Large Estuary Research Articles

Hypoxia also occurs in small highly turbid estuaries: the example of the Charente (Bay of Biscay)

Abstract. The French coast facing the Bay of Biscay (North-East Atlantic) is characterised by the presence of small macrotidal and turbid estuaries, including the Charente, which is geographically located between the two large estuaries of the Gironde and the Loire (south-west France). Multi-year, multi-site and high-frequency water quality surveys have shown that the Loire and, to a lesser extent, the Gironde suffer from summer hypoxia. These observations raised the question of the possible occurrence of hypoxia, particularly in one of these small estuaries, the Charente, which flows into the Bay of Marennes-Oléron, the first oyster-farming area in France. Unlike its two large neighbours, the Charente estuary is not continuously monitored, although it is subject to similar climatic changes and anthropogenic pressures, making it impossible to assess potential risks to the ecosystem. Here we present a first study of dissolved oxygen in the Charente estuary based on a combination of longitudinal studies along the estuary axis and instrumented sites to determine the intensity and spatial extent of deoxygenation. Temperature, dissolved oxygen and conductivity sensors were deployed at several sites during the summers of 2018, 2019 and 2020 to record temperature, salinity and dissolved oxygen every 15 min. The high-frequency dataset is compared with a long-term low-frequency dataset (1975–2022; 8–12 measurements per year) to determine whether or not there is a deterioration in the oxygenation of the Charente estuary. The high-frequency dataset shows a high variability in dissolved oxygen (DO) with a clear influence of the tidal cycle. During summer, DO concentrations are often below 5 mg L−1 and sometimes even below 2 mg L−1, indicating the presence of a summer estuarine oxygen minimum zone with an extension along the estuarine axis of about 20–25 km. Temperature is the main factor controlling DO in the Charente estuary, which limits preventive management strategies and, in the context of global warming, raises questions about the long-term suitability of estuarine conditions for the needs of the biological communities, particularly migratory fish.

Nutrient characteristics driven by multiple factors in large estuaries during summer: A case study of the Yangtze River Estuary

Nutrients directly control the level of primary productivity and are crucial for the stability of marine ecosystems. Focusing on the survey results in August 2020 of the Yangtze River Estuary, this study elucidated the distribution characteristics and controlling factors of three nutrients: NO3-N, PO4-P, SiO3-Si. The results showed that the concentrations of NO3-N, PO4-P, SiO3-Si in the study area were generally higher near the shore than far shore, with average concentrations of 11.40, 0.70, and 23.73 μmol/L, respectively. The ocean currents drove the distribution of nutrients, and the transport of CDW and YSCC increased the nutrient levels. The resuspension of sediment caused by factors such as terrain and weather may lead to an abnormal increase in nutrients in the bottom waters. The main controlling factors of the three nutrients were different. NO3-N was significantly affected by human activities, PO4-P and SiO3-Si were mainly affected by natural factors.

Environmental drivers of biogeography and community structure in a Mid-Atlantic estuary

Estuaries include some of the most productive yet anthropogenically impacted marine ecosystems on the planet, and provide critical habitat to many ecologically and economically important marine species. In order to elucidate ecological function in estuaries, we must understand what factors drive community dynamics. Delaware Bay is the third largest estuary in the United States and hosts over 200 species of migrant and resident fishes and invertebrates. The Delaware Division of Fish and Wildlife has conducted two long-term trawl surveys at monthly intervals in Delaware Bay since 1966. The two surveys collect data on environmental conditions, species composition, and number of fishes and macroinvertebrates across different size classes and life histories. Using a suite of multivariate approaches including hierarchical cluster analysis, canonical correlation analysis, and permutational multivariate analysis of variance, we characterized the fish and macroinvertebrate community in Delaware Bay and found that community composition and environmental conditions varied across spatial and seasonal scales. We identified four distinct biogeographic regions, based on environmental conditions and community composition, which were consistent across surveys. We found that the community was driven primarily by gradients in temperature and salinity and that abundant, frequently occurring species in the Bay have well-defined environmental associations. Our work represents the first attempt to use an existing historical survey to better understand how environmental parameters influence diversity and distribution of macrofauna within Delaware Bay, providing insight into how abiotic variables, influenced by climate, may impact the Delaware Bay ecosystem and similar estuarine ecosystems worldwide.

The Influence of Natural and Anthropogenic Environmental Pressures on European Eel Abundances in French Estuaries

The aim of this study was to investigate the influence of environmental characteristics and anthropogenic pressures on the abundance of estuarine European eels (Anguilla anguilla L.) during their continental growth phase. European eels were collected with fyke nets from spring to autumn in twenty-nine estuaries along the French English Channel and the Atlantic coast. Eel abundance (catch per unit effort, CPUE) was assessed for all eels and by size class for small (total length < 300 mm), intermediate (≥300 to <450 mm), and large (≥450 mm) eels. The environmental characteristics of the French estuaries were described by twelve descriptor variables, mainly related to hydro-morphological and sedimentary factors. Based on principal component analysis and hierarchical clustering analysis, estuary size was identified as the main explanatory variable and used to compare eel abundance. Eel abundance differed significantly according to estuary size, with higher abundances observed in small estuaries (7.22 to 13.00 ind. fyke nets 24 h−1) compared to large estuaries (0.13 to 0.71 ind. fyke nets 24 h−1). Spatial variation in eel abundance was correlated with differences in estuary size for all eel size classes. The influence of anthropogenic pressures on eel abundance was assessed by nine anthropogenic estuarine pressure indicators. The results indicate that high values of the anthropogenic pressure indicators were correlated with low eel abundance. This study highlights that large French estuaries subject to stronger anthropogenic pressures were less favourable habitats than small estuaries with less anthropogenic pressure.

Sediment–vegetation interactions determine the fate of fluvial sediment in the upper reaches of a large estuary

AbstractFeedbacks between sediment and plants in the submersed aquatic vegetation (SAV) beds of the Susquehanna Flats help modulate sediment delivery into the upper Chesapeake Bay from its major tributary (Susquehanna River). Recent modeling work has shown that SAV can steer the river plume, directly controlling sediment transport and fate. However, transport mechanisms likely differ between flood and non‐flood conditions and depend on event timing. An opportunity to evaluate these insights in the field occurred with several flood events in summer 2018. Sediment and biomass samples were collected after the flood in the large, continuous main SAV bed of the Flats and in smaller patches to the west of the main bed to evaluate the effect of SAV bed size (width). Sediment characteristics (grain size, organic content) and deposition rates were compared to previous observations during non‐flood conditions in the main bed in 2014–2015 and in the smaller patches in 2019. Overall, sediment deposition rates could be predicted by an empirical model including sediment load, vegetation biomass, and SAV bed width, reflecting the role of vegetation in steering the Susquehanna River plume and modulating sediment input to the upper Chesapeake Bay. Understanding spatiotemporal patterns of sedimentation is essential for realistic estimates of sediment and nutrient (especially nitrogen and carbon) storage in freshwater SAV systems, which have not received as much attention as their saltwater counterparts.

Use of satellite imagery to estimate distribution and abundance of Cumberland Sound beluga whales reveals frequent use of a glacial river estuary

Limiting disturbance in critical habitats is an important part of ensuring the well-being and sustainability of populations at risk, such as Cumberland Sound beluga whales (Delphinapterus leucas). Using non-disruptive Very High Resolution (VHR) satellite imagery, an emerging tool in cetacean monitoring, we aimed to estimate summer abundance and identify critical habitat for Cumberland Sound beluga whales. Specifically we looked in fiords that comprise their summer distribution, such as Clearwater Fiord where there is a large estuary, an important habitat to many beluga populations. Satellite images of the area were collected in 2020 and 2021, at 30 cm resolution, and in 2022 at 50 cm resolution. We evaluated beluga whale distribution using Kernel density, and identified critical habitats as areas consistently part of the beluga whale core distribution across years. Clearwater Fiord abundance estimates were corrected for whales that were too deep to be identified in the images. The estimates were significantly lower in 2021 (197 whales, 95%CI: 180-216) and 2022 (194 whales, 95%CI: 172-218) compared to 2020 (393 whales, 95%CI: 366-422). Other fiords were only imaged in 2021 and 2022, resulting in average corrected abundance estimates for all fiords of 462 (95% CI: 425-502) and 252 (95%CI: 226-280) beluga whales, respectively. Downsampling of 30 cm images to 50 cm resulted in up to 45% fewer whales detected. The only critical habitat identified within the summer distribution was in Clearwater Fiord, in or near the estuary freshwater plume and in a bay to the west of the plume. The identified critical habitats should be areas of consideration in the continued discussion on the protection and sustainability of the Cumberland Sound beluga whale population.

Does Salinity Gradient Affect Distributions of Byssally-attached Bivalves in Songkhla Lake, the Largest Estuary in Thailand?

Does Salinity Gradient Affect Distributions of Byssally-attached Bivalves in Songkhla Lake, the Largest Estuary in Thailand?

Biophysical Drivers of Coastal Treeline Elevation

AbstractSea level rise is leading to the rapid migration of marshes into coastal forests and other terrestrial ecosystems. Although complex biophysical interactions likely govern these ecosystem transitions, projections of sea level driven land conversion commonly rely on a simplified “threshold elevation” that represents the elevation of the marsh‐upland boundary based on tidal datums alone. To determine the influence of biophysical drivers on threshold elevations, and their implication for land conversion, we examined almost 100,000 high‐resolution marsh‐forest boundary elevation points, determined independently from tidal datums, alongside hydrologic, ecologic, and geomorphic data in the Chesapeake Bay, the largest estuary in the U.S. located along the mid‐Atlantic coast. We find five‐fold variations in threshold elevation across the entire estuary, driven not only by tidal range, but also salinity and slope. However, more than half of the variability is unexplained by these variables, which we attribute largely to uncaptured local factors including groundwater discharge, microtopography, and anthropogenic impacts. In the Chesapeake Bay, observed threshold elevations deviate from predicted elevations used to determine sea level driven land conversion by as much as the amount of projected regional sea level rise by 2050. These results suggest that local drivers strongly mediate coastal ecosystem transitions, and that predictions based on elevation and tidal datums alone may misrepresent future land conversion.

Effects of tidal cycles on the variability of microbial communities in a semiclosed bay

Shallow sediment-water plays an important role in transforming organic matter in estuaries. As a shallow bay often flanks a large estuary, the estuarine water enters the shallow bay during flood tides and exits during ebb tides. The inundation between flood and ebb tides in the shallow bay serves as an incubation of the bay water and sediment. However, little is known about the effects of tidal cycles on microbial diversity and biogeochemical processes. In Tangjiawan Bay, which is a small bay located on the west side of the Pearl River estuary, we examined changes in microbial diversity and environmental factors by collecting surface water samples between floods and ebbs. Using high-throughput sequencing targeting 16S and 18S rRNA genes, the results indicated that between floods and ebbs, the community composition of bacteria and eukaryotes differed significantly, the alpha diversity of bacteria and eukaryotes differed significantly, with floods harboring higher diversity. The analysis of RDA suggested that salinity and TOC were important in explaining community variation in both bacteria and eukaryotes. Moreover, the co-occurrence networks between bacteria and eukaryotes showed higher negative relationships in ebbs (83.87%) than in floods (64.29%), suggesting increased interactions between bacteria and eukaryotes during ebbs as the water was incubated in the bay. These findings demonstrated the dynamics of biogeochemical processes of nutrients and plankton communities in the shallow bay and tidal cycles are a dominant driving force in regulating variability in phytoplankton and bacterial community and the sediment-water interface exchange. The results indicate that we should not overlook at the importance of shallow water column fringing the shore lines.

Dams facilitate predation during Atlantic salmon (Salmo salar) smolt migration

Diadromous fish populations have incurred precipitous declines across the globe. Among many stressors, these species are threatened by anthropogenic barriers that impede movement, alter riverine habitat, and augment predator communities. In this study, we used acoustic transmitters ( n = 220) with predation and temperature sensors to characterize Atlantic salmon ( Salmo salar) smolt predation risk in the Penobscot River, Maine, USA. Across two seasons, we documented 79 predation events through a 170 km migratory pathway, which included three hydropower projects and a large estuary. We detected tagged smolts that were predated by fish ( n = 42), marine mammals ( n = 28), and birds ( n = 9). Using a multistate mark-recapture framework, we estimated that 46% of smolts were predated during downstream migration, which accounted for at least 55% of all mortality. Relative predation risk was greatest through impoundments and the lower estuary, where on average, predation rates were 4.8-fold and 9.0-fold greater than free-flowing reaches, respectively. These results suggest that predation pressure on Atlantic salmon smolts is exacerbated by hydropower projects and that predation in the lower estuary may be greater than expected.

Field observations and long short-term memory modeling of spectral wave evolution at living shorelines in Chesapeake Bay, USA

Living shorelines as a nature-based solution for climate change adaptation were constructed in many places around the world. The success of this type of projects requires long-term monitoring for adaptive management. The paper presents a novel framework leveraging scientific machine learning methods for accurate and rapid prediction of long-term hydrodynamic forcing impacting living shorelines using short-term measurements of water levels and wind waves in the largest estuary in the U.S. Different from existing data-driven wave prediction models focusing on significant wave heights, this study is focused on the prediction of wave energy spectra in shallow water using winds and tides as the input feature and short-term measurements of wave spectra and water depths as the label. Long Short-Term Memory (LSTM) models were developed using four-month wave measurements in the stormy seasons to predict integral wave parameters and energy spectra for multiple years. The developed models accurately predicted wave heights, peak periods, and energy spectra around the living shorelines, capturing complex wave dynamics, such as wave generation by wind, nonlinear wave-wave interactions, and depth-limited wave breaking in the shallow water of a large estuary. The validated models were then used to determine the long-term wave forcing impacting the living shorelines based on the modeled wave characteristics and spectra. Model results show that the surrogate models utilizing LSTM to predict wave spectra in the frequency domain enable long-term predictions of spectral wave evolution with a minimal computational cost. Our findings provide valuable insights into the efficacy of living shorelines in attenuating wave energy and demonstrate the utility of this approach in assessing the effectiveness of such living shoreline structures.

Unraveling the photochemical reactivity of dissolved organic matter in the Yangtze river estuary: Integrating incubations with field observations

Dissolved organic matter (DOM) sustains a substantial part of the organic matter transported seaward in large estuaries, where photochemical reactions significantly influence its transformation and fate. Irradiation experiments can provide valuable information on the photochemical reactivity (photo-labile, photo-resistant, and photo-product) of molecules. However, previous research paid less attention to exploring the controls of the initial DOM chemistry to irradiation experiments and examining the applicability of their further integration with field research. Here, we conducted irradiation experiments for samples from the freshwater and seawater endmember of the Yangtze River Estuary (YRE), which receives organic matter transport from the largest river in China, the Yangtze River. Molecules that occurred before and after irradiation experiments were characterized by the Fourier transform ion cyclotron resonance mass spectrometry. Results show that both post-irradiation samples have the lower aromaticity degree and reduced oxidation state, while the freshwater endmember sample exhibits more dramatic changes, indicating the controls of parent molecules to the effect of irradiation experiments. Integrating with the “molecular matching” approach, we compared the molecules occurring in field samples with the classified molecules (photo-resistant, photo-labile, and photo-product) acquired from performed irradiation experiments and correlated the relative intensity of photochemical reactivity types with salinity. When applying results from different experiments to conduct “molecular matching”, the photo-resistant and photo-labile relative intensity possess consistently positive and negative trends with increasing salinity, respectively. This suggests their reliability for molecular matching applications, while the inconsistent trends for the photo-product relative intensity with salinity suggest its uncertainty in assessing the photo-induced effects. Moreover, the molecular composition within the photochemical reactivity types in field samples also evolved along the salinity gradient and showed similar trends with the DOM changes after experimental irradiation. Despite various factors influencing estimations, it is revealed that a fraction of aromatic molecules and majority of carboxyl-rich alicyclic molecules considered with biologically persistent nature in the YRE freshwater zone are simultaneously not susceptible to photochemical transformation to potentially constitute a long-term marine carbon sink. This study emphasizes the importance and limitations of the combination of field research and laboratory-controlled experiments to provide a better understanding of the crucial role of photochemical reactions in affecting carbon cycling in large estuaries.

Assessing drivers of estuarine pH: A comparative analysis of the continental U.S.A.'s two largest estuaries

AbstractIn estuaries, local processes such as changing material loads from the watershed and complex circulation create dynamic environments with respect to ecosystem metabolism and carbonate chemistry that can strongly modulate impacts of global atmospheric CO2 increases on estuarine pH. Long‐term (> 20 yr) surface water pH records from the USA's two largest estuaries, Chesapeake Bay (CB) and Neuse River Estuary‐Pamlico Sound (NRE‐PS) were examined to understand the relative importance of atmospheric forcing vs. local processes in controlling pH. At the estuaries’ heads, pH increases in CB and decreases in NRE‐PS were driven primarily by changing ratios of river alkalinity to dissolved inorganic carbon concentrations. In upper reaches of CB and middle reaches of the NRE‐PS, pH increases were associated with increases in phytoplankton biomass. There was no significant pH change in the lower NRE‐PS and only the polyhaline CB showed a pH decline consistent with ocean acidification. In both estuaries, interannual pH variability showed robust, positive correlations with chlorophyll a (Chl a) during the spring in mid to lower estuarine regions indicative of strong control by net phytoplankton production. During summer and fall, Chl a and pH negatively correlated in lower regions of both estuaries, given a shift toward heterotrophy driven by changes in phytoplankton community structure and increases in the load ratio of dissolved inorganic nitrogen to organic carbon. Tropical cyclones episodically depressed pH due to vertical mixing of CO2 rich bottom waters and post‐storm terrestrial organic matter loading. Local processes we highlight represent a significant challenge for predicting future estuarine pH.

Physiological responses of scallops and mussels to environmental variability: Implications for future shellfish aquaculture

Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound's combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.

Importance of estuaries for the horse-eye jack Caranx latus in northeastern Brazil: a case study of underestimated connectivity at the land-sea interface

This study aimed to evaluate the importance of inshore estuarine habitats for the maintenance of offshore exploited stocks of the horse-eye jack Caranx latus, a marine tropical species of high economic value. Otoliths of 143 yearlings were used to develop a data set of multi-elemental fingerprints for different juvenile habitats of C. latus in northeastern Brazil, including 7 estuaries and the coastal zone. This data set was then compared to the signatures in the juvenile part of the otolith of 40 sub-adult and adult fish caught at sea to identify their origin. Although otolith multi-elemental concentrations overlapped for some of the estuaries investigated, the maximum overall discrimination accuracy between them was only 58%. However, grouping several estuaries according to their similarity in elemental signatures increased accuracy to 80%. In both cases, correct re-assignment rates for the coastal zone were above 94%, and strontium (Sr) was the most significant element in juvenile habitat discrimination. The remaining elements (B, Ba, Co, P, Rb, and Zn) allowed us to distinguish between 3 distinct groups of estuaries, for which correct re-assignment rates were 70-88%. Juvenile fingerprints in sub-adult and adult otoliths revealed that most of the fish in the local, exploited stock (75%) originate from an inshore estuarine habitat, particularly from larger estuaries under constant marine influence (32.5%). This biological connectivity between continental and coastal waters should be considered for the conservation of tropical marine coastal stocks in general, as it is likely to apply to other exploited marine species, in Brazil and elsewhere.

Seasonal variability in water‒air CO2 exchanges and carbon origin in a subtropical estuary

The seasonal and interannual variabilities in the water‒air net carbon dioxide (CO2) flux were investigated in the lower zone of the Patos Lagoon Estuary (PLE), the largest choked lagoon worldwide. The studied region experienced periods of CO2 ingassing (outgassing) during ocean-dominated (riverine-dominated) conditions. During ocean-dominated conditions (summer/autumn), CO2 uptake was an average of −15 mmol m–2 d–1, whereas under riverine-dominated conditions (winter/spring), CO2 emissions prevailed, reaching an average of 22 mmol m–2 d–1. The magnitude of CO2 uptake in summer/autumn was comparable to the CO2 released to the atmosphere in winter/spring in the mesomixohaline zone. However, the CO2 uptake in summer/autumn was 4-fold higher than the CO2 released in winter/spring in the euhaline zone of the PLE. Unlike most estuarine systems, the PLE acted as a net CO2 sink, with a net CO2 uptake of −2 mmol m–2 d–1 during the period investigated (May 2017 to June 2021). The water‒air CO2 exchanges are modulated mainly by the balance between continental freshwater discharge and the inflow/outflow of seawater. However, the combined effect of wind speed, biological activity, and water residence time adds complexity to understanding the carbon exchanges in this region. The higher concentration of organic matter entails the highest estuarine CO2 concentration during autochthonous production, which indicates heterotrophy in estuarine waters. Part of this carbon produced in the estuary is likely exported to the coast, as suggested by the high CO2 concentration in the estuary mouth. The CO2 export from the PLE to the coastal zone appears to make the lagoon resilient to regional anthropogenic CO2 build-up. Owing to the water‒air net CO2 flux range associated with complex PLE biogeochemistry dynamics, further investigations as a long-term time-series program will improve knowledge of regional CO2 exchanges in the context of climate and elucidate the role of large estuaries and coastal bays in the global carbon budget.

Discerning the Concentration and Bi‐Directional Flux of Ammonia in an Urban Estuary Using the Relaxed Eddy Accumulation Method

AbstractNarragansett Bay, the largest estuary in New England, is a heavily urbanized watershed impacted by deposition and runoff. Nutrient budgets and local policy rely on deposition data from a 1990 study that did not include any direct observations of dry deposition of gaseous ammonia (NH3(g)) and particulate ammonium (p‐NH4+) due to uncertainties in their flux direction and measurement difficulty. Recent work has shown that wet deposition of ammonium (NH4+) to the Bay has increased by a factor of 6 over the past three decades, leading to a 2.5‐fold increase in wet nitrogen (N) deposition. This documented increase in wet deposition of NH4+ is concurrent with managed nutrient reductions in urbanized estuaries but has potentially increased the impacts of atmospheric N deposition, including the dry deposition of NH3(g) and p‐NH4+. However, the lack of NH3(g) and p‐NH4+ measurements hinders our interpretation of this important N source. For the first time over Narragansett Bay, and to our knowledge over open water, dry (particulate and gas phase) total ammonia (NHx = NH3(g) + p‐NH4+) and the bidirectional NH3(g) flux were quantified using a relaxed eddy accumulation sampling technique. We find that dry deposition of NHx comprises 9.6% of total (wet + dry) N deposition. During the fall season, the dominant flux direction for NH3(g) is upward, which also has implications for urban air quality. We estimate that NH3(g) emitted from the Bay to the atmosphere makes up to 10% of the local NH3(g) emission budget for fall.

Design and redesign of a bottom trawl survey in Chesapeake Bay, USA

Fisheries-independent surveys that reliably sample a broad size range of exploited and ecologically important species provide valuable data in support of fisheries management and ecosystem science. The operational consistency of surveys over time and space is fundamental to the interpretation of data in the contexts of population dynamics processes, community interactions, policy impacts, and environmental forcing. However, the need to maintain historic sampling protocols over extended time periods limits the utilization of new technologies that could lead to improved data collection. Survey vessel replacements also become inevitable as the maturity of sampling programs becomes multidecadal. This case study describes the motivational origin, initial design, and redesign of a bottom trawl survey operating in Chesapeake Bay, the largest estuary in the United States. Regional aspirations to consider ecosystem principles in fisheries management aided initial development of the survey, and the need to collect specific data types to support that endeavor impacted several early design elements. Following the beginning years of full-scale survey operations, a consistently evolving awareness of potential areas of improvement for the survey grew from formal efforts to engage with scientific and industry partners on trawl gear design, leverage the program for additional survey opportunities, utilize gear testing technology, and analyze extant data. When the delivery of a new, state-of-the-art research vessel forced the transfer of survey operations to a new platform, all potential changes were incorporated simultaneously. A subsequent paired-tow experiment was conducted to build a calibration database that successfully provided estimates of relative selectivity for routinely sampled taxa. This experience yielded several lessons learned that are intended to aid investigators faced with adopting structural changes to fisheries-independent surveys in the future.

Effect of High-Density Polyethylene Microplastics on the Survival and Development of Eastern Oyster (Crassostrea virginica) Larvae.

Microplastic (MP) pollution is a growing global concern-especially in estuarine areas that serve as natural habitats and nurseries for many marine organisms. One such marine organism is the Eastern oyster (Crassostrea virginica), which is a reef-forming keystone species in the Chesapeake Bay, the largest estuary in the United States. To understand the potential impacts of MP pollution on the estuary ecosystem, the effects of high-density polyethylene (HDPE) MPs on Eastern oyster larval survival and development were investigated. Three cohorts of larvae were exposed to HDPE MPs with a size of 10-90 µm at a 10 mg/L concentration, after 7 to 11 days of fertilization. After exposure, the number and size of oyster larvae were measured twice a week for approximately 2 weeks until larval settlement. The experiment found that there were no significant differences in the rate of survival between the control and MP-addition treatments. However, we noticed that larval development was significantly delayed with the MP treatment. The percentage of larvae that were ready to settle was 64% with the control treatment compared to 43.5% with the MP treatment. This delay in growth resulted in a delayed larval settlement, which could adversely affect the survival of the Eastern oyster due to the increased risk of predation. The current study demonstrates that MPs could be a risk to the ecology of estuaries, and plastic pollution management is needed for the preservation of these estuaries.

Ecological risk assessment of the Paraíba River estuary (Brazil): Plan for a tier 1 screening phase for the ecotoxicological line of evidence

The knowledge produced in temperate regions is still used today to evaluate environmental problems in the tropics, without taking into consideration environmental differences, such as local conditions, the sensitivity and ecology of species, and exposure routes of contaminants, essential for understanding and determining the fate and toxicity of chemicals. Considering that Environmental Risk Assessment (ERA) studies for tropical systems are scarce and need to be adjusted, the present study aims at contributing to the awareness and development of tropical ecotoxicology. The estuary of the Paraíba River in Northeast Brazil was selected as a model study-case, as it is a large estuary, subjected to a heavy human pressure due to the numerous social, economic and industrial activities. The present study describes the framework for the problem formulation phase of the ERA process; it first includes a detailed integration of the scientific information available on the study area, to then derive the conceptual model, and finally present the analysis plan for the tier 1 screening phase. The latter is designed to be fundamentally supported by the ecotoxicological line of evidence, to ascertain, without delay, where and why there are environmental problems (i.e., adverse biological effects); ecotoxicological tools developed in temperate climates will be optimized to assess water quality in a tropical system. In addition to its intrinsic value for protecting the study area, the results of the present study are expected to provide an important baseline for conducting ERA in similar tropical aquatic systems across the globe.