Estuarine Scale Research Articles

Methods for a composite ecological suitability measure to inform cumulative restoration assessments in Gulf of Mexico estuaries

Ecosystem management requires a systematic, holistic approach that considers ecological and social outcomes. Effective restoration practices promote a balance of ecological and social goals by addressing ecological integrity, efficiently maximizing benefits while minimizing investment, and encompassing collaborative stakeholder engagement. Socio-ecological assessments can inform adaptive management and be utilized to prioritize restoration activities and monitor restoration effectiveness. In estuarine systems, socio-ecological assessments should evaluate the ability of habitats to support both ecologically and locally important species. The composite measure presented utilizes a combination of ecological and social measures to characterize ecological suitability for individual and multiple Gulf of Mexico estuarine species. The ecological suitability value (ES) for a given spatial unit is based on a suite of biophysical measures of the quality and extent of suitable habitat for each species, the species’ trophic importance in a food web context, and the importance of each species in relation to stakeholder values and benefits. ES values for individual spatial units can be aggregated to estimate the distribution of ecological suitability at the estuarine scale. The ES values are calculated using examples for each step in the process. The information provided by ecological suitability characterizations can support restoration prioritization decisions for Gulf of Mexico estuaries and can provide a baseline measure to gauge restoration effectiveness over time to inform cumulative restoration assessments.

Coastal engineering infrastructure impacts Blue Carbon habitats distribution and ecosystem functions

Intertidal estuarine habitats (e.g., saltmarshes and tidal flats) provide important ecosystem services to society, including coastal protection, food provision and Corg sequestration. Yet, estuaries and estuarine habitats have been subjected to intense human pressure, such as land-use change and artificialization of the shoreline to support economic activities and uses. Construction of engineering infrastructures (e.g., piers, bridges) in these areas alters estuary-wide hydromorphological conditions and thus sedimentation patterns at the estuarine scale, which are key drivers of habitats distribution and ecosystem structure, processes and functions. Most of the research on the impact of civil engineering structures on coastal habitats has focused on the biological communities that colonize them or the bottoms where they are placed, whereas their indirect impacts on adjacent habitats has been largely unexplored. Understanding the influence of man-made infrastructures on the distribution of estuarine habitats and functions is critical, particularly considering that shoreline armoring is expected to increase as a way to protect coastal areas from hazards derived from climate change. Shifts in habitat distribution and functions occur in several years or decades and relating them with the occurrence of past historical events is challenging when no monitoring data is available. By examining historical aerial photographs and different biogeochemical properties along a saltmarsh soil record, this study demonstrates that the construction of an infrastructure (i.e. bridge) caused a rapid transformation (~ 30 years) of a bare sandflat into a high marsh community and to significant changes in sediment biogeochemical properties, including the decrease in sediment accretion rate and Corg burial rates since then. This study contributes to increase the knowledge on the impact that the construction in coastal areas of civil engineering infrastructures can cause in intertidal habitats distribution and the ecological functions they provide for climate change adaption and mitigation.

Coupling near‐surface geomorphology with mangrove community diversity at the estuarine scale: A case study at Dongzhaigang Bay, China

ABSTRACTCoastal wetlands are key features of the Earth's surface and are characterized by a diverse array of coupled geomorphological and biological processes. However, the links between the distribution of biodiversity (for example, species and structural diversity) and the formation of coastal geomorphology are not well‐understood on a landscape scale most useful to coastal zone managers. This study describes the relationship between select geomorphological and biological mangrove community features (i.e. species composition and functional root type) in a landscape‐distributed coastal zone of Dongzhaigang Bay, north‐eastern Hainan Island, China. A total of 11 mangrove species and five functional aerial root types were encountered, with the location of species by root types being controlled by the elevation of the soil surface. Plank roots, prop roots and pneumatophores occupied the lowest intertidal elevations, while knee roots and fibrous roots of the mangrove fern, Acrostichum aureum, preferred the highest intertidal elevations. Surface sediment deposition in areas with mangroves was greater than deposition in non‐mangrove forest zones, establishing an important biological mechanism for this large‐area response because surface erosion/compaction was also more prominent within mangrove roots. Indeed, functional root type influenced the magnitude of deposition, erosion and compaction, with knee roots and pneumatophores being more effective in promoting deposition and preventing surface erosion/compaction than prop roots. These results indicate a potential role for vegetation type (especially functional root type) to influence coastal geomorphological processes at large landscape scales. While soil surface elevation is correlated to the distribution of mangrove species and functional root types, a significant feedback exists between elevation change and the capacity of those root types to influence coastal geomorphological differentiation within sustainable intertidal elevations. An enhanced understanding of geomorphological development, mangrove species distribution and functional root type may improve management to support nature‐based solutions that adjust more effectively to sea‐level rise through feedbacks.

Mapping essential habitat of estuarine fishery species with a mechanistic SDM and Landsat data

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

Coupling near-surface geomorphology with mangrove community diversity at the estuarine scale: a case study at Dongzhaigang Bay, China

Coupling near-surface geomorphology with mangrove community diversity at the estuarine scale: a case study at Dongzhaigang Bay, China

The calculation of flushing time for the upper Pasur River Estuary, Bangladesh

Estimation of estuarine flushing time, a time required to transport of pollutants or any other properties from estuaries to the coast, is very important for its resource management. In this study, we estimated flushing time (T) of the upper Pasur River Estuary (UPRE) for understanding the water quality condition in the dry and wet seasons. High-resolution salinity data were collected from the PRE at high water in the dry and wet seasons in 2014 and 2019. Flushing time was calculated using the freshwater fraction method (FFM) as well as e-folding flushing time scales was estimated empirically using the salinity (non-reactive conservative) and monthly river discharge data. System flushing during the dry season was thirteen times weaker than flushing during the wet season owing to decreasing river discharge by nearly 94%. In addition, the daily exchange volume was decreased by eight times during the dry season than during the wet season. As a consequence, the conditions of the UPRE are more dynamic during the wet season due to receiving huge amount of river discharge. During the dry season, only the e-folding time scales showed higher values in the salinity maximum zone (salt plug area). This implied that the e-folding time scale is an empirical approach and was able to encompass the tidal dispersion process whereas the FFM was unable to include that process. As the PRE is a macrotidal estuary, the tide assists to flush dissolved substances from the UPRE to the coast during the dry season having negligible river discharge. In addition, there was no significant variation in water quality parameter between the salt plug area (SP) and downstream of salt plug area (DSP) during the dry season. In order to have more accuracy, a three-dimensional hydrodynamic model would be useful to compute estuarine time scales precisely.

Assessing salt marsh loss and degradation by combining long‐term LANDSAT imagery and numerical modelling

AbstractThe precise evaluation of the conservation status of salt marshes, the understanding of the mechanisms behind loss and degradation and the anticipation of future threats are fundamental to assist management solutions able to reverse the declining trend observed in these environments. Previous methods combining remote sensing and hydrodynamic modelling have been revealed to be effective in assessing degradation in restricted marshes, but unable to characterise dynamics of marshes at the estuarine scale. This study proposes an alternative methodology to identify priority areas for conservation by combining LANDSAT satellite remote sensing and numerical modelling. Using the Ria de Aveiro as case‐study, the main objectives of this work are to: (1) identify vegetation loss and degradation in estuarine marshes; (2) determine the mechanisms behind marsh deterioration; (3) anticipate future threats posed by climate‐induced mean sea level rise and; (4) provide management solutions aiming to protect and recover degraded salt marshes. LANDSAT imagery reveals that the most deteriorated salt marshes are located on the central and upper lagoon regions, and the numerical results support that marsh loss and degradation result from the increased tidal action triggered by the deepening of the lagoon channels. The increase in tidal currents promoted the erosion of marsh shoreline, whereas the changes in the inundation patterns over the intertidal areas triggered interior drowning. Climate‐induced mean sea level rise will likely exacerbate marsh deterioration, increasing the urgency to implement a management plan aiming to protect marshes from erosion and promote sedimentation in submerged marshes, to ensure their sustainability.

Getting from Sea to Nurseries: Considering Tidal Dynamics of Juvenile Habitat Distribution and Connectivity in a Highly Modified Estuarine Riverscape

Productive and ecologically highly valuable ecosystems, macrotidal estuaries are also characterised by complex habitat and connectivity dynamics driven by tidal and freshwater influence. Organisms living in these constantly changing systems have to match their movement patterns to the shifting habitat mosaic using available windows of connectivity to access habitat patches of interest. This appears particularly important for the juvenile stages of many fish species colonising shallow and intertidal areas of the estuaries as summer nurseries. We apply tools from landscape ecology to investigate the estuarine habitat and connectivity dynamics on the example of juvenile seabass (Dicentrarchus labrax). We test under which conditions spatio-temporal bottlenecks to estuarine nursery colonisation may emerge for this species in a human-modified estuary. Combining a hydrodynamic model of the Seine estuary with remote sensing data allows us to capture structural changes in habitat availability and connectivity at the estuarine scale and at a fine spatio-temporal resolution. With chronological least-cost modelling of successive tidal steps, we assess patterns of nursery accessibility and estimate tidal colonisation fronts for different mobility scenarios. We show that, at certain hydrological conditions, tidal water level variation causes local disruptions of habitat availability and connectivity, creating temporary bottlenecks for seabass juveniles’ movement. Fish mobility appears determinant for their vulnerability to these connectivity disruptions. Our approach allows for quantitative assessment and visualisation of riverscape complexity related to tidal dynamics. It is applicable to other highly dynamic ecosystems, where the mobile nature of connectivity and habitats needs to be integrated into conservation and management planning.

Methodology to Evaluate the Coastal Susceptibility to Oil Spills Originated in Large Marine Areas – Costa Norte Project

Carvalho, G.V.; Cabral, M.M.; de Oliveira, A.L.S.C.; Garção, H.F., and Pellegrini, J.A.C., 2020. Methodology to evaluate the coastal susceptibility to oil spills originated in large marine areas – Costa Norte Project. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1344–1348. Coconut Creek (Florida), ISSN 0749-0208.Within Costa Norte Project – an R&D project focused on improving the understanding of the vulnerability of mangrove forests to oil spills in the Brazilian Equatorial Margin - the vulnerability concept is understood as composed by three factors: sensitivity, resiliency, and susceptibility. The latter is defined as the exposure level to oil spills and should consider all possible sources of this pollutant. This work presents a methodology to assess the susceptibility of an asset to oil spills that may occur anywhere within a large marine area. It benefits from the development of a multi-source stochastic oil dispersion algorithm to enable the modeling of oil spills originated from hundreds of sources and the development of a methodology to integrate multiple scales with increasingly higher resolutions. Once stored, the results allow the identification of susceptible areas considering a single or a subset of spill sources and the identification of potential origins of spills that may affect specific areas. The choices of the spill sources and the coastal areas to be considered are defined during post-processing, granting flexibility and interactivity exploring the results. The developed methodology presents the potential to assist public management and is illustrated by an offshore scale simulation considering 1,138 oil spill sources distributed along the Brazilian Equatorial Margin integrated to an estuarine scale model, forced by 1-year of metocean data.

A methodology to assess the probability of marine litter accumulation in estuaries

In this study, a general methodology that is based on numerical models and statistical analysis is developed to assist in the definition of marine litter cleanup and mitigation strategies at an estuarine scale. The methodology includes four main steps: k-means clustering to identify representative metocean scenarios; dynamic downscaling to obtain high-resolution drivers with which to force a transport model; numerical transport modelling to generate a database of potential litter trajectories; and a statistical analysis of this database to obtain probabilities of litter accumulation. The efficacy of this methodology is demonstrated by its application to an estuary along the northern coast of Spain by comparing the numerical results with field data. The necessary criteria to ensure its applicability to any other estuary were provided. As the main conclusion, the developed methodology successfully assesses the litter distribution in estuaries with minimum computational effort.

A Numerical Investigation on Tidally Induced Sediment Transport and Morphological Changes with Changing Sea Level in South-East England

The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale.

Propagule Dispersal Determines Mangrove Zonation at Intertidal and Estuarine Scales

Propagule dispersal has generally been recognized as a vital factor affecting the spatial structure of tropical forest plants. However, available research shows that this hypothesis does not apply to mangrove species the propagules of which are dispersed by water. Due to the lack of comprehensive and quantitative information as well as the high spatio-temporal heterogeneity of the mangrove environment, the exact factors affecting the spatial structure of mangrove forests are poorly understood. To assess this, we selected a mangrove estuary with high mangrove species richness that experiences great changes in water salinity. After investigating the zonation of mature mangrove individuals across tides and the estuary, we measured the size and initial specific gravity of the propagules and then selected the eight most common species from which to observe the changes in specific gravity, buoyancy, and root initiation during dispersal at different sites with different water salinity regimes. The relationships among distribution patterns, propagule establishment, and dispersal behavior were investigated. We found that mangrove propagule dispersal is not a passively buoyant process controlled by water currents. During dispersal, mangrove propagules can actively adjust their specific gravity and root initiation. The dynamic specific gravity of the propagules was negatively related to propagule buoyancy and surface elevation. The differences in propagule specific gravity corroborated the distribution patterns of the species across the intertidal zone and estuary. Mangrove zonation on both the intertidal and estuarine scale can be explained by the tidal sorting hypothesis, as zonation is controlled by the tidal sorting of the propagules according to buoyancy and by the differential ability of the propagules to establish in the intertidal zones. The results add new understanding of observed mangrove species zonation and should inform conservation managers when restoring mangroves or evaluating the potential impacts of global change and anthropogenic disturbances that might alter the hydrology, including the water salinity regime.

Restoring oysters to urban estuaries: Redefining habitat quality for eastern oyster performance near New York City.

Restoring and conserving coastal resilience faces increasing challenges under current climate change predictions. Oyster restoration, in particular, faces threats from alterations in precipitation, warming water temperatures, and urbanization of coastlines that dramatically change salinity patterns, foster the proliferation and spread disease, and disrupt habitat connectivity, respectively. New York City (NYC) coastal waters, once home to a booming oyster fishery for eastern oysters (Crassostrea virginica), are now nearly devoid of live oyster reefs. Oyster restoration in urban estuaries is motivated by the synergistic ecosystem benefits this native keystone species can deliver. Recent surveys have documented substantial remnant populations of adult oysters in the upper low salinity zone of the Hudson/Raritan Estuary (HRE) near Tarrytown, NY. This study assessed fitness-related performance across the HRE salinity gradient to evaluate habitat suitability on an estuarine scale. Oysters were hatchery-produced from wild, moderate-salinity broodstock, then outplanted for measurement of growth, survival, reproduction and disease prevalence over two years. Survival was generally higher in the lower salinity river sites and in the higher salinity Jamaica Bay sites relative to mesohaline NYC harbor sites. Growth rate was highest in Jamaica Bay and had high variation among other sites. Surprisingly, the highest proportion of individuals with sex-differentiated gametes and the highest average gonad maturation index was found at a low salinity site. Consistent with the advanced gametogenesis measured in experimental animals at low salinity, annual wild recruitment was documented near the low salinity remnant population in each of five monitored years. These results suggest that the remnant HRE oyster population is a robust, self-sustaining population that can be leveraged to support restoration of subpopulations in other parts of the estuary, but further research is required to determine if the mesohaline and near-ocean reaches of the HRE can support the full oyster life cycle.

Operational forecast framework applied to extreme sea levels at regional and local scales

ABSTRACTThe design, implementation and demonstration of a novel and generic computational forecast framework for multi-scale prediction of extreme sea levels and associated flooding is presented. Denoted Water Information Forecast Framework (WIFF), it integrates process-based models for waves, tides and surges from regional to local scales, predicting the flooding of coastal areas, and supporting the routine and emergency management of coastal resources. WIFF manages the simulations and the real-time monitoring data, archives the data and makes the information available through a WebGIS that targets users with distinct access privileges. Additionally, the web component of WIFF adapts automatically and transparently to any device. WIFF also provides ways to assess the model accuracy and generates tailored products based on model results and observations. WIFF is demonstrated in the prediction of extreme water levels in the Portuguese coast, simulating processes at different scales: at basin scales, waves are simulated in the North Atlantic and in the Portuguese shelf, and sea levels due to tides and atmospheric forcings are simulated in the Northeast Atlantic; at estuarine scales, high-resolution, fully coupled wave/circulation predictions are performed in the Tagus estuary to account for wave–current interactions. User-oriented georeferenced products are generated, including automatic model/data comparisons, targeting the needs of civil protection agents and combining for the first time an agile, service-oriented platform with high-resolution, process-rich predictions of the Tagus dynamics.

Relationship Between Estuarine Shellfish Fauna and Physical Environmental Characteristics for Estuary Conservation in Kyushu, Japan

The establishment of a conservation strategy or restoration goal for river estuaries requires knowledge of potential biota or possible habitat characteristics. In this study, we investigated the relationship between estuarine fauna and macro scale physical indicators on Kyushu Island, Japan to provide basic information for estuarine conservation. As a result of the classification of shellfish fauna by similarity, the Kyushu region was divided into three groups, namely, 1) southern Kyushu with high wave exposure, long fetch, and low tidal variation; 2) the Ariake and Yatsushiro seas with low wave exposure, short fetch, and high tidal variation; and 3) northern Kyushu with an intermediate fetch and tidal variation. In addition, a number of sites, such as Nakatsu Port, Sone tideland, and the Honmyou River, were classified into geographically different groups. This is because the physical characteristics of these sites were similar to classified groups or shellfish fauna were significantly altered by artificial impacts. As a result of discriminant analysis, the discrimination hit rate of species inhabiting the inner bay or tidal flat was high, whereas that for species using a wide variety of bottom sediment environment was low. To improve the accuracy of the discriminant model, it is necessary to collect more detailed physical information, such as habitat type, salinity concentration, or grain diameter of bottom sediment. To establish a conservation or restoration strategy, there is a need for classifying taxonomic groups or physical characteristics.

Distribution of Macrocrustaceans in Relation to Abiotic and Biotic Variables across the Yangtze River Estuary, China

Chao, M.; Shi, Y.; Quan, W., and Shen, X., 2015. Distribution of macrocrustaceans in relation to abiotic and biotic variables across the Yangtze River Estuary, ChinaIn this article, we report on a study of the spatial and seasonal distribution of macrocrustaceans and reveal the correlation between macrocrustacean community and environmental variables in the Yangtze River Estuary, China. A total of 44 species belonging to 21 families were identified during sample collection in May, August, and November 2010 and February 2011. Species richness of four survey trips showed significant differences among seasons and zones. The most frequent species identified were Neoeriocheir leptognathus (M.J. Rathbun, 1913) in February and May; Palaemon gravieri (Yu, 1930) in August; and Exopalaemon annandalei (Kemp, 1917) in November. The mean macrocrustacean abundance in May 2010, August 2010, November 2010, and February 2011 was 24.94, 19.82, 29.46, and 17.14 individuals/1000 m2, respectively. The distribution of macrocrustaceans demonstrated a significant variation among seasons and zones based on PERMANOVA analysis. In terms of the value of species dominance, P. gravieri was the most dominant species throughout the study period, which composed 27.4% of the total specimens obtained. The distribution of macrocrustacean abundance in relation to biotic and abiotic variables was studied by multivariate analysis of macrocrustaceans using cluster and canonical correspondence analyses. These results demonstrated three typical classifications of communities and a significant relationship between macrocrustaceans and environmental variables. Salinity was the determining factor for spatial distribution of species and temperature for species occurrence on the entire estuarine scale. Additionally, biotic variables such as abundance of Polychaeta, abundance of primary production, and abundance of estuarine resident fishes also found significant variables that correlated with the abundance of macrocrustaceans in the Yangtze River Estuary. The study on relationship between macrocrustaceans and environmental variables provided baseline information for future ecological risk assessment in the Yangtze River estuary.

Tidal bore dynamics in funnel‐shaped estuaries

AbstractThe formation and dynamics of tidal bores in funnel‐shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations. We show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation. A detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long‐term database (observations of more than 200 tides) acquired during four campaigns in the two main French tidal‐bore estuaries: the Seine and Gironde/Garonne estuaries. We describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary. Our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We also show that the secondary wavefield associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels. In particular, we observe an abrupt decrease of the whelp steepness when the Froude number goes below 1.1. This secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated.

Spawning site selection and contingent behavior in Common Snook, Centropomus undecimalis.

Reproductive behavior affects spatial population structure and our ability to manage for sustainability in marine and diadromous fishes. In this study, we used fishery independent capture-based sampling to evaluate where Common Snook occurred in Tampa Bay and if it changed with spawning season, and passive acoustic telemetry to assess fine scale behavior at an inlet spawning site (2007–2009). Snook concentrated in three areas during the spawning season only one of which fell within the expected spawning habitat. Although in lower numbers, they remained in these areas throughout the winter months. Acoustically-tagged snook (n = 31) showed two seasonal patterns at the spawning site: Most fish occurred during the spawning season but several fish displayed more extended residency, supporting the capture-based findings that Common Snook exhibit facultative catadromy. Spawning site selection for iteroparous, multiple-batch spawning fishes occurs at the lifetime, annual, or intra-annual temporal scales. In this study we show colonization of a new spawning site, indicating that lifetime spawning site fidelity of Common Snook is not fixed at this fine spatial scale. However, individuals did exhibit annual and intra-seasonal spawning site fidelity to this new site over the three years studied. The number of fish at the spawning site increased in June and July (peak spawning months) and on new and full lunar phases indicating within population variability in spawning and movement patterns. Intra-seasonal patterns of detection also differed significantly with sex. Common Snook exhibited divergent migration tactics and habitat use at the annual and estuarine scales, with contingents using different overwintering habitat. Migration tactics also varied at the spawning site at the intra-seasonal scale and with sex. These results have important implications for understanding how reproductive behavior affects spatio-temporal patterns of fish abundance and their resilience to disturbance events and fishing pressure.

Relative influence of deterministic processes on structuring marsh plant communities varies across an abiotic gradient

Understanding the processes determining community structure is one of the major goals of ecological research. Both deterministic and stochastic processes may shape community structure. The challenge is to understand the relative influence of each type of process across different environmental conditions. We investigated the influence of deterministic and stochastic processes on plant community assembly in tidal marshes across a strong abiotic (salinity) gradient in three estuaries in Georgia, USA using probabilistic Raup–Crick community dissimilarity. Our results indicated that deterministic processes had an increasingly important influence on structuring plant communities in salt and brackish marshes, probably due to high heterogeneity of microhabitats produced by the interplay between abiotic stress and biotic interactions. In contrast, the influence of deterministic processes on plant community assembly decreased in tidal freshwater marshes, suggesting an increasingly important role of stochastic processes in plant community assembly in tidal freshwater marshes, probably due to the higher species richness, higher recruitment from seed, and lower levels of abiotic stress in these habitats. At the estuarine scale (across tidal freshwater, brackish and salt marshes in each estuary), our results suggested that deterministic processes also had a relatively important influence on shaping plant community structure. Our results illustrated that plant community structure in tidal marshes is influenced by both deterministic and stochastic processes, but that the relative influence of these two types of processes varies across estuarine landscapes.

Geological consequences of the Saemangeum Dyke, mid-west coast of korea: A review

The Saemangeum Dyke is located in an estuarine setting, regulated in a complicated manner by a macrotidal regime, rivers, and winter monsoon. Accordingly, the constructed dyke resulted in a variety of artificial changes in geological characteristics in the estuary and its vicinity. To investigate those dyke-induced changes, the KORDI (Korea Ocean Research and Development Institute) performed sedimentological and sediment-dynamical observations from 2002 to 2010. On the basis of the KORDI results, the major geological changes and associated dynamical processes are reviewed. Five phenomena, among others, are focused on: depositional-channel creation; gap-related erosion; forced movements of surface sands; tidal-flat growth inside the dyke; and blanketing of mud over the sandy seafloor. These phenomena were unforeseen before the dyke construction, and reflect that the dyke could cause both erosion and deposition on an estuarine scale. The investigations conclude that the sediments in the dyke-influenced region were derived from the two rivers, Mangyeong and Dongjin, of the estuary. This is completely contrary to the offshore origin proposed before the dyke construction. As a result, the review supports the proposal that a thorough geological investigation and rational forecast is necessary prior to dyke construction to avoid economic loss and a fractious environmental debate.