The dynamics of winter sea ice and icefoot play a fundamental role in structuring intertidal ecosystems in subarctic environments. However, ongoing climate warming is rapidly altering ice regimes across northern shorelines. In the St. Lawrence Marine Estuary (Canada), reduced formation of stable icefoot increasingly exposes benthic habitats to winter-related disturbances. We investigated how such disturbance influences eelgrass (Zostera marina L.) meadows and associated benthic communities over a winter season (2024-2025). We used a sampling design that explicitly compared areas with no change (Stable state), strong cover reduction (Abraded), and bare sediment (Reference), as identified from aerial survey imagery. Substantial losses in eelgrass cover (~20%) were observed, with Abraded areas showing reduced taxa richness but comparable biomass to Stable areas. Our results revealed that persistent small mussel aggregates, still attached to remnant eelgrass rhizomes in Abraded areas, played a key role in maintaining biomass and community structure. Mussels acted as secondary foundation species, formed biogenic habitat and partially compensated for eelgrass loss by maintaining refuges and colonization surfaces for associated fauna. These findings suggest that resistance to winter disturbance depends not only on the severity of habitat loss but also on the persistence of interacting foundation species and their capacity for functional replacement. Reduced coastal protection by icefoot increases intertidal exposure to physical and physiological stressors, progressively altering subarctic benthic assemblages and shifting communities toward alternative states, potentially closer to boreal conditions. Such changes warrant greater attention regarding their consequences for ecosystem functioning and the services they provide to humans.

Ecosystem engineers are crucial to the development of coastal ecosystem communities and functions. However, a better understanding of how environmental stressors affect ecosystem engineering and thereby influence communities and ecosystem dynamics is needed. We conducted an in situ experiment in a blue mussel Mytilus spp. ecosystem to test the interacting effects of ecosystem engineering and multiple stressors on seasonal ecosystem development. Experimental mussel patches with two initial adult mussel densities were exposed to nutrient enrichment, and thermal stress over the growth season. We assessed invertebrate communities (abundance and diversity), sediment accumulation and fluxes of oxygen and ammonium. Initial mussel density, used as a proxy for the intensity of ecosystem engineering, drove the seasonal accumulation of sediments and invertebrate species and abundance. This positive feedback on the strength of ecosystem engineering during ecosystem development was associated with a negative effect of ecosystem engineering on oxygen and ammonium fluxes at the ecosystem level, potentially participating in a negative feedback loop between mussel density and metabolic activity. Stressors modulated the effect of ecosystem engineering: Nutrient enrichment relaxed the initial mussel density threshold needed for species accumulation and the effect of mussels on sediment accumulation and oxygen consumption was only seen in the presence of environmental stressors. These results emphasize the importance of considering the dynamics of both community structure and ecosystem functions driven by ecosystem engineers to understand their responses to multiple stressors.

The ecosystem services and functions of seagrass meadows are indisputable, and knowledge about their coverage is critical for coastal managers worldwide. In this study, the surface area coverage of the foundation species Zostera marina L. (eelgrass) was investigated in four contrasting subregions of the Estuary and Gulf of St. Lawrence (EGSL), eastern Canada. The meadows in all subregions mainly occupy intertidal zones. Our analysis covered broad spatial (meters to kilometers) and temporal (annual to decadal) scales and revealed unprecedented insights at a local and regional context. We processed surface reflectance products of the Landsat archive through the Google Earth Engine cloud computing platform. The processing scheme only considered emerged areas of intertidal zones from imagery acquired at the lowest tide levels because of inherent limitations imposed by water clarity and the poor radiometric quality for water applications of the early Landsat sensors. The polygons classified as eelgrass encompassed at least 25 % coverage of eelgrass for each patch, and the classification scheme showed a very good agreement with coastal ecosystem habitats maps generated by photointerpretation and field validation for the period between 2015 and 2019, with an overall accuracy of approximately 94 %. From the 40year period analyzed (1984-2023), the meadows' surface area dramatically increased 10- (from approx. 0.3 to 2.5 km2) to 21-fold (from approx. 0.8 to 16.7 km2). The percentage of the intertidal area occupied by eelgrass meadows varied by subregion, ranging between 17 % and 82 %. In some subregions, meadows expanded landward. Some meadows experienced relatively shortterm losses (interannual scale) in three subregions, although these losses differed in their timing. We propose several hypotheses involving hydrodynamic, sedimentological, drift ice and climatic processes that could explain long- and short-term variability of the meadow coverage. However, this complex relationship remains to be investigated. Overall, while showing suitable habitats for eelgrass colonization, this study also revealed the EGSL tidal flats as potentially important areas of biodiversity, carbon storage, and coastal protection against erosion.

Estuarine communities provide many ecosystem services and are highly vulnerable to global changes. Detrimental changes in land use and intense rainfall events increase the frequency and intensity of flooding, causing abrupt changes in estuarine conditions. As a result, marine organisms are more often exposed to freshwater conditions for several days after flooding. While estuarine organisms are able to thrive under fluctuating salinities, their responses to intense and prolonged hypoosmotic stress may differ. Understanding these responses is crucial as salinity variability is key to species distribution. Changes in hydrological regimes are occurring much faster in high latitudes environments, yet subarctic estuarian communities are rarely studied. Our study investigates the sensitivity of three key marine benthic macroinvertebrates inhabiting subarctic estuaries (Littorina saxatilis, Macoma balthica and Mytilus spp.) to different durations of freshwater exposure. In laboratory conditions, molluscs were exposed during six weeks to a gradient of 12 freshwater pulse durations, ranging from 0 to 9 d, interspersed with 24 h of exposure to sea water. Mortality and shell growth, as well as energy content for Mytilus spp., were compared after two, four and six weeks of exposure using linear mixed models and break-point analyses. All three species demonstrated tolerance to short-duration freshwater pulses (less than 2 d) repeated over several weeks. Littorina saxatilis exhibited the highest vulnerability, with mortality increasing under freshwater pulses longer than 2 d after two weeks. Macoma balthica displayed a comparable threshold but only after four weeks. Mytilus spp. displayed the greatest tolerance, with a threshold only detectable after six weeks of exposure and increasing mortality in treatments with freshwater pulses longer than 5 d. In addition, shell growth decreased with increasing duration of freshwater pulse only in L. saxatilis while it was not affected in M. balthica and Mytilus spp. Energy content in Mytilus spp. varied according to pulse duration and time, with the highest energy content being detected in the longer freshwater exposure periods, suggesting complex physiological responses to hypoosmotic stress. Altogether, our study indicates the existence of highly species-specific differences in freshwater vulnerability among marine benthic macroinvertebrates inhabiting subarctic estuaries. Our findings highlight the importance of using gradients of stress scenarios to identify ecologically relevant thresholds, helping in the prediction and management of extreme climate events like river floods on estuarine communities. Our study provides valuable recommendations for dam management and biodiversity conservation in estuarine ecosystems.

AimBiogenic structural complexity increases mobile animal richness and abundance at local, regional and global scales, yet animal taxa vary in their response to complexity. When these taxa also vary functionally, habitat structures favouring certain taxa may have consequences for ecosystem function. We characterised global patterns of epifaunal invertebrates in eelgrass (Zostera marina) beds that varied in structural and genetic composition.LocationNorth America, Europe and Asia.Time Period2014.Major Taxa StudiedPeracarid crustaceans and gastropod molluscs.MethodsWe sampled epifaunal invertebrate communities in 49 eelgrass beds across 37 degrees latitude in two ocean basins concurrently with measurements of eelgrass genetic diversity, structural complexity and other abiotic and biotic environmental variables. We examined how species richness, abundance and community composition varied with latitude and environmental predictors using a random forest approach. We also examined how functional trait composition varied along with community structure.ResultsTotal species richness decreased with latitude, but this was accompanied by a taxonomic shift in dominance from peracarid crustaceans to gastropods, which exhibited different sets of functional traits. Greater eelgrass genetic diversity was strongly correlated with both richness and abundance of peracarids, but less so for gastropods.Main ConclusionsOur results add to a growing body of literature that suggests genetic variation in plant traits influences their associated faunal assemblages via habitat structure. Because peracarids and gastropods exhibited distinct functional traits, our results suggest a tentative indirect link between broad-scale variation in plant genetic diversity and ecosystem function.

Estuaries face mounting anthropic pressures. Climate change is projected to increase heavy precipitations, while agricultural and logging activities reduce land permeability, leading to more frequent flooding events that lower estuarine salinity. These hyposaline conditions pose physiological challenges for marine species, potentially reducing taxonomic diversity and biomass, and ultimately, ecosystem functions and services. Polar and subpolar estuaries, historically understudied, will undergo significant changes in freshwater discharge timing and variability due to predicted shifts from snow to rainfall regimes in these high latitudes. The investigation of biotic communities structure through functional traits is crucial for understanding biodiversity changes, evaluating ecosystem tolerance, and addressing the loss of function under stressful conditions. Therefore, our study aims to characterize the taxonomic and functional diversity of hard-substrate benthic communities along a salinity gradient in small subarctic estuaries. We hypothesize that communities closer to the riverine input will be less taxonomically diverse and abundant and with smaller individuals, leading to a loss of functions due to environmental filtering. To test our hypotheses, we measured traditional (biomass, taxonomic richness and diversity) and functional (functional richness and Rao's quadratic entropy) indices, as well as observed traits, of epibenthic hard-substrate macroalgae and macroinvertebrates along a four-level salinity gradient found in five small subarctic estuaries in Quebec (Canada). As predicted, freshwater inputs induced a decrease in biomass, taxonomic richness, functional richness, and Rao's quadratic entropy, with a fivefold reduction in total biomass of the epibenthic community from marine to low salinity zones. Freshwater inputs significantly shaped both taxonomic and functional trait structures, as the proportion of suspension feeders and long-distance dispersers decreased with rising freshwater inputs. While there was no clear trend for the size-class structure of invertebrate taxa, macroalgae were smaller at low salinities. Estuarine communities in subarctic regions may be vulnerable to future alterations in flooding patterns caused by global change, potentially affecting key ecosystem services such as suspended matter filtration. Functional trait indices were found to be efficient and serve as a valuable complement to taxonomic measures in detecting community shifts along salinity gradients, highlighting their usefulness in developing effective conservation and management strategies.

Biogenic habitats, such as mussel beds, provide various functions in their associated ecosystems. However, these habitat-forming species are exposed to cumulative impacts as the number and diversity of anthropogenic stressors increase, particularly in estuarine ecosystems. Experiments designed to test the effect of single and multiple interacting stressors on mussel beds and associated biotic components are rare (i.e. in situ experiments are uncommon, as they usually occur in laboratory settings). We conducted a field experiment in the St. Lawrence estuary (Quebec, Canada) to address this gap. We transplanted blue mussels ( Mytilus spp.) to mimic mussel beds and exposed them to increased nutrient concentrations and thermal stress at three intervals (6.5, 10.5 and 15 weeks) during May through September. For each transplant, we evaluated epizoic microalgal biomass (as pigment biomass), microbial activity and oxygen uptake, and mortality levels and energy content in the tissues of Mytilus spp. following three exposure times. No effects were found for chlorophyll a biomass, microbial activity and oxygen uptake, and mortality in mussels. In contrast, we found thermal stress and nutrient input interacted to create antagonistic and synergistic effects on energy content in Mytilus spp. at different exposure times and exerted additive effects over time on phaeopigments and the ratio of chlorophyll a /phaeopigments. Our work highlights the importance of combining multiple biological components (i.e. multiple biological responses measured at different scales of biological complexity) and different experimental approaches to capture the complexity behind stressor interactions.

Assessments of greenhouse gas (GHG) emissions in managed areas are facing various challenges. A non-flow-through, non-steady-state (NFT-NSS) chamber coupled to a frame permanently inserted into the landfilled substrates is a standard method for quantifying GHG emissions in managed areas, such as pulp and paper mill sludge (PPMS) landfill sites. Frequent measurements are needed to minimize uncertainties on GHG emission factors at the landfill site scale. However, maintaining a frame inserted into the substrates for a long time period is often impossible due to landfilling management operations. Therefore, GHG measurements using NFT-NSS chambers placed directly on substrates’ surface could be an interesting option. Our objectives were to determine the relationships between CO2, CH4, and N2O fluxes measured with (F + ) and without (F-) a frame inserted in the substrates’ surface and to develop correction factors for fluxes measured without a frame. Measurements were made at different PPMS landfill sites in the province of Québec, Canada. Stronger GHG flux relationships were observed at the provincial (across sites) than the specific site scale: the variance in GHG fluxes from F- chambers explained up to 80 % of variance in fluxes from F + chambers. The measured CO2, CH4, and N2O fluxes in F- chambers were on average 53, 78, and 63 % lower, respectively, than those estimated by the models at provincial scale. The correction factors developed with this approach could greatly extend the number of sites where in situ GHG measurements can be done and would help refining GHG inventories at the provincial and national levels.

Habitat degradation and fragmentation reduce habitat structural complexity (e.g. amount of physical features) and increase habitat edges. While many studies have focused on the effects of habitat edges or complexity on biodiversity, relatively few have disentangled them or investigated their effects over time. We investigated how proximity to the edge of eelgrass Zostera subg. Zostera marina Linnaeus, 1753 habitat, shoot density and their interactions across seasons can influence the diversity pattern of epifaunal assemblages in meadows situated in a Mediterranean lagoon (France). We used a combination of field sampling and in situ manipulations with artificial seagrass units (ASUs) mimicking low and high shoot densities. During autumn and spring, we found that shoot density, Z. marina biomass and leaf area index (LAI) were higher inside the meadows than at the edge, while epiphyte load was the highest in spring at the edges. Epifaunal abundance and diversity were higher at the edge than inside the meadow for both natural shoots—regardless of the epiphyte load—and ASUs in spring. In autumn, epifaunal abundance varied positively with ASU density, regardless of the position in the meadow. Our results also showed that edges and habitat complexity affect the epifaunal structure differently across seasons. Therefore, we suggest that recruitment of macrofauna is the main mechanism explaining a positive edge effect during spring. This work highlights the need to consider seasonal dynamics in the assessment of habitat fragmentation and degradation.

Currents are unique drivers of oceanic phylogeography and thus determine the distribution of marine coastal species, along with past glaciations and sea-level changes. Here we reconstruct the worldwide colonization history of eelgrass (Zostera marina L.), the most widely distributed marine flowering plant or seagrass from its origin in the Northwest Pacific, based on nuclear and chloroplast genomes. We identified two divergent Pacific clades with evidence for admixture along the East Pacific coast. Two west-to-east (trans-Pacific) colonization events support the key role of the North Pacific Current. Time-calibrated nuclear and chloroplast phylogenies yielded concordant estimates of the arrival of Z. marina in the Atlantic through the Canadian Arctic, suggesting that eelgrass-based ecosystems, hotspots of biodiversity and carbon sequestration, have only been present there for ~243 ky (thousand years). Mediterranean populations were founded ~44 kya, while extant distributions along western and eastern Atlantic shores were founded at the end of the Last Glacial Maximum (~19 kya), with at least one major refuge being the North Carolina region. The recent colonization and five- to sevenfold lower genomic diversity of the Atlantic compared to the Pacific populations raises concern and opportunity about how Atlantic eelgrass might respond to rapidly warming coastal oceans.

Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m–2 s–1, 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m–2 s–1, which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m–2 s–1, while a compensation point (NPP = 0) of 13.7 μmol photons m–2 s–1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves’ light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents an MQR value for eelgrass in the St. Lawrence estuary, which is highly pertinent in the context of conservation and restoration of eelgrass meadows.

While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change.

Intertidal vegetation provides important ecological functions, such as food and shelter for wildlife and ecological services with increased coastline protection from erosion. In cold temperate and subarctic environments, the short growing season has a significant impact on the phenological response of the different vegetation types, which must be considered for their mapping using satellite remote sensing technologies. This study focuses on the effect of the phenology of vegetation in the intertidal ecosystems on remote sensing outputs. The studied sites were dominated by eelgrass (Zostera marina L.), saltmarsh cordgrass (Spartina alterniflora), creeping saltbush (Atriplex prostrata), macroalgae (Ascophyllum nodosum, and Fucus vesiculosus) attached to scattered boulders. In situ data were collected on ten occasions from May through October 2019 and included biophysical properties (e.g., leaf area index) and hyperspectral reflectance spectra (Rrs(λ)). The results indicate that even when substantial vegetation growth is observed, the variation in Rrs(λ) is not significant at the beginning of the growing season, limiting the spectral separability using multispectral imagery. The spectral separability between vegetation types was maximum at the beginning of the season (early June) when the vegetation had not reached its maximum growth. Seasonal time series of the normalized difference vegetation index (NDVI) values were derived from multispectral sensors (Sentinel-2 multispectral instrument (MSI) and PlanetScope) and were validated using in situ-derived NDVI. The results indicate that the phenology of intertidal vegetation can be monitored by satellite if the number of observations obtained at a low tide is sufficient, which helps to discriminate plant species and, therefore, the mapping of vegetation. The optimal period for vegetation mapping was September for the study area.

Distribution of Earth's biomes is structured by the match between climate and plant traits, which in turn shape associated communities and ecosystem processes and services. However, that climate-trait match can be disrupted by historical events, with lasting ecosystem impacts. As Earth's environment changes faster than at any time in human history, critical questions are whether and how organismal traits and ecosystems can adjust to altered conditions. We quantified the relative importance of current environmental forcing versus evolutionary history in shaping the growth form (stature and biomass) and associated community of eelgrass (Zostera marina), a widespread foundation plant of marine ecosystems along Northern Hemisphere coastlines, which experienced major shifts in distribution and genetic composition during the Pleistocene. We found that eelgrass stature and biomass retain a legacy of the Pleistocene colonization of the Atlantic from the ancestral Pacific range and of more recent within-basin bottlenecks and genetic differentiation. This evolutionary legacy in turn influences the biomass of associated algae and invertebrates that fuel coastal food webs, with effects comparable to or stronger than effects of current environmental forcing. Such historical lags in phenotypic acclimatization may constrain ecosystem adjustments to rapid anthropogenic climate change, thus altering predictions about the future functioning of ecosystems.

Around 50% of the world's lakes freeze seasonally, but the duration of ice‐cover is shortening each year and this is likely to have broad limnological consequences. We sampled freshwater ice and the underlying water in 19 boreal and polar lakes to evaluate whether lake ice contains an inoculum of algae, nutrients, and carbon that may contribute to lake ecosystem productivity. Boreal and Arctic lakes differed in ice duration (6 vs. >10 months), thickness (70 vs. 190 cm), and quality (predominantly snow ice vs. black ice), but in all lakes, there were consistent differences in biological and biogeochemical composition between ice and water. Particulate fractions were often more retained while most dissolved compounds were excluded from the ice; for example, the ice had more terrestrial particulate carbon, measured as fatty acid biomarkers (averages of 1.1 vs. 0.3 µg L−1) but lower dissolved organic carbon (2.2 vs. 5.7 mg C L−1) and inorganic phosphorus concentrations (4.0 vs. 7.5 µg C L−1) than the underlying water. The boreal ice further had three times higher chlorophyll‐a, than the water (0.9 vs. 0.3 µg L−1). Of the dissolved fractions, the contribution of protein‐like compounds was higher in the ice, and this in all lakes. These labile compounds would become available to planktonic microbes when the ice melts. Our results show that freshwater ice has an underestimated role in storage and transformation in the biogeochemical carbon cycle of ice‐covered lake ecosystems.

Multiple forms of environmental change and anthropogenic pressure co-occur in coastal marine ecosystems. These external forces affect ecosystem structure, functioning, and, eventually, services to humans. Studies that include more than 2 simultaneous stressors are still needed to understand potential interactions among multiple stressors. We evaluated single and interactive effects of density reduction of Zostera marina L. (a habitat-forming species), shading, and sediment nutrient enrichment on the response of Z. marina and its associated epifauna over 10 wk. Shading had the greatest effect on reducing the eelgrass relative leaf elongation rate (RLE), non-structural carbohydrate reserves, and eelgrass shoot density. A reduced eelgrass density sustained higher epifaunal densities and increased the eelgrass RLE. Sediment nutrient enrichment increased eelgrass shoot density but decreased epifaunal richness, diversity, and total abundance. Our disturbance and pair of stressors differed in their influence on diversity measures, but all affected assemblage structure. Most of the changes to the epifaunal assemblage and diversity likely occurred due to altered habitat availability and epiphytic algae load. We observed additive, antagonistic, and negatively synergistic interactions among our treatments, while most of the cumulative effects showed dominance by one stressor over another. Our results highlight the importance of field experiments that are based on multiple disturbances and stressors to determine their interaction type on communities.

Aim Studies on latitudinal patterns in plant defence have traditionally overlooked the potential effect that resource availability may have in shaping plant defence. Likewise, latitudinal patterns of tolerance traits have rarely been studied, yet they can be a critical component of plant defence. Therefore, the aim of our study was to examine latitudinal variation in the production of tolerance and resistance traits against herbivory along a latitudinal range and a natural gradient of resource availability from upwelling conditions. Location Canada, North America and Mexico. Time period Summer months of 2015. Major taxa used The seagrass Zostera marina. Methods We conducted experiments simulating macroherbivore (e.g., bird, fish) damage on the seagrass Z. marina at 10 sites across the Eastern Pacific coast (Canada-Mexico) and Quebec and analysed several traits related to resistance and tolerance strategies against herbivory. In addition, we examined the effects of potential seagrass changes in defence strategies by performing a series of feeding experiments with mesoherbivores in a subset of sites. Results We found that eelgrass resistance defences did not follow a linear latitudinal pattern but rather followed a bell-shaped curve which correlated with bottom-up control. In sites with higher nutrient availability, plants allocated resources to tolerance strategies and had lower resistance traits. Furthermore, seagrasses did not respond linearly to increased herbivory pressure; while they tolerated moderate levels of herbivory, they underwent a significant reduction in tolerance and resistance under high herbivory levels, which also made them more susceptible to consumers in feeding experiments. Main conclusions Our results highlight the importance that nutrient availability has in shaping latitudinal patterns of plant defence against herbivory and show how these defences may not respond linearly to increased herbivory pressure in seagrasses.

Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats.

Coastal ecosystems are recognized as important providers of ecosystem services such as carbon storage, increased fish productivity, and wave energy reduction. In a context of climate change, coastal ecosystems are exposed to erosion and subject to coastal squeeze, even as they provide natural coastal protection against extreme weather. While civil engineering solutions often take centre stage in mitigating coastal erosion and protecting infrastructure from storms and sea level rise, we seek to explore the social dimension of adaptive management of socio-ecological systems and more specifically the role of knowledge and learning. Using an ecosystem services (ES) framework, we provide a first evaluation of local stakeholders' perceptions of coastal habitats in maritime Quebec. The findings demonstrate the importance of a social approach for coastal ES valuation, in particular in addressing the complex question of cultural ES. A better understanding of the links between coastal stakeholders and their natural environment can help decision-makers and practitioners design conservation management and coastal adaptation measures mainstreaming the role of coastal habitats. Nevertheless, a change towards a socio-ecological perspective will require long-lasting processes that build on social capacities, such as flexible institutions and multilevel governance systems.