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Abstract: Abstract Hard-substrate invertebrate communities are key components of estuarine ecosystem function, and often contribute substantially to species diversity. Ecological theory, and growing evidence, suggests that predators may strongly shape hard-substrate community assembly and invasion dynamics, especially in tropical and sub-tropical estuaries. Yet evidence has been largely limited to high-salinity systems. The interplay between salinity and predator control therefore remains unclear, complicating predictions for oligohaline and mesohaline waters, and systems where pulsed low-salinity events are becoming more common. Working in a sub-tropical, urbanized estuary (Galveston Bay, TX, USA), we asked how salinity influenced predator effects on three metrics of epifaunal community assembly: biomass, species richness, and composition. We used a predator-exclusion experiment at five sites spanning a broad salinity gradient, repeated over 2 years of varying rainfall. Low-salinity conditions generally weakened the strength of predator effects, but responses varied by year and metric. In 2019, the wetter year, predation reduced species richness only at high-salinity sites, but had no detectable influence on composition. In 2020, the drier year, low salinity moderated effects of predation on composition, but neither salinity nor predation influenced richness. Our results emphasize that classic models of community regulation, even when supported by data, may be realized via different components of community assembly over time. Findings also underscore the potential for anthropogenic changes (e.g., via water diversions, development, and climate change) to have cascading, indirect effects on secondary production and epibiotic dynamics in estuaries by altering the extent to which predators influence epifaunal communities. PubDate: 2022-05-04
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Abstract: Abstract Coastal wetlands are important for carbon (C) storage and sequestration. Still, there are large knowledge gaps concerning the amount of “blue carbon” in coastal wetlands dominated by common reed (Phragmites australis). We quantified carbon stocks at the southern Baltic Sea coast at six representative Phragmites wetland sites at the Darss-Zingst-Bodden Chain (DZBC) and the Strelasund, which include different categories of adjacent land use (arable land, woodland, pasture, urban), topography (totally flat to undulating), and geographical restrictions (dyking). Sediment samples were taken to a depth of 1 m, in line with the IPCC guidelines, and total carbon concentrations and bulk densities were measured in 10 cm intervals. The sites stored, on average, 17.4 kg C m−2 with large variability between sites, ranging from 1.76 to 88.6 kg C m−2. The estimated average is generally in good agreement with carbon stocks reported for tidal salt marshes, mangroves, and seagrass meadows. According to our estimation, based on widths of the reed belts and carbon stocks at the sampled sites, approximately 264,600 t of blue carbon could be stored in the coastal reed belts along the DZBC, a typical lagoon system of the southern Baltic Sea. Our study underlines the importance of these unique ecotones between land and sea for storage and sequestration of blue carbon. Since Phragmites is also a common (sometimes invasive) species along other large brackish water basins, such as the Black Sea or Chesapeake Bay, these estimates can be used for improved precision of modeling blue carbon budgets. PubDate: 2022-05-04
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Abstract: Abstract Effective management and restoration of salt marshes and other vegetated intertidal habitats require objective and spatially integrated metrics of geomorphic status and vulnerability. The unvegetated-vegetated marsh ratio (UVVR), a recently developed metric, can be used to establish present-day vegetative cover, identify stability thresholds, and quantify vulnerability to open-water conversion over a range of spatial scales. We developed a Landsat-based approach to quantify the within-pixel vegetated fraction and UVVR for coastal wetlands of the conterminous United States, at 30-m resolution for 2014–2018. Here we present the methodology used to generate the UVVR from spectral indices, along with calibration, validation, and spatial autocorrelation assessments. We then demonstrate multiple applications of the data across varying spatial scales: first, we aggregate the UVVR across individual states and estuaries to quantify total vegetated wetland area for the nation. On the state level, Louisiana and Florida account for over 50% of the nation’s total, while on the estuarine level, the Chesapeake Bay Estuary and selected Louisiana coastal areas each account for over 6% of the nation’s total vegetated wetland area. Second, we present cases where this dataset can be used to track wetland change (e.g., expansion due to restoration and loss due to stressors). Lastly, we propose a classification methodology that delineates areas vulnerable to open-water expansion based on the 5-year mean and standard deviation of the UVVR. Calculating the UVVR for the period-of-record back to 1985, as well as regular updating, will fill a critical gap for tracking national status of salt marshes and other vegetated habitats through time and space. PubDate: 2022-05-02
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Abstract: Abstract Estuarine and coastal geomorphology, biogeochemistry, water quality, and coastal food webs in river-dominated shelves of the Gulf of Mexico (GoM) are modulated by transport processes associated with river inputs, winds, waves, tides, and deep-ocean/continental shelf interactions. For instance, transport processes control the fate of river-borne sediments, which in turn affect coastal land loss. Similarly, transport of freshwater, nutrients, and carbon control the dynamics of eutrophication, hypoxia, harmful algal blooms, and coastal acidification. Further, freshwater inflow transports pesticides, herbicides, heavy metals, and oil into receiving estuaries and coastal systems. Lastly, transport processes along the continuum from the rivers and estuaries to coastal and shelf areas and adjacent open ocean (abbreviated herein as “river-estuary-shelf-ocean”) regulate the movements of organisms, including the spatial distributions of individuals and the exchange of genetic information between distinct subpopulations. The Gulf of Mexico Research Initiative (GoMRI) provided unprecedented opportunities to study transport processes along the river-estuary-shelf-ocean continuum in the GoM. The understanding of transport at multiple spatial and temporal scales in this topographically and dynamically complex marginal sea was improved, allowing for more accurate forecasting of the fate of oil and other constituents. For this review, we focus on five specific transport themes: (i) wetland, estuary, and shelf exchanges; (ii) river-estuary coupling; (iii) nearshore and inlet processes; (iv) open ocean transport processes; and (v) river-induced fronts and cross-basin transport. We then discuss the relevancy of GoMRI findings on the transport processes for ecological connectivity and oil transport and fate. We also examine the implications of new findings for informing the response to future oil spills, and the management of coastal resources and ecosystems. Lastly, we summarize the research gaps identified in the many studies and offer recommendations for continuing the momentum of the research provided by the GoMRI effort. A number of uncertainties were identified that occurred in multiple settings. These include the quantification of sediment, carbon, dissolved gasses and nutrient fluxes during storms, consistent specification of the various external forcings used in analyses, methods for smooth integration of multiscale advection mechanisms across different flow regimes, dynamic coupling of the atmosphere with sub-mesoscale and mesoscale phenomena, and methods for simulating finer-scale dynamics over long time periods. Addressing these uncertainties would allow the scientific community to be better prepared to predict the fate of hydrocarbons and their impacts to the coastal ocean, rivers, and marshes in the event of another spill in the GoM. PubDate: 2022-05-01
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Abstract: Abstract Sea-level rise is impacting the longest undeveloped stretch of coastline in the contiguous United States: The Florida Big Bend. Due to its low elevation and a higher-than-global-average local rate of sea-level rise, the region is losing coastal forest to encroaching marsh at an unprecedented rate. Previous research found a rate of forest-to-marsh conversion of up to 1.2 km2 year−1 during the nineteenth and twentieth centuries, but these studies evaluated small-scale changes, suffered from data gaps, or are substantially outdated. We replicated and updated these studies with Landsat satellite imagery covering the entire Big Bend region from 2003 to 2016 and corroborated results with in situ landscape photography and high-resolution aerial imagery. Our analysis of satellite and aerial images from 2003 to 2016 indicates a rate of approximately 10 km2 year−1 representing an increase of over 800%. Areas previously found to be unaffected by the decline are now in rapid retreat. PubDate: 2022-05-01
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Abstract: Abstract Fisheries are a staple human activity supported by coastal lagoons. Together with water quality and trophic status, lagoon morphology is acknowledged as one of the main ecological drivers of fishery yields; however, the role of lagoon seascape structure is still poorly understood. This paper investigates how morphological variables, habitat distribution and seascape diversity and complexity affect yields of artisanal fishery performed with fyke nets in the Venice Lagoon (northern Adriatic Sea, Italy). Two spatial scales were considered in the analysis, with water quality parameters (temperature, salinity, dissolved oxygen, turbidity, water residence times, N, P and chlorophyll-a concentrations) being measured at a fine, fyke-net scale and morphological (average bottom elevation and sediment grain size) and habitat features (habitat proportion, diversity and complexity) being measured at a broader, seascape scale. Generalised linear mixed models were employed to model 8 years of nekton and green crab catches, disentangling the role of broad-scale morphology and seascape from that of fine-scale water quality. Broad-scale variables clearly influenced fishery target species. Among them, lagoon residents were associated with specific morphological and habitat characteristics, while marine migrants showed a stronger link with overall habitat diversity and complexity. This evidence emphasises how artisanal fishery in the Venice Lagoon relies on the conservation of morphological and habitat heterogeneity. Moreover, it highlights how habitat restoration performed at the seascape level should also be taken into account, in addition to controlling hydrology and water quality, when managing fishery resources in coastal lagoons. PubDate: 2022-05-01
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Abstract: Abstract Subsidence and accelerated sea level rise impact nesting area availability and flood probabilities of breeding islands for colonial nesting waterbirds. In 2017 and 2018, we monitored 855 nests of four species of colonial nesting waterbirds on Rabbit Island, LA, to determine factors affecting nest and chick success. Based on logistic exposure models of nests, tricolored herons had the greatest likelihood of survival to hatch (mean (95% confidence interval)) (77% (65.9–83.1%)), followed by brown pelicans (70% (59.9–98.5%)), roseate spoonbills (70% (38.9–83.8%)), and Forster’s terns (12% (10.7–12.2%)). Likelihood of survival to fledge was highest for tricolored herons (32% (12.8–40.7%)), followed by brown pelicans (28% (19.5–28.6%)), roseate spoonbills (47% (43.7–53.3%)), and Forster’s terns (0% (0.005–0.01%)). Nesting strategy and nest timing impacted survival rate; however, the effect depended on timing of inundation events as the timing of inundation events varied across years. Flooding was the primary cause of nest failure for most species. In 2003–2012, rapid expansion in brown pelican colony numbers and significant chick production occurred at Rabbit Island, but hydrologic records indicate no island inundation occurred during the breeding season from the beginning of the hydrologic record (2006) through 2011. Thus, our results contrast with those of previous studies conducted under different hydrologic conditions and demonstrate the challenges of short-term studies informing coastal restoration in a system that is influenced by multi-year to multi-decadal climatic cycles. PubDate: 2022-05-01
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Abstract: Abstract The macroecological variable of patchiness (Lloyd’s Ip index of patchiness, P) has recently been shown to be related inter- and intraspecifically to those of abundance (numbers m−2, A), and occupancy (% occurrence in samples, O) in lower latitude seagrass macrofaunas. For the first time in higher latitudes, intraspecific relationships between three spatial variables were investigated in the intertidal mudflat macrobenthos of the Scolt Head barrier island, southern North Sea (53° N, 01° E). Sampling was conducted between early July and late September 2009–2013 using 710-µm mesh for sample processing. Strong positive interspecific A-O and negative interspecific P-O and P-A relationships were present. Two of the most numerous and widespread assemblage components, however, occurred with effectively constant occupancy (Peringia ulvae, 100%, and Tubificoides benedii, 93%) across the whole 20-ha locality and therefore could not show intraspecific relationships of occupancy with other macroecological metrics. These two apart, only one other dominant species failed to show a significant positive intraspecific A-O relationship; no species showed significant P-A relations of any form; and only two showed the negative P-O ones that have been described elsewhere. The intraspecific A-O patterns appear to contrast with those of an earlier study at another North Sea locality (the Dutch Wadden Sea), although differences are more apparent than real, but the Scolt Head fauna showed fewer intraspecific P-O and P-A relations than those characterising similar circumstances in the two lower-latitude localities previously investigated. Neither developmental mode nor variation in local abundance appears to influence these patterns. A-O-P relations therefore seem widespread but may be subject to latitudinal modification. PubDate: 2022-05-01
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Abstract: Abstract This work investigates the impact of regional climatic changes upon the salinity field of Todos os Santos Bay (BTS), the third largest estuary in the country. A comprehensive meteorological and oceanographic data set was used, which included more than 50 years of rainfall, river discharge and air temperature, 7 years of hydrodynamic numerical simulations of the bay and adjacent shelf, and 3 years of observations of the salinity field. The results show a clear aridification (less humidity and warmer air temperatures) trend in the last 5–6 decades. In this period, the yearly mean fluvial discharges and total rainfall were reduced by up to 72% and 50%, respectively, of their climatological means, and the air temperature increased by up to 1.25 °C. Less freshwater inflow and higher temperatures caused an increase of the mean surface salinity of 0.6 for the whole bay and 1.2 in the most internal sectors. Hypersalinity events apparently occurred for the first time in the early 1990s, and reached a maximum intensity in 2013 during the worst regional draught in the historical record, when an estuarine density plug was observed. The hypersalinity events were intensified, and not caused by the damming of Paraguaçu River, whose summer discharges have decreased faster than anticipated by previous investigations. The original tropical climate of the region has become more Mediterranean, with relatively less rainfall occurring in the summer. The hydrographic changes of the BTS exemplify similar hydrological and hydrographic processes that might also be underway in tropical areas undergoing climate aridification. PubDate: 2022-05-01
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Abstract: Abstract Oyster populations within the coastal bays of Virginia have greatly declined, mainly due to overharvesting and disease, and past restoration efforts have largely focused on increasing their populations. Current restoration goals have now expanded to simultaneously procure the wider ecosystem services oysters can offer, including shoreline protection and ecosystem diversification. However, tradeoffs exist in designing artificial reefs because it is unlikely one design will optimize all services. This study compares the services provided by reef designs varying in elevation and width located adjacent to an intertidal marsh within a coastal bay of VA, USA. We quantified wave attenuation to determine potential coastal protection of the adjacent marsh, and changes to sediment composition and infaunal communities before and after reef construction for 3 years. After construction, we also quantified oyster size and population density to compare high and low elevation reef designs. High elevation reefs were more effective at attenuating waves and fostering oyster growth compared to low elevation reefs. Oysters atop high elevation reefs were on average approximately twice as dense and 20% larger than those on low elevation designs. Reef width had a minimal effect on oyster population density; densities on high and low reefs were similar for designs with one or three rows. The presence of oyster reefs also increased infaunal diversity and sediment organic matter. Our results indicate that artificial reef design can differentially affect the services provided through restoration, and elevation is especially important to consider when designing for oyster population enhancement and coastal protection. PubDate: 2022-05-01
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Abstract: Abstract Estuarine circulation is a vertical circulation that develops along the salinity gradient in estuaries and nearshore coastal waters. Fresher, and therefore less-dense, water flows out of the estuary in the surface layer, while a deeper inflow brings water from the open sea into the estuary. This study uses 7 years of in situ current measurements and hydrographic surveys to verify that this deeper inflow has two modes: a deep inflow that intrudes along the seabed, and a shallow-inflow that penetrates into the subsurface layer. These modes show seasonal variability, i.e., the deep-inflow mode occupies almost all of the winter season, whereas the shallow-inflow mode dominates during the summer. This mode change may play a key role in oxygen and carbon dioxide (CO2) dynamics in estuaries and nearshore coastal waters. When the transition from deep- to shallow-inflow begins in spring, a cold water mass forms on the seabed in the upper estuary. This cold water mass is isolated from heating sources and oxygenated water; consequently, the cold water mass becomes hypoxic and accumulates both inorganic nutrients and CO2 during spring and summer. When the transition from the shallow- to deep-inflow occurs, the CO2, which is trapped in the bottom-water, is emitted to the atmosphere. The mechanism that causes the seasonal mode change in estuarine circulation is driven by the spatial inhomogeneity in the heating or cooling of the lower layer, which generates a horizontal density gradient in the layer. This mechanism highlights the importance of temperature in estuarine dynamics, which has not been extensively studied previously. PubDate: 2022-05-01
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Abstract: Abstract Ship Shoal is an inner-shelf submarine shoal with large amounts of restoration quality sand that was dredged in 2013–2016 for the Caminada Headland Restoration Project in central Louisiana, USA. Here we provide the first assessment of the characteristics and rate of seasonal sediment infilling the South Pelto dredge pit on eastern Ship Shoal, which will inform future restoration initiatives. Vibracore and multicore samples collected in 2017 and 2018 from within and outside of South Pelto dredge pit revealed new interlaminated silts and clays (median grain size 4.3–6 ϕ, 16–48 µm) deposited at the bottom of the dredge pit, underlain by original Ship Shoal sand and older pro-delta deposits. Through analyzing beryllium-7 (7Be) inventories in multicores, we found that sedimentation rate varied seasonally from 4 to 12 cm (sedimentation rate 0.02–0.06 cm day−1) in fall 2017 to 8 to16 cm (0.05–0.15 cm day−1) in spring 2018. Mapping plume distribution along the continental shelf with satellite imagery corroborated with local wind/wave data revealed that the sediments deposited in South Pelto dredge pit are likely sourced from a combination of the Atchafalaya and Mississippi River plumes during the study period, in addition to possible resuspension from the ambient inner continental shelf and fine-grained material exported from proximal bays. Sedimentation in the dredge pit is not greatly affected by wall slope failure or bedload influx of ambient Ship Shoal sand. Infilling rate and material are slower and finer than past model prediction. Restoration quality sand on this sandy shoal in Louisiana is thus not renewable. PubDate: 2022-05-01
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Abstract: Abstract Understanding fish-habitat associations and distributions are important for making informed management decisions relevant to habitat restoration and species recovery. Chinook salmon, in particular, rely heavily on estuaries, and restoring these habitats has become an important component of recovery plans for threatened populations. Information regarding general distribution patterns, while often lacking, could be useful for restoration evaluation and planning. We used time series analysis to identify common trends in weekly Chinook salmon abundance among seven separate zones within the Snohomish River delta while evaluating the effect of temperature and outmigration abundance on observed patterns. We found two unique trends described seasonal Chinook salmon density and a significant negative effect of temperature on observed density throughout the estuary. The first trend indicated Chinook salmon density increased steadily from February through early June before decreasing into mid-summer. The second trend was characterized by an early spike and a gradual increase in density into early April before leveling off then decreasing into mid-June. The association of each zone with these trends was consistent with the distribution of tidal wetland habitat area among each zone. We postulate that these trends in seasonal Chinook density reflect patterns of movement and rearing, respectively, throughout the estuary and highlight how and where estuary habitat in the Snohomish delta supports life history diversity. Confirmation of seasonal rearing patterns may aid current restoration project evaluation, while a migratory seasonal trend may help prioritize future restoration in the Snohomish estuary by identifying where opportunity exists to support estuary rearing for Chinook salmon. Finally, our methodology and analytical approach for evaluating spatial and temporal variability in Chinook salmon distributions and abundance may be applied to other tidal deltas to make informed decisions or evaluations of both current and future restoration actions. PubDate: 2022-05-01
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Abstract: Abstract The blue crab Callinectes sapidus was first observed in the Ebro Delta in 2012 and since then captures have increased exponentially up to over 2 t per day, while its presence remains low in other Catalonian estuarine areas. Here, we use a stable isotope approach (δ15N and δ13C) to explore the dietary habits of adult blue crab in four different invaded habitats—bays, coastal lagoons, rice field drainage channels, and the Ebro River—in order to assess the strength of bottom-up forces and identify risks for native and aquaculture species, as well as patterns of site fidelity (male individuals). Mixing models showed average contributions of 35.89% from organic matter in sediments, 34.25% from animal resources (fish, crustaceans, gastropods, and bivalves), and 23.84% from vegetal resources (aquatic plants and algae), although there were important differences across habitat sites. In sites where bivalves were available, they can represent up to ca. 75% of the diet, thus threatening natural banks and local oyster and mussel farms. The average estimated trophic position of blue crabs in those sites was only 2.8, which confirms an omnivorous behavior but also can be attributed to the fact that mollusks were rare in the majority of the areas sampled in the Ebro Delta. Crabs from the same habitat site exhibited very little isotopic variability, suggesting that they remain in those environments long enough to reflect local salinity conditions. Overall, our results suggest that blue crabs are likely using all locally available resources and remain in certain sites, even when preferred animal preys are scarce and low-quality items are the main dietary option. PubDate: 2022-05-01
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Abstract: A subsurface oxygen minimum layer (OML) in intermediate water is identified and characterized in Rivers Inlet, a fjord on British Columbia’s central coast, using data from 1998 to 2018. The OML was observed in most years from May to September and was most persistent at the middle and head of the fjord. The Rivers Inlet OML develops in three stages: (i) in early spring, the cessation of winter storms from downwelling-favourable winds stops the ventilation of the water column; (ii) throughout spring and summer, the remineralization of organic matter, likely primarily phytoplankton, consumes oxygen in the intermediate waters; (iii) in late spring, deep-water renewal by oxygenated offshore water forms the base of the OML inside the inlet. The strength and persistence of the OML vary interannually, mainly due to variability in hemispheric-scale winds and primary production. In some years, the OML was hypoxic, which could influence the local marine ecosystem. Changes to downwelling, upwelling, or primary production in Rivers Inlet could affect the OML in the future. PubDate: 2022-05-01
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Abstract: Abstract Heatwaves are increasing in frequency, duration, and intensity in the atmosphere and marine environment with rapid changes to ecosystems occurring as a result. However, heatwaves in estuarine ecosystems have received little attention despite the effects of high temperatures on biogeochemical cycling and fisheries and the susceptibility of estuaries to heatwaves given their low volume. Likewise, estuarine heatwave co-occurrence with extremes in water quality variables such as dissolved oxygen (DO) and pH have not been considered and would represent periods of enhanced stress. This study analyzed 1440 station years of high-frequency data from the National Estuarine Research Reserve System (NERRS) to assess trends in the frequency, duration, and severity of estuarine heatwaves and their co-occurrences with atmospheric heatwaves, low DO, and low pH events between 1996 and 2019. Estuaries are warming faster than the open and coastal ocean, with an estuarine heatwave mean annual occurrence of 2 ± 2 events, ranging up to 10 events per year, and lasting up to 44 days (mean duration = 8 days). Estuarine heatwaves co-occur with an atmospheric heatwave 6–71% of the time, depending on location, with an average estuarine heatwave lag range of 0–2 days. Similarly, low DO or low pH events co-occur with an estuarine heatwave 2–45% and 0–18% of the time, respectively, with an average low DO lag of 3 ± 2 days and low pH lag of 4 ± 2 days. Triple co-occurrence of an estuarine heatwave with a low DO and low pH event was rare, ranging between 0 and 7% of all estuarine heatwaves. Amongst all the stations, there have been significant reductions in the frequency, intensity, duration, and rate of low DO event onset and decline over time. Likewise, low pH events have decreased in frequency, duration, and intensity over the study period, driven in part by reductions in all severity classifications of low pH events. This study provides the first baseline assessment of estuarine heatwave events and their co-occurrence with deleterious water quality conditions for a large set of estuaries distributed throughout the USA. PubDate: 2022-05-01
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Abstract: Abstract Small-scale fisheries, which are often distributed over large spatial scales and occur in rural settings, tend to lack financial resources and capacity to conduct research on local issues. One approach to overcome this challenge is to use relatively inexpensive environmental monitoring methods with stakeholder engaged science and participatory modeling. Here, we present a case study focused on water pollution impacts and tidal circulation in a mid-coast Maine (USA) estuary to develop a simulation model and a partnership approach that can support soft-shell clamming communities to effectively address water quality, namely bacteriological closures of mudflats. We deployed multiple low-cost drifter buckets, Lagrangian flotation devices that measured surface current speeds and provided validation data for a hydrodynamic model based on finite volume community ocean model (FVCOM). The drifter buckets resolved the influence of wind, tidal currents, and bathymetry on surface water circulation patterns between the main channel and adjacent mudflats, highlighting the impact of cross-estuary winds during slack tides on potential bacterial transport. We calculated residence time using the validated FVCOM model: in the prohibited area (~ 2.5 days), and the conditional area (~ 0.5 days). This information has already influenced local management decisions and helped shape new conservation projects. In addition to contributing new understanding about tidal patterns in this coastal region, our novel methodology of combining field techniques, FVCOM modeling, and stakeholder engagement helps show how engaged research approaches can improve regulatory outcomes for small-scale fisheries while also protecting public health. PubDate: 2022-05-01
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Abstract: Abstract Animal groups are known to exhibit collective behaviours that allow for effective responses to predators and environmental factors. Habitats with high levels of structural complexity have been shown to influence the collective tendencies of these animal aggregations. However, the effect of anthropogenically induced habitat complexity on collective tendency is still unknown. We examined the effect of a water control structure (WCS), located in an estuarine salt marsh system, on the collective behaviours of free ranging juvenile Gulf menhaden (Brevoortia patronus), a schooling forage fish. Using an acoustic imaging sonar, behavioural observations prior to and during predator attacks were collected in an open marsh canal as well as in the vicinity of the WCS. We found that fish in schools responded to the WCS by swimming in a less aligned and cohesive manner, while maintaining an increased ability to transfer social information. Our results demonstrate that collective tendency in schooling fish is affected by the presence of anthropogenically introduced habitat complexity, prior to and during predator attack. Our study, thus, strengthens the idea that the complex environmental conditions induced by the presence of man-made structures may play a large role in structuring collective behaviour and trophic interactions in aquatic environments. PubDate: 2022-05-01
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Abstract: Abstract Estuaries act as conduits for and modifiers of carbon delivery from watersheds to the coastal ocean. Here we hypothesize that a long residence time estuary receiving high nutrient and humic-rich dissolved organic carbon (DOC) loads from the watershed will efficiently produce and trap autochthonous carbon while conservatively transporting watershed-derived DOC to the coastal ocean. We assessed temporal changes in estuarine carbon dynamics in the New River Estuary, NC, USA (NRE) by measuring concentrations and 13C isotopic composition of particulate organic carbon (POC), DOC, and dissolved inorganic carbon (DIC) monthly for 16 months. Data were evaluated with respect to seasonal changes in each carbon pool inventory and non-conservative mixing along the estuarine axis. The estuary was predominantly a sink for POC trapping 65–95% of watershed-derived POC under low/moderate flow conditions and up to half of the autotrophic POC produced in the upper estuary seasonally. DIC inventories were dominantly driven by salinity. Monthly DIC and δ13C-DIC mixing curves rarely showed large deviations from non-conservative behavior but did reflect an estuarine gradient consistent with higher autotrophy upstream and increased heterotrophy downstream. Mixing curves for DOC primarily reflected conservative mixing of riverine DOC with seawater. However, there was a 50% increase summertime estuarine DOC inventory concurrent with a 2.5‰ decrease in δ13C-DOC suggesting diffuse lateral sources of isotopically light DOC with low lability. For POC, the NRE traps a large fraction of imported and autochthonous carbon and exports POC derived primarily from estuarine autotrophy. For DOC, we suggest that most of the DOC produced internally is mineralized within the estuary and that the NRE conservatively transports DOC derived from riverine and lateral wetland sources to the coastal ocean. PubDate: 2022-05-01
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