Abstract Conservation planning often relies on community‐level indicators including total abundance, distribution centroids and migration timing. However, in multispecies systems, these aggregate metrics can mask species‐specific redistribution under shared pressures, creating a misleading impression of stability and obscuring where and for which species management is most needed. Using standardized spring (March to May) shorebird counts from 2016 to 2024 at six major staging sites of the southern Yellow Sea, we quantified interannual trends in staging totals (bird‐days), abundance‐weighted latitudinal centroids and staging timing, and tested whether redistribution was better associated with population trajectory than with biogeographic or morphological correlates. Despite their smaller intertidal extent, the northern Jiangsu estuaries emerged as the central staging region: mollusc densities were more than an order of magnitude higher there, and the area‐standardized peak‐use density of shorebirds was 17 times higher than at southern sites. At the community level, the system appeared stable. Annual staging averaged 5.46 million bird‐days, and neither total bird‐days, regional centroid, nor staging date changed significantly over the study period. This apparent stability, however, masked marked species‐level reorganization. Across species, 24 declined and 22 increased. Spatial and phenological shifts were not explained by breeding or wintering position, migration distance, morphology or staging population size. Instead, the trajectory of population size was the dominant correlate: declining species shifted northwards and passed earlier, whereas increasing species expanded southwards and staged later. These opposing redistributions are consistent with density‐dependent buffering across a heterogeneous staging network, whereby abundance change reshapes competitive access to higher quality sites. Stable community totals therefore concealed emerging bottlenecks for declining species, particularly at prey‐rich northern estuaries where dependence on a narrow subset of the network may intensify vulnerability to disturbance or reduced accessibility. Synthesis and applications . In heterogeneous staging networks, community stability should not be treated as evidence of conservation security. Management should move beyond static totals towards trajectory‐based prioritization: maintain southern staging capacity to accommodate expanding species while safeguarding prey availability and accessibility at key northern estuaries where declining species are concentrating. More broadly, long‐term count data can identify what to protect, where and when. Read the free Plain Language Summary for this article on the Journal blog .

Background Rapid advances in animal tracking technologies have generated unprecedented volumes of high-resolution movement data. However, prevailing trajectory-based (Lagrangian) analytical approaches exhibit poor transferability across divergent sampling regimes and struggle to distinguish behaviors with overlapping movement signatures, leaving spatially defined ecological information underexplored. Methods We present an integrated, systematic framework that applies Eulerian, place-based spatiotemporal point pattern analysis to avian tracking data, offering a complementary perspective to traditional Lagrangian, path-based movement approaches. Using five species case studies of migratory shorebirds, waterfowl, and raptors, we integrated spatial statistical methods (e.g., Behaviorally-Anchored Local Moran, DBSCAN clustering) with geoprocessing tools in ArcGIS Pro and R (movepp package). This workflow enables movement states classification, delineation of breeding, stopover, and wintering habitats, and detection of fine-scale behaviors such as foraging, roosting and nesting, with activity pattern inferred from diel timing and habitat associations. Results The framework successfully identified migration phases and resolved movement dynamics at annual, seasonal, and diel scales. Derived point pattern metrics enabled the quantification of site fidelity and nest-site fidelity, as well as the characterization of circadian rhythms in habitat use. The detection of breeding behavior achieved high spatial and temporal precision, comparable to conventional analytical methods. Furthermore, this framework provides standardized and transferable indicators applicable across diverse species. Conclusions By bringing the toolkit of spatial point-pattern analysis to movement data, this framework provides innovative methodologies and practical guidelines to extract robust ecological insights from tracking point data in a fully reproducible and transferable manner. It improves comparative analyses of migratory strategies and supports targeted conservation planning by identifying multi-scale critical habitats and behavioral patterns across scales. Complementing conventional trajectory-based analytical paradigms, this approach broadens the dimensionality of behavioral interpretation from animal movement data.

Elevated microplastic loads in mangrove "blue carbon" ecosystems raise concerns for coastal ecological integrity and seafood safety, yet the drivers of shoreline accumulation remain poorly explained. We examined how land-based pond aquaculture shapes microplastic distributions along the Leizhou Peninsula (southern China), the region's largest mangrove coastline. Eighty-one surface sediment samples were collected from eight stations spanning mangrove forests and adjacent unvegetated mudflats. Microplastics were characterized using a laser direct infrared (LDIR) imaging spectrometer to determine polymer types and particle sizes (20-500 μm). Microplastic concentrations were higher in shoreline sectors with greater aquaculture intensity (P < 0.001). The aquaculture-related fraction increased with the area of ponds farther inland (r = 0.74-0.84; P < 0.05-0.01), rising by 0.0049% per unit pond-area increase, whereas ponds closest to the mangroves showed no clear association, pointing to a nonlocal input redistributed by alongshore transport before deposition and burial. Aquaculture-related microplastics were comparable between mangroves and mudflats, while non-aquaculture microplastics were more enriched on mudflats. Size distributions were dominated by fine particles, with slightly smaller microplastics in mangroves. Polymer profiles differed overall between habitats despite similar dominant polymers, indicating that separation was driven mainly by less abundant types. The Pollution Load Index (PLI) indicated a low level of contamination, whereas the Polymer Hazard Index (PHI) suggested a relatively high level of polymer-associated risk. These findings indicate that mitigation should account for coastline-scale aquaculture footprints and, critically, the alongshore transport that redistributes microplastics and creates accumulation hotspots, while addressing both aquaculture effluents and broader coastal inputs.

Eutrophication poses a major threat to the stability of global aquatic ecosystems, especially in urban wetlands highly influenced by human activities. It frequently alters species composition, which in turn affects the overall structure of ecosystems. However, how eutrophication impacts inter-species interactions across different trophic levels remains poorly understood. This study examines communities at varying nutrient status within the same urban wetland, including phytoplankton, zooplankton, and fish, while considering environmental factors such as dissolved oxygen, manganese (Mn), water depth, and the Trophic State Index (TSI). We assess how eutrophication influences species interactions across multiple trophic levels. Our results show that intra-trophic correlations were primarily driven by water depth, manganese, whereas inter-trophic correlations were predominantly governed by TSI. Specifically, inter-group correlations between different trophic levels decreased with raising TSI, while inter-species relationships within phytoplankton strengthened with increasing TSI. These findings provide crucial insights into the mechanisms underlying species coexistence in urban wetlands and highlight the need for targeted management strategies to maintain ecological stability in the face of eutrophication. Future research should explore temporal and spatial dynamics to better understand the complex responses of wetland ecosystems to nutrient fluctuations.

Finding ways to sustainably balance human needs with biodiversity conservation is increasingly challenging, especially on densely populated coasts. In China, rising demands for seafood and land intensify pressures on coastal habitats—the most critical refueling sites for migratory shorebirds along the East Asian-Australasian Flyway. Here we report on a continent-wide scale, decade-long field investigation on how China’s extensive intertidal mariculture impacts these vulnerable shorebirds. We show that commercial molluscs have become an essential resource for the molluscivorous shorebirds, determining their large-scale spatial distribution and temporal population dynamics during northward migration. We also reveal the unintended declines in both molluscs and shorebirds following a conservation-motivated mariculture ban, highlighting the “tragedy of the commons” as a consequence of unregulated public use. This study unveils the pivotal yet unforeseen role of China’s intertidal mariculture in sustaining shorebirds along the world’s most threatened flyway. If this delicate balance is disrupted without viable alternative food resources for the shorebirds, a considerable part of the flyway populations will be at risk. Evidence-based policymaking and management are required to harmonize seafood production with biodiversity conservation. China’s crowded coasts must balance seafood demand with conserving migratory shorebirds that rely on tidal flats along the East Asian–Australasian Flyway. This study suggests that well-managed mariculture feeds shorebirds and limits overharvest, benefiting seafood production and biodiversity.

Coastal ecosystems are known for their ability to sequester organic carbon (OC), termed “blue carbon”. The molecular composition of dissolved organic matter (DOM) can affect sediment OC content; however, the impact of benthic bioturbation on DOM properties and OC storage stability is not well understood. This study examined the effects of bioturbation by fiddler crabs on DOM molecular properties and OC storage stability along the Chinese coastline. These findings indicate that crab bioturbation enhanced the release of labile molecules by 59% on average. This increase is controlled by the coupling reactions of iron and manganese minerals, and is influenced by climatic gradients. Moreover, fiddler crab bioturbation diminishes the durability of blue carbon storage, with the most significant effects observed in mangrove forests, followed by bare mudflats, tidal creek banks, and saltmarshes. These results underscore the critical role of benthic bioturbation in global blue carbon budgets.

Coastal sediments are critical reservoirs of trace metals that pose persistent threats to coastal ecosystems and human health. The diffusive gradients in thin films (DGT) technique is powerful for assessing trace metal bioavailability in sediments. However, the spatial patterns, key mechanisms, and ecological risks of DGT-labile trace metals along China's coastline remain unresolved. Here, we collected sediment samples and installed DGT devices at 16 sites along China's east coast. We present the first continental-scale distributions of DGT-labile trace metals in China's coastal sediments, systematically quantify the controlling factors and pathways, and evaluate ecological risks through probabilistic modeling. The mean concentrations of DGT-labile Cu, Zn, Pb, and Cd were 7.10 (range: 2.33-16.61) μg/L, 3.83 (1.35-8.58) μg/L, 0.63 (0.12-2.64) μg/L, and 0.12 (0.03-0.36) μg/L, respectively, excluding the Huludao site, which exhibited extremely high levels. Spatially, higher DGT-labile concentrations of trace metals were observed primarily in the Bohai Sea and the East China Sea. Lower values were consistently recorded in the South China Sea and the Yellow Sea. Sediment physicochemical properties-electrical conductivity, clay, and sediment organic carbon-predominantly controlled labile Zn, Pb, and Cd distributions by enhancing solid-liquid resupply capacity through competitive adsorption and organic carbon mineralization. Whereas they regulated labile Cu via increasing metal solubility in porewater, mediated by organic complexation and chloro‑species formation. Lead isotopes indicate that natural sources dominated trace metals in most of China's coastal sediments. Anthropogenic hotspots exhibited source- and migration pathway-dependent DGT-labile trace metal concentrations. Probabilistic risk assessment indicates that Cu posed the highest ecological risk (mean risk quotient = 2.66; toxicity probability = 17.5 %). Metal mixtures had a considerable likelihood (22.6 %) of posing a toxic threat to aquatic biota. This study advances ecological risk assessment by demonstrating how sediment matrices function as environmental filters, providing actionable metrics for targeted remediation of the coastal ecosystem.

The global expansion of human activities has led to a dramatic reduction in natural wetlands. While effectively managed artificial wetlands hold the potential to counteract this decline, there is often a lack of knowledge regarding how to enhance their value for wildlife. To bridge this gap, we studied one of the world's largest saltworks in the Yellow Sea, China. This region has experienced significant natural wetland losses, resulting in marked declines in waterbird populations across the East Asian-Australasian Flyway (EAAF). Our research examined the impact of biotic factors such as prey abundance, and abiotic factors including water depth and management practices of saltpans, on the distribution of foraging shorebirds, as well as other waterbirds. Findings reveal that shorebirds, accounting for 95% of all waterbirds, heavily utilize saltpan evaporation ponds. Although various factors affect the distribution of shorebirds and other waterbirds, water depth and abandoned ponds (with low water depth) emerged as the primary factors. Notably, prey biomass (and abundance) did not exhibit a significant correlation with bird distribution across all shorebirds and other waterbirds, indicating that prey accessibility is more crucial than biomass in determining habitat suitability in these saltpans. Based on these insights, we propose tailored management strategies for the Yellow Sea saltpans that enhance conditions for shorebirds without impeding salt production, including lowering water levels through modifications to pond structures and reducing the volume of water evaporated during each stage of production. These straightforward, bird-friendly strategies provide practical solutions for adapting artificial wetlands to support migratory waterbirds in the EAAF and offer valuable insights for global waterbird conservation.

Species coexistence, largely maintained through mechanisms of niche differentiation, is fundamental for sustaining biodiversity and ecosystem resilience. For migratory shorebirds, the limited availability of staging sites intensifies interspecific competition, making coexistence mechanisms critical for refueling and survival during migration. This study examined the coexistence mechanisms of two threatened shorebird species, the Great Knot (Calidris tenuirostris) and Red Knot (Calidris canutus), in Nanpu wetland, a key stopover site along the East Asian-Australasian Flyway. Using noninvasive DNA metabarcoding of 81 droppings, we identified 32 MOTUs, revealing that both species primarily feed on Bivalvia. The Great Knot exhibited a more diverse diet, with Mactra quadrangularis (FOO = 71.43 %, RRA = 69.41 %) as its primary food source, whereas the Red Knot specializes in feeding on Potamocorbula laevis (FOO = 93.48 %, RRA = 80.15 %). Long-term survey data collected from 2014 to 2024 revealed that the abundance of Great Knots peaked in late April, whereas the number of Red Knots peaked 12.6 days later, in mid-May. These findings highlight how dietary differentiation and temporal partitioning enable the coexistence of these threatened species, offering valuable insights for the development of targeted conservation strategies to support species with specialized diets in adapting to fluctuations in food resources.

Per- and polyfluoroalkyl substances (PFAS) have gained significant global attention due to their extensive industrial use and harmful effects on various organisms. Among these, perfluoroalkyl acids (PFAAs) are well-studied, but their diverse precursors remain challenging to monitor. The Total Oxidizable Precursor (TOP) assay offers a powerful approach to converting these precursors into detectable PFAAs. In this study, the TOP assay was applied to samples from the East Asian-Australian Flyway, a critical migratory route for millions of shorebirds. Samples included shellfish from China's coastal mudflats, key stopover sites for these birds, and blood and liver samples from shorebirds overwintering in Australia. The results showed a substantial increase in perfluorocarboxylic acids (PFCAs) across all sample types following the TOP assay, with the most significant increases in shorebird livers (Sum PFCAs increased by 18,156%). Intriguingly, the assay also revealed unexpected increases in perfluorosulfonic acids (PFSAs), suggesting the presence of unidentified precursors. These findings highlight the need for further research into these unknown precursors, their sources, and their ecological impacts on shorebirds, other wildlife, and potential human exposure. This study also provides crucial insights into the TOP assay’s strengths and limitations in studying PFAS precursor dynamics in biological matrices.

Distance is a key constraint for animals in moving between suitable habitats, but is this also the case in staging long-distance migrating shorebirds that habitually cover thousands of kilometers during migrations? We conducted multi-year field observations, benthic prey sampling and satellite tracking, to compare how endangered great knots Calidris tenuirostris respond to the food shortage at two similarly functioning staging sites (Gaizhou and Beijingzi) in the northern Yellow Sea, China. Food availability declined by >95 % at both sites across the study period, with the intake rates of great knots declining by 87 %. However, whereas the number of great knots declined by 91 % at Gaizhou, only a 29 % decrease was seen at Beiijngzi. Satellite tracking showed that during the time when food was poor in Gaizhou, tagged great knots crossed 20 km to suitable alternative high-quality sites where food was not scarce. From Beijingzi, tagged great knots flew at least 124 km to find a good alternative. We show that longer distances to alternative sites decreased the probability of a bird leaving. Thus, habitat degradation in staging sites induced great knots to move to alternative sites, but only if such alternatives were relatively close. As staging habitats become more isolated, the negative effects of habitat degradation will be more serious due to a distance constraint on exploratory movements. This emphasizes the importance of maintaining networks of nearby high-quality refueling sites for migratory birds to provide buffers in seasons when local food conditions are lean.

Fiddler crabs, as coastal ecosystem engineers, play a crucial role in enhancing biodiversity and accelerating the flow of material and energy. Here we show how widespread crab burrows modify the carbon sequestration capacity of different habitats across a large climatic gradient. The process of crab burrowing results in the reallocation of sediment organic carbon and humus. Crab burrows can increase more greenhouse gases emissions compared to the sediment matrix (CO2: by 17–30%; CH4: by 49–141%). Straightforward calculations indicate that these increased emissions could offset 35–134% of sediment carbon burial in these two ecosystems. This research highlights the complex interactions between crab burrows, habitat type, and climate which reveal a potential lower carbon sink function of blue carbon ecosystems than previously expected without considering crab burrows. Bioturbation in wetlands can increase carbon dioxide and methane emissions, partially offsetting their sediment carbon burial capacity, according to a large-scale data set from sediment samples collected along the Chinese coastline and laboratory incubations.

Background Group living animals, such as shorebirds foraging on intertidal mudflats, may use social information about where to find hidden food items. However, flocking also increases intraspecific competition for resources, which may be exacerbated by food scarcity. Therefore, although aggregation may bring benefits, it may also increase the intensity of intraspecific competition. Methods We examined this trade-off in adult great knots Calidris tenuirostris , a molluscivorous long-distance migrating shorebird species, using interannual variation based on 2 years with different levels of food availability during their northward migratory staging in the northern Yellow Sea, China. We estimated individual home ranges and the extent of spatial overlap of home ranges of individually tagged birds in 2012 and 2015, whilst discounting for possible differences in body size, body mass, sex and migration schedule between years. Results We found that home range size was not associated with body mass, arrival date, body size, or sex of the individual. Despite a significant difference in food availability between the two study years, there was no significant change in the 50% and 95% home range size of great knots in the contrasting situations. However, there was a significantly smaller spatial overlap between individuals in the year when food was less available, suggesting that great knots operated more independently when food was scarce than when it was abundant. Conclusions These results suggest that minimizing intraspecific competition became more important when food was scarce. Where it is impossible to monitor all habitats en route , monitoring the local movements of shorebirds may offer a way to detect changes in habitat quality in real time.

Understanding species distribution patterns and what determines them is critical for effective conservation planning and management. In the case of shorebirds migrating along the East Asian-Australasian Flyway (EAAF), the loss of stopover habitat in the Yellow Sea region is thought to be the primary reason for the precipitous population declines. However, the rates of decline vary considerably among species, and it remains unclear how such differences could arise within a group of closely related species using apparently similar habitats at the same locales. We mapped the spatial distributions of foraging shorebirds, as well as biotic (benthic invertebrates consumed by migrating shorebirds) and abiotic (sediment characteristics) environmental factors, at a key stopover site in eastern China. Five of the six sediment characteristics showed significant spatial variation with respect to distance along the shoreline or distance from the seawall in the same tidal flat. The biomasses of four of the six most abundant benthic invertebrates were concentrated in the upper or middle zones of the tidal flat. The distribution patterns of all three focal shorebird species on the tidal flat were best explained jointly by this heterogeneity of sediment characteristics and invertebrate prey. These results suggest that the loss of tidal flats along the Yellow Sea, which is typically concentrated at the upper and middle zones, may not only reduce the overall amount of staging habitat, but also disproportionately affect the most resource-rich portions for the birds. Effective conservation of shorebird staging areas along the EAAF and likely elsewhere must consider the subtle habitat heterogeneity that characterizes these tidal flats, prioritizing the protection of those portions richest in food resources, most frequently used by focal bird species, and most vulnerable to anthropogenic threats. Article impact statement: Heterogeneity of tidal flats with respect to biotic and abiotic factors must be considered in shorebird conservation planning.

Summary The Wood Snipe Gallinago nemoricola is one of the least known shorebird species, and its habitat associations are very poorly understood. Here we provide the first assessment of the habitat use of the Wood Snipe during the breeding season. Between May and July 2021 at a 4-km2 alpine meadow in Sichuan province, China, we conducted population surveys and behavioural observations to identify sites where breeding Wood Snipe occurred and foraged. We quantified the habitat characteristics and food resource availability of these sites and compared them with randomly selected “background” sites. Comparison between 34 occurrence sites and 25 background sites indicated that during the breeding season, Wood Snipes are not distributed evenly across alpine meadow habitats, but preferred habitats in the lower part (3,378–3,624 m) of the alpine meadow with intermediate levels of soil moisture. In addition, comparison between 17 foraging sites and 24 background sites showed that the Wood Snipe tended to forage at sites with higher soil fauna abundance. We found weak evidence for denser vegetation cover at its height and no evidence for other biotic habitat variables such as vegetation composition or other abiotic habitat variables such as slope, soil penetrability, or disturbance level to influence Wood Snipe habitat associations. Our results suggest that the actual distribution range of the Wood Snipe during the breeding season may be smaller than expected from the extent of apparently suitable habitat. We advise caution in evaluating the potential habitat availability and distribution of the Wood Snipe, and call for further research to better understand the ecology of this rare species to inform its conservation.

Loss and/or deterioration of refuelling habitats have caused population declines in many migratory bird species but whether this results from unequal mortality among individuals varying in migration traits remains to be shown. Based on 13 years of body mass and size data of great knots (Calidris tenuirostris) at a stopover site of the Yellow Sea, combined with resightings of individuals marked at this stopover site along the East Asian-Australasian Flyway, we assessed year to year changes in annual apparent survival rates, and how apparent survival differed between migration phenotypes (i.e. migration timing and fuel stores). The measurements occurred over a period of habitat loss and/or deterioration in this flyway. We found that the annual apparent survival rates of great knots rapidly declined from 2006 to 2018, late-arriving individuals with small fuel stores exhibiting the lowest apparent survival rate. There was an advancement in mean arrival date and an increase in the mean fuel load of stopping birds over the study period. Our results suggest that late-arriving individuals with small fuel loads were selected against. Thus, habitat loss and/or deterioration at staging sites may cause changes in the composition of migratory phenotypes at the population-level.

Identifying where and when population 'bottlenecks' occur is critical to the conservation of migratory species, many of which are declining precipitously worldwide. Especially challenging is the evaluation of changes to staging sites. These sites are indispensable links in the migratory cycle but are typically used only briefly. We devised a field-based approach to assess the quality and carrying capacity of a critical staging site in Nanpu, China, for the declining, migratory Red Knot (Calidris canutus rogersi & C. c. piersmai) during northward migration. The Nanpu tidal flat supports 50,000-100,000 Red Knots annually, and while there, the knots feed almost exclusively on the bivalve Potamocorbula laevis. We simultaneously monitored changes in the abundance of Red Knots and bivalves across this entire staging site in spring 2018. After taking into account potential competition with other shorebird species, we estimated that the Nanpu tidal flat was capable of supporting approximately 1.46-1.70 times the observed level of Red Knot usage of this site, and therefore is operating below, but close to, carrying capacity with respect to food resources for Red Knots. This result suggests that any further habitat loss or degradation at this site could harm the Red Knot population along the entire East Asian-Australasian Flyway. Synthesis and applications. Quantitative monitoring and evaluation of habitat quality of staging sites are essential to successfully conserve declining migratory species. In particular, researchers and conservation practitioners should incorporate both population size and staging duration to more accurately assess the importance of different sites and to quantify how changes in staging habitat quality may translate into changes in the population sizes of migratory species at both local and global scales.

Invasion by smooth cordgrass ( Spartina alterniflora Loisel) has greatly impacted the intertidal ecosystems of China. Worldwide, chemical control is the most widely used method to control Spartina species, but it has not been widely implemented along the Chinese coast due to concerns about the potential impacts of herbicide residues on the environment and organisms. Macrobenthos, both natural and cultured on intertidal mudflats, is an important seafood resource, so human food safety is a particular concern. Here we tested the effectiveness of imazapyr (an imidazolinone herbicide inhibiting the synthesis of branched-chain amino acids) in controlling S. alterniflora from August 2020 to June 2021 on the Jiangsu Coast, an area severely impacted by S. alterniflora . We used two different concentrations of the herbicide and monitored the density of S. alterniflora seedlings and flower spikelets, the effects of herbicide use on macrobenthos, and residues in organisms and the environment at different times post-application. Ten months after application, imazapyr had killed all plants and within 30 days it inhibited the two reproductive processes of germination and flowering; there were no significant differences between the two concentrations used. Imazapyr residues were detected in the environment for up to 14 days post-application, but at very low concentrations and exponentially decreased with time. No residues were found in any macrobenthos. Imazapyr use did not result in a reduction of macrobenthos density. We conclude that the herbicide imazapyr effectively removes S. alterniflora with little collateral damage to other organisms and the environment. However, in view of the relatively small scale of our trials and the great extent of S. alterniflora in many sites in China, we recommend that larger scale field trails be conducted to assess any potential adverse effects when imazapyr is used at a landscape level.

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.

Migratory shorebirds are among the most threatened groups of birds. They rely on natural intertidal habitats outside the breeding season, but, to some extent have adjusted to using man-made habitats. Here, we assessed the importance of coastal saltpans - a type of anthropogenic wetland - for feeding in migratory shorebirds during their northward migration along the East Asian-Australasian Flyway (EAAF). We combined low tide counts on intertidal flats and nearby saltpans at the Luannan coastal wetland complex (Bohai Bay, China) with Bayesian mixing model analyses (BMMs) based on stable isotopes to evaluate the relative importance of coastal saltpans versus natural intertidal habitats as foraging grounds for migrating species. We grouped shorebird species (n = 24) according to feeding guild and body size, and found that both predictors explained the broad-scale patterns of foraging use of saltpans by shorebirds at low tide. The guild of water-surface foraging species (e.g. stilts and avocets), independently of body size, mostly fed in saltpans, and the small-medium visual (e.g. plovers) and tactile-surface (e.g. sandpipers) foraging species consumed a significant portion of their diet in this habitat. In contrast, most large tactile-surface foraging species barely foraged in saltpans at low tide. BMMs showed that shorebirds had a greater reliance on saltpans than did traditional counts of foraging birds in each habitat at low tide. Saltpan food is rich in essential fatty acids, so the contribution of saltpans to the diet of shorebirds should not be considered only in absolute values, but also in the quality of this contribution. Saltpans may therefore help conserve declining shorebirds if properly managed - for example by controlling water levels - to serve the specific feeding guilds that rely on them. While our focus is in the EAAF, the findings are relevant for other flyways and other non-tidal anthropogenic wetlands.