Estuarine Benthic Communities Research Articles

Contaminant pulse following wildfire is associated with shifts in estuarine benthic communities

Novel combinations of climatic conditions due to climate change and prolonged fire seasons have contributed to an increased occurrence of “megafires”. Such large-scale fires pose an unknown threat to biodiversity due to the increased extent and severity of burn. Assessments of wildfires often focus on terrestrial ecosystems and effects on aquatic habitats are less documented, particularly in coastal environments. In a novel application of eDNA techniques, we assessed the impacts of the 2019–2020 Australian wildfires on the diversity of estuarine benthic sediment communities in six estuaries in NSW, Australia, before and after the fires. Estuaries differed in area of catchment burnt (0–92%) and amount of vegetative buffer that remained post-fire between burnt areas and waterways. We found greater dissimilarities in the composition and abundance of eukaryotic and bacterial sediment communities in estuaries from burnt catchments with no buffer compared to those with an intact buffer or from unburnt catchments. Shifts in composition in highly burnt catchments were associated with increased concentrations of nutrients, carbon, including fire-derived pyrogenic carbon, and copper, which was representative of multiple highly correlated trace metals. Changes in the relative abundances of certain taxonomic groups, such as sulfate-reducing and nitrifying bacterial groups, in the most impacted estuaries indicate potential consequences for the functioning of sediment communities. These results provide a unique demonstration of the use of eDNA to identify wildfire impacts on ecological communities and emphasize the importance of vegetative buffers in limiting wildfire-associated impacts.

Natural stress vs. anthropogenic pressure. How do they affect benthic communities?

This study compares the role of salinity regime and chemical pollution in the biodiversity patterns of estuarine benthic communities. A specific field survey allowed us to explain the response of organisms to mixtures of chemicals and the effects of salinity regime and extreme events on the richness and composition of macroinvertebrate assemblages. The patterns obtained provide further evidence that both stress sources are key factors in macroinvertebrate communities' organization, but the type and magnitude of the changes differ. The abundance of opportunistic species increased according to the pollution gradient, while this indicator was less sensitive to salinity descriptors. In contrast, biotic indices responded to the salinity regime but did not show a consistent pattern in response to pollutants. Multivariate analyses reflected both environmental stress gradients. Overall, the results suggested that diversity increased in the habitats where the frequency and duration of extreme drought and flood events were low.

Effect of short-term meteorological disturbances on the submerged aquatic vegetation and associated fauna in the Patos Lagoon estuary, southern Brazil

Occluded fronts are naturally cyclogenic areas that have been intensified by global warming. Studies evaluating the effects of occluded fronts in the submerged aquatic vegetation (SAV) and its associated fauna in shallow estuarine areas may provide insights on the impacts of climate change-induced extreme weather events on coastal ecosystems functioning. The present dataset describes data on benthic fauna and flora in the Patos Lagoon Estuary (PLE), in southern Brazil, seasonally obtained during intense occluded fronts. Using a hierarchical sample design, based on Beyond BACI protocols (Before/After and Control/Impact), fauna and flora were sampled before and after four occluded fronts passage throughout 2019.Three habitats were sampled: SAV Meadow, SAV Edge and adjacent Sandflat. A total of 432 macrozoobenthic samples (216 samples for stratum); 216 samples for bellow and aboveground biomass, vegetation coverage, canopy height and marine macrophytes morphology; 144 samples by sedimentology and organic matter; 72 water column depth measurements; and 8 temperature and salinity measurements were collected during the study period. The data is available at the Global Biodiversity Information Facility (GBIF), in Darwin Core standard format (DwC), organized according to the OBIS-ENV-DATA model, with CC-BY-NC-4-0 license for use. The present dataset adds to the comprehension of the temporal variability of estuarine benthic communities in subtropical systems, and how short-term meteorological process can affect zoo and fitobenthic communities in the context of climate changes.

Influence of land-derived stressors and environmental variability on compositional turnover and diversity of estuarine benthic communities

It can be challenging to differentiate community changes caused by human activities from the influence of natural background variability. Using gradient forest analysis, we explored the relative importance of environmental factors, operating across multiple spatio-temporal scales, in influencing patterns of compositional turnover in estuarine benthic macroinvertebrate communities across New Zealand. Both land-derived stressors (represented by sediment mud content and total sediment nitrogen and phosphorus content) and natural environmental variables (represented by sea surface temperature, Southern Oscillation Index, and wind-wave exposure) were important predictors of compositional turnover, reflecting a matrix of processes interacting across space and time. Generalized linear models were used to determine whether measures of benthic macroinvertebrate diversity, which are commonly used as indicators of ecological health on a local scale, changed in a way that was consistent with the compositional turnover along the environmental gradient. As expected, compositional turnover along land-derived stressor gradients was negatively associated with diversity indices, suggesting a decline in ecological health as land-derived stressors increase. This study moves towards an ecosystem-based management approach that focusses on cumulative effects rather than single stressors by considering how multiple land-derived stressors influence indicators of estuarine health, against a background of natural variability across several spatio-temporal scales.

EDNA reveals estuarine benthic community response to nutrient enrichment – evidence from an in-situ experiment

Nutrient loading is a major threat to estuaries and coastal environments worldwide, therefore, it is critical that we have good monitoring tools to detect early signs of degradation in these ecologically important and vulnerable ecosystems. We carried out a seven-month manipulative experiment in two estuaries to assess the effects of nutrient loading on benthic communities. Environmental DNA metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom (rbcL), and bacterial (16S rRNA) communities to two levels of nutrient enrichment (150 and 600 g N m-2). Multivariate analyses demonstrated consistent changes in eukaryotic, diatom, and bacterial communities in response to enrichment, despite differing environmental conditions between sites (Fig. 1). These patterns aligned with changes in macrofaunal communities identified using traditional morphological techniques, confirming concordance between disturbance indicators detected by eDNA and current monitoring approaches. Clear shifts in eukaryotic and bacterial indicator taxa were seen in response to nutrient loading while changes in diatom communities were more subtle. Community changes were discernable between nutrient levels, suggesting that estuary health assessment tools could be developed to detect early signs of degradation. Existing eDNA-based biotic indices (microgAMBI and mtMBI) were able to detect these community shifts, suggesting transferability of these indices to other regions and systems. This work represents a first step towards the development of molecular-based estuary monitoring tools, which could provide a more holistic and sensitive approach to ecosystem health assessment with faster turn-around times and lower costs.

Taxonomic and functional response of estuarine benthic communities to experimental organic enrichment: Consequences for ecosystem function

Ecological theory states that the resilience of ecosystem functions to environmental disturbance depends on the biodiversity that underpins them, but field validations of this are rare. In this study, we explore how shifts in the composition of an intertidal macrofauna assemblage following organic matter enrichment affect the representation and composition of functional groups (FG) underpinning sandflat biogeochemistry and stability. Slow-release organic fertiliser was incorporated into experimental plots (1.44 m2) in a gradient study design (treatments ranged from 0 to 2250 g dw m−2). Macrofaunal communities were sampled 70 d later, after changes in sediment conditions associated with organic matter decomposition (hypoxia, acidification and increased concentrations of reduced solutes) had taken effect. Taxa-specific sensitivities to organic enrichment resulted in a significant diversity of responses within FGs, and density compensation was observed in one FG as a result of the disturbance; this enabled FGs to persist even at high levels of enrichment. Despite this, total community abundance decreased by 80% between low and high levels of enrichment and substantial declines in the abundance of dominant taxa reduced the viability of several FGs. Our study demonstrates a density-dependent relationship between macrofaunal biodiversity and ecosystem function, as declines in benthic primary production and nutrient recycling were significantly correlated with decreases in the abundance of key taxa. Despite the occurrence of stabilising mechanisms that provided resilience to FGs, taxonomic diversity was crucial for maintaining ecosystem function.

Environmental DNA metabarcoding reveals estuarine benthic community response to nutrient enrichment – Evidence from an in-situ experiment

Nutrient loading is a major threat to estuaries and coastal environments worldwide, therefore, it is critical that we have good monitoring tools to detect early signs of degradation in these ecologically important and vulnerable ecosystems. Traditionally, bottom-dwelling macroinvertebrates have been used for ecological health assessment but recent advances in environmental genomics mean we can now characterize less visible forms of biodiversity, offering a more holistic view of the ecosystem and potentially providing early warning signals of disturbance. We carried out a manipulative nutrient enrichment experiment (0, 150 and 600 g N fertilizer m−2) in two estuaries in New Zealand to assess the effects of nutrient loading on benthic communities. After seven months of enrichment, environmental DNA (eDNA) metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom only (rbcL) and bacterial (16S rRNA) communities. Multivariate analyses demonstrated changes in eukaryotic, diatom and bacterial communities in response to nutrient enrichment at both sites, despite differing environmental conditions. These patterns aligned with changes in macrofaunal communities identified using traditional morphological techniques, confirming concordance between disturbance indicators detected by eDNA and current monitoring approaches. Clear shifts in eukaryotic and bacterial indicator taxa were seen in response to nutrient loading while changes in diatom only communities were more subtle. Community changes were discernible between 0 and 150 g N m−2 treatments, suggesting that estuary health assessment tools could be developed to detect early signs of degradation. Increasing variation in community structure associated with nutrient loading could also be used as an indicator of stress or approaching tipping points. This work represents a first step towards the development of molecular-based estuary monitoring tools, which could provide a more holistic and standardized approach to ecosystem health assessment with faster turn-around times and lower costs.

Restored freshwater flow and estuarine benthic communities in the northern Gulf of Mexico: research trends and future needs.

Restoring river connectivity to rebuild and sustain land is a promising restoration strategy in coastal areas experiencing rapid land loss, such as the Mississippi river delta. Results of these large-scale hydrologic changes are preliminary, and there exists limited empirical evidence regarding how benthic communities will respond, specifically in Barataria Bay and Breton Sound in southeast Louisiana. In this review, the body of existing research in this geographic region pertaining to the drivers of benthic community response that are related to restored freshwater flow and sediment deposition is examined. Overall trends include (1) potential displacement of some species down-estuary due to reduced salinities; (2) temporary lower diversity in areas closest to the inflow; (3) increased benthic production along the marsh edge, and in tidal bayous, as a result of nutrient loading; (4) more habitat coverage in the form of submerged aquatic vegetation; and (5) reduced predation pressure from large and/or salinity-restricted predators. These trends highlight opportunities for future research that should be conducted before large-scale hydrologic changes take place.

Effects of carbonic anhydrase inhibition on biomass and primary production of estuarine benthic microalgal communities

Recent studies have focused on carbon concentrating mechanisms and the associated enzyme, carbonic anhydrase, to better understand the efficiency of CO2 uptake rates and carbon fixation in photoautotrophs. Some benthic microalgae (BMA) may be limited by inorganic carbon availability because high photosynthetic rates withdraw a large amount of CO2 and HCO3– in the top layer of sediment. Investigating the mechanisms that affect carbon acquisition are necessary if we are to fully understand the functioning and structuring processes of these systems. From this, we can better predict the potential impacts of increasing atmospheric CO2 concentrations on BMA communities. The purpose of this research was to examine a carbon concentrating mechanism used by BMA through their responses to induced carbon limitation. This approach was conducted through the removal of carbonic anhydrase (CA) activity using an inhibitor, ethoxyzolamide. Microcosm experiments were performed on intertidal muddy sediments from North Inlet Estuary, SC. Exposure to ethoxyzolamide resulted in a reduction of gross primary productivity (GPP) without a reduction in total BMA biomass. Furthermore, removed CA activity caused BMA cumulative GPP maxima to shift upward toward the surface in the sediment column. Active CA was necessary to maintain high GPP rates in these communities and allowed motile BMA to use a wider portion of the sediment column. Available HCO3– at lower depths could still be dehydrated into CO2 by microalgae with CA. Changes in global atmospheric CO2 concentrations leading to higher CO2 availability at the atmosphere-sediment interface may alter the structure and function of these BMA systems, and the vertical distribution of GPP. These consequences may have important implications for the biogeochemical cycling occurring in estuaries.

The scale-dependent effect of environmental filters on species turnover and nestedness in an estuarine benthic community.

Environmental filtering is a major mechanism structuring ecological communities. However, it is still not clear how different abiotic drivers composing the environmental filter interact with each other to determine local species assemblage and create spatial patterns in species distribution. Here, we evaluated the effects of two strong and uncorrelated environmental variables (salinity and sediment properties) on the β-diversity of an estuarine macrobenthic community while accounting for spatial effects. Our results show that the benthic community composition has a strong spatial structure along the estuary, which can be greatly explained by salinity and sediment variation. Salinity is most associated with species replacement (turnover), whereas sediment is more important for species loss (nestedness). However, the effects of sediment variation on nestedness are mainly detected at a smaller spatial scale (estuarine sectors), whereas the effects of salinity on species turnover are stronger as spatial scale increases (entire estuary). Our findings suggest that environmental filters can drive both turnover and nestedness components of β-diversity, but that their relative importance depends on the spatial scale of investigation. Although abiotic drivers associated with detrimental effects (sediment) usually result in nestedness, larger spatial scales encompass abiotic drivers associated with different suitable conditions (salinity), increasing the relative importance of the replacement component of species β-diversity.

Distribution, vertical position and ecological implications of shallow gas in Bahía Blanca estuary (Argentina)

There has been a growing interest in the study of shallow gas due its importance in relation to the marine environment, climate change and human activities. In Bahía Blanca estuary, Argentina, shallow gas has a wide distribution. Acoustic turbidity and blanking are the main seismic evidence for the presence of shallow gas in the estuary. The former prevails in the inner sector of the estuary where gas is either near or in contact with the seabed. Gas deposits are generally associated with paleochannels corresponding to the Holocene paleodeltaic environment. Distribution studies of shallow gas in this estuary are necessary because its presence implies not only a geological risk for harbor activities but also because it may have noxious effects on the marine ecosystem, mainly on benthic communities. The comparison of benthic communities at a gas site (GS) with those at a control site (CS) indicated that gas could generate impoverishment in terms of individuals' abundance (GS: N = 357; CS: N = 724). Also, diversity indices showed great differences in the community structure at each site. This indicates that methane gas may act as a natural disturbance agent in estuarine ecosystems. The presence of gas in seabed sediments must therefore be taken into account when distribution studies are conducted of estuarine benthic communities.

Benthic Invertebrate Community Composition and Sediment Properties in Barnegat Bay, New Jersey, 1965−2014

ABSTRACT Taghon, G.L.; Ramey, P.A.; Fuller, C.M.; Petrecca, R.F.; Grassle, J.P., and Belton, T.J., 2017. Benthic invertebrate community composition and sediment properties in Barnegat Bay, New Jersey, 1965−2014. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay–Little Egg Harbor, New Jersey. Extended time series of estuarine benthic community composition and the chemical and physical properties of sediment are necessary for distinguishing natural variation from possible anthropogenic influences, such as eutrophication. In July 2012, 2013, and 2014, 97 stations, randomly located throughout the Barnegat Bay–Little Egg Harbor estuary, were sampled. Benthic invertebrates were abundant, and the community was, in general, highly diverse. Although there was considerable spatial variability in sediment-particle sizes throughout the estuary, overall the total organic carbon content of the sediments was low (<1%). Comparable historical data from 1965–2010 are spotty...

New climatic targets against global warming: will the maximum 2\u2009\xb0C temperature rise affect estuarine benthic communities?

The Paris Agreement signed by 195 countries in 2015 sets out a global action plan to avoid dangerous climate change by limiting global warming to remain below 2 °C. Under that premise, in situ experiments were run to test the effects of 2 °C temperature increase on the benthic communities in a seagrass bed and adjacent bare sediment, from a temperate European estuary. Temperature was artificially increased in situ and diversity and ecosystem functioning components measured after 10 and 30 days. Despite some warmness effects on the analysed components, significant impacts were not verified on macro and microfauna structure, bioturbation or in the fluxes of nutrients. The effect of site/habitat seemed more important than the effects of the warmness, with the seagrass habitat providing more homogenous results and being less impacted by warmness than the adjacent bare sediment. The results reinforce that most ecological responses to global changes are context dependent and that ecosystem stability depends not only on biological diversity but also on the availability of different habitats and niches, highlighting the role of coastal wetlands. In the context of the Paris Agreement it seems that estuarine benthic ecosystems will be able to cope if global warming remains below 2 °C.

Priming of a DNA metabarcoding approach for species identification and inventory in marine macrobenthic communities.

In marine and estuarine benthic communities, the inventory and estimation of species richness are often hampered by the need for broad taxonomic expertise across several phyla. The use of DNA metabarcoding has emerged as a powerful tool for the fast assessment of species composition in a diversity of ecological communities. Here, we tested the amplification success of five primer sets targeting different COI-5P regions by 454 pyrosequencing to maximize the recovery of two simulated macrobenthic communities containing 21 species (SimCom1 and SimCom 2). Species identification was first performed against a compiled reference library of macrobenthic species. Reads with similarity results to reference sequences between 70% and 97% were then submitted to GenBank and BOLD to attempt the identification of concealed species in the bulk sample. The combination of at least three primer sets was able to recover more species than any primer set alone, achieving 85% of represented species in SimCom1 and 76% in SimCom2. Our approach was successful to detect low-frequency specimens, as well as concealed species, in the bulk sample, indicating the potential for the application of this approach on marine bioassessment and inventory, including the detection of "hidden" biodiversity that would hardly be possible based on morphology only.

A small-scale test of the species-energy hypothesis in a southern California estuary

Theoretical predictions of a direct positive association between productivity and diversity (P/D) have received considerable empirical support in marine systems, although this relationship tends to break down at smaller scales (<25km). Another theory commonly advanced in terrestrial systems, the species-energy hypothesis (SEH), relates productivity (=energy) to diversity indirectly through an increase in population abundances, which then reduces the likelihood of localized extinction and therefore enhances richness. The SEH has been supported on both global and local scales but has not been experimentally tested in estuarine systems or at the scale of a patch. We tested whether the predictions of the SEH (increased abundance and diversity) or the P/D hypothesis (increased diversity, no predictions for abundance) described the relationship between macroalgal productivity and the abundance and diversity of infauna and site-attached epifauna (hereafter macrofauna) and the microphytobenthos (MPB) in an estuarine benthic community. We conducted a single-factor experiment comparing the effects over time of three treatments comprised of two levels of macroalgae as an added energy source and a plastic mimic as a control that provided structure and habitat but no energy. Contrary to predictions of both the SEH and the P/D hypothesis, there were no measurable differences in taxonomic richness among treatments. However, in partial support of the SEH, we found that total macrofaunal abundance was 50% higher in both macroalgal treatments compared to the mimic and these were largely comprised of detritivores such as spionid polychaetes and oligochaetes. Phaeopigments increased in macroalgal plots but not the mimic, suggesting that added productivity decomposed, supplying more food for detritivores. As this taxonomic group is present in all plots, although in differing abundances, increasing energy flow through this pathway did not enhance taxonomic richness. Macroalgae stimulated the MPB (measured as chl a) more than did the mimic, and elevated chl b in macroalgal treatments indicated the increase was due to sporeling green macroalgae. However, benthic diatoms and dinoflagellates (estimated from chl c) were not affected by treatment. Thus, we found that at the patch level, neither the SEH nor the P/D hypothesis predicted patterns of diversity for estuarine macrofauna; rather, in this system, increased productivity simply supported higher abundances within the same taxonomic groups that occurred at all productivity levels.

Unraveling the interactive effects of climate change and oil contamination on laboratory-simulated estuarine benthic communities.

There is growing concern that modifications to the global environment such as ocean acidification and increased ultraviolet radiation may interact with anthropogenic pollutants to adversely affect the future marine environment. Despite this, little is known about the nature of the potential risks posed by such interactions. Here, we performed a multifactorial microcosm experiment to assess the impact of ocean acidification, ultraviolet B (UV-B) radiation and oil hydrocarbon contamination on sediment chemistry, the microbial community (composition and function) and biochemical marker response of selected indicator species. We found that increased ocean acidification and oil contamination in the absence of UV-B will significantly alter bacterial composition by, among other things, greatly reducing the relative abundance of Desulfobacterales, known to be important oil hydrocarbon degraders. Along with changes in bacterial composition, we identified concomitant shifts in the composition of oil hydrocarbons in the sediment and an increase in oxidative stress effects on our indicator species. Interestingly, our study identifies UV-B as a critical component in the interaction between these factors, as its presence alleviates harmful effects caused by the combination of reduced pH and oil pollution. The model system used here shows that the interactive effect of reduced pH and oil contamination can adversely affect the structure and functioning of sediment benthic communities, with the potential to exacerbate the toxicity of oil hydrocarbons in marine ecosystems.

Isolation and characterization of novel microsatellite loci in two species of burrowing shrimp, Neotrypaea californiensis and Upogebia pugettensis

Burrowing thalassinid shrimp are important ecosystem engineers in estuarine benthic communities. We characterized 31 microsatellite loci in two shrimp species, Neotrypaea californiensis and Upogebia pugettensis, which are of current management concern due to declining abundance and interactions with shellfish aquaculture. All loci were variable with three to 22 alleles per locus and observed heterozygosity of 0.22–1.00. There were only four deviations from Hardy–Weinberg expectations and no significant linkage disequilibrium. These are the first microsatellites characterized for these species and provide a useful tool for further characterization of population structure and diversity.

Spatial and temporal variability in species richness in a temperate intertidal community

Understanding changes in estuarine benthic communities has important implications for conservation and yet it is a challenge due to the high natural variability of these systems. We addressed this challenge through the study of temporal and spatial patterns of species richness in an intertidal benthic community in New Zealand North Island. Five different locations within the estuary were monitored seasonally over 12 yr. This data set allowed the study of species–time–area relationships (STAR) and the delineation of patterns in species richness, heterogeneity and turnover in space and time. The site with the highest species richness also had the highest within‐site heterogeneity in species richness, a high number of species occurring infrequently in time, the lowest mud content and the most variable wave climate. Similarities and differences between sites were generally maintained over time, although seasonal and multi‐year patterns in species richness occurred at all sites. The STAR showed a significant negative interaction between space and time, with species accumulation rates in space and time being equivalent at 4 spatial replicates (250 m2) and 2 temporal replicates (6 months). The lowest source of variability in species turnover was within site, and the highest source was over years. This was reflected in the lack of an asymptotic relationship in the species accumulation curve despite the 12 yr of monitoring. These results contribute to the knowledge of the variability in diversity patterns in estuaries and have important implications for long‐term monitoring of natural communities and the estimation of diversity for conservation.

Development and validation of an experimental life support system for assessing the effects of global climate change and environmental contamination on estuarine and coastal marine benthic communities

An experimental life support system (ELSS) was constructed to study the interactive effects of multiple stressors on coastal and estuarine benthic communities, specifically perturbations driven by global climate change and anthropogenic environmental contamination. The ELSS allows researchers to control salinity, pH, temperature, ultraviolet radiation (UVR), tidal rhythms and exposure to selected contaminants. Unlike most microcosms previously described, our system enables true independent replication (including randomization). In addition to this, it can be assembled using commercially available materials and equipment, thereby facilitating the replication of identical experimental setups in different geographical locations. Here, we validate the reproducibility and environmental quality of the system by comparing chemical and biological parameters recorded in our ELSS with those prevalent in the natural environment. Water, sediment microbial community and ragworm (the polychaete Hediste diversicolor) samples were obtained from four microcosms after 57days of operation. In general, average concentrations of dissolved inorganic nutrients (NO3 (-) ; NH4 (+) and PO4 (-3) ) in the water column of the ELSS experimental control units were within the range of concentrations recorded in the natural environment. While some shifts in bacterial community composition were observed between in situ and ELSS sediment samples, the relative abundance of most metabolically active bacterial taxa appeared to be stable. In addition, ELSS operation did not significantly affect survival, oxidative stress and neurological biomarkers of the model organism Hediste diversicolor. The validation data indicate that this system can be used to assess independent or interactive effects of climate change and environmental contamination on benthic communities. Researchers will be able to simulate the effects of these stressors on processes driven by microbial communities, sediment and seawater chemistry and to evaluate potential consequences to sediment toxicity using model organisms such as Hediste diversicolor.

Sex‐biases in distribution and resource use at different spatial scales in a migratory shorebird

In migratory species, sexual size dimorphism can mean differing energetic requirements for males and females. Differences in the costs of migration and in the environmental conditions occurring throughout the range may therefore result in sex-biases in distribution and resource use at different spatial scales. In order to identify the scale at which sexual segregation operates, and thus the scale at which environmental changes may have sex-biased impacts, we use range-wide tracking of individually color-ringed Icelandic black-tailed godwits (Limosa limosa islandica) to quantify sexual segregation at scales ranging from the occupation of sites throughout the non-breeding range to within-site differences in distribution and resource use. Throughout the range of this migratory shorebird, there is no evidence of large-scale sex differences in distribution during the non-breeding season. However, the sexes differ in their selection of prey types and sizes, which results in small-scale sexual segregation within estuaries. The scale of sexual segregation therefore depends on the scale of variation in resource distribution, which, in this system, is primarily within estuaries. Sexual segregation in within-site distribution and resource use means that local-scale anthropogenic impacts on estuarine benthic prey communities may disproportionately affect the sexes in these migratory shorebirds.