Estuarine Sites Research Articles

High prevalence of biliary neoplasia in white perch Morone americana: potential roles of bile duct parasites and environmental contaminants.

Recent surveys of white perch Morone americana from Chesapeake Bay, USA, revealed a high prevalence of hepatic and biliary lesions, including neoplasia, and bile duct parasites. Here, we describe lesions in the liver and gallbladder and evaluate for statistical associations among lesions, parasites, and biomarkers of chemical exposure in fish from 2 tributaries of Chesapeake Bay. Fish were collected from an estuarine site in the Choptank River (n = 122, ages 3-11), a tributary with extensive agriculture within the watershed, and the Severn River (n = 131, ages 2-16), a tributary with extensive urban development. Passive integrative samplers were deployed at the fish collection site and an upstream, non-tidal site in each river for 30 d. Intrahepatic biliary lesions observed in fish from both rivers included neoplasia (23.3%), dysplasia (16.2%), hyperplasia (46.6%), cholangitis (24.9%), and dilated ducts containing plasmodia of Myxidium sp. (24.9%). Hepatocellular lesions included foci of hepatocellular alteration (FHA, 15.8%) and neoplasia in 4 Severn River fish (2.3%). Age of fish and Myxidium sp. infections were significant risk factors for proliferative and neoplastic biliary lesions, age alone was a risk factor for FHA, and Goussia bayae infections were associated with cholangitis and cholecystitis. Lesion prevalence was higher in fish from the Severn River, which contained higher concentrations of PAHs, organochlorine pesticides, and brominated diphenyl ethers. Metabolite biomarkers indicated higher PAH exposures in Severn River fish. This study suggests Myxidium sp. as a promoter of bile duct tumors, but more data are needed to evaluate the biological effects of environmental contaminants in this species.

Infection prevalence and pathology of the cymothoid parasite Olencira praegustator in Atlantic menhaden

AbstractIsopod parasites in the family Cymothoidae can cause reduced growth, castration, or even mortality in their hosts. Olencira praegustator is a cymothoid that parasitizes the mouth and gill chamber of Brevoortia tyrannus (Atlantic menhaden), which is the basis for the largest fishery along the eastern coast of the USA and an important link within estuarine food webs. To better characterize interactions between O. praegustator and B. tyrannus, including parasite‐induced pathology, we sampled hosts and parasites from three estuarine sites on Kiawah Island, South Carolina. Over 5 weeks, we collected, measured, and weighed 169 juvenile menhaden; remarkably, 96% of these fish were infected with O. praegustator, typically with one isopod found in the mouth of each host. Based on the external morphologies of 163 examined isopods, 58 were female (35.6%), 9 of which were gravid, and 105 were male (64.4%). Although fish size was unrelated to isopod length or mass, isopod length was a direct predictor of the amount of damage observed on the host operculum, which in severe cases involved tissue atrophy and hemorrhage. Considering the high infection prevalence, significant damage associated with infections, as well as the impairing effects of other cymothoids on their hosts, the consequences of interactions between B. tyrannus and O. praegustator warrant additional investigation for understanding the management and ecology of Atlantic menhaden.

Heavy metal fractions in rhizosphere sediment vis-à-vis accumulation in Phoenix paludosa (Roxb.) mangrove plants at Dhamra Estuary of India: assessing phytoremediation potential

ABSTRACT Total and sequentially extracted fractions (exchangeable, bound to carbonate, bound to iron and manganese oxides, bound to organic matter and residual) of eight heavy metals (Cu, Mn, Zn, Ni, Fe, Cr, Cd and Pb) were estimated in rhizosphere sediment along with their accumulation in roots and leaves of Phoenix paludosa plants at Dhamra estuary. The Cu, Mn, Zn, Ni, Fe, Cr, Cd and Pb content in rhizosphere sediments were 162.2, 563.3, 289.1, 228.8, 31,524.3, 475.5, 8.5 and 256.8 mg/kg, respectively. For almost all the heavy metals, sequential extraction estimation showed residual>bound to iron and manganese>bound to organic matter>bound to carbonate>exchangeable fractions. Exceptionally very high residual Cr (77.36%) and organic matter-bound Cd fraction (41.10%) highlighted the sedimentary mine run-off and industrial activities as their main source of pollution, respectively. Phoenix paludosa exhibited maximum bio-concentration (0.34), bio-accumulation (0.51) and translocation (0.50) factor for Cd. The primary results revealed the phyto-accumulation behaviour of different heavy metals in Phoenix paludosa and showed its relatively higher remediation potential for Cd and Cr pollution. In view of the above facts, heavy metals-polluted estuarine sites can be remediated through afforestation of Phoenix paludosa plant species.

Tracing nutrient pollution from industrialized animal production in a large coastal watershed.

One of the highest concentrations of swine and poultry concentrated animal feeding operations (CAFOs) in North America is located on the Coastal Plain of North Carolina, in which the Cape Fear River basin is located. The CAFOs produce vast amounts of manure causing loading of nutrients and other pollutants to receiving waters. With the Cape Fear River basin vulnerable to nutrient pollution, as are many other watersheds with CAFOs, δ13C and δ15N stable isotopic signatures were identified from water samples collected within the Northeast Cape Fear, Black, and lower Cape Fear River watersheds to trace nutrient sources and their distribution downstream. The spatial and temporal variability of nutrients and isotopic signatures were also identified to understand water quality impacts of animal waste spraying season and proximity to CAFOs. Our results showed that significantly enriched δ15N signatures characterized sites in close proximity to CAFOs as well as point-source wastewater discharge areas, while the opposite was true for an unimpacted control stream and two estuarine sites. Additionally, the impacted sites yielded significantly (p < 0.05) higher nitrate concentrations than control and estuarine sites. Statistical analyses demonstrated that nitrate concentrations were positively correlated with heavier δ15N signatures, suggesting that animal waste, as well as human wastewater, are relatively more important sources of N to this large watershed than fertilizers from traditional row crop agriculture. Our results also suggested that during appropriate hydrological conditions CAFO-derived N can be detected many kilometers downstream from freshwater sources areas to the estuary.

Fish Assemblage Structure Comparison between Freshwater and Estuarine Habitats in the Lower Nakdong River, South Korea

Variabilities of biological communities in lower reaches of urban river systems are highly influenced by artificial constructions, alterations of flow regimes and episodic weather events. Impacts of estuary weirs on fish assemblages are particularly distinct because the weirs are disturbed in linking between freshwater and estuarine fish communities, and migration successes for regional fish fauna. This study conducted fish sampling at the lower reaches of the Nakdong River to assess spatio-temporal variations in fish assemblages, and effects of estuary weir on structuring fish assemblage between freshwater and estuary habitats. In total, 20,386 specimens comprising 78 species and 41 families were collected. The numerical dominant fish species were Tachysurus nitidus (48.8% in total abundance), Hemibarbus labeo (10.7%) and Chanodichthys erythropterus (3.6%) in the freshwater region, and Engraulis japonicus (10.0%), Nuchequula nuchalis (7.7%) and Clupea pallasii (5.2%) in the estuarine site. The fish sampled were primarily small species or the juveniles of larger species at the estuary region, while all life stages of fishes were observed at the freshwater habitats. The diversity patterns of fish assemblages varied greatly according to study site and season, with higher trends at estuarine sites during the warm-rainy season. No significant difference in diversity between freshwater and estuarine sites during the cold-dry season were found. Multivariate analyses of fish assemblage showed spatial and seasonal differences of assemblage structures. Higher effects of between-site variability but not within seasonal variability at each site were observed. Variations in assemblage structures were due to different contributions of dominant species in each habitat. Common freshwater species characterized the fish assemblage in the freshwater region, while marine juveniles were significantly associated with the estuarine habitat. The results from the ecological guild analyses showed distinct ecological roles for freshwater and marine species, and overlapping roles for fish sampled at the fishways. The lower reaches of the Nakdong River are an important ecosystem for both freshwater and marine juveniles. Nakdong River estuarine residents and migrant fishes, however, have been negatively affected by the construction of the weir (gravity dam), due to the obstruction to migration from and to freshwater habitats. Conservation and management policies aimed at minimizing anthropogenic influences on estuary ecosystems should focus on evaluating ecological functions of estuary weirs.

Isolation and characterization of potentially pathogenic Vibrio species in a temperate, higher latitude hotspot

The recent emergence of Vibrio infections at high latitudes represents a clear human health risk attributable to climate change. Here, we investigate the population dynamics of three Vibrio species: Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio cholerae within a British coastal estuarine site, with contrasting salinity and temperature regimes during an intense heatwave event. Water samples were collected weekly through the summer of 2018 and 2019 and filtered using membrane filtration and subsequently grown on selective media. Suspected vibrios were confirmed using a conventional species-specific PCR assay and further analysed for potential pathogenic markers. Results showed that Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio cholerae were present at high concentrations throughout both years, with their populations at substantially greater abundances corresponding to conditions of higher water temperatures during the heatwave of 2018 and at lower salinity sites, which is comparable to the results of previous studies. A subset of strains isolated during the extreme heatwave event in 2018 (46 Vibrio parahaemolyticus, 11 Vibrio cholerae and 4 Vibrio vulnificus) were genomically sequenced. Analysis of these 63 sequenced strains revealed a broad phenotypic and genomic diversity of strains circulating in the environment. An analysis of pathogenicity attributes identified a broad array of virulence genes across all three species, including a variety of genes associated with human disease. This study highlights the importance of the need for an increased Vibrio spp. surveillance system in temperate regions and the potential impact warming events such as heatwaves may have on the abundance of potentially pathogenic bacteria in the environment.

Using stable isotopes to assess river water dynamics and groundwater input in the largest European Arctic river (Severnaya Dvina).

Rivers play a key role in the water cycle on the earth via integrating all hydrological channels to return terrestrial precipitations back to the oceans. In addition, rivers, together with groundwater, are powerful transformers of the surface lithosphere, responsible for chemical weathering of rocks and the removal of solute into the ocean. Tracing the dynamics of surface water and groundwater versus atmospheric feeding of rivers presents important issues in Arctic regions due to the ongoing change of the structure of hydrological runoff. In this study, stable water isotopes were used to reveal the temporal dynamics of water sources and to predict their possible change under the conditions of ongoing climate warming of the largest European Arctic river, the Severnaya Dvina, and adjacent groundwater. The isotopic composition of the river waters of the studied region is formed by the mixing of atmospheric precipitation with groundwater. The isotopic depletion in the springtime is mainly due to the recharge of thawed snow waters. A less pronounced effect in the autumn-winter period is provided by the discharge of groundwater into rivers, including the meltwater of the Last Glacial Period. This depletion is partially offset due to discharge of isotopically light thawed snow waters and is linked to evaporation in headwater streams, reservoirs, and wetlands. The isotopic composition of groundwater with low mineralization was formed throughout the Holocene and to a large extent depends on paleoclimatic conditions in the study area. In addition to fresh groundwater, brackish groundwater also takes part in the river's recharge. These brackish waters are associated with ancient and modern marine transgressions on the estuarine site and with the dissolution of Ca sulfate rocks in a karst region located in the middle reaches of the river. According to isotope data, the average annual input of the underground source to the total river flow is 25%. The results of this work will serve as the basis for continuing monitoring of the isotopic composition of river waters with an assessment of hydrological processes and observation of short as well as long-term climatic and anthropogenic impacts.

Coupling Traditional and Emergent Technologies for Improved Coastal Zone Mapping

The shallow, turbid water of the Delaware Bay Estuary is the second most navigated waterway in the USA behind the Mississippi River and experiences tropical and extratropical cyclones from June through April bringing high winds, storm surge, precipitation, and coastal change. Mapping coastal areas within the Delaware Bay is particularly difficult due to inherent environmental factors such as low underwater visibility (less than 1 m), rapid tidal current (greater than 1 m/s), changeable weather, and strong mid-latitude winds. This study utilized four sonar systems, two manned vessels, two autonomous vessels, three real-time kinematics global positioning systems (RTK GPS), two unmanned autonomous aerial systems, and satellite imagery to quantify subaerial and subaqueous volume and feature changes following storm events. The study site was located at Broadkill Beach, Delaware, a microtidal beach inside the Delaware estuary and outside the National Coastal Mapping Program survey area. Six storms (four tropical and two extratropical cyclones) from 2012 to 2018 were surveyed pre- and post-storm. Key insights in sensors and platforms proved unmanned aerial systems (UAS) orthomosaic resolution to be superior for mapping shoreline, profile, and dune toe changes, swash zone features such as cusps, wrack lines, and infrastructure damage to beach crossovers. Subaqueous platforms performed well for most storm events with RMSE of 0.23 m or less. This uncertainty, including subaerial uncertainty (max = 0.016 m), can be reduced with precise GPS systems and ground truthing of elevations through additional sensors like RTK GPS and subbottom profilers. No clear pattern emerged between accretion and erosion for tropical or extratropical cyclones (TC or ETC). Low-energy beaches are rarely studied and therefore open-coast relationships are transplanted to these environments. Storm responses of the site did not match expected traditional cross-shore transport models as beach orientation and storm wind direction most likely induced longshore transport out of the system. UAS orthomosaics were critical in identifying wrack lines and debris which altered subaerial transport patterns at this low-energy site. This work highlights the importance of irregular, small-scale features such as relic jetties, wrack lines, and local wind waves in estuarine sites when traditional open-coast theory would diminish these processes. More importance should be placed on the use of high-resolution imagery and elevation data over widely spaced profiles when monitoring and managing low-energy sites experiencing episodic storms such as TC and ETC to accurately assess processes, relationships, and morphologic response.

Mechanisms responsible for N2O emissions from intertidal soils of the Yangtze Estuary.

Estuarine and coastal wetland ecosystems are important sources of atmospheric nitrous oxide (N2O). However, the underlying driver of emitted N2O from estuarine and coastal wetlands remains poorly understood. Here, natural-abundance isotope technique was applied to characterize the processes responsible for N2O emission from the intertidal soils of the Yangtze Estuary. Measured N2O emission rates ranged from 0.70 to 2.15μmolm-2h-1, with relatively high values at the upper estuarine sites. The δ15N, δ18O and SP (intramolecular 15N site preference) of emitted N2O varied from -4.5 to 6.7‰, 42.4 to 53.2‰, and 6.7 to 15.4‰, respectively. Gross N2O production and consumption rates were within the ranges of 3.16-14.34μmolm-2h-1 and 2.22-12.54μmolm-2h-1, respectively, showing a similar spatial pattern to N2O emission. N2O consumption proportion varied from 69.56 to 90.31%, which was generally lower at the upper estuarine sites. The gross production rates and consumption degree of N2O simultaneously controlled the variations in N2O emission. Bacterial denitrification was the dominant production pathway (78.22-97.36%), while hydroxylamine (NH2OH) oxidation contributed 2.64-21.78% to N2O production. Soil pH, Fe2+/Fe3+, sulfide and substrate availability were probably the main factors governing the N2O emission dynamics. Overall, these results highlight the substantial role of NH2OH oxidation and N2O consumption in N2O release in redox-dynamic soils of estuarine intertidal wetlands.

Microbial diversity and related secondary metabolite gene assortment at an estuarine mangrove ecosystem

Mangrove ecosystems are a major biodiversity hotspot of the world. The world heritage site Sundarbans is an archipelago with an estuarine mangrove ecosystem. It is assumed that each individual Island of the Sundarbans possess a unique biodiversity due to the seasonal variation of physicochemical parameters, along with tidal dynamics of Bay of Bengal. This study unfolds a time series analysis of microbial diversity using high-resolution 16S rRNA tag pyrosequencing. Eight soil samples were collected over three years at a pristine temperate estuarine site located at the sea mangrove interface at the island of Kalash. Apart from the predominant phyla such as Proteobacteria [31.6%], Chloroflexi [10.7%], Firmicutes [7%] Bacteroidetes [7%] and Actinobacteria [1.2%], soil from Kalash also contained a significant amount of rare phyla NC10 and WS3 categorized as microbial dark matter (MDM). Variation in bacterial community composition occurs mainly as a result of the seasonal changes and consequent alterations of physicochemical parameters leading to microbial adaptations. Further we performed functional metagenomics to estimate the possibility of the synthesis of new natural compounds by diverse Polyketide Synthase (PKS). The data indicated diverse microbial origins of keto synthase sequences from polyketide synthase genes. Presence of this unique keto synthases confirmed the existence of a potential microbiome which may be capable of producing novel small molecules. This is the pioneering report to correlate the microbial community structure of Sundarbans with their potential to produce essential bioactive compounds.

Inventory of aliphatic hydrocarbons in a tropical mangrove estuary: a biomarker approach

Aliphatic hydrocarbons in the sediments of the estuarine mangrove forests of Cochin region, Southwest coast of India were characterized to assess the sources of organic matter (OM) and to validate the effectiveness of the various geochemical indices to identify multiple OM sources and the complex geochemistry of these tropical coastal environments. The total concentration of the n-alkanes varied from 606.39 to 826.25 µg/g [dry weight (dw)] in mangrove sediments, to values between 230.10 and 287.67 µg/g in estuarine sediments. The n-alkane distribution in the study region indicated a strong odd over even predominance in both mangrove and estuarine sediments. Assessment using terrestrial OM indices such as Carbon Preference Index (CPI), Terrigenous Aquatic Ratio (TAR), and Terrestrial Marine Discriminant (TMD) suggested that a large fraction of OM in the mangrove sediments was derived from mangrove plant litter and a better preservation of mangrove OM in the sedimentary environment has occurred. These findings are supported by the higher content of total lipid, tannin, and lignin, as well as by the depleted δ13C values. Low ratios of CPI, TAR, and TMD at estuarine sites E2 and E3 indicated a mixed origin of OM. Natural or biogenic indices such as natural n-alkanes ratio (NAR), Σn-alkanes/n-C16, n-C29/n-C17, and LMW/HMW revealed that all the mangrove stations and the estuarine station E1 received OM from natural or biogenic sources, whereas a significant anthropogenic input was noticed for estuarine stations E2 and E3. Indices like Pr/Ph, Pr/n-C17, Ph/n-C18 further confirmed the mixed nature of OM accumulated under the anoxic environment.

Occurrence of perfluoroalkyl substances in selected Victorian rivers and estuaries: An historical snapshot

This reconnaissance study was undertaken in 2012 to examine the occurrence of common perfluoroalkyl substances (PFAS), including perfluoroalkyl sulphonic acids and perfluoroalkyl carboxylic acids in rivers and estuaries in Port Philip Bay, Victoria, Australia. In total, 19 PFAS were screened in grab samples of water using a combination of solid phase extraction and liquid chromatography - mass spectrometry measurement techniques. Eighteen of the PFAS screened were observed in samples. The highest level of PFOS observed at a freshwater site was 0.045 μg/L; this concentration is approximately half the draft Australian 95% species protection level for total PFOS. The highest level of PFOA in the study (0.014 μg/L) was some four orders of magnitude lower than the draft Australian trigger value for PFOA (220 μg/L). However, none of the PFAS observed at the freshwater sites had research quotient (RQ) or toxicity unit (TU) values above 1 or -3, respectively. The highest concentration of PFOS observed at an estuarine site was 0.075 μg/L; the highest level of PFOA, 0.09 μg/L). There are no Australian marine water quality trigger values for PFAS, so potential risk was assessed using the European environment quality standards (EQS) adopted in EU Directive 2013/39/EU, RQ and TU methods. In that context, none of the PFAS observed at estuary sites had concentrations higher than the EU standards, or RQ above 1 or Log10TU above -3. Together these assessments suggest none of the PFAS screened would have posed an acute risk to organisms in the fresh or estuary waters studied at the time of sampling on an individual or collective basis. However, the detection of these PFAS in Victorian estuaries highlights that the issue is not just an issue for more densely populated countries in the northern hemisphere, but also potentially of concern in Australia. And, in that context, more sampling campaigns in Port Philip Bay are of paramount importance to assess the potential risk pose by these compounds to aquatic ecosystems.

Predicting sediment and nutrient concentrations from high-frequency water-quality data.

Water-quality monitoring in rivers often focuses on the concentrations of sediments and nutrients, constituents that can smother biota and cause eutrophication. However, the physical and economic constraints of manual sampling prohibit data collection at the frequency required to adequately capture the variation in concentrations through time. Here, we developed models to predict total suspended solids (TSS) and oxidized nitrogen (NOx) concentrations based on high-frequency time series of turbidity, conductivity and river level data from in situ sensors in rivers flowing into the Great Barrier Reef lagoon. We fit generalized-linear mixed-effects models with continuous first-order autoregressive correlation structures to water-quality data collected by manual sampling at two freshwater sites and one estuarine site and used the fitted models to predict TSS and NOx from the in situ sensor data. These models described the temporal autocorrelation in the data and handled observations collected at irregular frequencies, characteristics typical of water-quality monitoring data. Turbidity proved a useful and generalizable surrogate of TSS, with high predictive ability in the estuarine and fresh water sites. Turbidity, conductivity and river level served as combined surrogates of NOx. However, the relationship between NOx and the covariates was more complex than that between TSS and turbidity, and consequently the ability to predict NOx was lower and less generalizable across sites than for TSS. Furthermore, prediction intervals tended to increase during events, for both TSS and NOx models, highlighting the need to include measures of uncertainty routinely in water-quality reporting. Our study also highlights that surrogate-based models used to predict sediments and nutrients need to better incorporate temporal components if variance estimates are to be unbiased and model inference meaningful. The transferability of models across sites, and potentially regions, will become increasingly important as organizations move to automated sensing for water-quality monitoring throughout catchments.

Effects of allochthonous dissolved organic matter input on microbial composition and nitrogen-cycling genes at two contrasting estuarine sites.

Heterotrophic bacteria are important drivers of nitrogen (N) cycling and the processing of dissolved organic matter (DOM). Projected increases in precipitation will potentially cause increased loads of riverine DOM to the Baltic Sea and likely affect the composition and function of bacterioplankton communities. To investigate this, the effects of riverine DOM from two different catchment areas (agricultural and forest) on natural bacterioplankton assemblages from two contrasting sites in the Baltic Sea were examined. Two microcosm experiments were carried out, where the community composition (16S rRNA gene sequencing), the composition of a suite of N-cycling genes (metagenomics) and the abundance and transcription of ammonia monooxygenase (amoA) genes involved in nitrification (quantitative PCR) were investigated. The river water treatments evoked a significant response in bacterial growth, but the effects on overall community composition and the representation of N-cycling genes were limited. Instead, treatment effects were reflected in the prevalence of specific taxonomic families, specific N-related functions and in the transcription of amoA genes. The study suggests that bacterioplankton responses to changes in the DOM pool are constrained to part of the bacterial community, whereas most taxa remain relatively unaffected.

Demonstrated transfer of cyanobacteria and cyanotoxins along a freshwater-marine continuum in France

The frequency of cyanobacterial proliferations in fresh waters is increasing worldwide and the presence of associated cyanotoxins represent a threat for ecosystems and human health. While the occurrence of microcystin (MC), the most widespread cyanotoxin, is well documented in freshwaters, only few studies have examined its occurrence in estuarine waters. In this study we evaluated the transfer of cyanobacteria and cyanotoxins along a river continuum from a freshwater reservoir through an interconnecting estuary to the coastal area in Brittany, France. We sampled regularly over 2 years at 5 stations along the river continuum and analysed for phytoplankton and cyanotoxins, together with physico-chemical parameters. Results show that cyanobacteria dominated the phytoplanktonic community with high densities (up to 2 × 106 cells mL−1) at the freshwater sites during the summer and autumn periods of both years, with a cell transfer to estuarine (up to 105 cells mL−1) and marine (2 × 103 cells mL−1) sites. While the temporal variation in cyanobacterial densities was mainly associated with temperature, spatial variation was due to salinity while nutrients were non-limiting for cyanobacterial growth. Cyanobacterial biomass was dominated by several species of Microcystis that survived intermediate salinities. Intracellular MCs were detected in all the freshwater samples with concentrations up to 60 μg L−1, and more intermittently with concentrations up to 1.15 μg L−1, at the most upstream estuarine site. Intracellular MC was only sporadically detected and in low concentration at the most downstream estuarine site and at the marine outlet (respectively <0.14 μg L-1 and <0.03 μg L−1). Different MC variants were detected with dominance of MC-LR, RR and YR and that dominance was conserved along the salinity gradient. Extracellular MC contribution to total MC was higher at the downstream sites in accordance with the lysing of the cells at elevated salinities. No nodularin (NOD) was detected in the particulate samples or in the filtrates.

Seasonal variation in the diet of estuarine bivalves.

Estuarine food webs are generally considered to be supported by marine pelagic and benthic primary producers and by the import of dead organic matter from the open sea. Although estuaries receive considerable amounts of freshwater phytoplankton and organic compounds from adjacent rivers, the potential contribution of these living and dead matter to estuarine food webs is often assumed to be negligible and, therefore, not examined. Based on stable isotope analyses, we report the importance of freshwater suspended particulate organic matter (FW-SPOM) for fuelling estuarine food webs in comparison to estuarine SPOM and microphytobenthos. This previously neglected food source contributed 50–60% (annual average) of food intake of suspension-feeding bivalves such as cockles (Cerastoderma edule), mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) at the Balgzand tidal flats, an estuarine site in the western Wadden Sea (12–32 psu). For these species, this proportion was particularly high in autumn during strong run-off of SPOM-rich freshwater, whilst estuarine SPOM (20%-25%) and microphytobenthos (15%-30%) were relatively important in summer when the freshwater run-off was very low. These findings have implications for our understanding of the trophic interactions within coastal food webs and for freshwater management of estuarine ecosystems.

Dissolved Organic Matter Composition in a Marsh‐Dominated Estuary: Response to Seasonal Forcing and to the Passage of a Hurricane

AbstractDissolved organic matter (DOM) is a large and complex mixture of compounds with source inputs that differ with location, season, and environmental conditions. Here, we investigated drivers of DOM composition changes in a marsh‐dominated estuary off the southeastern United States. Monthly water samples were collected at a riverine and estuarine site from September 2015 to September 2016, and bulk, optical, and molecular analyses were conducted on samples before and after dark incubations. Results showed that river discharge was the primary driver changing the DOM composition at the mouth of the Altamaha River. For discharge higher than ~150 m3/s, dissolved organic carbon (DOC) concentrations and the terrigenous character of the DOM increased approximately linearly with river flow. For low discharge conditions, a clear signature of salt marsh‐derived compounds was observed in the river. At the head of Sapelo Sound, changes in DOM composition were primarily driven by river discharge and possibly by summer algae blooms. Microbial consumption of DOC was larger during periods of high discharge at both sites, potentially due to the higher mobilization and influx of fresh material to the system. The Georgia coast was hit by Hurricane Matthew in October 2016, which resulted in a large input of carbon to the estuary. The DOC concentration was ~2 times higher and DOM composition was more aromatic with a stronger terrigenous signature compared to the seasonal maximum observed earlier in the year during peak river discharge conditions. This suggests that extreme events notably impact DOM quantity and quality in estuarine regions.

Comparative Innate and Adaptive Immune Responses in Atlantic Bottlenose Dolphins (Tursiops truncatus) With Viral, Bacterial, and Fungal Infections.

Free-ranging Atlantic bottlenose dolphins (n = 360) from two southeastern U.S. estuarine sites were given comprehensive health examinations between 2003 and 2015 as part of a multi-disciplinary research project focused on individual and population health. The study sites (and sample sizes) included the Indian River Lagoon (IRL), Florida, USA (n = 246) and Charleston harbor and associated rivers (CHS), South Carolina, USA (n = 114). Results of a suite of clinicoimmunopathologic tests revealed that both populations have a high prevalence of infectious and neoplastic disease and a variety of abnormalities of their innate and adaptive immune systems. Subclinical infections with cetacean morbillivirus and Chlamydiaceae were detected serologically. Clinical evidence of orogenital papillomatosis was supported by the detection of a new strain of dolphin papillomavirus and herpesvirus by molecular pathology. Dolphins with cutaneous lobomycosis/lacaziasis were subsequently shown to be infected with a novel, uncultivated strain of Paracoccidioides brasiliensis, now established as the etiologic agent of this enigmatic disease in dolphins. In this review, innate and adaptive immunologic responses are compared between healthy dolphins and those with clinical and/or immunopathologic evidence of infection with these specific viral, bacterial, and fungal pathogens. A wide range of immunologic host responses was associated with each pathogen, reflecting the dynamic and complex interplay between the innate, humoral, and cell-mediated immune systems in the dolphin. Collectively, these studies document the comparative innate and adaptive immune responses to various types of infectious diseases in free-ranging Atlantic bottlenose dolphins. Evaluation of the type, pattern, and degree of immunologic response to these pathogens provides novel insight on disease immunopathogenesis in this species and as a comparative model. Importantly, the data suggest that in some cases infection may be associated with subclinical immunopathologic perturbations that could impact overall individual and population health.

Occurrence of neonicotinoids and fipronil in estuaries and their potential risks to aquatic invertebrates

This study aimed to evaluate and qualify field-based potential risks of seven neonicotinoid and phenylpyrazole (fipronil) insecticides on aquatic invertebrates, including estuary-resident marine crustaceans. One hundred and ninety-three estuarine water samples, with salinity ranging from 0.5 to 32.7, were collected from four estuarine sites in the Seto Inland Sea of Japan, in 2015–2018 and the insecticide levels were measured. Five neonicotinoid and fipronil insecticides were successfully identified, and their occurrence varied temporally. Marine crustaceans were simultaneously harvested every month from one of the estuarine water sampling sites in 2015–2017. Three predominant crustacean species, kuruma prawn (Penaeus japonicus), sand shrimp (Crangon uritai), and mysid (Neomysis awatschensis), were captured and their seasonal presence was species independent. A 96-h laboratory toxicity study with the insecticides using kuruma prawn, sand shrimp, and a surrogate mysid species (Americamysis bahia) indicated that fipronil exerted the highest toxicity to the three crustaceans. Using both toxicity data and insecticide occurrence in estuarine water (salinity ≥10, n = 169), the potential risks on the three marine crustaceans were quantified by calculating the proportion of mixture toxicity effects (Pmix). The Pmix of seven neonicotinoids on the crustaceans was less than 0.8%, which is likely to be too low to indicate adverse effects caused by the insecticides. However, short temporal detection of fipronil (exclusively in June and July) significantly affected the Pmix, which presented the maximal Pmix values of 21%, 3.4%, and 72% for kuruma prawn, sand shrimp, and mysid, respectively, indicating a significant effect on the organisms. As for estuarine water (salinity <10), some water samples contained imidacloprid and fipronil exceeding the freshwater benchmarks for aquatic invertebrates. The present study provides novel insights into the seasonally varying risks of insecticides to estuarine crustaceans and highlights the importance of considering whether ecological risk periods coincide with crustacean presence.

Characterization of Pacific oyster Crassostrea gigas proteomic response to natural environmental differences

Global climate change is rapidly altering coastal marine ecosystems important for food production. A comprehensive understanding of how organisms will respond to these complex environmental changes can come only from observing and studying species within their natural environment. To this end, the effects of environmental drivers - pH, dissolved oxygen content, salinity, and temperature - on Crassostrea gigas physiology were evaluated in an outplant experiment. Sibling juvenile oysters were outplanted to eelgrass and unvegetated habitat at five different estuarine sites within the Acidification Nearshore Monitoring Network in Washington State, USA to evaluate how regional environmental drivers influenced molecular physiology. We tested the effects environmental conditions at outplant sites and habitat to determine if macrophyte presence and diurnal cycling buffered pH conditions and changed the oysters expressed proteome. A novel, two-step, gel-free proteomic approach was used to identify differences in protein abundance in C. gigas ctenidia tissue after a 29 day outplant by 1) identifying proteins in a data independent acquisition survey step and 2) comparing relative quantities of targeted environmental response proteins using selected reaction monitoring. While there was no difference in protein abundance detected between habitats or within Puget Sound, C. gigas outplanted at Willapa Bay had significantly higher abundances of antioxidant enzymes and carbohydrate metabolism proteins. Environmental factors at Willapa Bay, such as higher average temperature, could have driven this protein abundance pattern. These findings generate a suite of new hypotheses for lab and field experiments to compare the effects of regional conditions on physiological responses of marine invertebrates.