogeochemical cycles, but comprehensive studies comparing archaeal communities among multiple estuaries with unified experimental protocols during the same sampling periods are scarce. Here, we investigated the distribution, community assembly, and cross-domain microbial co-occurrence of archaea in surface waters across four major estuaries (Yellow River, Yangtze River, Qiantang River, and Pearl River) of China cross climatic zones (~ 1,800 km) during the winter and summer cruises. Results The relative abundance of archaea in the prokaryotic community and archaeal community composition varied with estuaries, seasons, and stations (reflecting local environmental changes such as salinity). Archaeal communities in four estuaries were overall predominated by ammonia-oxidizing archaea (AOA) (aka. Marine Group (MG) I; primarily Nitrosopumilus), while the genus Poseidonia of Poseidoniales (aka. MGII) was occasionally predominant in Pearl River estuary. The cross-estuary dispersal of archaea was largely limited and the assembly mechanism of archaea varied with estuaries in the winter cruise, while selection governed archaeal assembly in all estuaries in the summer cruise. Although the majority of archaea taxa in microbial networks were peripherals and/or connectors, extensive and distinct cross-domain associations of archaea with bacteria were found across the estuaries, with AOA as the most crucial archaeal group. Furthermore, the expanded associations of MGII taxa with heterotrophic bacteria were observed, speculatively indicating the endogenous demand for co-processing high amount and diversity of organic matters in the estuarine ecosystem highly impacted by terrestrial/anthropogenic input, which is worthy of further study. Conclusions Our results highlight the lack of common patterns in the dynamics of estuarine archaeal communities along the geographic gradient, expanding the understanding of roles of archaea in microbial networks of this highly dynamic ecosystem.

Background: Archaea are key mediators of estuarine biogeochemical cycles, but comprehensive studies comparing archaeal communities among multiple estuaries with unified experimental protocols during the same sampling periods are scarce. Here, we investigated the distribution, community assembly, and cross-domain microbial co-occurrence of archaea in surface waters across four major estuaries (Yellow River, Yangtze River, Qiantang River, and Pearl River) of China cross climatic zones (~ 1,800 km) during the winter and summer cruises. Results: The relative abundance of archaea in the prokaryotic community and archaeal community composition varied with estuaries, seasons, and stations (reflecting local environmental changes such as salinity). Archaeal communities in four estuaries were overall predominated by ammonia-oxidizing archaea (AOA) (aka. Marine Group (MG) I; primarily Nitrosopumilus), while the genus Poseidonia of Poseidoniales (aka. MGII) was occasionally predominant in Pearl River estuary. The cross-estuary dispersal of archaea was largely limited and the assembly mechanism of archaea varied with estuaries in the winter cruise, while selection governed archaeal assembly in all estuaries in the summer cruise. Although the majority of archaea taxa in microbial networks were peripherals and/or connectors, extensive and distinct cross-domain associations of archaea with bacteria were found across the estuaries, with AOA as the most crucial archaeal group. Furthermore, the expanded associations of MGII taxa with heterotrophic bacteria were observed, speculatively indicating the endogenous demand for co-processing high amount and diversity of organic matters in the estuarine ecosystem highly impacted by terrestrial/anthropogenic input, which is worthy of further study. Conclusions: Our results highlight the lack of common patterns in the dynamics of estuarine archaeal communities along the geographic gradient, expanding the understanding of roles of archaea in microbial networks of this highly dynamic ecosystem. [ABSTRACT FROM AUTHOR]

Recruitment of estuarine organisms can vary dramatically from year to year with abiotic and biotic conditions. The San Francisco Estuary (California, USA) supports a dynamic ecosystem that receives freshwater flow from numerous tributaries that drain one of the largest watersheds in western North America. In this study, we examined distribution and habitat use of two forage fish larvae of management interest, Longfin Smelt Spirinchus thaleichthys and Pacific Herring Clupea pallasii, during a low-flow and a high-flow year to better understand how their rearing locations (region and habitat) may affect their annual recruitment variability. During the low-flow year, larval and post-larval Longfin Smelt were distributed landward, where suitable salinity overlapped with spawning habitats. During the high-flow year, larval Longfin Smelt were distributed seaward, with many collected in smaller tributaries and shallow habitats of San Francisco Bay. Local spawning and advection from seaward habitats were speculated to be the primary mechanisms that underlie larval Longfin Smelt distribution during the high-flow year. Larval Pacific Herring were more abundant seaward in both years, but a modest number of larvae were also found landward during the low-flow year. Larval Pacific Herring abundance was lower overall in the high-flow year, suggesting advection out of the area or poor recruitment. Future monitoring and conservation efforts for Longfin Smelt and Pacific Herring should recognize that potential mechanisms underlying their recruitment can vary broadly across the San Francisco Estuary in any given year, which suggests that monitoring and research of these two species expand accordingly with hydrologic conditions that are likely to affect their spawning and larval rearing distributions.

This study evaluated metal contamination in surface sediments and macroalgae of mangroves and port complexes on the Brazilian equatorial margin. Samples were collected between August 2020 and February 2021 at seven points in a mangrove swamp under the influence of port activity and at two points without port activity. Metal concentrations in the macroalgae and sediments were determined using inductively coupled plasma‒optical emission spectrometry. All macroalgal species bioaccumulated metals, as demonstrated by their bioaccumulation factors. The geochemical contamination indices indicated that the estuarine complex was influenced by port activity as moderately contaminated by Pb, Cr, Mn, and Fe and considerably contaminated by Zn and Cu. The enrichment factor confirmed significant mineral enrichment of Zn and Cu in this environment. The concentrations of the metals in the sediment followed the order Fe > Mn > Cr > Zn > Cu > Pb at most sampling points. Cladophoropsis membranacea recorded the highest bioaccumulation values for Pb (0.44), Rhizoclonium africanum for Zn (1.08), Cr (0.55), and Fe (0.30), and Bostrychia radicans for Mn (2.22). The bioaccumulation pattern of metals in the most abundant macroalgal species followed the order Bostrychia radicans (Mn > Zn > Cu > Cr > Pb > Fe) and Rhizoclonium africanum (Zn > Mn > Cr > Cu > Pb > Fe). [ABSTRACT FROM AUTHOR]

If this is the case, restoration and conservation of these threatened oyster reefs may enhance ontogenetic movement opportunities for the species by providing key juvenile habitats, which could further aid in the long-term stability and protection of blue groper populations. Conservation, demography, life history, recruitment, charismatic megafauna, estuarine ecosystem, intertidal reef, temperate reef, threatened species This observation of an iconic and threatened species using threatened oyster reefs as a juvenile habitat is significant, not only because it enhances our understanding of I A. viridis i and their ontogenetic movement, but because of the opportunity that this presents for the engagement and funding of ongoing and future oyster reef restoration projects. Keywords: charismatic megafauna; conservation; demography; estuarine ecosystem; intertidal reef; life history; recruitment; temperate reef; threatened species EN charismatic megafauna conservation demography estuarine ecosystem intertidal reef life history recruitment temperate reef threatened species 1 5 5 12/05/22 20221201 NES 221201 Understanding the life cycle and the demography of individual species is critical for the management of threatened populations and integral to understanding the ecology of various ecosystems and habitats (Kimirei et al., [11]; Perez & Munch, [15]). [Extracted from the article]

Society's interest in rare earth elements (REEs) and their increasing use in many fields is leading to enrichments in aquatic environments, such as estuaries. This study of the Seine estuary assessed the distribution of REEs along the food web, including different species from 5 phyla representing different trophic levels. Total REE concentrations, which were higher in algae, mollusks, crustaceans and annelids (4.85–156; 1.59–4.08; 2.48 ± 1.80 and 0.14 ± 0.11 μg/g dw, respectively) than in vertebrates (0.03–0.15 μg/g dw), correlated with δ15N indicated a trophic dilution. REE contributions in the studied species were higher for light REEs than for heavy and medium REEs. Positives anomalies for Eu, Gd, Tb and Lu were highlighted particularly in vertebrates, possibly due to species-dependent bioaccumulation/detoxification or related to anthropogenic inputs. The calculated BAF and BSAF indicated an important partitioning of REEs in organisms compared to the dissolved phase and a limited transfer from sediment to organisms. [Display omitted] • REEs were subjected to trophic dilution along the food web. • All studied species showed similar REE contribution: LREEs > HREEs > MREEs. • Eu, Gd, Tb and Lu positive anomalies were reported especially in vertebrates. • BSAF results showed a limited transfer of REEs from sediment to biota. • REE bioaccumulation was higher in gonads than in muscles of fish. [ABSTRACT FROM AUTHOR]

Phytoplankton is an important primary producer of the estuarine ecosystem, which is essential for the biogeochemical cycle of water elements and nutrient transfer. The Pearl River estuary (PRE) is a dynamically complex estuary, and the environment of PRE is significantly impacted by anthropogenic activities, variation of phytoplankton community structure in the PRE are complex. This review aims to compare phytoplankton species, species diversity, and abundance variation characteristics from the 1980s and 2020s, evaluate the overall trend of phytoplankton in the PRE, and discuss the main environmental factors affecting phytoplankton growth in the PRE. The data from the past 40 years in PRE showed that the number of phytoplankton species significantly decreased (p < 0.05). There was no significant difference in the abundance of phytoplankton at the 10-year scale, however, the fluctuation range of the abundance has increased. Under the conditions of a decreasing species number and no significant difference in abundance, the species diversity of phytoplankton showed a downward trend. In addition, the dominant phytoplankton species in the nearshore waters were relatively homogenous, and the abundance of phytoplankton in the nearshore waters was higher than that in the open waters, which suggested that human activities have a great influence. This review can form the basis for facilitating health management in the PRE ecosystem. Further, relevant guidelines can be developed and implemented for promoting the ecological health of the Guangdong-Hong Kong-Macao Greater Bay Area and ensuring its sustainable development.

Estuarine ecosystems interconnect freshwater and marine environments, and comprise multiple highly dynamic and complex microhabitats. The resident microbiota in estuary is influenced by contrasting microenvironmental heterogeneity. However, the bacterial patterns and assembly processes in different microhabitats of estuarine ecosystem are not well studied. Here, we investigated the bacterial diversity, functions and community assembly mechanisms of mangrove soil, river sediment and overlying water in a subtropical estuary. Results showed that similar profiles of bacterial communities existed in the mangrove soil and river sediment and were dominated by Proteobacteria, Bacteroidetes and Acidobacteria. In terms of different microhabitats, the lowest alpha diversity of bacterial communities was found in overlying water and were dominated by Proteobacteria, Actinobacteria and Bacteroidetes. Meanwhile, the functional potential genes associated with carbon metabolisms were also substantially different in the three microhabitats. The relative abundance of genes connected to aerobic carbon respiration was significantly higher in overlying water than in the other two microhabitats. Bacterial communities in river sediments were enriched for genes associated with aerobic methane oxidation. The strong environmental heterogeneity of the three nearby microhabitats shaped the taxonomic and functional composition of the bacterial communities in estuarine ecosystem. Moreover, the plant rhizosphere effect increased the proportion of the dispersal limitation processes in mangrove soils compared to that in river sediments, while the overlying water was fluid and had less environmental selection processes compared to that in mangrove soil and river sediment. The bacterial communities in river sediment construct a more clustered network, while the overlying water network showed the highest complexity. Our findings reveal the differences of bacterial patterns and community assembly mechanisms in distinct microhabitats of estuarine ecosystems, and provide important insights for a comprehensive understanding of the mechanisms to maintain estuarine wetland conservation under environmental changes.

The tropical mangrove at the Estação Ecológica do Lameirão (Southeastern Brazil), an ecosystem of high socio-economic value, receives a large load of pollutants from domestic, industrial, and agricultural sources. Samples of interstitial water, sediments, and crustacean specimens were collected at different periods and regions throughout the study area to measure the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and tin (Sn) along the mangrove, as well as the bioaccumulation behavior in the crab Ucides cordatus. Subsequently, we correlated the accumulation of metals in U. cordatus with the concentrations of metals in the environment and physicochemical and climatic factors. Furthermore, we compared the bioconcentration factors (BFCs) of trace elements with the concentration levels obtained from the mangrove sediment. The fluctuation of rain and tide throughout the study period caused oscillations in the concentrations of trace elements. This condition induced bioconcentration records (BFC > 1), influencing the bioaccumulation trend in U. cordatus. We also identified that the lowest metal concentration values in the sediment were close to the river, indicating that the rivers cause a dilution effect. Finally, we found that the hepatopancreas had the highest levels of bioaccumulated heavy metals, explained by its detoxifying ability. In females of U. cordatus, we found a slightly lower accumulation of trace elements when compared to males, possibly related to the high rate of ecdysis in females. Ucides cordatus is a species widely used for human consumption. Our results show that the mangrove environment influences the concentration of trace elements in this organism, which the authorities should consider in mapping safer fishing areas. [ABSTRACT FROM AUTHOR]

This study assesses MP in water, sediment, gills, and digestive tract of the oyster Magallana gigas in three Bahía Blanca estuary sites, Argentina, using, Pollution Load Index (PLI) and SEM/EDX (Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy) and FTIR (Fourier-transform infrared spectroscopy) techniques. A total of 51 MPs were detected in water (mean: 16 items L -1 ) and 126 in sediments (mean: 1399 items Kg -1 ) with no significant differences between sites. In oysters, 186 MPs were found, with no significant differences in the MPs load between gills (mean: 2.41 items g -1 w.w), digestive tract (2.06 ± 2 items g -1 w.w), and the total tissues. Transparent fiber MPs were predominant, with cellulose, polyamides, polyethylene terephthalate and polyethylene being common polymers. SEM/EDX showed Si, Fe, Cl, Na, Ti, Al, K, Ca and suspended particulate matter on MP surfaces. The PLI indicated a low-risk level for estuary bivalves and water, suggesting minimal MPs impact., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The identification and monitoring of essential fishery habitat (EFH) is primary and important for the conservation of estuarine fishery habitat and sustainable fisheries management. However, mapping EFH of estuarine fishery species with generally statistical species distribution model (SDM) remains difficult due to their complex life histories and the extensive spatiotemporal variability of habitat variables. Thus, we proposed a mechanistic SDM by analyzing a more direct and certain relationship at a pre-selected suitable life stage with prior knowledge of species life history, not a rough statistical analysis of overlapping cause–effect relationships operating across multiple life history stages in reverse. Landsat data was used to describe the extensive spatiotemporal variability of estuarine habitat variables. A window filtration was contributed most to select the suitable life stage with a score scheme. As mapping EFH needs to feasibly locate the representative and essential habitats over large estuarine scale, we constructed two indicators to represent “habitat importance” and “descriptor predictability” in the score scheme, which was semi-quantified with three primary factors (habitat function, duration of life history stage, inversion limitation of critical descriptors from Landsat data). Through selecting the suitable life stage for the mechanistic SDM, the usage of Landsat archives could be extended, which is beneficial from a few optically / thermally active determinants. The applicability of the mechanistic SDM was tested by mapping EFH of Eriocheir sinensis in the Yangtze River Estuary (YRE), China. The window filtration of E. sinensis’ life history stages in the YRE showed that the berry stage was filtered as the suitable stage with the highest scores both in habitat importance and descriptors predictability. Then the distribution of E. sinensis was modelled, predicated, and assessed at berry stage by comparing outward in a generally statistical way and inward with other filter window. The mechanistic model at berry stage showed the best explanatory and predictive power in both occurrence and abundance models, validating that the optimized SDM had much stronger capability in model fit and prediction. The score scheme was also verified to set reasonably and effectively through the model comparisons at different filter window stages. With the predicated distribution of E. sinensis, the core ranges of EFH were mapped at berry stage, which were mostly distributed in sub-tidal areas neighbored to wetlands, showing the habitat requirement of shallow water for hiding. Meantime, the determinants’ variance partitioning, in which dissolved oxygen (DO) and total suspended sediment (TSS) exceeded over 65%, complementally illustrated that core EFH may also require high water quality. The identification of EFH locations with our mechanistic SDM would provide spatial-explicit information and guidance to fishery habitat protection and fishery resources maintenance. Additionally, this study also explored a new way to utilize a few predictors from the extensively used Landsat data in an alternative way. This study could extend the limitations of SDM in EFH mapping and bridge gaps between spatiotemporal explicit modelling and remote sensing data accommodations, which is meaningful for fishery habitat conservation.

The Paraiba River estuary is the largest and most important estuary of Paraiba state, northeastern Brazil. It is under intense environmental degradation by the surrounding human population, and possibly several fish species are at risk in this habitat. Scientific sampling of the ichthyofauna started in the late 1970's and proceeded until recently. We present a list of fish species captured in this estuary, based on voucher specimens housed at the Federal University of Paraiba collection. Four orders of Chondrichthyes and 26 orders of Osteichthyes were identified. A total of 187 fish species, including eight species of Chondrichthyes and 179 Osteichthyes, with 123 genera and 57 families were identified. Perciformes dominated in terms of richness (32 species), followed by Acanthuriformes and Clupeiformes. Comparing estuaries along the Brazilian northeastern coast and considering our large time sampling span, a higher richness would be expected. According to the IUCN Red List, Urotrygon microphthalmum is considered Critically Endangered and more seven species are classified as Vulnerable: Rhizoprionodon porosus, Rhinoptera bonasus, Megalops atlanticus, Epinephelus itajara, Hyporthodus niveatus, Lutjanus cyanopterus, and Cynoscion acoupa. Three of these species also appear in the same category in the threatened Brazilian list, all of which have declining population trends. Concerning the Elasmobranchii, Carcharhinus porosus is listed as Critically Endangered in our country and globally. This inventory organizes and broadens knowledge on the fish community that occurs in this important ecosystem, with inferences about life habits, ecological guilds and conservation status of the fish species. [ABSTRACT FROM AUTHOR]

Context: Zooplanktivorous fish are a key link between abundant zooplankton and higher trophic levels but the foraging behaviour of zooplanktivorous fish is not fully understood. Selective feeding behaviours have been observed, with many species of planktivorous fish targeting certain species and sizes of zooplankton for prey. However, why certain size classes of zooplankton are preferred remains unclear. Aim: This study investigated prey selection by three zooplanktivorous fish species through the lens of optimal foraging theory. Methods: We assessed the size structure of zooplankton in the environment and compared this with the size distribution of zooplankton in gut contents from three zooplanktivorous fish. Key results: The targeted prey size of Atypichthys strigatus and Scorpis lineolata aligns with the prey size classes in the environment that contain the highest overall biomass. Trachurus novaezelandiae showed little evidence of targeting these size classes. Conclusions: These prey sizes therefore represent the most efficient prey to target because the return on foraging effort is greatest. By contrast, T. novaezelandiae showed only an underselection of large and small prey. Implications: By incorporating this information on this key trophic link between zooplankton and fish, ecosystem models could better resolve the size dependant predation, particularly in size-based models. This paper shows that 2 of 3 species of estuarine fish target specific sizes of zooplankton rather than eating everything they encounter. This pattern is driven by the fish attempting to maximise the biomass consumed by targeting the zooplankton size classes with the most overall biomass in the environment. [ABSTRACT FROM AUTHOR]

Redigobius is a genus of goby fish belonging to order Gobiiformes. Redigobius is currently represented by 15 species worldwide of which Redigobius bikolanus is a widespread species. This species was recorded previously from Middle Andaman Island in 2002. There was not a single evidence of the species after that time, from Indian region. Recently, during a faunal survey in great Nicobar Island resulted in collection of a R. bikolanus for the first time and proving evidence for range extension of the same from Nicobar group of Islands. The species was collected from one of the estuarine creeks of Great Nicobar island. Details of the morphological data, live colouration and wild habitat are provided for the new record.

Planktonic microorganisms in aquatic ecosystems form complex assemblages of highly interactive taxa and play key roles in biogeochemical cycles. However, the microbial interactions within bacterial and microeukaryotic communities, and the mechanisms underpinning the responses of abundant and rare microbial taxa to environmental disturbances in the river estuary remain unknown. Here, 16S and 18S rRNA gene sequencing were used to investigate the compositional changes and the co-occurrence patterns of bacterial and microeukaryotic communities. The results showed that the rare taxa in the bacterial communities were more prevalent than those in the microeukaryotic communities and may influence the resilience and resistance of microorganisms to environmental variations in estuarine ecosystems. The environmental variations had strong effects on the microeukaryotic communities and their assembly mechanisms but not on the bacterial communities in our studied area. However, based on co-occurrence network analyses, the bacterial communities had stronger links and more complex interactions than microeukaryotic communities, suggesting that bacterial networks may help improve the buffering capacities of the estuarine ecosystem against environmental change. The keystone taxa of bacteria mainly belonged to rare subcommunities, which further illustrates that rare taxa may play fundamental roles in network persistence. Overall, these results provide insights into the microbial responses of aquatic ecosystems to environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) integrated with metabarcoding is a promising and powerful tool for species composition and biodiversity assessment in aquatic ecosystems and is increasingly applied to evaluate fish diversity. To date, however, no standardized eDNA-based protocol has been established to monitor fish diversity. In this study, we investigated and compared two filtration methods and three DNA extraction methods using three filtration water volumes to determine a suitable approach for eDNA-based fish diversity monitoring in the Pearl River Estuary (PRE), a highly anthropogenically disturbed estuarine ecosystem. Compared to filtration-based precipitation, direct filtration was a more suitable method for eDNA metabarcoding in the PRE. The combined use of DNeasy Blood and Tissue Kit (BT) and traditional phenol/chloroform (PC) extraction produced higher DNA yields, amplicon sequence variants (ASVs), and Shannon diversity indices, and generated more homogeneous and consistent community composition among replicates. Compared to the other combined protocols, the PC and BT methods obtained better species detection, higher fish diversity, and greater consistency for the filtration water volumes of 1 000 and 2 000 mL, respectively. All eDNA metabarcoding protocols were more sensitive than bottom trawling in the PRE fish surveys and combining two techniques yielded greater taxonomic diversity. Furthermore, combining traditional methods with eDNA analysis enhanced accuracy. These results indicate that methodological decisions related to eDNA metabarcoding should be made with caution for fish community monitoring in estuarine ecosystems. [ABSTRACT FROM AUTHOR]

Abstract This study was carried out to assess the levels of trace metals (Fe, Zn, Mn and Cu) in the macroalgae and sediment of the Sundarban mangrove estuary in Bangladesh. In this connection, macroalgae, water and sediment samples were collected seasonally (pre-monsoon, monsoon and post-monsoon) for a year from the study area. The surface water of the estuary was found to be quite rich in NO3, PO4 and NH4, which is more than that of the sediment pore water. Trace elements were determined using an atomic absorption spectrophotometer. The amount of trace metals in the samples were found in the order of Fe > Mn > Zn > Cu. Enrichment factor was done for trace metals in sediment and showed non-crustal origin of Zn and Cu in the monsoon period. Analysis of variance revealed the seasonal variation of trace metal concentration in sediment (except Mn; p > 0.05) and macroalgae (except Zn; p > 0.05). Iron in sediment showed significant positive correlation both with Fe (r = 0.84, p

Glomalin-related soil protein (GRSP), a ubiquitous microbial product, plays a crucial role in particle aggregation and metal adsorption, but the underlying mechanisms remain unknown. Here, GRSP fraction was extracted from estuarine ecosystems and systematically characterized to elucidate the aggregation mechanisms and its impact on coastal environment improvement. We found that GRSP fraction (gravimetric mass of extracted GRSP, 5.1–24.3 mg g−1) was a globally relevant novel bioflocculant and that protein (linked to Bradford protein assay, 1.64–4.37 mg g−1) was the active flocculant constituent. The zeta potential, FTIR, XPS, and 13C NMR analyses identified its key constituents and structure, and revealed that the charge neutralization and bridging were GRSP fraction aggregation mechanisms. Thermogravimetric-infrared spectrometry analysis showed that GRSP fraction was highly thermostable, and the main volatile pyrolysis products included H2O, CO2, CO, and CH4. The SEM-EDX and XPS Fe valence spectroscopy suggested that GRSP fraction contained rich Fe (11.91 ± 0.48%) and could form Fe-rich flocs with particles. We also found that GRSP fraction has a high adsorption capacity (76–95%) for Cu, Zn, Pb and Cd, and its flocculation properties provide new insights into metal adsorption. The analysis of particle aggregation mechanism and its metal adsorption capacity is of great significance to elucidate the role of GRSP fraction in coastal environment improvement.

ABSTRACT Viruses are ubiquitous and abundant in the oceans, and viral metagenomes (viromes) have been investigated extensively via several large-scale ocean sequencing projects. However, there have not been any systematic viromic studies in estuaries. Here, we investigated the viromes of the Delaware Bay and Chesapeake Bay, two Mid-Atlantic estuaries. Deep sequencing generated a total of 48,190 assembled viral sequences (>5 kb) and 26,487 viral populations (9,204 virus clusters and 17,845 singletons), including 319 circular viral contigs between 7.5 kb and 161.8 kb. Unknown viruses represented the vast majority of the dominant populations, while the composition of known viruses, such as pelagiphage and cyanophage, appeared to be relatively consistent across a wide range of salinity gradients and in different seasons. A difference between estuarine and ocean viromes was reflected by the proportions of Myoviridae, Podoviridae, Siphoviridae, Phycodnaviridae, and a few well-studied virus representatives. The difference in viral community between the Delaware Bay and Chesapeake Bay is significantly more pronounced than the difference caused by temperature or salinity, indicating strong local profiles caused by the unique ecology of each estuary. Interestingly, a viral contig similar to phages infecting Acinetobacter baumannii (“Iraqibacter”) was found to be highly abundant in the Delaware Bay but not in the Chesapeake Bay, the source of which is yet to be identified. Highly abundant viruses in both estuaries have close hits to viral sequences derived from the marine single-cell genomes or long-read single-molecule sequencing, suggesting that important viruses are still waiting to be discovered in the estuarine environment. IMPORTANCE This is the first systematic study about spatial and temporal variation of virioplankton communities in estuaries using deep metagenomics sequencing. It is among the highest-quality viromic data sets to date, showing remarkably consistent sequencing depth and quality across samples. Our results indicate that there exists a large pool of abundant and diverse viruses in estuaries that have not yet been cultivated, their genomes only available thanks to single-cell genomics or single-molecule sequencing, demonstrating the importance of these methods for viral discovery. The spatiotemporal pattern of these abundant uncultivated viruses is more variable than that of cultured viruses. Despite strong environmental gradients, season and location had surprisingly little impact on the viral community within an estuary, but we saw a significant distinction between the two estuaries and also between estuarine and open ocean viromes.

It is important in fisheries management to evaluate the effects of environmental factors on changes in the abundance of species, particularly those inhabiting estuaries. The Yangtze River estuary is the largest in the western Pacific Ocean and serves as a spawning, feeding and nursery ground to species of economic and ecological importance, such as Collichthys lucidus and Lophiogobius ocellicauda. By using 3 years of environmental variables and data on the abundance of C. lucidus and L. ocellicauda gathered seasonally through trawl surveys, we compared four generalised additive models (GAMs), each comprising different spline terms, to analyse the influence of the measured variables on the abundance of both species. Deviance explained, Akaike information criterion and generalised cross-validation were used to select the optimal GAM after evaluating the fit and predictive performance of the models. Generalised additive model (GAM) with spline 'te' was the optimal model, and predicted that the abundance of both species was influenced by season and by variables temperature, salinity and chlorophyll-a concentration. For C. lucidus, abundance increased during spring and summer, and, for L. ocellicauda, it was higher during winter. Given the socioeconomic importance of both species, we contend that determining the drivers causing abundance fluctuations of estuarine species can support the putting in place of robust monitoring and assessment plans for such fisheries. [ABSTRACT FROM AUTHOR]

Deciphering land use and land cover (LULC) change patterns, identifying the variables that act as the major driving forces of change, and predicting possible changes are necessary tools of decision support for policymakers. Estuarine landscapes world over are under extreme pressure of developmental activities because of their resources. The developmental activities lead to unforeseen changes in the traditional land use practices, making it necessary for investigation of the possible outcomes. The present study aims to study the changing pattern of LULC in the East Godavari River Estuarine Ecosystem (EGREE) landscape during 1977–2015 using temporal satellite data and to predict the possible LULC changes by 2029. Cellular Automata-Markov model (CAMM) with and without the multi-criteria evaluator (MCE) and the multi-layer perceptron (MLP) models were used for future LULC prediction. Between 1977 and 2015, mangroves were converted to aquaculture (5.81 km2) on the landward side and were also lost to submergence at the seaward side (15 km2). All of the coastal scrub (69 km2) was lost to beach clearing. Over this period, the aquaculture area rose to 177 km2. The CAMM with MCE was found to yield better predictions. A further rise was predicted in aquaculture (16%), built-up (30%), and Casuarina plantations (28%) by 2029. The study highlighted the LULC change patterns in EGREE, an important estuarine landscape of India. The information generated in this study can act as baseline information for the stakeholders and policy makers in decision-making of developmental projects, land acquisition, and diversion of agricultural land to non-agricultural purposes. [ABSTRACT FROM AUTHOR]

Planktonic microorganisms in aquatic ecosystems form complex assemblages of highly interactive taxa and play key roles in biogeochemical cycles. However, the microbial interactions within bacterial and microeukaryotic communities, and the mechanisms underpinning the responses of abundant and rare microbial taxa to environmental disturbances in the river estuary remain unknown. Here, 16S and 18S rRNA gene sequencing were used to investigate the compositional changes and the co-occurrence patterns of bacterial and microeukaryotic communities. The results showed that the rare taxa in the bacterial communities were more prevalent than those in the microeukaryotic communities and may influence the resilience and resistance of microorganisms to environmental variations in estuarine ecosystems. The environmental variations had strong effects on the microeukaryotic communities and their assembly mechanisms but not on the bacterial communities in our studied area. However, based on co-occurrence network analyses, the bacterial communities had stronger links and more complex interactions than microeukaryotic communities, suggesting that bacterial networks may help improve the buffering capacities of the estuarine ecosystem against environmental change. The keystone taxa of bacteria mainly belonged to rare subcommunities, which further illustrates that rare taxa may play fundamental roles in network persistence. Overall, these results provide insights into the microbial responses of aquatic ecosystems to environmental heterogeneity.

The clearance of organic suspended particles by bivalve mollusks in estuarine ecosystems has been considered a critical regulating service. In Neotropical estuaries and associated mangrove ecosystems, the mangrove oyster, Crassostrea rhizophorae , is a key species in such process. To evaluate C. rhizophorae clearance rates (CR bd), biodeposit experiments were carried out at dry (2015) and wet (2016) seasons, in three sites of the Vitória Bay Estuarine System (VBES), southeastern Brazil. The average CR bd was 0.67 L.g−1.h−1, which can be regarded as low CR. Although organic fraction predominates in the particulate matter (>60%), high estuarine salinity caused by low river discharge during prolonged regional drought, impaired oyster feeder rates. When the CR bd take into account the estimate entire mangrove oyster biomass at the VBES (3.77 × 105 kg.km−2) it yields a rate of 6.51 × 106 m3.kg−1.day−1, corresponding to a mean daily capacity of organic seston removal of 26% of the total estuarine volume. Even conservative, this result highlights the importance of mangrove oyster for the estuarine regulation, emphasizing its ecological importance and the need to sustain the critical ecosystem services of regulating estuarine environmental quality. [ABSTRACT FROM AUTHOR]

This brief research compares the bioconcentration of heavy metals (Cd, Cr, Cu, Pb, Ni, and Zn) in the soft tissues of native oysters Crassostrea rhizophorae (Guilding, 1828) from two areas in the Potengi estuary, northeastern coast of Brazil. The purpose was to test the hypotheses of relevant differences in bioaccumulation while the environmental conditions change upstream. The downstream station showed higher concentrations for cadmium and nickel, and the upstream one revealed increased values for body weight, condition index, chromium, lead, and zinc (p < 0.05). The copper variation between sites was negligible, but as for zinc and chromium, the metal content observed was above guidance levels. Results revealed two aspects that were mainly influencing the bioavailability and bioaccumulation of metals in oysters. First, the predominance of marine or riverine characteristics of each site, and second, the relative proximity to the point of introduction of the pollutant even though stations were not quite far apart. C. rhizophorae accumulated heavy metals in significant concentrations, endorsing its efficiency as a biomonitor.

This study was carried out to assess the levels of trace metals (Fe, Zn, Mn and Cu) in the macroalgae and sediment of the Sundarban mangrove estuary in Bangladesh. In this connection, macroalgae, water and sediment samples were collected seasonally (pre-monsoon, monsoon and post-monsoon) for a year from the study area. The surface water of the estuary was found to be quite rich in NO3, PO4 and NH4, which is more than that of the sediment pore water. Trace elements were determined using an atomic absorption spectrophotometer. The amount of trace metals in the samples were found in the order of Fe > Mn > Zn > Cu. Enrichment factor was done for trace metals in sediment and showed non-crustal origin of Zn and Cu in the monsoon period. Analysis of variance revealed the seasonal variation of trace metal concentration in sediment (except Mn; p > 0.05) and macroalgae (except Zn; p > 0.05). Iron in sediment showed significant positive correlation both with Fe (r = 0.84, p < 0.05) and Mn (r = 0.87, p < 0.01) in macroalgae. Similarly, Cu in sediment demonstrated a significant positive correlation with Cu in macroalgae (r = 0.81, p < 0.01). The findings reveal a significant communication of metals in sediment and macroalgae. [ABSTRACT FROM AUTHOR]

• Loss of estuarine microbial biodiversity partly resulted from hypoxia and salinity. • The bottom-up and top-down forces restrained the microbial N removal potential. • Eukaryotes played key roles in estuarine N removal processes. • Hypoxia and salinity may amplify microbe-mediated N removal potential decline. Reactive nitrogen (N) enrichment is a common environmental problem in estuarine ecosystems, while the microbial-mediated N removal process is complicated for other multi-environmental factors. Therefore, A systematic investigation is necessary to understand the multi-trophic microbiota-mediated N removal characteristics under various environmental factors in estuaries. Here, we studied how multiple factors affect the multi-trophic microbiota-mediated N removal potential (denitrification and anammox) and N 2 O emission along a river-estuary-bay continuum in southeastern China using the environmental DNA (eDNA) approach. Results suggested that hypoxia and salinity were the dominant environmental factors affecting multi-trophic microbiota-mediated N removal in the estuary. The synergistic effect of hypoxia and salinity contributed to the loss of taxonomic (MultiTaxa) and phylogenetic (MultiPhyl) diversity across multi-trophic microbiota and enhanced the interdependence among multi-trophic microbiota in the estuary. The N removal potential calculated as the activities of key N removal enzymes was also significantly constrained in the estuary (0.011), compared with the river (0.257) and bay (0.461). Structural equation modeling illustrated that metazoans were central to all sediment N removal potential regulatory pathways. The top-down forces (predation by metazoans) restrained the growth of heterotrophic bacteria, which may affect microbial N removal processes in the sediment. Furthermore, we found that the hypoxia and salinity exacerbated the N 2 O emission in the estuary. This study clarifies that hypoxia and salinity constrain estuarine multi-trophic microbiota-mediated N removal potential and highlights the important role of multi-trophic interactions in estuarine N removal, providing a new perspective on mitigating estuarine N accumulation. [Display omitted] [ABSTRACT FROM AUTHOR]

It could be concluded that tidal coastal zones contain high level of micro-minerals in soil and plants. Paradoxically, local goats inhabiting in this particular ecosystem are deficient in Fe, Cu and Mn. This might be an adaptive response of animals in that area. Tanins are well-known inhibitor of Fe absorption from intestine. Regular consumption of tanins and other plant alkaloids during grazing and browsing might also be responsible for low bio-availability of the minerals in the plasma. Further research is warranted to have more insight on mineral status of small ruminants in fascinating ecosystem of Sundarbans.

Highlights • Stable isotope models can indicate the primary pathways of materials and energy supply for the estuarine community. • Estuarine consumers showed a low reliance on food sources originating from the Yellow River. • The diets of consumers in estuary were conforming to a marine based pattern. • Stable isotope analysis of food sources can provide data to inform the conservation of coastal ecosystems. Abstract Estuarine food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Until now, studies precisely quantifying the main energy sources in estuarine food webs have been limited for diverse species. The main pathway by which primary nutrients and energy are transported is not explicit and impedes conservation and restoration of estuarine ecosystems in Marine Protected Areas (MPAs). In this study, carbon and nitrogen stable isotopes were measured, to assess the primary food sources for consumers in the subtidal zone of the Yellow River Estuary. More than half of the detected consumers showed a balanced diet, with no significant feeding preferences. The remaining consumers mainly relied on microphytobenthos (MPB) and Cordgrass (Spartina). MPB contributions ranged from 31% to 38% for fishes and from 24% to 33% for invertebrates, while the contribution of Spartina ranged from 30% to 43% for fishes and from 24% to 38% for invertebrates, respectively. MPB was regarded as the primary autochthonous food source, while Spartina was regarded as the primary allochthonous source. Consumers showed a low reliance on food sources originating from the Yellow River, with diets conforming more to a marine based pattern. This study provides the first detailed investigation of the contribution of food sources in the subtidal zone of the Yellow River Estuary. The results of this study enhance our understanding of energy pathways in estuarine ecosystems, in addition to providing data to inform the conservation and restoration of coastal ecosystems. [ABSTRACT FROM AUTHOR]

This paper attempts to assess the vulnerability to climate change of human communities in selected mouzas of Sagar Island, South 24 Parganas District of India. A primary household survey has been conducted to collect data on socio-demographic profile, livelihood strategy, health, food, water, social network, natural disaster and climate variation indicators, were selected for Livelihood Vulnerability Index (LVI) and Livelihood Vulnerability Index-Intergovernmental Panel on Climate Change (LVI-IPCC) analyses to measure and compare the vulnerability of mouzas (administrative unit) currently suffering from frequent flooding, coastal erosion and embankment breaching on an annual basis. Secondary data collected from the Indian Meteorological Department, the Water Resources Information System of India and the Global Sea Level Observing System have been used to identify dynamics of climate change by employing statistical and Geographic Information System (GIS) techniques. A GPS survey has been conducted to identify locations of embankment breaching, and satellite images obtained from the National Aeronautics and Space Administration and U.S. Geological Survey (NASA USGS) Government website have been applied to shoreline and land use change detection, using a supervised maximum likelihood classification. The results indicate that the study area has experienced increasing temperature, changing precipitation patterns, rise in sea level, higher storm surges, shoreline change, constant land loss, embankment breaching and changing land use, which have had impact on vulnerability, particularly of poorer people. The LVI (0.48 to 0.68) and LVI-IPCC (0.04 to 0.14) scores suggest that the populations of Dhablat, Bankimnagar, Sumatinagar, Muri Ganga and Sibpur mouzas are highly vulnerable (LVI scores of 0.60 to 0.68 and LVI-IPCC scores of 0.11 to 0.14) to climate change both because the communities are more exposed to it, and because poor access to food, health facilities and water makes them extremely sensitive to it and lowers their adaptive capacity. The findings of this study could be crucial to framing further development and adaptation strategies relating to climate change, and to safeguarding the estuarine ecosystem and the vulnerable population. [ABSTRACT FROM AUTHOR]

Abstract Ocean acidification events are recognized as important drivers of change in biological systems. Particularly, the impacts of acidification are more severe in estuarine systems than in surface ocean due to their shallowness, low buffering capacity, low salinity and high organic matter from land drainage. Moreover, because they are transitional areas, estuaries can be seriously impacted by a vast number of anthropogenic activities and in the last decades, carbon nanomaterials (CNMs) are considered as emerging contaminants in these ecosystems. Considering all these evidences, chronic experiment was carried out, trying to understand the possible alteration on the chemical behaviour of two different CNMs (functionalized and pristine) in predicted climate change scenarios and consequently, how these alterations could modify the sensitivity of one the most common marine and estuarine organisms (the polychaeta Hediste diversicolor) assessing a set of biomarkers related to polychaetes oxidative status as well as the metabolic performance and neurotoxicity. Our results demonstrated that all enzymes worked together to counteract seawater acidification and CNMs, however oxidative stress in the exposed polychaetes to both CNMs, especially under ocean acidification conditions, was enhanced. In fact, although the antioxidant enzymes tried to cope as compensatory response of cellular defense systems against oxidative stress, the synergistic interactive effects of pH and functionalized CNMs indicated that acidified pH significantly increased the oxidative damage (in terms of lipid peroxidation) in the cotaminated organisms. Different responses were observed in organisms submitted to pristine CNMs under pH control, where the lipid peroxidation did not increase along with the increasing exposure concentrations. The present results further demonstrated neurotoxicity caused by both CNMs, especially noticeable at acidified conditions. The mechanism of enhanced toxicity could be attributed to slighter aggregation and more suspended NMs in acidified seawater (as demonstrated by the DLS analysis). Therefore, ocean acidification may cause a higher risk of CNMs to marine ecosystems. Graphical abstract Unlabelled Image Highlights • Slighter aggregation and more suspended carbon nanomaterials in acidified seawater • Under pH acidified both carbon nanomaterials generated greater oxidative stress in polychaetes. • Functionalized carbon nanomaterials increased oxidative stress and neurotoxicity under both pHs. • Ocean acidification may cause a higher risk of carbon nanomaterials to marine ecosystems. [ABSTRACT FROM AUTHOR]

Soil quality, especially its toxic elements content, plays an important part in clarifying the sustainability of an estuarine ecosystem. In this study, six toxic elements (As, Pb, Cd, Zn, Cr, Cu) in soils and sediments of the Ba Lat estuary, northern Vietnam, were assessed using the ICP-MS technique. Soil properties, such as major minerals, soil particles, organic carbon content, were also measured using an X-ray diffractometer (XRD) system and other common methods. The FE-EPMA technique was applied to explore the surface chemical properties of the soil and sediment particles. Detailed information about arsenic and heavy metal forms in the samples was analyzed by the sequential extraction method. Sixty-seven surface soil and sediment samples were collected. In addition, several soil and sediment cores (1 m of depth) were also taken from mangrove forests and paddy fields to evaluate their toxic element content. The chemical analyses have shown that the surface layers of the river sediment and mangrove forest soil contain accumulated As and heavy metals, which could have been transported from the upstream Red River. The average concentrations of heavy metals (Pb, Cd, Zn, Cr, Cu) did not exceed the allowable limit for agricultural soil; however, these elements tend to accumulate on the surface layer of the soil and sediment profiles. The spatial distribution of the toxic elements suggests that intensive human activities in the upstream Red River in recent decades were the cause of elevated levels of these toxic elements in the estuarine ecosystem of Ba Lat estuary. [ABSTRACT FROM AUTHOR]

Abstract The influence of anthropogenic nutrient loading on the stable isotopic signatures (δ13C and δ15N) in the suspended particulate organic matter (SPOM) is still not fully understood. Water quality and the values of δ13C and δ15N in the SPOM were investigated in the surface water of Daya Bay during the spring of 2016 and 2017. The results indicated that the Dan'ao River is the main point source of nutrient pollution in Daya Bay. The δ15N POM was very low in the Dan'ao River. The distribution pattern for this parameter in Daya Bay was determined chiefly by Dan'ao River discharge. Variations in δ15N POM were ascribed mostly to the input of 15N-depleted DIN assimilated by the estuarine phytoplankton in Daya Bay. Extremely high NH 4 + level in the river discharge should be responsible for the low δ15N POM in the river water. The distribution of δ13C POM in Daya Bay was regulated mainly by the input of 13C-depleted riverine SPOM. In the present study, the influence of phytoplankton growth on the δ13C POM was not significant. Moreover, episodic rain events significantly influenced the temporal and spatial variations in water quality and isotopic signature in Daya Bay. The relatively depleted SPOM 15N in 2016 may have been correlated with the strong El Niño events of 2015–2016. Increases in the frequency and volume of rainfall associated with El Niño may have enhanced nutrient loading and the risk of algal red tide in the Daya Bay. In general, significant 15N depletion in SPOM could be the characteristic of hypereutrophic riverine waters. This study suggested that δ15N POM may be an effective indicator of the strength of riverine nutrient loading in Daya Bay. Graphical abstract Unlabelled Image Highlights • Dan'ao River was the main point source of nutrient pollution in Daya Bay. • Significantly low δ15N POM in the hypereutrophic riverine waters • δ15N POM was regulated mainly by 15N-depleted DIN assimilated by phytoplankton. • Episodic rainfall and El Niño event increased nutrient loading from Dan'ao River. [ABSTRACT FROM AUTHOR]

The present study unravels the microalgal diversity and dynamics of a tropical estuarine ecosystem (Muttukadu, of Indian south east coast) and applies tools like isolation of useful species to utilize in aquaculture as well as to conserve the native strains. The study was carried out for a period of 18 months. Selected diversity indices (Simpson index, Dominance index, Shannon- Weiner index, Pielou's evenness index and Margalef richness index) were used to describe the trends of diversity in the estuary during the study period. Spatial and temporal changes in microalgal diversity in the estuary were analysed. Sixty three species of microalgae belonging to Chlorophyceae, Bacillariophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae, Eustigmatophyceae, Prymnesiophyceae, Prasinophyceae and Zygnematophyceae were identified. Out of these, members of Bacillariophyceae formed the dominant flora (48.5%) with twenty six species, followed by Cyanophyceae (29.2%) and Chlorophyceae (13.6%). The species diversity was increased after the flood during December-2015 in south east coast of India. More than two dozens of microalgal strains useful for larval nutrition in aquaculture were isolated during the study period. Nutrient profiling of isolates revealed the presence of essential fatty acids (EPA & DHA) in high percentage in some of the isolates. Altogether, the present study is the first report of this kind from Muttukadu which gives the insight on a) the seasonal changes in abundance of microalgae species in a tropical estuary and b) suitable time for the isolation of potential species for aquaculture and conservation of various species in the laboratory conditions. [ABSTRACT FROM AUTHOR]

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

The present study was carried out to examine the distribution and assemblage structure of zooplankton in relation to environmental parameters of tropical coastal estuarine ecosystem impounding Bight of Benin, Nigeria. The estuarine water samples were collected between January and December, 2014 from three sampling zones (Brushpark, Open water and Wetland) then were fixed in 4% formalin. A total of twenty-eight (28) species belonging to four (4) groups were recorded in this study. These groups were rotifera, copepoda, cladocerans and ostracodas, and were all widely distributed in the three investigated zones. Higher richness, dominance and abundance indices were recorded in Zone I when compared to both Zones II and III. Cluster analysis showed five distinct species communities. The canonical correspondence analysis (CCA) showed a distinct smattering positive and negative correlation on the distribution of zooplankton indicating that the relative abundance of any species was dependent on specific environmental variables.

Spatiotemporal changes in the biomass and abundance of the two dominant bivalve species Corbicula japonica and Arcuatula senhousia were investigated at 14 stations positioned along the Ohashi River from November 2005 to August 2007. Corbicula japonica predominantly inhabited the upstream section of the primary branch and Kensaki stream of the Ohashi River, whereas A. senhousia predominantly inhabited the downstream section of the Ohashi River. However, the distributions were highly variable among stations and seasons. Intrusions of saline water from Lake Nakaumi varied with astronomical and climatological factors, and consequently, the halocline of the Ohashi River is subject to spatiotemporal changes. Changes in distributions of C. japonica and A. senhousia occurred in relation to a flood event, indicating that environmental disturbances affect the distributions of the two bivalve species. Responses of the two species to continual saline water intrusion were also observed during the period of normal flow conditions. We suggest that the distribution of the two species is closely related to the dynamics of the ambient saline water, which is the most important factor correlated to changes in the distributions of C. japonica and A. senhousia in the Ohashi River. [ABSTRACT FROM AUTHOR]