This study investigates the effect of intertidal zonation on sediment characteristics, organic matter content, and microbial community distribution in Gomso Bay, Republic of Korea—an ecologically significant estuarine system and part of the UNESCO-designated Getbol, Korean Tidal Flats. It was hypothesized that physicochemical properties and microbial communities differ significantly among the inner, middle, and outer tidal zones due to variations in tidal exposure, sediment texture, and organic matter accumulation. Sediment samples were collected from nine sites across these zones and analyzed for total organic carbon (TOC), acid volatile sulfide (AVS), and trace metals (As, Cd, Cr, Cu, Hg, Li, Ni, Pb, Zn), along with sediment texture. Microbial community structure was examined using 16S rRNA gene amplicon sequencing to evaluate the influence of zonation on microbial diversity and composition. Results revealed distinct spatial variations along the intertidal gradient. Inner tidal zones with finer sediments showed higher TOC, AVS, and metal concentrations, whereas outer zones with coarser sediments exhibited lower values. Microbial composition also varied, with aerobic microorganisms dominating the high tidal flats and anaerobic taxa prevailing in the low tidal flats. Heterotrophic and autotrophic bacteria were more abundant in the outer zone, while chemolithotrophs predominated in the inner zone. Redundancy and Pearson’s correlation analyses further indicated significant relationships between sediment texture, TOC, AVS, heavy metals, and microbial diversity. Overall, the findings confirm that tidal zonation drives distinct sedimentary and microbial patterns, highlighting the ecological complexity of intertidal ecosystems.

Abstract. The ecology of benthic foraminifera in tidal flats has been extensively studied at local scales, but its seasonal and spatial dynamics across broader intertidal gradients remain poorly understood. This study investigates seasonal variations in the composition and structure of living benthic foraminiferal assemblages across contrasting intertidal habitats in the eastern English Channel. We analyzed 256 surface sediment samples (192 for foraminifera and 64 for sediment properties) collected over four seasons at various sites in the Hauts-de-France region (northern France) along the eastern English Channel. Multivariate analyses revealed significant seasonal changes in the assemblage structure. Linear discriminant analysis identified two dominant seasonal groups. Opportunistic taxa, such as Haynesina germanica and Ammonia confertitesta, dominate during colder seasons, while more diverse and thermophilic species including Elphidium selseyense, Quinqueloculina dimidiata, and Trochammina inflata characterize warmer months. These findings provide new insights into the phenology of benthic foraminifera and contribute to a better understanding of seasonal ecological processes in temperate intertidal ecosystems.

Microphytobenthos spatio-temporal dynamics across an intertidal gradient in a tropical estuary using Sentinel-2 imagery.

Abstract Background and aims Organic matter additions in coastal wetlands contribute to blue carbon sequestration and adjustment to sea-level rise through vertical substrate growth, with accurate modelling of these dynamics requiring information of root mass and volume additions across tidal gradients. This study aims to characterise the influence of vegetation zonation and tidal position on root mass and volume dynamics within substrates. Methods The root ingrowth technique was coupled with sediment cores to quantify below-ground root mass and volume production, standing stocks and turnover across two years to 90 cm depth at Kooweerup, Victoria, Australia. Results We indicate a complex non-linear relationship between fine root mass production and tidal position, influenced by variable vegetation structures across mangrove (442–3427 g m−2 yr−1), saltmarsh (540–860 g m−2 yr−1) and supratidal forest (599 g m−2 yr−1) zones. Fine root volume additions ranged from 274 to 4055 cm3 m−2 yr−1 across sampling locations. Root production was greatest for older mangroves and tidally defined optimal zones of production were evident for mangrove and saltmarsh. Live roots extended deeper than typically studied, reaching depths of 1.0 m in forested zones. Conclusion This information of root mass and volume additions across wetland live rooting zones can be used to improve highly parameterised models accounting for carbon sequestration and substrate vertical adjustment along intertidal gradients. We recommend that future studies measure root production across the entire active rooting zone or to 1 m depth to align with standard carbon accounting measurement depths.

ABSTRACTPlant size is closely linked to its leaf trait characteristics, which are essential for determining its form and function. These relationships constitute a fundamental component of the global spectrum of plant diversity. Despite this, the size–trait relationships in coastal mangroves have often been overlooked, with a common assumption that they would mirror those found in terrestrial tropical trees. However, recent studies have begun to challenge this assumption, revealing unique adaptations and trait variations in mangroves that are influenced by their specific environmental conditions, such as salinity and nutrient availability. In this research, we investigated the leaf structural traits, plant height, and diameter at breast height or basal height (DBH) of 10 shrub and tree species. This study was carried out along an intertidal gradient within a mangrove forest located in Southeast China. We found that leaf traits differed significantly between shrubs and trees in their response to intertidal gradients, indicating that different species have evolved specific adaptations to thrive in their respective intertidal zones. This insight can help us decipher the selective pressures that have shaped trait evolution. Among all species, leaf carbon (C) economics (leaf dry mass content, leaf mass per area, and leaf density) decreased significantly with increasing plant height and DBH. For each growth form and intertidal zone, the relationships between plant size (height or DBH) and leaf C economics traits were consistent with those in the pooled dataset. Our study reveals that mangrove plants exhibit size‐related adjustments in leaf C economic strategies, indicating that plant size potentially acts as a proxy for the “slow–fast” continuum of plant performance. This discovery is pivotal for advancing our understanding of plant functional ecology and for enhancing the precision of global C cycle models, which are highly responsive to perturbations in atmospheric CO2 and climate change.

Both intra- and interspecific competition influence the partitioning of limited resources; the relative importance of each type of competition in resource distribution is influenced by several factors, including resource availability and population abundance. Several hermit crab species of the genera Calcinus and Clibanarius coexist, competing for the shells of the same gastropod species. The relative abundance of these species varies along the intertidal gradient, from a bias toward Clibanarius in the upper intertidal to a tendency toward Calcinus in the lower intertidal. We assessed the strength of intra- versus interspecific competition in Cli. albidigitus and Cal. californiensis by comparing the number of successful usurpations of preferred shells in single-species versus mixed-species trials. We performed these comparisons under four scenarios, varying the total individuals and their relative abundance (1.7:1, 1:1, or 1:1.7 ratio) to simulate demographic conditions along the intertidal gradient. There were more shell usurpations in mixed-species trials under all scenarios except for the 1:1 ratio at high total abundance. Calcinus californiensis usurped more shells than Cli. albidigitus in all mixed-species treatments, even in cases where Cli. albidigitus was more abundant. Our results show that interspecific competition is stronger than intraspecific competition, which could drive the competitive exclusion of Cli. albidigitus, the comparatively weaker species.

Distribution, ecological risk, and sediment-influencing mechanisms of heavy metals in surface sediments along the intertidal gradient in typical mangroves in Hainan, China

There is much controversy surrounding factors that affect the distribution of mangrove plants across the intertidal gradient. It was previously hypothesized that mangrove zonation was attributed to tidal sorting (TSH) of its propagules according to size (weight) or differential ability of propagules to establish in deep water. However, observational and experimental evidence have provided little support for the actual mechanism(s) of mangrove zonation. In general, species distribution pattern is the consequence of propagule dispersal. The specific gravity of water-borne mangrove propagules may affect their buoyancy, with inherent links to dispersal, thereby potentially influencing tree zonation. Propagule specific gravity can influence the distribution of mangroves in the context of global change, particularly in response to changes in seawater salinity. In this study, we measured the specific gravity and weight of 35 mangrove species propagules. There was no correlation between the weight of the propagule and its specific gravity. The specific gravity of propagules of true mangrove species was significantly greater than that of semi-mangrove. The results of the correlation between propagule specific gravity and the relative surface elevation of field distribution support the hypothesis that propagules are subject to tidal sorting and are not related to weight but to specific gravity. This newfound understanding of mangrove dispersal and distribution is critical in the context of mangrove protection and restoration, especially in projecting the effects of anthropogenic activities and global change on mangrove communities.

Non-indigenous species and their realized niche in tidepools along the South-East Pacific coast

Changes in the leaf functional traits of mangrove plant assemblages along an intertidal gradient in typical mangrove wetlands in Hainan, China

Seed banks play an important role in determining the spatial and temporal distribution of halophytes in salt marshes. We tested the ability of native Spartina maritima and invasive S. densiflora spikelets to disperse by flotation on water with different salinity concentrations, and the longevity of spikelet viability relative to environmental conditions including dry or wet storage at low or moderate temperatures, and aqueous salinity concentrations from fresh to sea water. We quantified pre-dispersal seed production and pre- and post-dispersal focal Spartina spp. presence in seed banks along intertidal gradients within salt marshes at the Gulf of Cádiz (Southwest Iberian Peninsula). Spartina densiflora spikelets, especially from middle and high elevation marshes, showed greater ability than S. maritima to remain afloat, which suggests this species could be dispersed over longer distances. Wet-stored Spartina seeds were able to maintain viability for months, while seeds under dry storage rapidly lost viability. This decline was most significant for S. maritima, and for seeds stored at moderate temperatures. Storage of spikelets under wet and cold conditions optimized spikelet viability. Native S. maritima did not establish transient or persistent seed banks, while invasive S. densiflora established transient seed banks mainly at higher marsh elevations. Our results on the dynamics of seed dispersal and seed banks and seedling recruitment provide fundamental knowledge that can be applied for conservation of native S. maritima, management of invasive S. densiflora, and ecological restoration of tidal salt marshes.

Herbivore and predator pressure in tidepools along an intertidal gradient: no consumption refuge for invasive species!

The microbial communities of sandy beaches are poorly described despite the biogeochemical importance and ubiquity of these ecosystems. Using metabarcoding of the 16S and 18S rRNA genes, we investigated the diversity, microhabitats (with or between sand grains) and intertidal distributions of microorganisms (including meiofauna) from pristine sandy beaches in British Columbia, Canada, and hypothesized that abiotic variations due to microhabitat or intertidal gradients influence the distribution of microorganisms on local scales. Bacterial, archaeal and protistan communities of the sand were clearly distinct from interstitial communities, and from planktonic communities of the overlying seawater, which correlated with differences in function and lifestyle (e.g., sulphur reduction and gliding motility). In contrast, meiofaunal communities could not be distinguished by sample type, suggesting that they are more frequently mobilized between these microhabitats. Across intertidal zones, high intertidal, mid intertidal and low intertidal/swash communities were distinct and correlated with moisture, organic carbon and phosphate content, implying that the distribution of microorganisms is influenced by intertidal abiotic gradients. However, few taxa at the genus or species level individually contributed to this zonation pattern; rather, a unique combination of multiple microbial taxa was probably responsible. Although significant differences in microbial community composition on sandy beaches can be attributed to microhabitat and intertidal gradients, further investigations are needed to assess community assembly processes, the consistency of these distributions, and the functions of the majority of the microorganisms observed in the sand and their effects on the biogeochemistry and ecology of sandy beaches.

Due to the chemico-physical differences between air and water, the transition from aquatic life to the land poses several challenges for animal evolution, necessitating morphological, physiological and behavioural adaptations. Microbial symbiosis is known to have played an important role in eukaryote evolution, favouring host adaptation under changing environmental conditions. We selected mangrove brachyuran crabs as a model group to investigate the prokaryotes associated with the gill of crabs dwelling at different tidal levels (subtidal, intertidal and supratidal). In these animals, the gill undergoes a high selective pressure, finely regulating multiple physiological functions during both animal submersion under and emersion from the periodical tidal events. We hypothesize that similarly to other marine animals, the gills of tidal crabs are consistently colonized by prokaryotes that may quantitatively change along the environmental gradient driven by the tides. Using electron microscopy techniques, we found a thick layer of prokaryotes over the gill surfaces of all of 12 crab species from the mangrove forests of Saudi Arabia, Kenya and South Africa. We consistently observed two distinct morphotypes (rod- and spherical-shaped), positioned horizontally and/or perpendicularly to the gill surface. The presence of replicating cells indicated that the prokaryote layer is actively growing on the gill surface. Quantitative analysis of scanning electron microscopy images and the quantification of the bacterial 16S rRNA gene by qPCR revealed a higher specific abundance of prokaryote cells per gill surface area in the subtidal species than those living in the supratidal zone. Our results revealed a correlation between prokaryote colonization of the gill surfaces and the host lifestyle. This finding indicates a possible role of prokaryote partnership within the crab gills, with potential effects on animal adaptation to different levels of the intertidal gradient present in the mangrove ecosystem.

Metal effects on germination and seedling development in closely-related halophyte species inhabiting different elevations along the intertidal gradient

ABSTRACTMangrove forests are important biotic sinks of atmospheric CO2 and play an integral role in nutrient-cycling and decontamination of coastal waters, thereby mitigating climatic and anthropogenic stressors. These services are primarily regulated by the activity of the soil microbiome. To understand how environmental changes may affect this vital part of the ecosystem, it is key to understand the patterns that drive microbial community assembly in mangrove forest soils. High-throughput amplicon sequencing (16S rRNA) was applied on samples from arid Avicennia marina forests across different spatial scales from local to regional. Alongside conventional analyses of community ecology, microbial co-occurrence networks were assessed to investigate differences in composition and structure of the bacterial community. The bacterial community composition varied more strongly along an intertidal gradient within each mangrove forest, than between forests in different geographic regions (Australia/Saudi Arabia). In contrast, co-occurrence networks differed primarily between geographic regions, illustrating that the structure of the bacterial community is not necessarily linked to its composition. The local diversity in mangrove forest soils may have important implications for the quantification of biogeochemical processes and is important to consider when planning restoration activities.IMPORTANCE Mangrove ecosystems are increasingly being recognized for their potential to sequester atmospheric carbon, thereby mitigating the effects of anthropogenically driven greenhouse gas emissions. The bacterial community in the soils plays an important role in the breakdown and recycling of carbon and other nutrients. To assess and predict changes in carbon storage, it is important to understand how the bacterial community is shaped by its environment. Here, we compared the bacterial communities of mangrove forests on different spatial scales, from local within-forest to biogeographic comparisons. The bacterial community composition differed more between distinct intertidal zones of the same forest than between forests in distant geographic regions. The calculated network structure of theoretically interacting bacteria, however, differed most between the geographic regions. Our findings highlight the importance of local environmental factors in shaping the microbial soil community in mangroves and highlight a disconnect between community composition and structure in microbial soil assemblages.

Rhizocephalan cirripedes are a very unique group of parasites infecting decapod crustaceans, but apart from a few well-studied species, little is known on their ecology and impact on hosts. Here we report on the results of a 14-month study of infestations of the rhizocephalan Parasacculina leptodiae in the rocky shore crab Leptodius exaratus along the shores of Kuwait in the Persian (Arabian) Gulf. Monthly samples along an intertidal gradient revealed a slightly higher prevalence of P. leptodiae in female (18%) compared to male crabs (11%) and marked differences in prevalence among the sampling sites. Crabs from more sheltered locations in Kuwait Bay showed lower prevalence of P. leptodiae compared to crabs from more exposed sites. Seasonal patterns were largely absent, but prevalence in female crabs showed some monthly variation depending on the site. Rhizocephalan prevalence was generally highest in both crab sexes at the lower shores. This possibly resulted from lower exposure of crabs to infective stages in the higher intertidal and movements of infected crabs to lower parts of the shore. Prevalence of ovigerous females significantly declined with increasing local parasite prevalence. This suggests that the well-known castrating effects of rhizocephalans on individual hosts can also affect local crab reproduction at the population level which has not been shown before. Our results indicate that the rhizocephalan P. leptodiae is a common parasite of the rocky shore crab L. exaratus along the shores of Kuwait, with potential effects on the crab’s population dynamics which warrants further study.

Abstract True mangroves are vascular plants (Tracheophyta) that evolved into inhabiting the mid and upper intertidal zone of tropical and subtropical soft-sediment coasts around the world. While several dozens of species are known from the Indo-West Pacific region, the Atlantic-East Pacific region is home to only a mere dozen of true mangrove species, most of which are rare. Mangrove trees can form dense monospecific or multispecies stands that provide numerous ecosystem services. Despite their eminent socioecological and socioeconomic relevance and the plethora of studies on mangroves, many details of the ecology of mangrove ecosystems remain unknown; and our knowledge about general ecological principles in mangrove ecosystems is scarce. For instance, the functional trait concept has hardly been applied to mangroves. Here we provide an inventory of 28 quantitative and 8 qualitative functional traits of true mangrove species and stipulate some insight into how these traits may drive ecosystem structure and processes. The differentiation between true mangroves and mangrove associates, which can dwell inside as well as outside mangrove forests, is reflected by a number of leaf traits. Thus, true mangroves exhibit lower specific leaf area, lower leaf N content, and lower K∶Na ratio, and higher leaf succulence, higher Na and Cl content, and higher osmolality than mangrove associates. True mangrove species that form pure stands produce larger leaves and exhibit higher N content per leaf area, higher leaf K and Ca content, greater maximum plant height, longer propagules, and lower root porosity than more sporadic species. The species-specific expression of most traits does not reflect the species' position along intertidal gradients, suggesting that adaptation to tidal inundation does not explain these traits. Rather, many of the traits studied herein exhibit strong phylogenetic signals in true mangroves. Thus, wood density is high in most species of the Rhizophoraceae, irrespective of their habitat or maximum height. On the other hand, species of the genus Sonneratia exhibit low wood density and do not grow taller than 20 m. Some leaf traits of true mangroves are more like those of plants from drier environments, reflecting the perception that a saline environment creates physiological drought stress. Along the same line, most true mangrove species exhibit sclerophyllous leaf traits. The few major mangrove tree species of the Atlantic-East Pacific are as distinct from each other, with regard to some traits, as are the many mangrove species of the Indo-West Pacific. We hypothesize that this phenomenon explains the similarly high biomass of mangrove forests in both the species-rich Indo-West Pacific and the species-poor Atlantic-East Pacific.

Modelling mangrove forest structure and species composition over tidal inundation gradients: The feedback between plant water use and porewater salinity in an arid mangrove ecosystem

The sign and magnitude of the effects of thermal extremes on an intertidal kelp depend on environmental and biological context