Showing papers in "Estuaries and Coasts in 2015"

True Value of Estuarine and Coastal Nurseries for Fish: Incorporating Complexity and Dynamics

Abstract: Coastal ecosystems, such as estuaries, salt marshes, mangroves and seagrass meadows, comprise some of the world's most productive and ecologically significant ecosystems. Cur- rently, the predominant factor considered in valuing coastal wetlands as fish habitats is the contribution they make to off- shore, adult fish stocks via ontogenetic migrations. However, the true value of coastal nurseries for fish is much more extensive, involving several additional, fundamentally important ecosystem processes. Overlooking these broader aspects when identifying and valuing habitats risks suboptimal conservation outcomes, especially given the intense competing human pressures on coastlines and the likelihood that protection will have to be focussed on specific locations rather than across broad sweeps of individual habitat types. We describe 10 key components of nursery habitat value grouped into three types: (1) connectivity and population dynamics (includes connectivity, ontogenetic migration and seascape migration), (2) ecological and ecophys- iological factors (includes ecotone effects, ecophysiological fac- tors, food/predation trade-offs and food webs) and (3) resource dynamics (includes resource availability, ontogenetic diet shifts and allochthonous inputs). By accounting for ecosystem com- plexities and spatial and temporal variation, these additional components offer a more comprehensive account of habitat value. We explicitly identify research needs and methods to support a broader assessment of nursery habitat value. We also explain how, by better synthesising results from existing re- search, some of the seemingly complex aspects of this broader view can be addressed efficiently.

Large Natural pH, CO2 and O2 Fluctuations in a Temperate Tidal Salt Marsh on Diel, Seasonal, and Interannual Time Scales

Abstract: Coastal marine organisms experience dynamic pH and dissolved oxygen (DO) conditions in their natural habitats, which may impact their susceptibility to long-term anthropogenic changes Robust characterizations of all temporal scales of natural pH and DO fluctuations in different marine habitats are needed; however, appropriate time series of pH and DO are still scarce We used multiyear (2008–2012), high-frequency (6 min) monitoring data to quantify diel, seasonal, and interannual scales of pH and DO variability in a productive, temperate tidal salt marsh (Flax Pond, Long Island, US) pHNBS and DO showed strong and similar seasonal patterns, with average (minimum) conditions declining from 82 (81) and 125 (114) mg l−1 at the end of winter to 76 (72) and 63 (28) mg l−1 in late summer, respectively Concomitantly, average diel fluctuations increased from 022 and 22 mg l−1 (February) to 074 and 65 mg l−1 (August), respectively Diel patterns were modulated by tides and time of day, eliciting the most extreme minima when low tides aligned with the end of the night Simultaneous in situ pCO2 measurements showed striking fluctuations between ∼330 and ∼1,200 (early May), ∼2,200 (mid June), and ∼4,000 μatm (end of July) within single tidal cycles These patterns also indicate that the marsh’s strong net heterotrophy influences its adjacent estuary by ‘outwelling’ acidified and hypoxic water during ebb tides Our analyses emphasize the coupled and fluctuating nature of pH and DO conditions in productive coastal and estuarine environments, which have yet to be adequately represented by experiments

Paradigms in the Recovery of Estuarine and Coastal Ecosystems

Abstract: Following widespread deterioration of coastal ecosystems since the 1960s, current environmental policies demand ecosystem recovery and restoration. However, vague definitions of recovery and untested recovery paradigms complicate efficient stewardship of coastal ecosystems. We critically examine definitions of recovery and identify and test the implicit paradigms against well-documented cases studies based on a literature review. The study highlights a need for more careful specification of recovery targets and metrics for assessing recovery in individual ecosystems. Six recovery paradigms were identified and examination of them established that partial (as opposed to full) recovery prevails, that degradation and recovery typically follow different pathways as buffers act to maintain the degraded state, and that recovery trajectories depend on the nature of the pressure as well as the connectivity of ecosystems and can differ between ecosystem components and among ecosystems. A conceptual model illustrates the findings and also indicates how restoration efforts may accelerate the recovery process.

Rates and Forcing of Marsh Edge Erosion in a Shallow Coastal Bay

Abstract: Salt marshes can experience a significant land loss through erosion and retreat of their perimeter edges. Rates of shoreline change between 1957 and 2007 were determined for four salt marshes in a Virginia coastal bay using aerial photographs and the Digital Shoreline Analysis System (DSAS). High average rates of lateral erosion of 1.0–1.6 m year−1 were found at three marshes, while the edge of the fourth marsh, along the mainland edge of the bay, remained stable. Erosion rates were temporally consistent during the 50-year period at the three eroding sites, although there was a significant spatial variation in rates of change along the length of the edges at these sites. A simple parametric wave model and the SWAN (Simulating WAves Nearshore) spectral wave model were used to calculate incident wave energy flux along the marsh boundaries at each of the sites. Values of wave energy flux agreed fairly well between the two models but are sensitive to the manner in which wave energy flux is calculated. A stronger relationship was found between wave energy flux and volumetric erosion rates along the marsh edges than with lateral erosion rates. This is an important consideration when examining the effects of future sea level rise on marsh loss.

Estimating Relative Sea-Level Rise and Submergence Potential at a Coastal Wetland

Abstract: A tide gauge records a combined signal of the vertical change (positive or negative) in the level of both the sea and the land to which the gauge is affixed; or relative sea-level change, which is typically referred to as relative sea-level rise (RSLR). Complicating this situation, coastal wetlands exhibit dynamic surface elevation change (both positive and negative), as revealed by surface elevation table (SET) measurements, that is not recorded at tide gauges. Because the usefulness of RSLR is in the ability to tie the change in sea level to the local topography, it is important that RSLR be calculated at a wetland that reflects these local dynamic surface elevation changes in order to better estimate wetland submergence potential. A rationale is described for calculating wetland RSLR (RSLRwet) by subtracting the SET wetland elevation change from the tide gauge RSLR. The calculation is possible because the SET and tide gauge independently measure vertical land motion in different portions of the substrate. For 89 wetlands where RSLRwet was evaluated, wetland elevation change differed significantly from zero for 80 % of them, indicating that RSLRwet at these wetlands differed from the local tide gauge RSLR. When compared to tide gauge RSLR, about 39 % of wetlands experienced an elevation rate surplus and 58 % an elevation rate deficit (i.e., sea level becoming lower and higher, respectively, relative to the wetland surface). These proportions were consistent across saltmarsh, mangrove, and freshwater wetland types. Comparison of wetland elevation change and RSLR is confounded by high levels of temporal and spatial variability, and would be improved by co-locating tide gauge and SET stations near each other and obtaining long-term records for both.

Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: I. Along-Channel Water Level Variations, Pacific Ocean to Bonneville Dam

Abstract: This two-part paper provides comprehensive time and frequency domain analyses and models of along-channel water level variations in the 234-km-long Lower Columbia River and Estuary (LCRE) and documents the response of floodplain wetlands thereto. In Part I, power spectra, continuous wavelet transforms, and harmonic analyses are used to understand the influences of tides, river flow, upwelling and downwelling, and hydropower operations (“power-peaking”) on the water level regime. Estuarine water levels are influenced primarily by astronomical tides and coastal processes and secondarily by river flow. The importance of coastal and tidal influences decreases in the landward direction, and water levels are increasingly controlled by river flow variations at periods from ≤1 day to years. Water level records are only slightly nonstationary near the ocean, but become highly irregular upriver. Although astronomically forced tidal constituents decrease above the estuary, tidal fortnightly and overtide variations increase for 80–200 km landward, both relative to major tidal constituents and in absolute terms. Near the head of the tide at Bonneville Dam, strong diel and weekly fluctuations caused by power-peaking replace tidal daily (diurnal and semidiurnal) and fortnightly variations. Tides account for 60–70 %, river flow and seasonal processes 5–20 %, and weather 2–4 % of the total variance in the seaward 60 km of the system. In the landward 70 km of the LCRE, seasonal-fluvial variations account for 80–90 % of the variance, power-peaking 1–6 %, and tides <5 %. In Part II, regression models of water levels and inundation patterns are used to understand the distribution of floodplain wetlands, and a system zonation is defined based on bedrock geology, hydrology, and biota.

Quantifying the Residence Time and Flushing Characteristics of a Shallow, Back-Barrier Estuary: Application of Hydrodynamic and Particle Tracking Models

Abstract: Estuarine residence time is a major driver of eutrophication and water quality. Barnegat Bay-Little Egg Harbor (BB-LEH), New Jersey, is a lagoonal back-barrier estuary that is subject to anthropogenic pressures including nutrient loading, eutrophication, and subsequent declines in water quality. A combination of hydrodynamic and particle tracking modeling was used to identify the mechanisms controlling flushing, residence time, and spatial variability of particle retention. The models demonstrated a pronounced northward subtidal flow from Little Egg Inlet in the south to Pt. Pleasant Canal in the north due to frictional effects in the inlets, leading to better flushing of the southern half of the estuary and particle retention in the northern estuary. Mean residence time for BB-LEH was 13 days but spatial variability was between ∼0 and 30 days depending on the initial particle location. Mean residence time with tidal forcing alone was 24 days (spatial variability between ∼0 and 50 days); the tides were relatively inefficient in flushing the northern end of the Bay. Scenarios with successive exclusion of physical processes from the models revealed that meteorological and remote offshore forcing were stronger drivers of exchange than riverine inflow. Investigations of water quality and eutrophication should take into account spatial variability in hydrodynamics and residence time in order to better quantify the roles of nutrient loading, production, and flushing.

Fish Interactions with a Commercial-Scale Tidal Energy Device in the Natural Environment

Abstract: Fish are a key part of the marine ecosystem likely to be affected by hydrokinetic tidal turbines, but little is known about their behavior around such obstacles in the natural environment. In September 2010, two DIDSON acoustic cameras were used to observe fish interactions with a commercial-scale turbine in Cobscook Bay, Maine. Twenty-two hours (nearly two tidal cycles) of footage were collected. Behaviors of individual fish and schools were classified (e.g., entering, avoiding, passing, or remaining in the wake of the turbine). We analyzed the effects of turbine motion (rotating or not rotating), diel condition (day or night), and fish size (small, ≤10 cm; large, >10 cm) on individual fish behaviors, and compared behaviors of individual fish to schools of fish. When the turbine was rotating, the probability of fish entering the turbine decreased by over 35 % from when it was not. The probability that fish would enter the turbine was higher at night than during the day, and this difference was greater for small fish than for large fish (probability of small fish entering = 0.147 day, 0.513 night; large fish = 0.043 day, 0.333 night). Fish were almost always present in the wake of the turbine. Schools of fish had a 56 % lower probability of entering the turbine than individual fish, and reacted at greater distances from the turbine (median distance of 2.5 m for schools, 1.7 m for individuals). This study indicates that fish behavior in response to tidal turbines appears to be similar to responses to obstacles such as trawls, and highlights the importance of environmental context in determining the effects of a tidal turbine on fish.

From Red Tides to Green and Brown Tides: Bloom Dynamics in a Restricted Subtropical Lagoon Under Shifting Climatic Conditions

Abstract: Relationships between shifts in climatic and other environmental conditions and changes in the character and dynamics of phytoplankton blooms were examined in three interconnected subtropical lagoons on the east coast of Florida, i.e., Mosquito Lagoon, Indian River Lagoon, and Banana River Lagoon, from 1997 to 2013. Phytoplankton blooms were a common feature through most of the study period in two of the lagoons. From 1997 to 2009, blooms in the latter two lagoons were typically dominated by dinoflagellates in the warm wet season and diatoms in the cool dry season. Blooms of the dominant bloom-forming dinoflagellate species Pyrodinium bahamense were positively correlated to rainfall levels, indicating a link to enhanced external nutrient loads. In 2011–2013, major blooms were observed in all three lagoons, but unlike the previous 14 years, they were dominated by picoplanktonic eukaryotes, including a chlorophyte, Pedinophyceae sp., and the brown tide species Aureoumbra lagunensis. The results suggest that extreme climatic conditions, including record cold winter water temperatures and low rainfall levels, were major driving factors in this state shift in the character of blooms, through a wide range of effects including die-offs of benthic flora and fauna, suppression of grazer populations, alteration of nutrient regimes, and uncharacteristic water column conditions, such as elevated salinities and light attenuation.

Impact of Climate Change on Estuarine Zooplankton: Surface Water Warming in Long Island Sound Is Associated with Changes in Copepod Size and Community Structure

Abstract: In coastal ecosystems with decades of eutrophication and other anthropogenic stressors, the impact of climate change on planktonic communities can be difficult to detect. A time series of monthly water temperatures in the Central Basin of Long Island Sound (LIS) from the late 1940s until 2012 indicates a warming rate of 0.03 °C year−1. Relative to the early 1950s, there has been a concurrent decrease in the mean size of the dominant copepod species Acartia tonsa and Acartia hudsonica, an increase in the proportion of the small copepod Oithona sp., and the disappearance of the two largest-sized copepod genera from the 1950s. These changes are consistent with predictions of the impact of climate change on aquatic ectotherms. This suggests that even in eutrophic systems where food is not limiting, a continued increase in temperature could result in a smaller-sized copepod community. Since copepods dominate the zooplankton, which in turn link primary producers and upper trophic levels, a reduction in mean size could alter food web connectivity, decreasing the efficiency of trophic transfer between phytoplankton and endemic larval fish.

A Century of Ocean Warming on Florida Keys Coral Reefs: Historic In Situ Observations

Abstract: There is strong evidence that global climate change over the last several decades has caused shifts in species distributions, species extinctions, and alterations in the functioning of ecosystems. However, because of high variability on short (i.e., diurnal, seasonal, and annual) timescales as well as the recency of a comprehensive instrumental record, it is difficult to detect or provide evidence for long-term, site-specific trends in ocean temperature. Here we analyze five in situ datasets from Florida Keys coral reef habitats, including historic measurements taken by lighthouse keepers, to provide three independent lines of evidence supporting approximately 0.8 °C of warming in sea surface temperature (SST) over the last century. Results indicate that the warming observed in the records between 1878 and 2012 can be fully accounted for by the warming observed in recent decades (from 1975 to 2007), documented using in situ thermographs on a mid-shore patch reef. The magnitude of warming revealed here is similar to that found in other SST datasets from the region and to that observed in global mean surface temperature. The geologic context and significance of recent ocean warming to coral growth and population dynamics are discussed, as is the future prognosis for the Florida reef tract.

Carbon Storage in Seagrass Beds of Abu Dhabi, United Arab Emirates

Abstract: “Blue Carbon” initiatives have highlighted the significant role of seagrasses in organic carbon (C org) burial and sequestration. However, global databases on the extent of C org stocks in seagrass ecosystems are largely comprised of studies conducted in monospecific beds from a limited number of regions, thus potentially biasing global estimates. To better characterize carbon stocks in seagrass beds of varying structure and composition, and to further expand the current “Blue Carbon” database to under-represented regions, we evaluate the extent of C org stocks in the relatively undocumented seagrass meadows of the Arabian Gulf. Surveys were conducted along the coast of Abu Dhabi (UAE) and encompassed sites ranging from sheltered embayments to offshore islands. Seagrass beds consisted of Halodule uninervis, Halophila ovalis and Halophila stipulacea. While seagrasses were widely distributed along the coast, both living and soil C org stores were relatively modest on an areal basis. Total seagrass biomass ranged from 0.03 to 1.13 Mg C ha−1, with a mean of 0.4 ± 0.1 (±SEM), and soil C org stocks (as estimated over the top meter) ranged from 1.9 to 109 Mg C ha−1, with a mean of 49.1 ± 7.0 (±SEM). However, owing to the expansive distribution of seagrasses in the Arabian Gulf, seagrass “Blue Carbon” stocks were large, with 400 Gg C stored in living seagrass biomass and 49.1 Tg C stored in soils. Thus, despite low C org stores for any given location, the overall contribution of seagrass beds to carbon storage are relatively large given their extensive coverage. This research adds to a growing global dataset on carbon stocks and further demonstrates that even seagrass beds dominated by small-bodied species function to store carbon in coastal environments.

Importance of Mangrove Carbon for Aquatic Food Webs in Wet–Dry Tropical Estuaries

Abstract: Mangroves are traditionally considered to provide important nutrition to tropical estuarine consumers. However, there is still controversy about this, and the extent and importance of these inputs are largely unquantified. In particular, there is no information for food webs of small estuaries that dominate wet–dry tropical coasts, where freshwater inflow is intermittent, leading to highly seasonal inputs of nutrients from terrestrial systems. Since the relative importance of the different sources depends on the type and extent of different habitats and on hydrological and topographic conditions, results from other regions/type of systems cannot be extrapolated to these estuaries. Here, δ13C is used to determine the importance of mangrove-derived carbon for Penaeus merguiensis (detritivore; shrimp), Ambassis vachellii (planktivore; fish), and Leiognathus equulus (benthivore; fish) from six small wet–dry tropical estuaries that differ in mangrove (C3) cover and in type of terrestrial vegetation adjacent to the estuary. Bayesian mixing models confirmed that mangrove material was important to consumers in all estuaries. There was a gradient in this importance that agreed with the extent of mangrove forests in the estuaries, as C3 sources were the most important contributors to animals from the three estuaries with the greatest (>40 %) mangrove cover. There was also evidence of incorporation of C3 material for the three estuaries with lower (<30 %) mangrove cover. Since these latter estuaries had no adjacent terrestrial C3 forests, the detected C3 influence can only be of mangrove origin. This shows that mangroves are important contributors to these food webs, underlining the importance of mangroves in supporting estuarine nursery ground value and fisheries productivity.

The Ecosystem Engineer Crassostrea gigas Affects Tidal Flat Morphology Beyond the Boundary of Their Reef Structures

Abstract: Ecosystem engineers that inhabit coastal and estuarine environments, such as reef building oysters, do not only stabilise the sediment within their reefs, but their influence might also extend far outside their reefs, affecting tidal flat morphology and protecting the surrounding soft-sediment environment against erosion. However, quantitative information is largely missing, and the spatially extended ecosystem engineering effects on the surrounding soft-sediment largely unstudied. To quantify this, we measured elevations around eleven natural Crassostrea gigas reefs occurring on tidal flats in the Oosterschelde estuary (the Netherlands). These tidal flats experience strong erosion as a consequence of human interventions in the system. Various reef sizes were chosen to test the proportional effects of reefs on tidal flat morphology. Measurements were used to create 3-dimensional surface maps to obtain properties of the reefs and the surrounding soft-sediment environment. The area of the oyster reefs ranged from 2 to 1,908 m2. Reef length varied between 1 and 61 m, reef width between 1 and 45 m, and reef height between 0.20 and 1.08 m. Reefs varied in shape, going from round shape structures to more elongated ones. We observed elevated areas (>5 cm elevation from the background intertidal slope) on the lee side of all reefs, caused by the interaction between the reef’s structure and locally prevailing wave conditions. The elevated area (i.e. the spatially extended ecosystem engineering effect) affected by the reef was of the same order of magnitude as the reef area. The elevated area was related to reef properties such as reef length, width, and height. Reef length, however, appeared to be the best predictor. These findings contribute to management solutions for coastal adaptation and protection. Our study clearly showed that oyster reefs not only protect the tidal flat under their footprint, but as well an area beyond the boundary of the reef.

A Budget Analysis of Bottom-Water Dissolved Oxygen in Chesapeake Bay

Abstract: A coupled hydrodynamic-dissolved oxygen model is developed to simulate the seasonal cycle of dissolved oxygen (DO) in Chesapeake Bay and investigate processes regulating summer hypoxia in the estuary. A budget analysis of DO in the bottom water reveals a balance between physical transport and biological consumption. In addition to the vertical diffusive flux, the longitudinal and vertical advective fluxes are important suppliers of DO to the bottom water. The longitudinal advective flux is affected not only by gravitational circulation but also by wind-driven currents. The vertical advective flux is affected by wind-driven lateral circulation and shows a strong dependence on wind speed and direction. Up-estuary winds weaken the landward bottom flow and generate a clockwise lateral circulation that exchanges DO between the deep channel and adjacent shoals, thereby reducing the longitudinal advective flux and increasing the vertical advective flux. In contrast, down-estuary winds amplify the longitudinal flux and reduce the vertical flux. During the summer, water column respiration contributes to about 74 % of the total biological consumption and sediment oxygen demand accounts for about 26 %. Sensitivity analysis model runs are conducted to analyze how changing river flows and winds affect the hypoxia prediction and oxygen budget balance. Due to the compensating changes in longitudinal and vertical fluxes, the hypoxic volume is relatively insensitive to changes in the river flow. In contrast, the timing and size of hypoxic volume changes with wind speed. Sensitivity analysis also shows that plankton oxygen production, water column respiration, and sediment oxygen demand all affect the hypoxia prediction and bottom oxygen balance.

Climate Change Influences Carrying Capacity in a Coastal Embayment Dedicated to Shellfish Aquaculture

Abstract: A spatially explicit coupled hydrodynamic-biogeochemical model was developed to study a coastal ecosystem under the combined effects of mussel aquaculture, nutrient loading and climate change. The model was applied to St Peter’s Bay (SPB), Prince Edward Island, Eastern Canada. Approximately 40 % of the SPB area is dedicated to mussel (Mytilus edulis) longline culture. Results indicate that the two main food sources for mussels, phytoplankton and organic detritus, are most depleted in the central part of the embayment. Results also suggest that the system is near its ultimate capacity, a state where the energy cycle is restricted to nitrogen-phytoplankton-detritus-mussels with few resources left to be transferred to higher trophic levels. Annually, mussel meat harvesting extracts nitrogen (N) resources equivalent to 42 % of river inputs or 46.5 % of the net phytoplankton primary production. Under such extractive pressure, the phytoplankton biomass is being curtailed to 1980’s levels when aquaculture was not yet developed and N loading was half the present level. Current mussel stocks also decrease bay-scale sedimentation rates by 14 %. Finally, a climate change scenario (year 2050) predicted a 30 % increase in mussel production, largely driven by more efficient utilization of the phytoplankton spring bloom. However, the predicted elevated summer temperatures (>25 °C) may also have deleterious physiological effects on mussels and possibly increase summer mortality levels. In conclusion, cultivated bivalves may play an important role in remediating the negative impacts of land-derived nutrient loading. Climate change may lead to increases in production and ecological carrying capacity as long as the cultivated species can tolerate warmer summer conditions.

Patterns in Taxonomic and Functional Diversity of Macrobenthic Invertebrates Across Seagrass Habitats: a Case Study in Atlantic Canada

Abstract: Functional diversity (FD) characterizes the role of species within communities based on their morphological, behavioural and life history traits Taxonomic diversity is not always a surrogate for FD, and ecosystem functioning is more dependent on functional traits rather than species richness Despite this, most diversity studies in seagrass ecosystems do not consider the functional trait landscape Here, we compare and contrast the taxonomic and functional diversity and composition of macrobenthic invertebrates (infauna and small epifauna) across a gradient of seagrass habitats (bare sediment, bed edge and bed interior) at three sites in Nova Scotia, Canada We also determine the relationship between taxonomic diversity and FD to gain insight into the consequences of species loss At two sites, we found that taxonomic diversity (species number and Margalef and Simpson’s indices) increased from bare sediments to the bed interior, while FD (Rao index) did not or else showed a weaker pattern At a third site, both taxonomic and functional diversity tended to increase across the seagrass gradient Despite the differences in relationships between taxonomic and functional diversity, functional trait composition tended to be distinct across seagrass habitats at all sites Regressions showed that FD increased either hyperbolically or linearly with taxonomic diversity Our study suggests that for seagrass ecosystems similar to the ones sampled, the implications of species loss for ecosystem functioning may not be easily predicted from data of taxonomic diversity alone This study provides some of the first data of taxonomic and functional diversity in seagrass ecosystems, which can be used to inform conservation objectives and management practices

Impacts of Coastal Development on the Ecology of Tidal Creek Ecosystems of the US Southeast Including Consequences to Humans

Abstract: Upland areas of southeastern United States tidal creek watersheds are popular locations for development, and they form part of the estuarine ecosystem characterized by high economic and ecological value. The primary objective of this work was to define the relationships between coastal development, with its concomitant land use changes and associated increases in nonpoint source pollution loading, and the ecological condition of tidal creek ecosystems including related consequences to human populations and coastal communities. Nineteen tidal creek systems, located along the southeastern US coast from southern North Carolina to southern Georgia, were sampled in the summer, 2005 and 2006. Within each system, creeks were divided into two primary segments based upon tidal zoning—intertidal (i.e., shallow, narrow headwater sections) and subtidal (i.e., deeper and wider sections)—and then watersheds were delineated for each segment. Relationships between coastal development, concomitant land use changes, nonpoint source pollution loading, the ecological condition of tidal creek ecosystems, and the potential impacts to human populations and coastal communities were evaluated. In particular, relationships were identified between the amount of impervious cover (indicator of coastal development) and a range of exposure and response measures including increased chemical contamination of the sediments, increased pathogens in the water, increased nitrate/nitrite levels, increased salinity range, decreased biological productivity of the macrobenthos, alterations to the food web, increased flooding potential, and increased human risk of exposure to pathogens and harmful chemicals. The integrity of tidal creeks, particularly the headwaters or intertidally dominated sections, was impaired by increases in nonpoint source pollution associated with sprawling urbanization (i.e., increases in impervious cover). This finding suggests that these habitats are valuable early warning sentinels of ensuing ecological impacts and potential public health and flooding risk from sprawling coastal development. The results also validate the use of a conceptual model with impervious cover thresholds for tidal creek systems in the southeast region.

Effects of Temperature in Juvenile Seabass ( Dicentrarchus labrax L.) Biomarker Responses and Behaviour: Implications for Environmental Monitoring

Abstract: The effects of temperature on European seabass (Dicentrarchus labrax L.) juveniles were investigated using a 30-day bioassay carried out at 18 and 25 °C in laboratory conditions. A multiparameter approach was applied including fish swimming velocity and several biochemical parameters involved in important physiological functions. Fish exposed for four weeks to 25 °C showed a decreased swimming capacity, concomitant with increased oxidative stress (increased catalase and glutathione peroxidase activities) and damage (increased lipid peroxidation levels), increased activity of an enzyme involved in energy production through the aerobic pathway (isocitrate dehydrogenase) and increased activities of brain and muscle cholinesterases (neurotransmission) compared to fish kept at 18 °C. Globally, these findings indicate that basic functions, essential for juvenile seabass surviving and well performing in the wild, such as predation, predator avoidance, neurofunction and ability to face chemical stress may be compromised with increasing water temperature. This may be of particular concern if D. labrax recruitment phase in northwest European estuaries and coastal areas happens gradually in more warm environments as a consequence of global warming. Considering that the selected endpoints are generally applied in monitoring studies with different species, these findings also highlight the need of more research, including interdisciplinary and multiparameter approaches, on the impacts of temperature on marine species, and stress the importance of considering scenarios of temperature increase in environmental monitoring and in marine ecological risk assessment.

Sediment Deposition and Accretion Rates in Tidal Marshes Are Highly Variable Along Estuarine Salinity and Flooding Gradients

Abstract: Vertical accretion in estuarine marshes depends on rates of sediment deposition and is a complex function of different interacting variables. In times of climate change and associated sea-level rise, knowledge about the relation between these variables and sediment deposition and accretion rates is gaining high importance. Therefore, we studied spatial and temporal variation in short-term sediment deposition rates and its possible predictors in three marsh types along an estuarine salinity gradient. Between March 2010 and March 2011, bi-weekly sediment deposition was quantified along three transects, reflecting the variability in elevation (low to high marsh) and distance to the sediment source, in each of one tidal freshwater, brackish, and salt marsh at the Elbe Estuary (Germany). Simultaneously, water-level fluctuations and suspended sediment concentration (SSC) were recorded, and aboveground plant biomass was sampled once in late summer and once by the end of winter, respectively. Annual sediment deposition (17.5 ± 4.0 kg m−2) and calculated accretion rates (20.3 ± 4.7 mm year−1) were highest in the brackish low marsh and were between 51 and 71 % lower in the low tidal freshwater and the salt marsh, respectively. Highest SSC and longest inundations were found during fall and winter. Flooding duration and frequency were higher in the tidal freshwater than in the brackish and the salt marsh. Aboveground, plant biomass of the regularly flooded vegetation stratum (0–50 cm above soil surface) did not differ between marsh types, but the spatial pattern changed between late summer and early spring. In all three marsh types, decreasing sediment deposition rates with increasing distances from the sedimentation source were recorded. The applied multiple regression models were able to explain 74, 79, and 71 % of variation in sediment deposition patterns in tidal freshwater, brackish, and salt marshes, respectively. SSC was the most important model predictor variable. Our results emphasize the importance of considering spatial and temporal variations in sediment deposition rates and its predictors. According to our findings, sediment deposition rates in the investigated tidal low marshes of the Elbe Estuary seem to be sufficient to compensate moderate rates of sea-level rise. Contrastingly, high salt marshes might be vulnerable due to insufficient input of sediment and might regress into low marshes, partly.

The Dynamics of Plant-Mediated Sediment Oxygenation in Spartina anglica Rhizospheres—a Planar Optode Study

Abstract: Belowground sediment oxygenation in rhizo- spheres of wetland plants promotes nutrient uptake, serve as protection against toxic reduced compounds and play an important role in wetland nutrient cycling. The presence of ~1.5-mm-wide oxic zones around roots of the intertidal marsh grass Spartina anglica was demonstrated below the sediment surface using planar optode technology recording 2D images of the sediment oxygen distribution. Oxic root zones were restricted to the root tips stretching up to 16 mm along the roots with an oxygen concentration up to 85 μmol L �1 detect- ed at the root surface. Radial oxygen loss across the root surface ranged from 250 to 300 nmol m �2 s �1 , which is comparable to other wetland plants. During air exposure of the aboveground biomass, atmospheric oxygen was the pri- mary source for belowground oxygen transport, and light availability only had a minor effect on the belowground sediment oxygenation. During inundations completely sub- merging the aboveground biomass cutting off access to atmo- spheric oxygen, oxic root zones diminished significantly in the light and were completely eliminated in darkness. Within the time frame of a normal tidal inundation (~1.5 h), photo- synthetic oxygen production maintained the presence of oxic root zones in light, whereas oxic root zones were eliminated within 1 h in darkness. The results show that the sediment oxygenation in Spartina anglica rhizospheres is temporally dynamic as well as spatially variable along the roots.

Patterns in Larval Fish Diversity, Abundance, and Distribution in Temperate South African Estuaries

Abstract: Estuaries are important nursery areas for fishes worldwide but large-scale studies of spatial patterns of use are lacking. This study presents data on larval fish diversity, abundance and distribution within and among a range of temperate estuary types, spanning 25 systems sampled from 1998 to 2008 in South Africa. A standardized boat-based plankton towing technique was used. Estuary type and physico-chemical conditions played a defining role in the trends observed. Estuary resident Clupeidae and Gobiidae dominated the mid-channel larval catch, particularly the preflexion stages in permanently and intermittently open estuaries and in estuarine lakes. Permanently open estuaries were also characterized by high numbers of larvae and early juveniles of marine migrant fishes. Density was higher in warmer months (spring and summer), which coincides with peak spawning in coastal habitats coupled with zooplankton maxima in the warm-temperate region. A strong seasonal component was also evident in larval fish catches in cool-temperate systems, but this peak coincided with late winter rainfall. River inflow provides a strong influence on food availability and larval survival. Species richness and diversity was higher in estuaries with either extensive habitat variability and/or a strong, natural good supply of river flow. This was particularly evident in the higher numbers of marine migrant larvae in these systems. Freshwater deprived estuaries also displayed high species diversity due to the higher incidence of marine straggler species. Characterization of salinity into zones provided a valuable means to understand distribution and abundance dynamics. Mesohaline zones had the highest density of larval fishes, providing ideal food patches. A select suite of species dominate the larval fish assemblages in the various estuary types studied. These patterns persist but species abundance and rank may vary interannually based on productivity and larval fish survival.

Intraspecific Variability in the Response of the Edible Mussel Mytilus chilensis (Hupe) to Ocean Acidification

Abstract: Ocean acidification (OA) has been shown to affect significantly the net calcification process and growth rate of many marine calcifying organisms. Recent studies have shown that the responses of these organisms to OA can vary significantly among species. However, much less is known concerning the intraspecific variability in response to OA. In this study, we compared simultaneously the responses of two populations of the edible mussel Mytilus chilensis (Hupe) exposed to OA. Three nominal CO2 concentrations (380, 700, and 1,000 μatm of CO2) were used. Negative effects of CO2 increase on net calcification rate were only found in individuals from Huelmo Bay. However, no effects were found in individuals from Yaldad Bay. Moreover, OA had not significant effects on the shell dissolution rate in individuals from both localities. This suggests that the negative effect of the OA on the net calcification rate of this species is explained by shell deposition, but not by the shell dissolution processes. We do not know the specific underlying mechanisms responsible for these differences, but some possibilities are discussed. These results highlight that the responses of marine organism to OA can be highly variable even within the same species. Therefore, more studies across the distribution range of the species, considering environmental variability, are needed for a better understanding of the consequences of OA on marine organisms. Finally, because mussels exert influence on their physical and biological surroundings, the negative effects of a CO2 increase could have significant ecological consequences.

Fish Assemblages in Louisiana Salt Marshes: Effects of the Macondo Oil Spill

Abstract: Marsh-resident fishes play important roles as both predators and prey in coastal systems, influence secondary production, and are important trophic links to adjacent coastal waters. As such, they also serve as sentinel species in efforts to understand the magnitude and implications of anthropogenic habitat disturbance or degradation. An evaluation of the juvenile and adult marsh fish response to the Macondo oil spill in 2010 was conducted in 2012 and 2013 by sampling in both oiled and unoiled marshes in coastal Louisiana. To complement this analysis, we also examined marsh-fish assemblage structure across several subhabitats (marsh edge, creeks, ponds, depressions). The fauna, collected with traps, was dominated by cyprinodontiform fishes (Fundulus grandis, Fundulus xenicus) and complemented by others in this group (Cyprinodon variegatus, Poecilia latipinna, Fundulus pulvereus, Fundulus jenkinsi, Fundulus similis). Among the dominant species, abundance was often the highest in ponds and marsh surface depressions, with many fish species also commonly found in creeks, but few fish were collected along the marsh edge. Comparisons across representative oiled and unoiled sites from Caminada, Terrebonne, and Barataria Bays did not reflect any consistent differences in species composition, abundance, and size as a function of oiling 2–3 years after the oil spill reached Louisiana marshes. This interpretation may be confounded by multiple stressors, including natural events (e.g., oil redistribution by storms, and seasonal flooding of the marsh surface), and other man-made perturbations (e.g., freshwater discharge).

Denitrification and Anaerobic Ammonium Oxidization Across the Sediment–Water Interface in the Hypereutrophic Ecosystem, Jinpu Bay, in the Northeastern Coast of China

Abstract: Denitrification and anaerobic ammonium oxidization (anammox) are considered the most important processes of removing reactive nitrogen from natural aquatic environments. We measured and compared in situ rates of the two processes across the sediment–water interface of Jinpu Bay using continuous-flow experiments combined with a 15NO3 − tracing technique to determine their relative importance in this hypereutrophic coastal ecosystem. Rates of denitrification and anammox ranged from 1.76 to 327.97 and 0.33 to 36.32 μmol N m−2 day−1, respectively. Both the denitrification and anammox processes were observed to be associated closely with the bioavailability of organic matter and concentrations of sulfide and iron oxides in sediments. Denitrification was the dominant pathway of eliminating reactive nitrogen and on average accounted for about 90 % of the total removed nitrogen. Totally, both the denitrification and anammox processes removed about 20 % of the externally derived inorganic nitrogen within the system. Most of the external nitrogen was still retained in the ecosystem, which may cause the severe eutrophication and algae blooms occurring at the study area.

Spatiotemporal Variation of Trace Elements and Stable Isotopes in Subtropical Estuaries: I. Freshwater Endmembers and Mixing Curves

Abstract: Understanding spatial and temporal variation in chemical constituents across salinity gradients is essential for using proxies to track riverine inflow, mixing processes, and migration of mobile fauna. We analyzed the freshwater endmembers and mixing curves of a suite of trace element concentrations (Mg, Ca, Mn, Sr, and Ba) and stable isotope ratios (δ18O and 87Sr/86Sr) in tributaries and estuaries of the south Texas coastal bend region. While Sr/Ca and 87Sr/86Sr were consistent across tributaries due to the dominance of carbonate bedrock underlying the region, Ba/Ca showed some river-specific variation perhaps due to upstream urbanization. In contrast, both Mn/Ca and δ18O showed a high degree of variability between 2 years due to their sensitivity to redox conditions and net evaporation, respectively. Mixing curves for Ca and Sr were moderately curvilinear, suggesting the potential importance of alternative processes altering mixing relationships, such as submarine groundwater discharge (SGD). Mixing of Mg was linear and consistent with conservative behavior, while Ba showed a low salinity peak and there was no apparent mixing relationship for Mn. Mixing of 87Sr/86Sr was curvilinear as expected, although the steepness of the mixing curve was lower than expected under linear mixing assumptions, further indicating the possible influence of SGD. Unexpectedly, δ18O values were elevated above marine values across the entire salinity gradient, perhaps due to drought conditions during the sampling period. Together, these results point to the individualistic spatiotemporal dynamics of chemical constituents and illustrate the care that must be taken when choosing an appropriate proxy for salinity.

A Comparison of Bulk Estuarine Turnover Timescales to Particle Tracking Timescales Using a Model of the Yaquina Bay Estuary

Abstract: The ability to determine a bulk estuarine turnover timescale that is well defined under realistic conditions is in high demand for estuarine research and management. We compare how turnover timescales vary with tidal and river forcing from idealized forcing scenarios using a three- dimensional circulation model of the Yaquina Bay estuary in order to understand the limitations and benefits of different timescale methods for future application. Using model results, we compare bulk formula approaches—the tidal prism meth- od, freshwater fraction method, and a relatively new estuarine timescalecalculationmethodbasedonthetotal exchangeflow (TEF)—to directly calculated timescales from particle track- ing inorder toassessthe utility ofthe bulkformula timescales. All of the timescales calculatedhad similar magnitudes during high river discharge but varied significantly at low discharge and had different dependences on tidal amplitude. Even in the application of a single estuary-averaged timescale, we did not find that any of the bulk timescales described the estuary over a realistic range of tidal and river discharge forcing. During high discharge, the Yaquina Bay timescale is on the order of 2-5 tidal cycles based on the particle tracking analysis, but during low discharge, the turnover time varies across methods and spatial considerations appear to be more important.

CO2-Driven Ocean Acidification Disrupts the Filter Feeding Behavior in Chilean Gastropod and Bivalve Species from Different Geographic Localities

Abstract: We present experimental data obtained with newly hatched veliger larvae of the gastropod Concholepas concholepas and juveniles of the mussel Perumytilus purpuratus exposed to three pCO2 levels. Egg capsules of C. concholepas were collected from three geographic locations in northern (Antofagasta), central (Las Cruces), and southern Chile (Calfuco), and then incubated throughout their entire intra-capsular life cycle at three nominal pCO2 levels, ~400, 700, and 1,000 ppm. Similarly, P. purpuratus were collected from both Las Cruces and Calfuco and exposed to the same pCO2 levels during 6 weeks. Hatched gastropod larvae and mussel juvenile were fed with the haptophyte Isochrysis galbana. Clearance and ingestion rates were estimated for newly hatched larvae, and for juvenile mussel these rates were measured at two observation times (3 and 6 weeks). Our results clearly showed a significant negative effect of elevated pCO2 on the clearance and ingestion for both C. concholepas larvae and P. purpuratus juveniles, which dropped between 15 up to 70 % under high pCO2 conditions. The present study has also shown large variations in the sensitivities of C. concholepas larvae from different local populations (i.e. Antofagasta, Las Cruces, and Calfuco). The influence of both corrosive upwelling waters and the influence of freshwater discharges from Maipo River may explain the minor negative effect of high pCO2 conditions in hatched larvae from Las Cruces’ egg capsules, which would suggest that they are inherently more tolerant to ocean acidification (OA) than organisms that live on regions with a lower pCO2 variability. The present study suggests the need for site-specific studies and reveals the important effect of low pH conditions on feeding activity. Furthermore, this study supports the notion that feeding is a key physiological process susceptible to the effects of OA in marine invertebrates.

Effects of Seed Source, Sediment Type, and Burial Depth on Mixed-Annual and Perennial Zostera marina L. Seed Germination and Seedling Establishment

Abstract: Seed germination and seedling establishment directly affect the resiliency of seagrasses to disturbance or environmental stress. The objectives of this study were to compare maximum seed germination, time to germination, nongerminated seed viability, and initial seedling biomass between mixed-annual and perennial Zostera marina seed populations in coarse (>90 % sand) and fine (<50 % sand) sediments and at shallow (1 cm) and deep (5 cm) burial depths. Perennial seeds collected from Virginia and North Carolina had greater maximum germination, shorter time to germination, and greater seedling biomass compared to mixed-annual seeds collected from North Carolina. For both mixed-annual and perennial seeds, maximum germination and seedling biomass were the greatest in shallow fine sediments. Mixed-annual seeds buried at 1 cm had a shorter time to germination than in the deep treatments; however, sediment type did not affect mean time to germination. Perennial seeds had a shorter time to germination in shallow compared to deep burial depths and in fine compared to coarse sediments. Cues for germination were present at the deeper depths; however, the cotyledon failed to emerge from the sediment surface resulting in mortality at depths of 5 cm. The greater performance of perennial compared to mixed-annual seeds and seedlings demonstrate the trade-offs which can occur between Z. marina reproductive strategies. Reduced germination of Z. marina seeds buried ≥5 cm and in coarse sediments may represent a possible bottleneck in successful sexual reproduction, feasibly affecting the resiliency to and recovery from disturbance for both perennial and mixed-annual Z. marina beds.

Limited Vegetation Development on a Created Salt Marsh Associated with Over-Consolidated Sediments and Lack of Topographic Heterogeneity

Abstract: Restored salt marshes frequently lack the full range of plant communities present on reference marshes, with upper marsh species underrepresented. This often results from sites being too low in the tidal frame and/or poorly drained with anoxic sediments. A managed coastal realignment scheme at Abbotts Hall, Essex, UK, has oxic sediments at elevations at which upper marsh communities would be expected. But 7 years after flooding, it continued to be dominated by pioneer communities, with substantial proportions of bare ground, so other factors must hinder vegetation development at these elevations. The poorly vegetated areas had high sediment shear strength, low water and organic carbon content and very flat topography. These characteristics occur frequently on the upper parts of created marshes. Experimental work is required to establish causal links with the ecological differences, but other studies have also reported that reduced plant β-diversity and lower usage by fish are associated with topographic uniformity. Uniformity also leads to very different visual appearance from natural marshes. On the upper intertidal, sediment deposition rate are slow, water velocities are low and erosive forces are weak. So, topographic heterogeneity cannot develop naturally, even if creeks have been excavated. Without active management, these conditions will persist indefinitely.