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The origin of sedimentary organic matter (SOM) has often been mentioned as a driver of SOM reactivity. This was quantified by statistically relating the isotopic and lipid composition of SOM to benthic nutrient fluxes in 200 intertidal mudflats sampled along the Brittany coast (France). The origin of SOM explained 24% and 31% of the variance of $\text{NH}_4^+$ and $\text{PO}_4^{3-}$ fluxes, respectively. The $\text{NH}_4^+$ fluxes were driven by the uptake by phytoplankton of dissolved anthropogenic N exported from agricultural catchments. Their sedimentation is favoured by low hydrodynamic conditions, enriching the sediments with labile OM. The $\text{PO}_4^{3-}$ fluxes were driven by the sedimentation of particulate P exported through agricultural soil erosion.

Despite their high productivity and their key role in coastal processes, microphytobenthic biofilm studies remain relatively scarce because in situ, meteorological hazards make it difficult to acquire reproducible measurements, also due to difficulties in properly reproducing field conditions in the laboratory. Therefore, in order to better understand the processes of microphytobenthic primary production, we have developed an automated laboratory system and procedure with variable light intensity, with a large number of replicates. This article aims to provide a description of the creation of a P-I curve based on a total of 128 vertical profiles recorded on a sediment core taken in situ, placed in the automated system and studied under controlled conditions of temperature and air humidity while light intensity was varied automatically, thus allowing to work in standard and replicable conditions. With measured production levels of up to 14.68 ± 3.70 mmol O2.m-2.h-1 and a productivity of 0.06 ± 0.01 mmol O2.m-2.h-1 per gram of Chl a corresponding to what is generally found in temperate environments, we have shown that our system is suitable for high frequency measurements and, by combining surficial measurements of modulated fluorescence and oxygen microprofiling in sediments, complementary information from a large dataset on photosynthetic and microphytobenthic migratory activity may be obtained under standard conditions. The development of this tool has made it possible to highlight a stabilization time for oxygen fluxes. For our study conducted in a temperate environment, we observed a time lag of a few minutes that should be considered when acquiring PE curves in the laboratory to study microphytobenthic photosynthetic capacities. This tool also allowed to describe microphytobenthic migration in response to light exposure, with successive steps observed through fluorescence and oxygen profiles. First, microphytobenthos migrated towards the surface until the optimal intensity of production at 475 µmol photons.m-2.s-1, then from this intensity as well as towards 780 µmol photons.m-2.s-1, downwards migratory movements were detected. This system is a working basis which can open interesting perspectives for the study of the effect of other abiotic (or biotic) parameters.

The erosional and accretional profile changes of an intertidal mudflat are examined using available field data and the cross-shore numerical model CSHORE that is extended to allow for a mixture of sand and mud. The semidiurnal migration of the still water shoreline and surf zone is resolved numerically to predict the net cross-shore and longshore sediment transport rates influenced by the small cross-shore (undertow) and longshore currents induced by breaking waves of about 0.2 m height. Alongshore sediment loss or gain is included by approximating the alongshore sediment transport gradient using an equivalent alongshore length. The calibrated CSHORE reproduces the measured erosional (accretional) profile change of about 0.1 m (0.1 m) over a cross-shore distance of 950 m during the erosional (accretional) interval of 206 (195) days. The mudflat profile changes are equally affected by mud characteristics, the semidiurnal tide amplitude, and the wave height, period, and direction. In addition, the alongshore water level gradient and wind stress influence longshore current and sediment transport. This study shows the importance of sediment transport in the surf zone that may have been excluded in previous numerical modeling. [ABSTRACT FROM AUTHOR]

Coastal marine sediments can be either major scrubbers or eutrophication contributors to surface waters. Standard methods for direct measurement of nutrient fluxes at the sediment-water interface do not consider hydrodynamic forcing although several ex-situ studies suggest that sediment resuspension can dramatically increase dissolved fluxes. We provide a new model to quantify dissolved phosphate (PO 4 3−) resuspension flux (J R) based on physical representation of its identified components: diffusion stimulation by exposure of deeper sediment layer with higher PO 4 3− concentration in the porewater (J D), pore water mixing with overlying water (J M) and net adsorption/desorption from suspended sediments (J K). This approach was applied to field data from a Seine intertidal mudflat periodically submitted to millimetric erosion. On a tidal scale, the model output reveals a J R of 272.3 ± 360.0 μmol m−2 h−1 (± 52% from parameter uncertainty), well above flux calculated by application of Fick's first law (0.15 ± 0.85 μmol m−2 h−1) or by ex situ core incubation (40.8 μmol m−2 h−1). Iron bound phosphorus within suboxic layers buffers PO 4 3− concentrations in superficial sediments leading to negligible contributions of J D and J M to total fluxes. Conversely, J K appears to be the main exchange pathway, even though improvements in turbidity measurement would allow this term to be defined more precisely. Correction required to enhance and control model robustness are described. These results show the importance of considering the dissolved PO 4 3− resuspension flux in dynamic environments. • Original model for PO 4 3− resuspension flux calculation from in situ estuarine data. • Mean resuspension flux was 272.3 ± 360.0 μmol P m−2 h−1 on a tidal scale. • Desorption pathway is critical for its magnitude and model improvement perspectives. • Standard methods underestimate PO 4 3− benthic flux in dynamic environments. [ABSTRACT FROM AUTHOR]

Two new lipo-decapeptides, namely taeanamides A and B (1 and 2), were discovered from the Gram-positive bacterium Streptomyces sp. AMD43, which was isolated from a mudflat sample from Anmyeondo, Korea. The exact molecular masses of 1 and 2 were revealed by high-resolution mass spectrometry, and the planar structures of 1 and 2 were elucidated using NMR spectroscopy. The absolute configurations of 1 and 2 were determined using a combined analysis of 1H-1H coupling constants and ROESY correlations, the advanced Marfey's method, and bioinformatics. The putative nonribosomal peptide synthetase pathway for the taeanamides was identified by analyzing the full genome sequence data of Streptomyces sp. AMD43. We also found that taeanamide A exhibited mild anti-tuberculosis bioactivity, whereas taeanamide B showed significant bioactivity against several cancer cell lines. [ABSTRACT FROM AUTHOR]

Microphytobenthos (MPB) are a key primary producer of intertidal mudflats. MPB face strong variability in incident irradiance during low tides. Despite photoprotection and photoacclimation, such variations can translate into the photoinhibition of MPB cells. This study explores the effect of photoinhibition on MPB primary production (PP) over a large and productive temperate mudflat (Brouage mudflat, NW France). We used a regional and high‐resolution tri‐dimensional hydrodynamic model coupled to an MPB model with or without photoinhibition. Photoinhibition leads to a 20% (−0.79 × 103 t C) decrease of the simulated MPB PP over the entire mudflat. As the upper shore is exposed to light more frequently and longer than the lower shore, the decrease of MPB PP is higher on the upper shore (−29%) than on the lower shore (−5%). With the highest photosynthetically active radiation cumulated over the mudflat, the decrease of MPB PP due to photoinhibition is the highest during spring and spring tides (−22% and −23%, respectively). The model suggests MPB photoinhibition is sensitive to the photoacclimation status of MPB cells through the light saturation parameter. This first modeling attempt to account for MPB photoinhibition is highly constrained by our current theoretical knowledge and limitations on the MPB growth physiology, but it suggests that this process can have a substantial impact on the MPB PP. As such, assessing the MPB photosynthetic response to the highly variable environmental conditions that prevail in large and productive intertidal mudflats is a real challenge for quantifying MPB PP from a synoptic to inter‐annual time scale. Plain Language Summary: Benthic micro‐algae or microphytobenthos (MPB) inhabiting the surficial sediment sustain the high biological production of intertidal mudflats. MPB achieve photosynthesis by aggregating into a dense biofilm at the mud surface during daytime low tides. As MPB can be exposed to short‐term variations and high light levels, they change their short‐term physiology and position within the sediment to protect themselves. However, such strategies can be outbalanced by a too long stressful light exposure. In this study, we explore with a numerical model the impact of photoinhibition on MPB primary production (PP) over a large and very productive mudflat (NW France). The model suggests that photoinhibition can strongly impact MPB PP. With photoinhibition, the yearly PP decreases by 20% over the whole mudflat. The model suggests MPB PP is sensitive to the photoacclimation status of MPB cells, that is, their light use efficiency at a given light level. This first modeling attempt to account for MPB photoinhibition is highly constrained by our current theoretical knowledge and limitations on the MPB growth physiology, but it suggests that this process can have a substantial impact on the MPB PP. Key Points: With or without photoinhibition, simulated yearly MPB PP is higher on the upper and middle shores than on the lower shorePhotoinhibition leads to a 20% (−0.79×103 t C yr−1) decrease of MPB PP over the entire mudflatThe photoinhibition process in the model is sensitive to the photoacclimation status of MPB cells [ABSTRACT FROM AUTHOR]

Benthic macrofauna are a key component of intertidal ecosystems. Their mobility and behavior determine processes like nutrient cycling and the biogeomorphic development of intertidal flats. Many physical drivers of benthic macrofauna behavior, such as sediment grain size, have been well-studied. However, little is known about how sediment bulk density (a measure of sediment compaction and water content) affects this behavior. We investigated the effect of bulk density on the burrowing rate, burrowing depth, bioturbation activity, and oxygen consumption of bivalves (Limecola balthica, Scrobicularia plana, and Cerastoderma edule) and polychaetes (Hediste diversicolor and Arenicola marina) during a 29-day mesocosm experiment. We compared four sediment treatments consisting of two sediments of differing grain size classes (sandy and muddy) with two bulk densities (compact and soft). Overall, bulk density had a strong effect on benthic macrofauna behavior. Benthic macrofauna burrowed faster and bioturbation more intensely in soft sediments with low bulk density, regardless of grain size. In addition, L. balthica burrowed deeper in low bulk density sediment. Finally, we found that larger bivalves (both C. edule and S. plana) burrowed slower in compact sediment than smaller ones. This study shows that benthic macrofauna change their behavior in subtle but important ways under different sediment bulk densities which could affect animal-sediment interactions and tidal flat biogeomorphology. We conclude that lower bulk density conditions lead to more active macrofaunal movement and sediment reworking.

Aim: Molluscs are important grazers, filter and deposit feeders, scavengers and predators, which in turn are food for shorebirds, fish and people. Some species, targeted as human food, have been cultured along the Chinese coast for hundreds of years. To examine whether aquacultural practices have meanwhile affected biodiversity gradients, we measured mollusc community structure along the coast of China in habitats which are intensively used by humans. Location: Chinese coast. Methods: We sampled 21 intertidal sites spanning 20 latitudinal degrees and 18,400 km of coastline. We assessed alpha diversity to verify whether mollusc communities exhibit the expected biodiversity gradient with latitude and beta diversity gradients with distance. To examine whether human activities such as transportation and culturing could have affected these patterns, we distinguished commercial from non‐commercial mollusc species and compared the differences in distribution, density, alpha diversity and beta diversity. Results: We found non‐commercial species showed the expected biodiversity gradients. Commercial species (a) dominated the intertidal mollusc communities at 19 of the 21 sites and compared with non‐commercial species, (b) exhibited wider geographical distributions, (c) showed no significant change in Bray‐Curtis index (abundance‐based beta diversity) with either geographical or climatic distance, (d) exhibited lower average dissimilarities and (e) did not show a decrease in species richness and Shannon diversity with latitude. Combining all species, trends were the same as for the commercial species. Main conclusions: A few cultured species dominated the intertidal mollusc communities in high densities along the Chinese coastline, taking over the ecological roles of the native species but not driving them extinct. In this way, aquacultural practices have exerted a homogenizing influence strong enough to erase basic biodiversity gradients. Since molluscs are food for the growing human population and the shrinking populations of migratory animals, coastal planning and management of both intertidal habitats and the exploitative activities employed need to incorporate these dimensions. [ABSTRACT FROM AUTHOR]

Two new lipo-decapeptides, namely taeanamides A and B (1 and 2), were discovered from the Gram-positive bacterium Streptomyces sp. AMD43, which was isolated from a mudflat sample from Anmyeondo, Korea. The exact molecular masses of 1 and 2 were revealed by high-resolution mass spectrometry, and the planar structures of 1 and 2 were elucidated using NMR spectroscopy. The absolute configurations of 1 and 2 were determined using a combined analysis of 1H-1H coupling constants and ROESY correlations, the advanced Marfey’s method, and bioinformatics. The putative nonribosomal peptide synthetase pathway for the taeanamides was identified by analyzing the full genome sequence data of Streptomyces sp. AMD43. We also found that taeanamide A exhibited mild anti-tuberculosis bioactivity, whereas taeanamide B showed significant bioactivity against several cancer cell lines.

Microphytobenthos (MPB) at the sediment surface of intertidal mudflats are known to show a high spatial and temporal variability in response to the biotic and abiotic conditions prevailing at the mud surface. It makes long-term and large-scale monitoring of MPB Gross Primary Production (GPP) difficult to set up. In this study, we developed the first 3D physical-biological coupled model (MARS-3D) that explicitly simulates GPP of intertidal MPB at the mudflat scale, and we compared the outputs with in situ and space remote sensing MPB GPP data. We discuss the sources of discrepancies between the modeling and the remote sensing approach in the light of future developments to be done. For instance, the remote sensing algorithm provides a very synoptic view of the mudflat GPP. It is well-suited to achieve diagnostic estimates of MPB GPP at the synoptic spatial and temporal scale. By contrast, the MARS-3D model provides a more dynamic representation of the MPB activity and prognostic estimates of MPB GPP over the mudflat. It is very relevant to resolve the seasonal and inter-annual dynamics of MPB. Getting comparable GPP estimates derived from the remote sensing algorithm and 3D physical-biological coupled model will further require a better convergence in terms of equations structure, biological constants parameterization, and source data used (i.e., vegetation index vs. chlorophyll a). Setting a common parameterization in both the numerical model and remote sensing algorithm might be challenging in a perspective of mapping MPB PP over large mudflats from a synoptic to inter-annual time scale, but it could open the door to a new way of quantifying MPB GPP over large intertidal mudflats.

The gross primary production (GPP) of intertidal mudflat microphytobenthos supports important ecosystem services such as shoreline stabilization and food production, and it contributes to blue carbon. However, monitoring microphytobenthos GPP over a long-term and large spatial scale is rendered difficult by its high temporal and spatial variability. To overcome this issue, we developed an algorithm to map microphytobenthos GPP in which the following are coupled: (i) NDVI maps derived from high spatial resolution satellite images (SPOT6 or Pléiades), estimating the horizontal distribution of the microphytobenthos biomass; (ii) emersion time, photosynthetically active radiation (PAR), and mud surface temperature simulated from the physical model MARS-3D; (iii) photophysiological parameters retrieved from Production–irradiance (P–E) curves, obtained under controlled conditions of PAR and temperature, using benthic chambers, and expressing the production rate into mg C h–1 m–2 ndvi–1. The productivity was directly calibrated to NDVI to be consistent with remote-sensing measurements of microphytobenthos biomass and was spatially upscaled using satellite-derived NDVI maps acquired at different seasons. The remotely sensed microphytobenthos GPP reasonably compared with in situ GPP measurements. It was highest in March with a daily production reaching 50.2 mg C m–2 d–1, and lowest in July with a daily production of 22.3 mg C m–2 d–1. Our remote sensing algorithm is a new step in the perspective of mapping microphytobenthos GPP over large mudflats to estimate its actual contribution to ecosystem functions, including blue carbon, from local and global scales.

The extreme dynamics of the Amazonian coast and associated mudbanks raises questions about their unknown resistant infauna. In order to fill the gap, we investigated the seasonal variations of species composition, abundance and population structure of Tanaidacea in two dynamic mudbanks near the coast of French Guiana. Despite the low species richness recorded for this taxon, the very high densities and biomass of tanaids constituted a potential plentiful trophic resource for many coastal species, such as shorebirds, fish, shrimps, and crabs. The estuarine habitat at Sinnamary presented more tanaid species than the bare marine mudflat at Awala-Yalimapo. All species showed strong female-biased sex ratios and differed in range of total length and stage of maturity. The species with smaller body size with sexual maturity occurring at an earlier stage were dominant and widely distributed. Pore water salinity and predator pressure may be considered key factors driving seasonal variations of tanaid abundance and population structure. This study gives a novel insight into the macrobenthos communities along the highly dynamic Amazonian coast. [ABSTRACT FROM AUTHOR]

Understanding of bottom sediment erodibility is necessary for the sustainable management and protection of coastlines, and is of great importance for numerical models of sediment dynamics and transport. To investigate the dependence of sediment erodibility on degree of consolidation, we measured turbidity, waves, tidal currents, intratidal bed-level changes, and sediment properties on an exposed macrotidal mudflat during a series of tidal cycles. We estimated the water content of surface sediments (in the uppermost 2 cm of sediment) and sub-surface sediments (at 2 cm below the sediment surface). Bed shear stress values due to currents ( τ c ), waves ( τ w ), and combined current–wave action ( τ cw ) were calculated using a hydrodynamic model. In this study, we estimate the critical shear stress for erosion using two approaches and both of them give similar results. We found that the critical shear stress for erosion ( τ ce ) was 0.17–0.18 N/m 2 in the uppermost 0–2 cm of sediment and 0.29 N/m 2 in sub-surface sediment layers (depth, 2 cm), as determined by time series of τ cw values and intratidal bed-level changes, and values of τ ce , obtained using the water content of bottom sediments, were 0.16 N/m 2 in the uppermost 2 cm and 0.28 N/m 2 in the sub-surface (depth, 2 cm) sediment. These results indicate that the value of τ ce for sub-surface sediments (depth, 2 cm) is much greater than that for the uppermost sediments (depth, 0–2 cm), and that the τ ce value is mainly related to the water content, which is determined by the extent of consolidation. Our results have implications for improving the predictive accuracy of models of sediment transport and morphological evolution, by introducing variable τ ce values for corresponding sediment layers, and can also provide a mechanistic understanding of bottom sediment erodibility at different sediment depths on intertidal mudflats, as related to differences in the consolidation time. [ABSTRACT FROM AUTHOR]

ABSTRACT Geng, L.; Gong, Z.; Lanzoni, S., and D'Alpaos, A., 2018. A New Method for Automatic Definition of Tidal Creek Networks. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 156–160. Coconut Creek (Florida), ISSN 0749-0208. Tidal creek delineation is the first step in the analysis of the structure and dynamics of tidal creek networks. This study proposed a new creek definition method, in which we determined the critical elevation of creek delineation by the local elevation distribution. This method can be applied to intertidal zones with inclined bed surfaces, showing a better applicability than existing methods. By comparing creek characteristics within a certain small tidal flat using different delineation methods, we evaluated the accuracy of this new method. The size measured by the new method nicely matches results obtained on the basis of the method proposed by Fagherazzi et al. (1999). [ABSTRACT FROM AUTHOR]

In order to examine the seasonal and spatial distributions of benthic animals in the intertidal mudflat of the southern Yellow River Delta, field investigations were carried out in 2007 and 2008 and multiple methods were applied. Results showed that, the biomass of macro benthos ranged at 0.75-1151.00 g wet m−2 and averaged at 156.31 g wet m−2, in which Mactra veneriformis accounted for 75.6%-93.4% of the total macro benthic biomass. More than 90% of macro benthos inhabited in the middle and low tide lines, and higher biomass occurred in early summer and lower in winter. Statistical analysis showed that: 1) M. veneriformis growth was primarily favored at higher temperature and lower salinity; 2) after long time interaction, benthic bivalve grazers led to patching distributions of Chlorophyll a (Chl a); 3) macro benthic biomass positively related with Chl a when the concentration of Chl a was low, but they were negatively related when Chl a concentration was high; and 4) furthermore, the biomass of benthic bivalves peaked in the sediment with median grain size about 0.55 mm, but decreased gradually in coarse or fine sediments. The secondary productivity ranged at 0.37-283.68 g m−2yr−1 and averaged at 47.88 g m−2 yr−1, in which 69.7% was contributed by M. veneriformis It was estimated that primary production was transformed to secondary production at a rate of 6.87% approximately, which implies that there is a local sustainability of high bivalve production. [ABSTRACT FROM AUTHOR]

Spartina alterniflora is a dominant invasive species along the coast of China. A surprising phenomenon that the oyster reef formation is substituting the S. alterniflora invasion, was recently observed in the west coast of Bohai Bay, North China. As the intertidal mudflat ecosystem is critical for coastal blue carbon, this paper aims to evaluate the climatic effect of the alternation from the perspective of potential CH 4 and N 2 O production. The sediment geochemical properties and potential CH 4 and N 2 O productions were therefore measured in sediments dominated by Spartina alterniflora (SA), oyster reef (OR), mixture of S. alterniflora and oyster reef (SA-OR) and bare mudflat (BM) at an intertidal mudflat. Meanwhile, sediment microbial community structure and function genes were also determined utilizing metagenome high-throughput sequencing technology. Our results indicated that the formation of oyster reef in S. alterniflora invaded intertidal mudflat might slightly reduce the sediment potential CH 4 production and enhance the sediment potential N 2 O production. The oyster reef formation could alter the community composition of methanogens and the abundance of functional genes in methanogenesis, and transform the main pathway from methylotrophic to hydrogenotrophic methanogenesis in surface sediments. Metagenome sequencing revealed that the oyster reef formation may promote nitrification, inhibit dissimilatory nitrate reduction (DNRA) and nitrate assimilation functions, and reduce the abundance of nosZ genes. Mantel analysis showed that pH, soluble salt and dissolved carbon (DC) were the most important factors influencing the composition of microbial community. In general, our results imply that the growth of oyster reef in the S. alterniflora invaded area has opposing effects from the prospective of the potential CH 4 and N 2 O production. [Display omitted] • Substitution of S. alterniflora by C. gigas may reduce CH 4 but raise N 2 O emission. • Oyster reef may promote the nitrification, inhibit DNRA and reduce nosZ genes. • Oyster reef formation may turn methylotrophic into hydrogenotrophic methanogenesis. • Microbial community is strongly influenced by pH, salt content and dissolved carbon. [ABSTRACT FROM AUTHOR]

Intertidal mudflats are land–sea interaction areas and play important roles in global nutrient cycles. However, a comprehensive understanding of microbial communities in these mudflats remains elusive. In this study, mudflat sediment samples from the Dongtan wetland of Chongming Island, the largest alluvial island in the world, were collected. Using a modified metatranscriptomic method, the depth-wise distributions of potentially active microbial communities were investigated based on small subunit ribosomal RNA (SSU rRNA) sequences. Multiple environmental factors were also measured and analyzed in conjunction with the prokaryotic composition profiles. A prokaryotic diversity analysis based on the metatranscriptome datasets revealed two or threefold higher diversity indices (associated with potentially active microbes participating in biogeochemical processes in Dongtan) compared with the diversity indices based on 16S rRNA gene amplicons. Bacteria were numerically dominant relative to archaea, and the potentially active prokaryotic taxa were mostly assigned to the bacterial phyla Chloroflexi, Acidobacteria, and Bacteroidetes and the classes Delta- and Gamma-proteobacteria, along with the archaeal lineages phylum Bathyarchaeota and the order Thermoplasmatales. The total nitrogen and carbon content of the sediment samples were environmental factors that significantly affected the depth-wise distributions of both bacterial and archaeal communities. Furthermore, the activity of potentially active taxa (including the prevalent order Desulfobacterales and family Anaerolineaceae) appeared to be significantly underestimated by PCR-based methods, notably at the DNA level, and indicates that using normal PCR amplification of DNA limits the study of potential microbial activity. This is the first study of potentially active microbial communities in depth-wise sediments from Dongtan. The improved knowledge of microbial communities in Dongtan provides a foundation for exploring biogeochemical cycling and microbial functions.

In intertidal sediments, circadian oscillations (i.e., tidal and diel rhythms) and/or depth may affect prokaryotic activity. However, it is difficult to distinguish the effect of each single force on active community changes in these natural and complex intertidal ecosystems. Therefore, we developed a tidal mesocosm to control the tidal rhythm and test whether diel fluctuation or sediment depth influence active prokaryotes in the top 10 cm of sediment. Day- and nighttime emersions were compared as they are expected to display contrasting conditions through microphytobenthic activity in five different sediment layers. A multiple factor analysis revealed that bacterial and archaeal 16S ribosomal RNA (rRNA) transcript diversity assessed by pyrosequencing was similar between day and night emersions. Potentially active benthic Bacteria were highly diverse and influenced by chlorophyll a and phosphate concentrations. While in oxic and suboxic sediments, Thaumarchaeota Marine Group I (MGI) was the most active archaeal phylum, suggesting the importance of the nitrogen cycle in muddy sediments, in anoxic sediments, the mysterious archaeal C3 group dominated the community. This work highlighted that active prokaryotes organize themselves vertically within sediments independently of diel fluctuations suggesting adaptation to physicochemical-specific conditions associated with sediment depth. [ABSTRACT FROM AUTHOR]

Intertidal mudflats are land-sea interaction areas and play important roles in global nutrient cycles. However, a comprehensive understanding of microbial communities in these mudflats remains elusive. In this study, mudflat sediment samples from the Dongtan wetland of Chongming Island, the largest alluvial island in the world, were collected. Using a modified metatranscriptomic method, the depth-wise distributions of potentially active microbial communities were investigated based on small subunit ribosomal RNA (SSU rRNA) sequences. Multiple environmental factors were also measured and analyzed in conjunction with the prokaryotic composition profiles. A prokaryotic diversity analysis based on the metatranscriptome datasets revealed two or threefold higher diversity indices (associated with potentially active microbes participating in biogeochemical processes in Dongtan) compared with the diversity indices based on 16S rRNA gene amplicons. Bacteria were numerically dominant relative to archaea, and the potentially active prokaryotic taxa were mostly assigned to the bacterial phyla Chloroflexi, Acidobacteria, and Bacteroidetes and the classes Deltaand Gamma-proteobacteria, along with the archaeal lineages phylum Bathyarchaeota and the order Thermoplasmatales. The total nitrogen and carbon content of the sediment samples were environmental factors that significantly affected the depthwise distributions of both bacterial and archaeal communities. Furthermore, the activity of potentially active taxa (including the prevalent order Desulfobacterales and family Anaerolineaceae) appeared to be significantly underestimated by PCR-based methods, notably at the DNA level, and indicates that using normal PCR amplification of DNA limits the study of potential microbial activity. This is the first study of potentially active microbial communities in depth-wise sediments from Dongtan. The improved knowledge of microbial communities in Dongtan provides a foundation for exploring biogeochemical cycling and microbial functions. [ABSTRACT FROM AUTHOR]

The polychaete (sabellariid-spionid) reefs at Jeram shore (Malaysia) grow up on soft-bottom mudflats and appear short-lived. It is postulated that such reef building results from the succession of polychaete species in response to the changing environment modulated by the extreme hydrometeorological events. To elucidate the biological succession of the reef cycle in relation to the environment, two reef patches on the intertidal mudflat were studied, both spatially (horizontal and vertical community structure) and temporally (June 2012 to January 2014). The Jeram polychaete reef cycles through four phases within a year: pre-settlement phase (March-May), growth phase comprising primary (May-November) and secondary (October-January) successional stages, stagnation phase (December-January), and destruction phase (January-March). The reef dynamics appear to be linked to the regional monsoon climate and local hydrological conditions. At the onset of the southwest monsoon (May), strong erosive forces initiate the reef's primary succession of the growth phase where the dominant polychaete Sabellaria jeramae colonize and rapidly grow on the exposed lag deposits of shells. During the northeast monsoon (November-March), stronger depositional forces cover the developed reef with fine sediments that are colonized by another polychaete, the spionid Polydora cavitensis during the reef's secondary succession of the growth phase. On the muddy substrate surrounding the reef clumps, mudflat polychaetes were the most abundant macrobenthos followed by anomurans, gastropods, carideans, and brachyurans. However, these mudflat macrobenthos play no obvious or direct role in initiating the growth of the reef which is likely the result of settlement of dispersed polychaete larvae from unknown offshore reefs. On the other hand, the reef presence has a positive effect on the presence or abundance of surrounding mudflat macrobenthos such as mudflat polychaetes, shrimps, crabs, and gastropods. [ABSTRACT FROM AUTHOR]

Intertidal mudflats are rich and fluctuating systems in which the upper 20 cm support a high diversity and density of microorganisms that ensure diversified roles. The depth profiles of microbial abundances and activities were measured in an intertidal mudflat (Marennes-Oléron Bay, SW France) at centimeter-scale resolution (0–10 cm below the sediment surface). The aim of the study was to detect microbial stratification patterns within the sediments and the way in which this stratification is shaped by environmental drivers. Two sampling dates, i.e. one in summer and another in winter, were compared. The highest activities of the microbial communities were observed in July in the surface layers (0–1 cm), with a strong decrease of activities with depth. In contrast, in February, low microbial bulk activities were recorded throughout the sediment. In general, prokaryotic abundances and activities were significantly correlated. Variation partitioning analysis suggested a low impact of predation and a mainly bottom-up-controlled prokaryotic community. Hence, in the top layer from the surface to 1–3.5 cm depth, microbial communities were mainly affected by physicochemical variables (i.e. salinity, phosphate and silicate concentrations). Below this zone and at least to 10 cm depth, environmental variables were more stable and prokaryotic activities were low. The transition zone between both layers probably represents a rather smooth gradient (environmental ecocline). The results of our study provide a better understanding of the complex interactions between micro-organisms and their environment in a fluctuating ecosystem such as an intertidal mudflat. [ABSTRACT FROM AUTHOR]

Intertidal mudflats are a dominant feature in many estuarine systems and may be a significant component of the feeding grounds available for many fish and bird species. Therefore, it is crucial to determine the importance and role that this particular habitat plays for the different estuarine communities. Spatial and temporal dynamics of macrobenthic communities in an intertidal mudflat of the Tagus estuary were assessed in order to determine the role of this habitat in the whole estuarine functioning. Benthic macroinvertebrate communities were sampled monthly in two intertidal areas (upper and lower) and in the adjoining subtidal area for one year. Macroinvertebrate density and biomass in the intertidal mudflat were higher than in the subtidal area, but no clear trends were found between the lower and upper intertidal area. Spatial patterns in the community were more pronounced than seasonal patterns. This benthic community was characterised by high densities of Pygospio elegans, Scrobicularia plana, Cyathura carinata, Hydrobia ulvae and Nereis diversicolor. Abundance and biomass values in this intertidal mudflat were considered low in comparison with other estuarine habitats, namely seagrass beds. Nevertheless, this habitat plays an important role for the main species present in the community, acting as a key area for recruitment, with high concentrations for many invertebrate species.

The objective was to determine the influence of nutrients on primary production on a tropical mudflat at Buloh River estuary, where the culture of blood cockle is the most important in the country and anthropogenic disturbance increasingly threatens it. Water and sediment samples were collected during spring tide at every 150- to 200-m intervals along three transects (north, river mouth, south) set approximately 2 km apart from each other in the wet (November–December 2014) and dry period (February–March 2015). Samples were analysed for their nutrient (N, P, Si) and chlorophyll-a concentrations. Water column chlorophyll concentration on the mudflat to the south of the river mouth was higher compared to the northern site, attributable to the southerly river discharge that contributed to the nutrient (N, P, Si) loadings. During the wet period, the high proportion (up to 92 %) and concentration (77 µM) of ammonia in the dissolved inorganic nitrogen (DIN) pool appeared to suppress primary production. However, primary production dramatically increased during the subsequent dry period when phosphate-repleted and reduced ammonia conditions prevailed (low N/P ratio). Compared to the previous wet period, chlorophyll concentration in the water column increased 47-fold, while surface sediment chlorophyll increased 67-fold. The dense microalgae with their rapid nutrient uptake resulted in a shift in nutrient status, from relatively high DIN (N/P = 20.7) to potentially nitrogen-limiting (N/P = 4.5) and silica-limiting (Si/N = 0.8) conditions. Given the highly fluctuating primary production on the mudflat, future plans to increase stocking density and allocation of more mudflat area for blood cockle farming will need to consider the carrying capacity of the culture area. [ABSTRACT FROM AUTHOR]

Variations in suspended sediment concentrations (SSCs) in tidal mudflats are an important influence on the ecological environment, morphological evolution, and pollutant transport. To better understand how the behavior of suspended sediment influences small-scale variations in SSC in the water column, we took simultaneous measurements of water depth, wave height, current velocity, SSC profiles, and intratidal bed-level changes during a series of continuous tidal cycles on a highly turbid macrotidal mudflat, part of a larger accretional coastal mudflat on the Jiangsu Coast, China. We estimated the relative contributions of erosion, deposition, and advection processes to variations in SSC from the field data. We used an empirical orthogonal function (EOF) analysis to examine the influence of hydrodynamic factors (water depth, wind, wave height, and current velocity) and environmental factors (salinity and temperature) on SSC variability, to determine why the contributions of the three processes (erosion, deposition, and advection) to the variability in SSC differed. Our results showed that on average, advection flux was about an order of magnitude higher than erosion–deposition flux of corresponding tide, and that advection, driven by the tidal current velocity, wind, and associated alongshore transport, accounted for most of the variability in SSC at the study site over a complete tidal cycle. An abundant sediment supply and limited resuspension of the bed sediments meant that advection was the main transport process. Our results also demonstrate that detailed analyses of transport processes provide useful information on the sources and fates of suspended sediments, and support the interpretation of morphological changes in accretional intertidal mudflats. [ABSTRACT FROM AUTHOR]

Morio, O. Sedrati, M., Goubert, E., Floc'h F., Furgerot L., and Garlan, T., 2016. Morphodynamic of a sandy-muddy macrotidal estuarine beach under contrasted energy conditions (Vilaine estuary, France). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue No. 75, pp. 258-262. Coconut Creek (Florida), ISSN 0749-0208 Estuarine and bay beaches are important areas for human activities. These beaches are variably affected by tides, waves, and winds that can commonly generate marked topographic and sedimentological contrasts. Betahon beach (South Brittany, France) is an intermediate-type beach exhibiting a low-tide terrace linked to a steeply sloping gravelly-sandy upper foreshore, and separated by a shore-parallel bluff from a mudflat on the lower foreshore. The beach exhibits linear ridge and runnel (R-R) bedforms perpendicular to the shoreline. Seasonal monitoring of the beach shows mudflat accretion by fluid mud deposition and erosion of R-R bedforms. A core obtained from the mudflat shows alternations of mud and sand. In order to understand the cross-shore dynamics of the beach, topographic surveys and wave and current monitoring were carried out during two contrasting energy conditions. Bed return flows occurred during high-energy events, inducing an infill of runnels by non-cohesive fine sediments and coarser sediments from the reflective upper beach. During low-energy conditions, a longshore flow channel was identified between the shore-parallel low-tide terrace bluff and the mudflat. Throughout the tide, on-shore currents prevailed over the mudflat, inducing the filling of runnels and the base of the bluff with fluid mud. [ABSTRACT FROM AUTHOR]

Although microbes play important roles during the bioremediation process using macrobenthos in degraded environments, their response to macrobenthos bioturbation remains poorly understood. This study used 16S rRNA gene-Illumina Miseq sequencing to investigate the microbial communities and their response to bioturbation by artificially introducing macrobenthos to the mudflat of Sansha Bay, southeast China. A total of 56 phyla were identified, dominated by δ- and γ-Proteobacteria, with a total percentage of over 50%. Others, such as Acidobacteria, Chloroflexi, Bacteroidetes, Planctomycetes and Alphaproteobacteria occupied 4–7% respectively. Eighteen genera indicating the microbial communities response to bioturbation and seasonal change were identified. Bioturbated samples contained more ecologically important genera, and untreated samples contained more genera ubiquitous in marine environments. The physicochemical characteristics did not change significantly probably due to the short time of bioremediation and low survival rate of macrobenthos, confirming that microbial communities are more sensitive and can serve as sentinels for environmental changes. [ABSTRACT FROM AUTHOR]

Phosphorus (P) supplies from the sediment are important when evaluating the impacts of nutrient dynamics on the ecosystem. Many studies have reported P dynamics based on gradients of pore water (PW)-phosphate (PO43-) concentrations at the sediment-water interface and iron-related abiotic reactions in response to redox conditions. However, the aim of the present study is to evaluate the contributions of intracellular (IC)-P and marine organism- mediated reactions to P-dynamics under variable environmental conditions. The focus of this study is the intertidal mudflat habitat of the innermost part of Ariake Bay, Kyushu, Japan, during winter. The vertical distribution of several forms of P fraction [i.e. PW- and IC-dissolved inorganic/organic-P (DIP/DOP), and particulate inorganic/organic- P (PIP/POP)], the number of microalgae and bacteria, and chlorophyll α concentrations in the sediment were measured. The results obtained revealed that the IC-P pool, especially IC-DOP, accounted for 76% of the total dissolved P in the surface sediment layer, mainly associated with the microphytobenthos. Additionally, phytoplankton, which comprised more than 60% of the surface microalgae in tidal-flat sediments, are considered to carry river-derived- P to the intertidal flats via inner bay-specific physical movements and disturbances. Incubation experiments on mud sediment under oxic/anoxic conditions suggest that dissolved P fluxes between the IC pool and PW occur actively in response to redox conditions, according to the balance between microalgal uptake and bacterial degradation. These results indicate that evaluation of the IC-P pool is indispensable to understanding P cycling in intertidal mudflats, and that microalgae could play important roles not only as food sources, but also as P reservoirs and sources of PO43-. [ABSTRACT FROM AUTHOR]

Nonribosomal peptide synthetases (NRPS) are actively sought out, due to pharmacologically important activities of their metabolites. In marine environment, the most prevalent nonribosomal peptide antibiotic producers are sponges inhabiting microorganisms. Conversely, strains from marine sediments and more especially from intertidal mudflats have not been extensively screened for the presence of new NRPS. In this study, for the first time, a collection of one hundred intertidal mudflat bacterial isolates (Marennes-Oléron Bay, France) was assessed for (1) the presence of NRPS genes by degenerated PCR targeting conserved adenylation domains and (2) for their production of antimicrobial molecules. (1) Bacteria with adenylation domains (14 strains) were identified by 16S rRNA gene sequence analysis and grouped into Firmicutes (one strain) and Proteobacteria (13 strains). In silico analysis of the NRPS amino acid sequences ( n = 7) showed 41-58% ID with sequences found in the NCBI database. Three new putative adenylation domain signatures were found. (2) The culture supernatant of one of these strains, identified as a Bacillus, was shown to strongly inhibit the growth of Staphylococcus aureus, S. epidermidis, and Enterococcus faecalis. This study portends that the intertidal mudflat niche could be of interest for the discovery of new NRPS genes and antimicrobial producing strains. [ABSTRACT FROM AUTHOR]