Tidal Flat Research Articles

Geomorphological Evolution in the Tidal Flat of a Macro-Tidal Muddy Estuary, Hangzhou Bay, China, over the Past 30 Years

Tidal flat plays an important role in coastal development because of its ecological and spatial resources. We take the southern tidal flat in the macro-tidal turbid Hangzhou Bay as an example to study the long-term (1990–2020) evolution of the muddy tidal flat, using remote sensing data and field observational data. The detailed bathymetric elevation of the tidal flat is obtained, using remote sensing images of Landsat and Sentinel-2, combined with the real-time kinematic (RTK) data. The correlation coefficient between the remote sensing data and the RTK data is 0.73. The tidal flat and vegetation areas are affected by reclamation. The total tidal flat area decreased by 467.78 km2. The vegetation area declined from 64.98 km2 in 2000 to 13.41 km2 in 2015 and recovered to 41.62 km2 in 2020. The largest change in tidal flat slope occurs in the eastern and western sides of the tidal flat, compared with the wide middle part. The total length of tidal creeks decreased to 45.95 km in 2005 and then increased to 105.83 km in 2020. The middle- and low-grade tidal creeks accounted for 91.4%, with a curvature slightly larger than 1 in 2020. High-grade tidal creeks occur inside the vegetation areas, with less bending and fewer branch points. Vegetation promotes the development of tidal creeks but limits the lateral swing and bifurcation. These results provide a basis for the management of global tidal flat resources and ecosystems.

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

The shape of fringing tidal flats in engineered estuaries

For the management of estuaries and the preservation of tidal flats it is crucial to understand the tidal flat shape and development. Previous work focused predominantly on the quasi-equilibrium shape of tidal flats along open coasts with a dominant cross-shore flow and wave exposure. This paper evaluates the shape of fringing tidal flats in engineered estuaries, where longshore velocities generally dominate. Using a long-term (20 years) topographic data set of an anthropogenically modified estuary in the Netherlands (the Western Scheldt estuary), we relate key profile shape parameters and changes over time to natural and anthropogenic processes. In an engineered estuary, the tidal flat shape depends on the estuary geometry, hydrodynamic forcings and human interventions. In contrast to open coast tidal flats, the presence of the channel and dominant longshore flow determines the available cross-shore length (accommodation space) of the tidal flat and the shape of the tidal flat. This accommodation space defines the maximum tidal flat height and opportunity for marsh development. We propose the use of the Index of Development, indicating to what extend tidal flats have space to develop. This index is not only influenced by longshore and cross-shore flow, but also (or even more) by hydraulic structures, dike realignments and channel migration. Especially the latter two strongly influence the accommodation space and thereby the maximum tidal flat height and the opportunity for marsh development. For large stretches of the Western Scheldt, the accommodation space is too small, and the majority of the tidal flats do not vertically extent to mean high water. The success of tidal flat and marsh restoration projects depends on the accommodation space.

Landcover-based detection of rapid impacts of extreme storm on coastal landscape

On September 24, 2022, Post-Tropical Hurricane Fiona made landfall in Atlantic Canada and caused unprecedented damages to the coastal communities and ecosystems therein. The aftermath triggered local government and communities in Prince Edward Island (PEI), Canada to rethink current policies and practices for coastal protection in the context of climate change. This historic hazard represents the escalating frequency and intensity of extreme weather events that globally threaten coastal regions, accelerating coastal erosion and endangering communities. This study employs landcover-based detection to assess rapid storm impact of Fiona on coastline of PEI using Sentinel-2 satellite images, to gauge the efficacy of landcover-based detection and quantify storm-induced coastal environmental changes. Our results indicate that, following Fiona, over 51 km2 coastal land loss due to the erosion at beach foreshore and inundation at tidal flat, and over 11 km2 sand dune loss mainly on the PEI north shore. This constitutes a 3.5 % loss of coastal land resources within the 1798 km2 PEI coastal zone. Fiona also caused over 194 km2 area in coastal buffer zone showed temporal fluid-mud from the eroded sediments of sand dunes, cliffs, and tidal flats, suggesting the significant sediment loss from vertical structures in addition to the direct retreat. The landcover-based method can be regarded as a valuable tool for the storm impacts on coastal environments. Based on the coastal change pattern, more sustainable coastal protection and adaptation measures should be developed, focusing on reducing hydrodynamic intensity and improving erosion capacity, with consideration of the increasing likelihood of more intense and frequent storm events in a warming climate.

Active Adaptive Strategies of Mallard Feet in Response to Changes in Wetness and Compactness of the Sand Terrain.

Mallards (Anas platyrhynchos) exhibit exceptional locomotive abilities in diverse terrains, such as beaches, swamps, and tidal flats. This capability is primarily attributed to their unique webbed toe structure and cooperative locomotion posture of their feet. Therefore, this study aims to further delve into the active adaptive strategies of mallard feet in response to diverse external environmental conditions. Six adult male mallards were selected for this research. Their locomotion on sandy surfaces with differing wetness levels and varying degrees of compaction were captured using a high-speed camera, and analysis of instantaneous and continuous changes in the primary joint angles of the mallards' feet, including the toe-webbed opening and closing angles, the tarsometatarsal-phalangeal joint (TMTPJ), and the intertarsal joint (ITJ). It was found that on loose sandy surfaces, increasing wetness expanded the ground contact area of the mallards' feet. This led to greater flexion at the TMTPJ joint during mid-stance, accompanied by decreased flexion of the ITJ during touch-down and mid-stance. Conversely, on compacted sand, increasing wetness resulted in a reduced foot effect area and lessened ITJ flexion at both touch-down and mid-stance. Furthermore, on looser sand, the ground contact area of the mallards' feet decreased, with an increase in ITJ buckling at touch-down. During the swing phase, sand wetness and compactness effected minimally on the feet of the mallards. On dry and loose sand ground, mallards will contract their second and fourth toes with webbing upon ground contact, covering and compacting the sand beneath, while increasing ITJ flexion to mitigate sinking. This adaptation reduces the energy expended on sand and enhances body stability. In wet and compacted sand conditions, mallards expand their second and fourth toes upon ground contact and reduce ITJ flexion. Therefore, this coordinated foot and ITJ locomotion offers mallards a natural advantage when moving on various environmental media.

It's time to broaden what we consider a 'blue carbon ecosystem'.

Photoautotrophic marine ecosystems can lock up organic carbon in their biomass and the associated organic sediments they trap over millennia and are thus regarded as blue carbon ecosystems. Because of the ability of marine ecosystems to lock up organic carbon for millennia, blue carbon is receiving much attention within the United Nations' 2030 Agenda for Sustainable Development as a nature-based solution (NBS) to climate change, but classically still focuses on seagrass meadows, mangrove forests, and tidal marshes. However, other coastal ecosystems could also be important for blue carbon storage, but remain largely neglected in both carbon cycling budgets and NBS strategic planning. Using a meta-analysis of 253 research publications, we identify other coastal ecosystems-including mud flats, fjords, coralline algal (rhodolith) beds, and some components or coral reef systems-with a strong capacity to act as blue carbon sinks in certain situations. Features that promote blue carbon burial within these 'non-classical' blue carbon ecosystems included: (1) balancing of carbon release by calcification via carbon uptake at the individual and ecosystem levels; (2) high rates of allochthonous organic carbon supply because of high particle trapping capacity; (3) high rates of carbon preservation and low remineralization rates; and (4) location in depositional environments. Some of these features are context-dependent, meaning that these ecosystems were blue carbon sinks in some locations, but not others. Therefore, we provide a universal framework that can evaluate the likelihood of a given ecosystem to behave as a blue carbon sink for a given context. Overall, this paper seeks to encourage consideration of non-classical blue carbon ecosystems within NBS strategies, allowing more complete blue carbon accounting.

Ecophysiological responses of Phragmites australis populations to a tidal flat gradient in the Yangtze River Estuary, China.

Phragmites australis is a prevalent species in the Chongming Dongtan wetland and is capable of thriving in various tidal flat environments, including high salinity habitats. P. australis population displays inconsistent ecological performances, highlighting the need to uncover their survival strategies and mechanisms in tidal flats with diverse soil salinities. Upon comparing functional traits of P. australis at multiple tidal flats (low, middle, and high) and their responses to soil physicochemical properties, this study aimed to clarify the salt-tolerant strategy of P. australis and the corresponding mechanisms. These results showed that leaf characteristics, such as specific leaf area and leaf dry matter content, demonstrated more robust stability to soil salinity than shoot height and dry weight. Furthermore, as salt stress intensified, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxisome (POD) in P. australis leaves at low tidal flat exhibited an increased upward trend compared to those at other tidal flats. The molecular mechanism of salt tolerance in Phragmites australis across various habitats was investigated using transcriptome sequencing. Weighted correlation network analysis (WGCNA) combined with differentially expressed genes (DEGs) screened out 3 modules closely related to high salt tolerance and identified 105 core genes crucial for high salt tolerance. Further research was carried out on the few degraded populations at low tidal flat, and 25 core genes were identified by combining WGCNA and DEGs. A decrease in the activity of ferroptosis marker gonyautoxin-4 and an increase in the content of Fe3+ in the degenerated group were observed, indicating that ferroptosis might participate in degradation. Furthermore, correlation analysis indicated a possible regulatory network between salt tolerance and ferroptosis. In short, this study provided new insights into the salt tolerance mechanism of P. australis population along tidal flats.

Abiotic origins of self‐organized ridge‐runnel patterns on tidal flats

AbstractStriking large‐scale spatial patterns in ecosystems, generated by self‐organization through biotic and abiotic feedback processes, influence ecosystem functioning and response to global environmental change. A remarkable example of this are the regular ridge‐runnel patterns found on tidal flats, which play an important role in mudflat‐marsh transitions. Yet the mechanisms driving their formation, and whether they are abiotic or biotic in origin, have not been elucidated. The underlying mechanisms are unraveled in this study through a combination of field measurements and targeted laboratory experiments. In the field, we find that on the ridges of the pattern, the sediment bed level is less dynamic and more resistant to erosion than in the runnels. In laboratory flume experiments, we find that erosion‐resistant surfaces, like those found on the ridges, can arise on time scales of hours to days due to the drying of the cohesive sediment bed, while this is prevented in waterlogged sediments in runnels. A disturbance‐recovery experiment on benthic algae then confirms that biological processes require a longer developmental period than the time scale at which we have observed drying‐induced erosion resistance to develop. Together, these results demonstrate that ridge‐runnel patterns begin from an abiotic initiation point that can subsequently provide a template for further biological establishment and self‐organization. Recognition of abiotic processes as catalysts of self‐organization can improve our understanding of ecosystem responses to environmental changes.

Morphodynamics of macrotidal channels in Korean tidal flats: implications for the role of monsoon precipitation and the stratigraphic architecture of tidal point bars

Abstract Tidal channels exert a crucial control on sediment transport and drive geomorphic changes in the tidal environment. Despite their ubiquitous occurrence, long-term morphodynamics and processes driving the morphologic changes remain less well understood than fluvial counterparts. Spanning from straight to dendritic, Korean tidal channels become more sinuous and densely populated with elevation due to higher mud content. Mutually evasive current patterns resulted in a cuspate meander bend, where a flood barb develops at the seaward side of the bend. Multiannual observation revealed that tidal channels migrate from up to 80 m per year in the lower intertidal zone of open-coast sandy tidal flats to nearly stationary for several years in the upper intertidal zone of protected muddy tidal flats. Migration rates are temporarily pronounced during the summer monsoon, when heavy rainfall-induced surface runoff intensifies ebb tidal asymmetry and promotes headward erosion. Meander bends are mostly landward-skewed and shift downstream, implying that ebb currents primarily drive the long-term channel morphodynamics. Tidal point bars commonly display ebbward dipping, inclined heterolithic stratification (IHS) dominated by bedforms formed by subordinate flood tidal currents. An overall ebb dominance and mutually evasive current patterns account for the counterintuitive stratigraphic architecture of point bars in Korean tidal channels.

Tidal Flat Erosion Processes and Their Dynamic Mechanisms on the South Side of Sheyang River Estuary, Jiangsu Province

Tidal flats are accumulations of fine-grained sediment formed under the action of tides and play a very important role in coastal protection. The northern part of Jiangsu coast, as a typical example of muddy coasts found all over the world, has experienced serious erosion since the Yellow River shifted northward, and the range of erosion has been gradually extending southward, now reaching the south of the Sheyang River estuary (SYRE). In order to address coastal erosion near the SYRE through protective measures, there is an urgent need for research on the spatial and temporal variation of coastal erosion processes and their control mechanisms in the SYRE and adjacent coastal areas. For this study, the tidal flats on the south side of the SYRE were selected as the study area, and the sediment dynamics in the upper and lower intertidal flat were observed in different seasons to investigate the erosion processes and their dynamic mechanisms. The results show that the tidal current and wave action in the observed intertidal flats are stronger in winter than in summer, and these intertidal flats erode under the combined action of waves and currents. During winter, the net transport of the near-bottom suspended sediment and bedload is primarily towards the southeast, while in summer, the direction tends toward the north and northeast. The net transport fluxes are larger in the lower part of the intertidal flat than in the upper part in summer and also larger in winter than in summer within the lower intertidal flat. Furthermore, the tidal flat erosion in the study area manifests as shoreline retreat and flat surface erosion. The average shoreline retreat rate increased from 23.3 m/a during 2014–2019 to 43.5 m/a during 2019–2021, and the average erosion depth of the lower and upper parts of the intertidal flat over a tidal cycle is, respectively, 1.98 cm and 0.24 cm in winter and 1.65 cm and 0.26 cm in summer. The ratio of the wave-induced bottom shear stress to the tidal current-induced bottom shear stress is 0.40~0.46 in the lower intertidal flat and increases to 0.66~0.67 in the upper intertidal flat, indicating that the intertidal flat erosion in the study area is primarily driven by tidal currents, with significant contributions from wave action, especially in the upper intertidal flat.

Quantifying spatiotemporal variations in tidal flats and coastal land use in Jiangsu Radial Sandbars through remote sensing

The Jiangsu Radial Sandbars in China have experienced significant changes due to extensive human activities in past decades. This study provides new insights by coupling multitemporal remote sensing analysis with landscape pattern assessment to comprehensively evaluate tidal flat evolution and land use suitability from 1984 to 2020. The integrated remote sensing approach enabled continuous high-resolution mapping of tidal flats, revealing a 25.9% area loss equaling 123.2 km2, driven mostly by land reclamation, while also quantifying coastline accretion patterns through shoreline position analysis. The coastal landscape analysis systematically assessed land use changes and human impacts through metrics such as diversity and fragmentation, which revealed intensified seaward expansion and increased fragmentation of unused land and underdeveloped nearshore sea areas. The suitability evaluation considered land resources, ecological factors and socioeconomics to assess four key land use types. The method of coupling with landscape analysis provided integrated insights, including 1) identifying ecologically sensitive zones for prioritized conservation based on landscape patterns; 2) quantifying the intensity and spatial pattern of human activities and their impacts; and 3) comprehensively evaluating land use suitability by integrating landscape analysis with other factors. Future research should explore management strategies, assess the impact of climate change, and make predictions to inform policy-making.

Description of Roseibium sediminicola sp. nov. Isolated from Sediment of a Tidal Flat on the Yellow Sea Coast.

A Gram-stain-negative, aerobic, rod-shaped, motile, flagellated bacterial strain, designated as CAU 1639T, was isolated from the tidal flat sediment on the Yellow Sea in the Republic of Korea. Growth of the isolate was observed at 20-37°C, at pH 5.0-10.5 and with 0-7% (w/v) NaCl. The genomic DNA G + C content was 60.8%. Phylogenetic analysis, grounded on 16S rRNA gene sequencing, revealed that strain CAU 1639T was closely related to species within the genus Roseibium. It shared the highest similarity with Roseibium album CECT 5095T, followed by Roseibium aggregatum IAM 12614T and Roseibium salinum Cs25T, with 16S rRNA gene sequence similarity ranging from 98.0-98.4%. It was observed that the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values ranged between 72.5-79.5 and 20.0-22.9%, respectively. The polyphasic taxonomic analysis reveals that strain CAU 1639T represents a novel species in the genus Roseibium with the proposed name Roseibium sediminicola sp. nov. The type strain is CAU 1639T (= KCTC 82430T = MCCC 1K06081T).

A tale of two end members: Tidal deposits in a semi‐arid, low subsidence, open coastal setting versus a high runoff, high subsidence, restricted environment

AbstractJurassic and Palaeocene tidal deposits of the epeiric Western Interior Sea in Wyoming, USA, differ significantly due to their contrasting climates and tectonic, geographic and depositional settings. Tidally generated, cross‐bedded sandstone bodies contained by incisions are common to both settings and can potentially be uncritically attributed to marine flooding of fluvial systems. Key differences in lithology, ichnology and relationships with surrounding sediment reveal fundamentally different depositional settings, however. The Jurassic system occupied a low accommodation, semi‐arid environment, with geographically open shorelines as relative sea‐level fell, creating an unconformable contact with the underlying, storm wave‐dominated shelf and shoreface deposits. Siliciclastic, intertidal flats formed adjacent to coastal aeolian and fluvial environments during brief turnarounds from the degradational (forced regressive) to aggradational and retrogradational (transgressive) system tract. Basinward of these environments, metre to decimetre‐scale cross‐bedded, bioclastic, subtidal compound dunes and tidal inlet complexes accumulated in areas of minimal clastic flux and within incisions created by submarine tidal currents. By contrast, the Palaeocene tidal systems formed in a high accommodation, subtropical setting, as rising sea levels forced the fluvial to marine transition zone landward and flooded coastal swamps, forming geographically irregular, back‐barrier complexes and tidally influenced fluvial systems. High volumes of siliciclastics, terrigenous organic material and freshwater were delivered by the rivers and created physicochemical stress on the marine embayments. Sandy tidal flat deposits accumulated in lagoons and interdistributary bays, but unlike the Jurassic examples, they do not mark a turnaround from the falling stage to the transgressive system tract. The potential preservation window for tidalites is significantly greater vertically in the aggradational to retrogradational setting than in the degradational system due to greater accommodation. The preservation window is vertically smaller, but areally greater in the Jurassic, forced regressive system because of basinward enhancement of tidal currents driven by complex palaeobathymetry caused by tectonic activity of local pre‐Laramide uplifts.

Mapping Annual Tidal Flat Loss and Gain in the Micro-Tidal Area Integrating Dual Full-Time Series Spectral Indices

Tracking long-term tidal flat dynamics is crucial for coastal restoration decision making. Accurately capturing the loss and gain of tidal flats due to human-induced disturbances is challenging in the micro-tidal areas. In this study, we developed an automated method for mapping the annual tidal flat changes in the micro-tidal areas under intense human activities, by integrating spectral harmonization, time series segmentation from dual spectral indices, and the tide-independent hierarchical classification strategy. Our method has two key novelties. First, we adopt flexible temporal segments for each pixel based on the dual full-time series spectral indices, instead of solely using a fixed period window, to help obtain more reliable inundation frequency features. Second, a tide-independent hierarchical classification strategy based on the inundation features and the Otsu algorithm capture the tidal flat changes well. Our method performed well in Guangdong, Hong Kong, and Macao (GHKM), a typical area with micro-tidal range and intense human activities, with overall accuracies of 89% and 92% for conversion types and turning years, respectively. The tidal flats in GHKM decreased by 24% from 1986 to 2021, resulting from the loss of 504.45 km2, partially offset by an accretion of 179.88 km2. Further, 70.9% of the total loss was in the Great Bay Area, concentrated in 1991–1998 and 2001–2016. The historical trajectories of tidal flat loss were driven by various policies implemented by the national, provincial, and local governments. Our method is promising for extension to other micro-tidal areas to provide more scientific support for coastal resource management and restoration.

Spatial and temporal variation in long-term sediment accumulation in a back-barrier salt marsh

In situ persistence of salt marshes in the face of sea-level rise relies on their ability to maintain substrate elevation through sufficient vertical accretion of sediment. However, sedimentation rates in salt marshes vary spatially and temporally, which complicates the assessment of their ability to keep up with sea-level rise. Here, we explore the spatial and temporal variation in sediment accumulation in a single back-barrier salt marsh site. Using one-time in situ measurements at the landscape scale, we obtained synoptic information of elevation and sediment thickness over the entire salt marsh in a chronosequence over centuries. Repeated measurements along short elevation transects (0.3–0.9 m +MHT) revealed decadal changes, complementing the broader marsh data with detailed information on elevation, thickness of the marsh deposits and accumulation rates. Thickness of the deposits was largely related to the elevation gradient: the sediment layer was thinner at the higher marsh (near the dunes and far away from the intertidal flats), and thicker at the lower marsh (near the intertidal flats). Moreover, the thickness of the layer increased with salt marsh age along the chronosequence, and age accounted for 72 % of variability in sediment accumulation. The rate of sediment accumulation was higher than the local rate of sea-level rise in the younger marsh, whereas it was equal to the rate of sea-level rise in the older marsh. In the older salt marsh, sediment accumulation was lower, possibly due to autocompaction in the thicker, older layers. Both at the landscape scale and along short elevation transects within individual drainage basins, sediment accumulation decreased with distance to sediment supply routes. However, their relative importance depended on the scale of observation. Distance to creeks accounted for 17 % of the variability in sediment accumulation at the landscape scale, compared to 4 % at the smaller scale. Similarly, the influence of distance to intertidal flats varied from 1 % at the landscape scale to 13 % at the smaller scale. Our main findings indicate that lower-elevation older marshes and higher-elevation younger marshes far away from sediment sources are at risk of not keeping pace with the local rate of sea-level rise and are potentially vulnerable to increased flooding.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Mutual facilitation between foundation species Mytilus edulis and Lanice conchilega promotes habitat heterogeneity on tidal flats

Foundation species that modify their habitat can facilitate other species, including other foundation species. Most studies focus solely on a single foundation species, overlooking such facilitation cascades. In this study, we investigated the interactions between the two coastal foundation species Mytilus edulis (blue mussel) and Lanice conchilega (sand mason worm). We investigated whether these species engage in facilitative interactions or if their association simply reflects a shared ecological niche on the soft-sediment intertidal flats of the Dutch Wadden Sea. To do so, we performed species distribution modeling, manipulative field experiments, and field surveys. We found a positive association between both foundation species, with a 2.45 times higher occurrence of both species compared to a random distribution. In addition, these species partially occupied the same ecological niche. We demonstrated that L. conchilega provided settlement substrate for M. edulis spat, increasing densities by 400 times compared to bare plots. Furthermore, M. edulis reefs facilitated L. conchilega occurrence in the wake of the reef. Biogenic reef development revealed that this interspecific facilitation resulted in spatial habitat heterogeneity. Therefore, we conclude that interspecific facilitation can significantly enhance the occurrence of these two important intertidal foundation species. Acknowledgment of such complex facilitation interactions has an untapped potential for improving the success of restoration and conservation programs.

Enhancing Seed Harvest of Wild Manila Clam (Ruditapes philippinarum) through Fiberglass Mesh Installation in the Tidal Flat of Jugyo, West Coast of Korea

Enhancing Seed Harvest of Wild Manila Clam (Ruditapes philippinarum) through Fiberglass Mesh Installation in the Tidal Flat of Jugyo, West Coast of Korea

Lithofacies and Sediment Sequences of a Microtidal, Wave-Dominated Tropical Estuary in Somone Lagoon (Senegal, West Africa)

Estuary sedimentary sequences have been the focus of several papers in the last decades; however, the majority these papers were centered in mesotidal and macrotidal estuaries of the middle latitudes. This present paper studies, from a sedimentological point of view, the infilling of a microtidal, wave-dominated tropical estuary, where wide tidal flats, mangroves and sabkhas are developed. Somone Lagoon is a Senegalese protected environment, very rich from an ecological point of view and with a definitive touristic vocation. For this work, 14 piston cores were studied. Additionally, the grain size, calcium carbonate and organic matter contents of 61 sediment samples vertically distributed in these cores were analyzed. The distribution of facies and the vertical sequences of sediments show the influence of the tropical seasonal fluctuations of fluvial sediment supply and evaporation processes. A high degree of bioturbation and an elevated organic content can be interpreted as the result of a high capacity of retention of the organic material into the estuary influenced by the weak tidal currents typical of a microtidal regime. These processes, acting since the last Holocene invasion of sea level, caused an advanced state of infilling of this estuarine system where both flood tidal deltas and bay head deltas prograde above the fine facies of the central domain of the estuary.

Diagenetic development of rhizoliths in the Ironshore Formation (Pleistocene) of the Cayman Islands

Rhizoliths in the Ironshore Formation on the Cayman Islands, up to 12 cm in diameter and 1 m long, developed in skeletal grainstones that accumulated on sand flats above high tide level. Internally, these well-preserved rhizoliths are characterized by well-defined concentric zones, centered around the central root opening, that reflect radial variations in calcite–aragonite content, decreases in micrite content, increases in porosity, and radial variations in trace element (e.g., Ca, Ni, S, Si, and Sr) concentrations. The stable isotopes, δ13C and δ18O, which vary in accord with the internal zones are more variable than the δ13C and δ18O of the host sediments. For the rhizoliths there is a high correlation between the δ13C and δ18O values and the calcite content. The contrast between the rhizoliths and their host sediments is largely a reflection of the more intense diagenetic processes that were largely mediated by the microbial populations that were concentrated in the rhizosphere that developed around each plant root. Microbial activity, which mediated micritization of the skeletal sands and micrite precipitation in the intergranular pores, was largely responsible for development of the internal zonation in the rhizoliths. Use of the δ13C values to determine if the rhizoliths developed in association with C3 or C4 vegetation failed because the δ13C values correlate with the calcite content that developed largely as diagenetic products.