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Areal extent of native mangroves, Avicennia marina, has doubled in Bay of Islands since 1951. This expansion is widely attributed to deforestation and poor land-use practices beginning in the late 1800s to early 1900s, and led to greatly transformed intertidal and supratidal habitats. One example has been the ecological isolation and crowding (sometimes, colonisation) by mangroves of shelly beaches, together with their associated 'chenier-like' spits – themselves now among the rarest of New Zealand's inshore marine habitats, with only six still relatively intact ecologically out of at least 44 in the Bay of Islands. These shores were also where pre Contact Māori often gathered to harvest intertidal cockles Austrovenus stutchburyi and to fish, archaeological signatures typically becoming obscured once mangroves colonised upper shores. Although recent seaward intrusion by mangroves into the cockle habitat of the Parekura Bay study site appears to have been proportionately small, there may be potential for more as elevated levels of sedimentation persist. With wholesale mangrove removals demonstrably ineffective in re-establishing original communities, the ongoing ecological and archaeological disruption of endemic soft, shelly contexts through largely human-mediated mangrove colonisation might be curbed in certain situations through strategic, proactive removal of new mangrove recruits, particularly on expanding edges. [ABSTRACT FROM AUTHOR]

Wave- and current-supported fluid mud on gently sloped continental shelves represents a type of sediment gravity flow capable of rapidly transporting substantial sediment over short periods, significantly contributing to coastal geomorphic evolution. To investigate the dynamics of intertidal fluid mud events, in-situ observations were conducted from May 9 to May 18, 2017, using a seabed tripod system at the lower intertidal flat of the central Jiangsu coast, China. Fluid mud was observed following a medium wind-wave event, with a maximum significant wave height of 0.42 m. The liquefied seabed, loosened by liquefaction, facilitated bed erosion and sediment resuspension. Fluid mud layers, with mean suspended sediment concentrations (SSCs) exceeding 10 g/L, periodically formed during high slack tide, early flood, and late ebb phases. These layers varied in thickness from 4 cm to 20 cm and exhibited strong stratification caused by suspended sediment. Fluid mud disappeared when the bottom turbulence kinetic energy exceeded a threshold of 0.00045 m2/s2 due to an increase in current velocity. The downslope movement of intertidal fluid mud was estimated using a theoretical buoyancy-friction model and validated by observed offshore-directed velocity jets at 0.1 m above the seabed during high slack tide phases. Additionally, onshore winds favored fluid mud formation during early flood phases, while offshore winds favored it during late ebb phases. These observations suggest that fluid mud can form on intertidal flats under conditions where tidal flows and winds align, contributing to a deeper understanding of the formation mechanisms of shallow gravity flows and the improvement of sediment transport models. [ABSTRACT FROM AUTHOR]

The ecosystem services and functions of tidal flats have been overlooked for many decades, and tidal flat loss has been identified as a serious threat to many taxa in recent years, especially for migratory waterbirds. Despite the understanding of tidal flats change on the global scale, there are still a lot of unknowns on the small scale, including tidal flats in Taiwan, which are important stopover sites for migratory waterbirds along the East Asian–Australasian Flyway. Therefore, we collated historic topographic maps, Landsat Archive images between the 1920s and the 2020s to determine the trajectories of tidal flat change along the coastline of Taiwan. Our results show that tidal flat coverage expanded between the 1920s and the 1950s, but lost approximately 266 km2 (58%) between the 1950s and the 2010s. The status of the tidal flats along the western coastline of Taiwan has been identified as “Endangered” based on the criteria of the IUCN Red List of Ecosystems. According to the aims of the Global Biodiversity Framework, we suggest rethinking the land use plans along the coastline to mitigate the tidal flat loss, especially the controversial issues concerning the expansion of green energy infrastructure. To realize the Nature Positive goals by 2030, recovering and restoring the tidal flat ecosystem could be one of the key strategies. [ABSTRACT FROM AUTHOR]

Polychaetes are important benthic macrofauna that lives in sediments, usually in intertidal flats with high organic content and high sulfide. It has been suggested that polychaete bioturbation could perform environmental remediation. During the process, the microbial community plays important roles. Here, we used high-throughput sequencing technology to study the bioturbation effects on the bacterial community in the polychaete (Perinereis aibuhitensis) burrows at different tidal positions in intertidal flat. The results showed that the bacterial communities were dramatically influenced by the polychaete bioturbation. The ACE, Chao, and Shannon indices of the polychaete burrows increased in summer. Dominant phyla in the polychaete burrows were Proteobacteria, Campilobacterota, Desulfobacterota, Chloroflexi, and Bacteroidota, and the dominant bacterial families were Sulfurvaceae, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, Desulfobulbaceae, and Sulfurimonadaceae. Results of linear discriminant analysis effect size (LEfSe) showed that groups that include organic matter degraders, such as Bacteroidota, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, and groups that include sulfur oxidizers, such as Campilobacterota, Sulfurovaceae, Rhodobacteraceae, Desulfobulbaceae, and Sulfurimonadaceae, were significantly increased due to the polychaete bioturbation. The polychaete bioturbation reduced the complexity of the bacterial co-occurrence network while increased its modularity and homogeneity. The polychaete bioturbation also changed the functional groups, which significantly enhanced in functional groups of aerobic nitrite oxidation, nitration, dark thiosulfate oxidation, dark sulfur oxidation, and dark sulfite oxidation, while nitrogen respiration and nitrate respiration decreased. These results provide insight into the impact of bacterial communities under the intertidal polychaete bioturbation. [ABSTRACT FROM AUTHOR]

China's coastal wetlands provide breeding, migration stopover, and wintering habitats for about 230 waterbird species, which is more than a quarter of all waterbirds in the world. Large-scale and high intensity human activities have resulted in serious loss and degradation of coastal wetlands over the past half century, causing population declines in many waterbirds. Through a literature review and expert surveys, this article reviews conservation measures taken in recent decades to protect waterbirds in China's coastal wetlands and provides recommendations for future conservation action from three aspects: policy and administration, habitat conservation and management, and multiparty participation. Over the past decades, many conservation legislation, regulations and action plans at the national level and more site-specific measures and interventions have been implemented, with notable improvement in the effectiveness in policy making and multi-stakeholder participation. Accordingly, some threats to waterbirds have been mitigated and many key sites for waterbirds have been designated as strictly protected nature reserves. However, some critical issues still remain, mostly related to habitat conservation and management, such as coastal wetland restoration, control of invasive Spartina alterniflora, control of environmental pollution, and improvement of artificial habitat quality. We highlight that protecting natural tidal wetlands and improving habitat quality are critical for the conservation of coastal waterbirds, especially those highly dependent on the intertidal wetlands. China has demonstrated strong commitment to ecological conservation and restoration for the future, in terms of both funding and policies for biodiversity and wetland ecosystems. It is important that this commitment to conserve coastal waterbirds is supported continuously by science- and evidence-based decisions and actions.

Tidal gates cause adverse effects on the ecological environment through the downstream acceleration of sediment deposition. This deposition process and its quantitative analysis have become a hot topic in marine science. A large-scale physical model experiment of morphological responses to the construction of a tidal gate in an estuarine tributary was performed in this study. The sediment distribution characteristics, morphologic patterns, and further analysis of the adjacent intertidal flats were investigated, triggered by the construction of tidal gates at the mouth of the Nanxi River in Zhejiang, China. The results indicated that the flood and ebb tide velocities change dramatically after the construction of the tributary tidal gates. Large amounts of sediment from the mouth of the estuary could not be entirely carried away from the flood phase to the ebb phase, resulting in downstream deposition in the vicinity of the gates. The ebb tide caused erosion of the tidal flats' surface in the silted intertidal zone that gradually developed into a tidal channel network. The tidal channel bifurcated in the middle–upper part of the intertidal flats through continuous headward erosion, thus promoting the landward expansions of channels. Applying a set of logistic growth models to the mean sinuosity, Hausdorff dimension, and junction number data indicated that the tidal channel development progressively tended toward a state of morphodynamic equilibrium. [ABSTRACT FROM AUTHOR]

Intertidal flats are important shallow-water habitats and buffers against coastal erosion. Strong, short-lasting meteorological events, such as storms and rainfall, are the main mechanisms of transporting (in)organic materials and sediments. Two in-situ mooring systems were installed simultaneously in the tidal channel and mudflat of Jeungdo, Korea, to understand the dynamic behaviors of suspended sediment and chlorophyll- a (chl- a) under the episodic events. During fair-weather periods with a distinct tidal cycle, the sediment in the mudflat was resuspended during the flood and then advected to the tidal channel during the ebb. The maximum suspended sediment concentration (SSC) and chl- a under storm event were approximately 9 and 2 times higher than those under fair-weather periods, respectively. Under rainfall event, the maxima were approximately 7 and 1.2 times higher than fair-weather, suggesting that sediment and microphytobenthos were highest resuspended by the meteorological events. In addition, a time lag (∼ 1.5 h) between SSC and chl- a occurred in the tidal channel during ebb tide with a rainfall event. During the post-rainfall periods, the SSC and chl- a increased, showing a positive relationship with the bed shear stress, suggesting that the rainfall event could reduce sediment stabilization. • We examined sediment and microphytobenthos dynamics during storm and rainfall events. • Episodic meteorological events influenced the redistributing sediment and chl- a. • The (de)coupling and resuspension time-lag between sediment and chl- a are evidenced. • Rainfall could reduce the stabilization of sediment and microphytobenthos. [ABSTRACT FROM AUTHOR]

Summary: Intertidal shoals are pronounced morphological features found in many estuaries worldwide. Apart from maintaining an ecologically unique intertidal environment, shoals also protect adjacent dyke systems by attenuating waves. The fate of sandy shoals under anticipated sea level rise (SLR) scenarios is underexplored. The current research investigates the long‐term morphodynamic evolution of estuarine sandy shoals under forcing by short fetch, locally generated wind‐waves, tides, and SLR by means of a numerical, process‐based model (Delft3D). The focus lies on a sheltered shoal complex in the Western Scheldt, the Netherlands. Starting from the initial, 1963 bathymetry, we model 50‐year morphodynamic development with schematized wind‐wave forcing. We analyze in detail the impact of locally generated wind‐waves on shoal formation. Finally, we impose regional SLR of 1.10 m and 1.95 m for 100 years. Model results show that, on the spatial scale of intertidal flats, small, locally generated wind‐waves lower and widen the shoals while the adjacent channels deepen. However, on the estuarine system scale, wind‐waves do not lead to fundamentally different channel–shoal patterns and morphodynamic evolution trends. This suggests that channel–shoal formation is mainly due to tide residual sediment transports, with wind‐waves playing a secondary role. SLR leads to a notable intertidal area loss, despite a continuous heightening of the shoals, implying that morphodynamic adaptation lags behind SLR. The inclusion of wind‐waves does not fundamentally change the reaction of the estuarine shoal to SLR. Future research may focus on exploring the impact of including multiple sediment classes. [ABSTRACT FROM AUTHOR]

Erosion of cohesive sediments is a ubiquitous phenomenon in estuarine and intertidal environments. Several methods have been proposed to determine the surface erosion threshold (τc0), which are still debatable because of the numerous and uncertain definitions. Based on erosion microcosm experiments, we have compared three different methods using (1) eroded mass (EM), (2) erosion rate (ER), and (3) suspended sediment concentration (SSC), and suggested a suitable method for revealing the variation of erodibility in intertidal sediments. Erosion experiments using a microcosm system were carried out in the Muuido tidal flat, west coast of South Korea. The mean values of τc0 for three methods were: 0.20 ± 0.08 Pa (EM); 0.18 ± 0.07 Pa (ER); and (3) 0.17 ± 0.09 Pa (SSC). The SSC method yielded the lowest τc0, due to the outflow of suspended sediment from the erosion chamber of the microcosm. This was because SSC gradually decreased with time after depleting the erodible sediment at a given bed shear stress (τb). Therefore, the regression between SSC and applied τb might skew an x-intercept, resulting in the underestimation (or “not-determined”) of τc0. The EM method yielded robust and accurate (within the range of τb step at which erosion begins) results. The EM method represents how the erodible depth thickens as τb increases and therefore seems better suited than the SSC and ER methods for representing depth-limited erosion of cohesive sediments. Furthermore, this study identified the spatiotemporal variations of τc0 by EM method in an intertidal flat. The τc0 in mud flat was about two times higher than that in mixed flat. Compared to the end of tidal emersion, the sediment was 10–40% more erodible at the beginning stage.

The distribution of macrobenthos in the intertidal area of Buntal Bay, Sarawak was studied based on systematic sampling conducted in 2014. This study aimed to determine the intertidal macrobenthic horizontal distribution and their relationship with environmental parameters. An analysis of the intertidal flat marobenthos community suggested that polychaetes dominated the community in terms of the number of individuals and species followed by crustaceans and molluscs. Polychaetes of families Nephtyidae, Spionidae, Capitellidae, and Magelonidae contributed to the high densities of macrobenthos. Multivariate analysis performed by the Biotic and Environmental linking analysis indicated that communities in Transect 1 and Transect 2 were best correlated with food availability (sediment chlorophyll a), and heterogeneity of sediment type (percentage of fine sand and very fine sand). Heterogeneity of sediment characteristic and food availability were identified as potentially playing a key role in the shaping of the intertidal macrobenthic distribution in Buntal Bay.

Tidal gates cause adverse effects on the ecological environment through the downstream acceleration of sediment deposition. This deposition process and its quantitative analysis have become a hot topic in marine science. A large-scale physical model experiment of morphological responses to the construction of a tidal gate in an estuarine tributary was performed in this study. The sediment distribution characteristics, morphologic patterns, and further analysis of the adjacent intertidal flats were investigated, triggered by the construction of tidal gates at the mouth of the Nanxi River in Zhejiang, China. The results indicated that the flood and ebb tide velocities change dramatically after the construction of the tributary tidal gates. Large amounts of sediment from the mouth of the estuary could not be entirely carried away from the flood phase to the ebb phase, resulting in downstream deposition in the vicinity of the gates. The ebb tide caused erosion of the tidal flats’ surface in the silted intertidal zone that gradually developed into a tidal channel network. The tidal channel bifurcated in the middle–upper part of the intertidal flats through continuous headward erosion, thus promoting the landward expansions of channels. Applying a set of logistic growth models to the mean sinuosity, Hausdorff dimension, and junction number data indicated that the tidal channel development progressively tended toward a state of morphodynamic equilibrium.

Proliferation of urban structures and mangrove forests in estuaries are altering the shading of intertidal sediments. Urbanization also tends to increase nutrient loads in estuaries, which can have numerous direct and indirect effects on estuarine flora and fauna. Mangrove canopy shades the sediment and provides nutrients to the ecosystem via leaf litter. Microphytobenthos, macrofauna, sediment erodibility, and various biogeochemical properties of sediments have been shown to differ significantly between unshaded intertidal sediment and nearby sediment under a mangrove canopy. This study tested the effects of experimental manipulation of shading and addition of nutrients on the microphytobenthos, macrofauna, sediment erodibility, and selected biogeochemical properties of exposed intertidal flat next to the seaward edge of a mangrove forest. In the first of two experiments, plots were shaded with roofs to give lightly shaded plots and heavily shaded plots, for comparison with unshaded control plots; nutrients were added in an orthogonal design. Sediment and benthos were sampled after 2 weeks. Nutrients were omitted in the second experiment, with plots sampled after 2 weeks or approximately 3 months. The only effect of nutrients was a small negative effect on chlorophyll a and colloidal carbohydrate. Light shading (clear roofs) generally increased measures of microphytobenthos biomass (e.g., Fo and chlorophyll a) and biogeochemical properties associated with microphytobenthos such as colloidal carbohydrate. Heavy shading (black roofs) generally decreased measures of microphytobenthos biomass and microphytobenthos-associated biogeochemical properties. Effects on the fauna were much smaller and inconsistent with previous studies, after 3 months, assemblages were different under heavy shading compared to light shading and unshaded control plots, with differences primarily driven by changes in the oligochaetes. Natural or anthropogenic changes in shading at larger spatial scales are likely therefore to directly and indirectly change microphytobenthos, sediment properties, macrofauna and hence ecosystem functions; but any flow-on effects to the fauna are difficult to predict without further experiments to understand the indirect and direct responses of fauna to changing microphytobenthos and properties of intertidal sediment.

Salt marshes, providing numerous ecosystem services, are degrading worldwide. To effectively aid conservation and restoration efforts, increased knowledge on marsh expansion processes and the initial establishment of pioneer vegetation is essential. In this study, we disentangle environmental drivers that affect the lifecycle of the annual pioneer Salicornia procumbens at the salt marsh edge. We studied the effect of various environmental variables on the start of germination, germination success and mortality before seed-set in a field experiment in the Dutch Wadden Sea at Westhoek. Our results indicate that temperature and sedimentation inhibited the initiation of germination. Once germination occurred, higher precipitation rates increased germination success. In contrast, sedimentation rates above 0.5 mm day−1 halved germination success through burial of freshly sprouted seedlings. Unexpectedly, natural germination was low, indicating that seed availability may have been limited, despite a seed source nearby. Frequent inundation, extended periods without inundation (through desiccation of the soil) and a highly dynamic bed level increased mortality before seed-set. Consequently, bed-level dynamics (erosion, sedimentation and bed-level variation) impact seed production dually (decrease germination and increase mortality) and thus potentially reproduction success. A high seed reproduction is crucial for annuals, such as S. procumbens, to re-establish the following year. Next to advancing our general knowledge of natural salt marsh expansion, results in this study can also be used to assess the potential of a given site for salt marsh stimulation or restoration. Seed availability and local bed-level dynamics are key in the successful establishment of a salt marsh pioneer: Salicornia procumbens. [ABSTRACT FROM AUTHOR]

Intertidal flats lying as a buffer zone between land and sea provide critical services including protection against storm surges and coastal flooding. These environments are characterized by a continuous redistribution of sediment and changes in topography. Sea level rise, anthropogenic pressures, and their related stressors have a considerable impact on these areas and are expected to put them under more stress; hence the increased need for frequent and updated topography maps. Comparing to traditional surveying approaches, spaceborne remote sensing is able to provide topography maps more frequently with a lower cost and a higher coverage. The latter is currently considered as an established tool for measuring intertidal topography. In this study, an improved approach of the waterline method was developed to derive intertidal Digital Elevation Models (DEMs). The changes include a faster, more efficient and quasi-automatic detection and post-processing of waterlines. The edge detection technique consists in combining a k-means based segmentation and an active contouring procedure. This method was designed to generate closed contours in order to enable an automatization of the post-processing of the extracted waterlines. The waterlines were extracted from Sentinel-1 and Sentinel-2 images for two bays located on the French Coast: the Arcachon lagoon and the Bay of Veys. DEMs were generated for the Arcachon Bay between 2015 and 2018, and for the Bay of Veys between 2016 and 2018 using satellite acquisitions made during summer (low storm activity period). The comparison of the generated DEMs with lidar observations showed an error of about 19–25 cm. This study also demonstrated that the waterline method applied to Sentinel images is suitable for monitoring the morpho-sedimentary evolution in intertidal areas. By comparing the DEMs generated between 2016 and 2018, the Arcachon Bay and the Bay of Veys experienced net volume losses of 1.12 × 106 m3 and 0.70 × 106 m3 respectively. The generated DEMs provide useful and needed information for several scientific applications (e.g., sediment balance, hydrodynamic modelling), but also for authorities and stakeholders for coastal management and implementation of ecosystem protection policies. [ABSTRACT FROM AUTHOR]

This study investigated the environmental characteristics and macrobenthic community structures of an intertidal flat located on Yubu Island in the western coastal area of the Yellow Sea of South Korea. The study site has been well known for the migratory bird protection designated by UNESCO. We collected the samples of surface and depth core sediments and macrobenthos from the unused saltern and the area surrounding it in July 2017. Our results demonstrated that the means of mud, total carbon, and total nitrogen contents were 50%, 0.35% and 0.05%, respectively, and the origin of sediment composed of marine sources. The sedimentation rate ranged from 0.99 to 1.66 cm y−1, which was higher than other tidal flats in the Yellow Sea. The result of a topographic analysis indicated that the area in the unused saltern was 289.489 m2, and the length and width were 625 m and 500 m, respectively. A total of 13 species occurred with a mean density of 92 ind. m−2 and a mean biomass of 58.6 gWWt m−2. The Heteromastus filiformis (23.1%, 21 ind. m−2) was the most dominant species, followed by Perinereis linea (19.2%, 18 ind. m−2) and Tubuca arcuata (17.3%, 16 ind. m−2). Thus, this environmental information will help to establish policies to protect migratory birds in the future.

The shape and size of sedimentary bedforms play a key role in the reconstruction of sedimentary processes in modern and ancient environments. Recent laboratory experiments have shown that bedforms in mixed sand–clay develop at a slower rate and often have smaller heights and wavelengths than equivalent bedforms in pure sand. This effect is generally attributed to cohesive forces that can be of physical origin, caused by electrostatic forces of attraction between clay minerals, and of biological origin, caused by 'sticky' extracellular polymeric substances (EPS) produced by micro‐organisms, such as microalgae (microphytobenthos) and bacteria. The present study demonstrates, for the first time, that these laboratory experiments are a suitable analogue for current ripples formed by tidal currents on a natural mixed sand–mud–EPS intertidal flat in a macrotidal estuary. Integrated hydrodynamic and bed morphological measurements, collected during a spring tide under weak wave conditions near Hilbre Island (Dee Estuary, north‐west England, UK), reveal a statistically significant decrease in current ripple wavelength for progressively higher bed mud and EPS contents, and a concurrent change from three‐dimensional linguoid to two‐dimensional straight‐crested ripple planform morphology. These results agree well with observations in laboratory flumes, but the rate of decrease of ripple wavelength as mud content increased was found to be substantially greater for the field than the laboratory. Since the formation of ripples under natural conditions is inherently more complex than in the laboratory, four additional factors that might affect current ripple development in estuaries, but which were not accounted for in laboratory experiments, were explored. These were current forcing, clay type, pore water salinity and bed EPS content. These data illustrate that clay type alone cannot explain the difference in the rate of decrease in ripple wavelength, because the bed clay contents were too low for clay type to have had a measurable effect on bedform development. Accounting for the difference in current forcing between the field and experiments, and therefore the relative stage of development with respect to equilibrium ripples, increases the difference between the ripple wavelengths. The presence of strongly cohesive EPS in the current ripples on the natural intertidal flat might explain the majority of the difference in the rate of decrease in ripple wavelength between the field and the laboratory. The effect of pore water salinity on the rate of bedform development cannot be quantified at present, but salinity is postulated herein to have had a smaller influence on the ripple wavelength than bed EPS content. The common presence of clay and EPS in many aqueous sedimentary environments implies that a re‐assessment of the role of current ripples and their primary current lamination in predicting and reconstructing flow regimes is necessary, and that models that are valid for pure sand are an inappropriate descriptor for more complex mixed sediment. This study proposes that this re‐assessment is necessary at all bed clay contents above 3%. [ABSTRACT FROM AUTHOR]

The distribution of macrobenthos in the intertidal area of Buntal Bay, Sarawak was studied based on systematic sampling conducted in 2014. This study aimed to determine the intertidal macrobenthic horizontal distribution and their relationship with environmental parameters. An analysis of the intertidal flat marobenthos community suggested that polychaetes dominated the community in terms of the number of individuals and species followed by crustaceans and molluscs. Polychaetes of families Nephtyidae, Spionidae, Capitellidae, and Magelonidae contributed to the high densities of macrobenthos. Multivariate analysis performed by the Biotic and Environmental linking analysis indicated that communities in Transect 1 and Transect 2 were best correlated with food availability (sediment chlorophyll a), and heterogeneity of sediment type (percentage of fine sand and very fine sand). Heterogeneity of sediment characteristic and food availability were identified as potentially playing a key role in the shaping of the intertidal macrobenthic distribution in Buntal Bay. [ABSTRACT FROM AUTHOR]

In order to identify the food sources of the intertidal snail, Batillaria multiformis, stable isotope (δ13C, δ15N) and gut content analyses were conducted. Snails and their possible food sources were collected from the riversea transects at the mouths of the Iroha and Katsura rivers in northeastern Kyushu, Japan, which differ in land use parameters (e.g., the ratio of agricultural area in the catchment area). There was a shift in the δ13C of the snail along the transects, showing higher values at the upstream stations (-15.8 and -14.8‰) and lower values (-17.5 and -17.1‰) at the seaward stations. The δ15N showed no significant spatial gradient along the transects, but a significant difference was observed (t-test, p<0.001) between the Iroha (mean, 10.0‰) and Katsura (11.1‰) rivers. A Bayesian mixing model and the biomass of possible food sources on the tidal flats showed that (1) the major food sources were marine phytoplankton, seaweeds, and benthic microalgae, and that (2) the dependency on marine phytoplankton increased in the seaward stations. However, gut content analysis revealed that most of the identifiable dietary items across all stations were benthic diatoms, which is considered to be due to the short-term result of ingestion on the sediment surface at low tide. Increasing dependency on phytoplankton at seaward stations was considered to be due to consumption of suspended particles in the water column at high tide by filter feeding. Differences in the δ15N between the two rivers suggest the possibility of using the δ15N of snails as an indicator of watershed characteristics. [ABSTRACT FROM AUTHOR]

Specimens of the intertidal snail, Batillaria multiformis were collected from 25 river mouths in the Kunisaki Peninsula and the Nakatsu and Usa districts in southwestern Japan to assess the relationships between their isotopic compositions (δ13C and δ15N) and watershed characteristics. Among 22 watershed parameters, which were classified into the land use, human population, topography, geology, and vegetation in the catchment area of each river, five parameters were significantly correlated with the δ15N of snails (Pearson's correlation coefficient r: all p<0.05). The δ15N values increased with a decrease in the inclination of the ground, volcanic rock rate, and forested land rate and with an increase in the cultivated land and paddy field rates. The δ13C and δ15N analyses showed minor contributions of terrestrial plants to the diet of snails and their dependence on estuarine and marine producers, mainly on benthic microalgae, for food. These findings suggest that the δ15N values of intertidal snails were determined by the consumption of estuarine and/or marine producers, which assimilated nutrients derived from the watersheds. [ABSTRACT FROM AUTHOR]

Field work combining in-situ mooring and erosion experiments was conducted in the intertidal flat of Asan Bay to reveal the relationship between sediment erodibility and external forcing and the contribution of local erosion to sediment transport. A total of 25 tidal cycles occurred during the mooring period with 6-h submergence and 5.7-h air exposure. The erosion rate (E) for sediment bed during air exposure was 0.007 g m−2 s−1, which was 36% of E (0.019 g m−2 s−1) during submergence. Although the sediment bed was influenced by consolidation during air exposure, the erodibility of the submerged bed was closely associated with the unconsolidated deposits of sediments newly supplied from tidal channel and bed shear stress (τ cw) induced by current-wave interactions. In particular, τ cw could be enhanced by strong winds, which depended on the ratio (H s / h) of significant wave height and water level, directly disturbing the sediment bed. Under weak winds (H s / h < 0.06), the newly deposited sediments with high erodibility increased the bed elevation. A small amount of the sediment bed was eroded (E : 0.006 g m−2 s−1), as a floc erosion, with a slight decrease in suspended sediment concentration (SSC T). This increased the contribution (57.2%) of eroded sediments to SSC T. Under strong winds (H s / h > 0.06) with enhanced τ cw , meanwhile, the erodible sediment in the bed was depleted accompanied by a decrease in bed elevation. A large amount of sediment bed was eroded (E : 0.025 g m−2 s−1), as a surface erosion, resulting in the rapid increase in SSC T and the enhanced seaward sediment flux. The sediments eroded from the bed were supplied to water column accounting for 86.8% of SSC T. This suggests that seaward sediment transport under strong winds could be caused by surface erosion shifting from floc erosion in the intertidal flat. [Display omitted] • In-situ erodibility of submerged bed was unaffected by consolidation in exposure. • Bed erosion type was shifted between floc and surface erosions depending on winds. • Surface erosion by strong wind increased fraction of eroded sediment in suspension. • Seaward exported sediments were mostly originated from bed under strong wind. [ABSTRACT FROM AUTHOR]

Artificial sand replenishments are globally used as innovative coastal protection measures. In these replenishments elevated porewater concentrations of trace elements are found. The present study investigated possible ecotoxicological risks at 2 intertidal depositional sites, the Sand Engine as a recent innovative Dutch coastal management project and a semiartificial tidal flat. Using the sediment quality triad approach, we considered 3 major lines of evidence: geochemical characterization, toxicity characterization using bioassays with the estuarine amphipod Corophium volutator, and ecological field survey. In both depositional areas C. volutator is at risk: moderate (Sand Engine) and low (tidal flat). For tidal flat, the bioavailability of trace elements differs between the field site and the laboratory. Contamination from arsenic and copper is present, but the low survival rate of C. volutator from the bioassay suggests the presence of additional contaminations. The highly morphological dynamic environment of Sand Engine creates a less favorable habitat for C. volutator, where local spots with stagnant water can temporarily create hypoxic conditions and sulfate becomes reduced. The dynamic system mobilizes especially arsenic, triggering adverse ecotoxic effects at low original sediment concentrations. To conclude, the sediment quality triad approach shows that a semiartificial tidal flat is preferred over a highly dynamic coastal management project like the Sand Engine. The Sand Engine concept does not provide suitable conditions for macrobenthos species like C. volutator; therefore, limiting the nature development goal set together with the coastal protection goal. Assessing each line of evidence from the approach together with additional measurements established more precise and realistic conclusions, showing that evaluating the contributions of this method is necessary to understand the causes of risk in a site‐specific manner. Environ Toxicol Chem 2018;37:2933–2946. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The drastic land cover change and its impacts in the Yellow Sea have long been significant issues in terms of coastal vulnerabilities, but holistic data analysis is limited. The present study first reports 40 years long geographical changes of the Yellow Sea coasts including all three neighboring countries of China, North Korea, and South Korea. We delineated tidal flats by analysis of Landsat series satellite imageries (662 scenes) between 1981 and 2016. A total area of the Yellow Sea tidal flats has been considerably reducing for the past 36 years, from ∼10,500 km 2 (1980s) to ∼6700 km 2 (2010s), say ∼1% annual loss. A majority loss of tidal flats was mainly due to the grand reclamations that conducted in almost entire coast of the Yellow Sea, particularly concentrated in the 1990s-2000s. Coastal reclaimed area during the past four decades reached ∼9700 km 2 , including ongoing and planned projects, which corresponds to over half the area of precedent natural tidal flats of the Yellow Sea. The potential carbon stocks in the eight representative regions with large scale reclamation indicated significant loss in carbon sink capacity in the South Korea's coast (∼99%), while evidenced a lesser loss from the China's coast (∼31%). It was noteworthy that the progradation of tidal flats after the reclamation in China's coast significantly reduced the loss of carbon sequestration. According to the ecosystem services valuation for the Yellow Sea, a total loss was estimated as ∼8 billion USD yr −1 with relatively high proportional loss (up to 25%) of climate regulating services (viz., carbon sequestration). Overall, huge losses in ecosystem services being provided by the Yellow Sea natural tidal flats need immediate action to prevent or at least alleviate accelerating ecological deteriorations. Finally, future conservative policy direction on coastal wetlands management has been proposed towards enhancement of marine ecosystem services. [ABSTRACT FROM AUTHOR]

Benthic microorganisms play a significant role in the remineralization of sedimentary organic matter (OM). In order to constrain the growth rate, turnover and carbon metabolism of microbial communities in anoxic sandy sediments, we quantified the rate of inorganic carbon (IC) assimilation and of lipid production via a recently developed dual isotope-labelling assay that can differentiate autotrophic vs. heterotrophic production in a 22 cm sediment core from the Janssand tidal flat (Wadden Sea, Germany). Despite an extremely low concentration of total organic carbon (TOC) in the majority of samples (<0.3%), the concentration of total fatty acids (TFAs) was in the range 4.5 to 28.4 μg/mg TOC, suggestive of a high contribution of fresh microbial and algal biomass to the TOC pool. This was corroborated by a production rate of microbial FAs, which ranged from 0.3 to 4.7 μg TFAs/g dw /yr (where dw = dry wt) and the mean turnover time of microbial FAs was 6 ± 5 yr. The enhanced production rate of iso- and anteiso- branched FAs was consistent with the presence of an active population of sulfate reducing Deltaproteobacteria . The assimilation rate of IC into bacterial lipids was relatively low (0.16 ± 0.07 μg C/g dw /yr) in OM-lean sandy sediments (i.e. upper 17 cm), such that the IC assimilation to lipid production ratio values was typically <0.3, indicating that heterotrophic bacteria were dominant and dark IC fixation played a minor role at the study site. The measured rates of FA production converted to an anaerobic heterotrophic C demand of 0.4–1.8 µg C/g dw /d, assuming a bacterial growth efficiency of 10%. Such high biomass proportion, production rate and C demand suggested that dissolved OM must play a vital role in sustaining the active heterotrophic microbial populations in these sandy sediments. [ABSTRACT FROM AUTHOR]

Changes in the composition, structure and seasonal succession patterns were observed in a local community of interstitial ciliates over a period of 21 years (1991–2011). General trends in species structure transformation were revealed. During 1991–2004 years Trachelocerca incaudata, Remanella margaritifera, Coleps tesselatus, and Uronema marina, dominated in the community. However, in 2005–2011 the number of specific interstitial ciliate species, and of Apotrachelocerca arenicola in particular, increased considerably. These changes were caused by the increase in the silt content in the sediments. Long-term changes were realized at different stages of seasonal development of the community including both, more structurally simple earlier period (in the beginning of spring) and more structurally complex mature period (at the end of summer). The most mature state of ciliate community was temporally (in the inter-year scale) stable, but discretely (drastically) transformed from one variant (in 1991–2004) to another one (in 2005–2011). The simpler state of ciliate community was more variable between years and transformed gradually from one polymorphic variant (in 1991–1995, 1998, 2000–2005, 2009–2010) to another one (in 2006–2008, 2011). This suggests that discrete and stable mature communities can be assembled via different annual trajectories.

Oligochaetes (Annelida) are active bioturbators that can be present in high densities in the transition zone between intertidal flats and salt marshes, though their occurrence and functional role remain understudied. This study aimed to clarify the biogeomorphic role of oligochaete bioturbation in facilitating or hindering vegetation establishment. Two microcosm experiments were performed to assess the effect of oligochaete bioturbation on sediment properties, oxidation depth, algal biomass, seed distribution, and germination success of pioneer species Salicornia spp. Oligochaetes created burrow networks in the sediment matrix, which, together with upward conveyor belt feeding, lead to substrate mixing. Sediment reworking rates of oligochaetes were compared with those of polychaete macrofauna. Bioturbation and bio-irrigation of burrows can stimulate resource flows into the sediment. Oxidation depth increased almost tenfold in the presence of oligochaetes. Their bioturbation did not seem to affect sediment properties such as dry bulk density, porosity, and organic matter content. Sediment reworking, however, significantly reduced algal biomass at the surface with possible cascading effects on sediment stability and erodibility. Oligochaete conveyor belt feeding buried Salicornia spp. seeds until below the critical germination depth, thus negatively affecting Salicornia spp. germination and seedling establishment. Our study indicates that small, though numerous, oligochaete bioturbators may reduce lateral expansion potential of salt marshes by hindering the establishment of pioneer vegetation in the transition zone. Additionally, in dynamic fine-grained habitats, these oligochaetes have the feature to quickly oxygenate the sediment top layer. [ABSTRACT FROM AUTHOR]

Intertidal flats are highly productive areas that support large numbers of invertebrates, fish, and birds. Benthic diatoms are essential for the function of tidal flats. They fuel the benthic food web by forming a thin photosynthesizing compartment in the top-layer of the sediment that stretches over the vast sediment flats during low tide. However, the abundance and function of the diatom film is not homogenously distributed. Recently, we have realized the importance of bivalve reefs for structuring intertidal ecosystems; by creating structures on the intertidal flats they provide habitat, reduce hydrodynamic stress and modify the surrounding sediment conditions, which promote the abundance of associated organisms. Accordingly, field studies show that high chlorophyll a concentration in the sediment co-vary with the presence of mussel beds. Here we present conclusive evidence by a manipulative experiment that mussels increase the local biomass of benthic microalgae; and relate this to increasing biomass of microalgae as well as productivity of the biofilm across a nearby mussel bed. Our results show that the ecosystem engineering properties of mussel beds transform them into hot spots for primary production on tidal flats, highlighting the importance of biological control of sedimentary systems. [ABSTRACT FROM AUTHOR]

The paper analyzes the seasonal and long-term dynamics of marine interstitial ciliates communities as a result of the processes of system self-organization (of increasing complexity) in constantly fluctuating environment. The traits of simple structure of ciliate community include substantial variability in the composition (even in case of stable environment) and the lack of sustainable combinations of species. The mechanism of the current state maintenance is the lack of energy supply in certain periods or in specific loci of space, as well as large amplitude and unpredictable fluctuations of environmental factors. An indication of the community’s complexity is availability of stable combinations of species in time and space. The mechanisms of formation of stable species combinations are a constant flow of external energy, optimal values and stability of environmental factors (including repeatability of seasonal cycles) and the use of space resources by species according the principle of complementarity of ecological niches.

Tidal flats provide habitat for biodiversity, protection from storm surges and sea level rise, and a range of other ecosystem services. However, no simple method exists for mapping tidal flats over large (>1,000 km) extents, and consequently their global status and distribution remain poorly understood. Existing mapping methods are restricted to small areas with known tidal regimes because tidal flats are only fully exposed for a brief period around low tide. Here we present a method for mapping tidal flats over very large areas and demonstrate its utility by mapping the tidal flats of China, the Democratic People’s Republic of Korea and the Republic of Korea. We (i) generated tide height predictions at the acquisition time of all Landsat Archive images of our study area using a validated regional tide model, (ii) selected suitable images acquired in the upper and lower 10% of the tidal range, (iii) converted high and low tide images to a land and water class image derived from the Normalized Differenced Water Index (NDWI) and, (iv) subtracted the high tide classified image from the low tide classified image, resulting in delineation of the tidal flat. Using this method, we mapped the tidal flats for 86.8% of the study area coastline (13,800 km). A confusion matrix for error assessment indicated an accuracy of >85% for the resulting tidal flat map. Our method enables coastal morphology to be mapped and monitored at continental scales, providing critical data to inform coastal adaptation measures for sea level rise, for monitoring coastal habitat loss and for developing ecosystem-based coastal conservation measures.