Kelp forests, recently recognized for their potential to capture and store carbon, remain relatively underexplored in their actual contributions to carbon budgets. Here, we investigated the carbon release dynamics of the sugar kelp, Saccharina latissima, a dominant kelp species of shallow subarctic zones, which is seasonally impacted by ice scour. Our study focused on autumn and winter, combining field assessments with laboratory experiments to quantify and compare mechanisms of biomass and carbon loss, and thus contributing new insights into seasonal kelp-derived carbon flows in these environments. Daily dislodgement rates were comparable to temperate regions, with higher rates in autumn than winter, contrary to our initial hypothesis about ice scouring effects. Apical blade erosion rates aligned with previous regional studies but were lower than temperate sites, possibly due to reduced bryozoan encrustation and colder waters. Laboratory measurements revealed higher dissolved organic carbon (DOC) release compared to other kelp species, while particulate organic carbon (POC) loss was 8-fold higher than DOC release. This study underscores the need for comprehensive annual measurements to refine carbon budgets, especially in subarctic kelp forests, where carbon contributions are likely underestimated, particularly in shallow, seasonally dynamic environments.

Kelp forests offer substantial carbon fixation, with the potential to contribute to natural climate solutions (NCS). However, to be included in national NCS inventories, governments must first quantify the kelp-derived carbon stocks and fluxes leading to carbon sequestration. Here, we present a blueprint for assessing the national blue carbon capacity of kelp forests in which data synthesis and Bayesian hierarchical modeling enable estimates of kelp carbon production, storage, and export capacity from limited data. Applying this blueprint to Canada's extensive coastline, we estimate kelps hold 0.6 to 2.8 Tg C in short-term biomass, producing 1.1 to 6.2 Tg C yr-1, of which 0.04 to 0.4 Tg C yr-1 could be exported to the deep ocean. While modest compared to terrestrial sinks, our findings suggest kelps have comparable carbon sequestration to marine and freshwater wetlands, warranting further consideration in Canada's NCS inventories. Our transparent, reproducible blueprint represents an important step towards accurate carbon accounting for kelp forests.

Kelp forests are known to be very productive ecosystems and constitute a central component of the marine carbon cycle in coastal areas. Nevertheless, crucial carbon-related data are missing to be able to include them properly in carbon budgets. A thorough understanding of the kelp contribution to the carbon cycle is especially important in regions prone to experiencing strong seasonal fluctuations in environmental conditions, such as subarctic regions. This study aimed to quantify primary productivity through growth rates and oxygen fluxes of a dominant kelp species in subarctic regions, Saccharina latissima, and to link oxygen fluxes to environmental parameters. Our results showed that strong primary productivity oxygen fluxes coincided with high light levels in July and most of August, while growth rates stayed similar all summer. An overall decline in all primary productivity proxies happened from late August, suggesting a seasonal slowing down of S. latissima metabolism. The estimated quantity of carbon stored in tissue during growth represented from 6% to 28% of the gross primary productivity. Further research is needed to explore how and how much carbon transits through living kelp tissue in different seasons, to better understand the contribution of subarctic kelp to coastal carbon budgets.

Kelps are a dominant macrophyte group and primary producer in Arctic nearshore waters that provide significant services to the coastal ecosystem. The quantification of these services in the Arctic is constrained, however, by limited estimates of kelp depth extent, which creates uncertainties in the area covered by kelp. Here, we test the environmental drivers of the depth extent of Arctic kelp. We used Southampton Island (SI), Nunavut, Canada, as an example region after an initial survey found deep Arctic kelp (at depths to at least 50 m) with relatively low grazing pressure within diverse hydrographic conditions. We found abundant rocky substrata, but no influence of substratum type on kelp cover. The kelp cover increased with depth until 20 m and then decreased (the median maximum depth for all stations was 37 m). The best predictor of kelp depth extent was the number of annual open (ice-free) water days with light (r2 = 44–52%); combining depth extent data from SI with published data from Greenland strengthened this relationship (r2 = 58–71%). Using these relationships we estimated the maximum kelp-covered area around SI to be 27,000–28,000 km2, yielding potential primary production between 0.6 and 1.9 Tg Cyr−1. Water transparency was a key determinant of the underwater light environment and was essential for explaining cross-regional differences in kelp depth extent in SI and Greenland. Around SI the minimum underwater light required by kelp was 49 mol photons m−2 yr−1, or 1.4% of annual integrated incident irradiance. Future consideration of seasonal variation in water transparency can improve these underwater light estimations, while future research seeking to understand the kelp depth extent relationship with nutrients and ocean dynamics can further advance estimates of their vertical distribution. Improving our understanding of the drivers of kelp depth extent can reduce uncertainties around the role of kelp in Arctic marine ecosystems.

Les forêts de laminaires sont des écosystèmes riches et productifs, longeant les côtes des zones tempérées à polaires. Dans les eaux du golfe du Saint-Laurent, les platiers rocheux de l’île d’Anticosti abritent des forêts de laminaires qui sont encore très peu caractérisées. En 2021 et en 2022, 2 échantillonnages en plongée sous-marine ont permis de caractériser les communautés de laminaires présentes sur 14 sites au sud-ouest de l’île d’Anticosti. Cinq espèces de laminaires ( Saccharina latissima , Alaria esculenta , Hedophyllum nigripes / Laminaria digitata , Agarum clathratum , Saccorhiza dermatodea ) ont été recensées, avec une grande variabilité d’assemblage entre les sites. Les densités (de 10 ± 5 à 99 ± 20 individus·m −2 ) et les biomasses (de 0,3 ± 0,1 à 6,4 ± 1,0 kg·m −2 ) étaient semblables à celles dans d’autres écosystèmes à laminaires de l’est du Canada. Des relations allométriques sur S. latissima ont permis de mettre en évidence des différences entre les sites, probablement dues aux conditions environnementales locales. Cette caractérisation des forêts de laminaires du sud-ouest de l’île d’Anticosti ouvre des perspectives sur le potentiel écologique et économique de cet écosystème.

Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m2) that would otherwise be transported to deeper water accumulate inside these features, representing an underestimated subsidy. Our work documents the distribution and dimensions of ice pits in Fildes Bay, Antarctica, and evaluates their relationship to the biomass and species composition of algae found within them. It also assesses the rates of deposition and advective loss of algae in the pits. The 17 ice pits found in the study area covered only 4.2% of the seabed but contained 98% of drift algal biomass, i.e., 60 times the density (kg/m2) of the surrounding seabed. Larger ice pits had larger and denser algal accumulations than small pits and had different species compositions. The accumulations were stable over time: experimentally cleared pits regained initial biomass levels after one year, and advective loss was less than 15% annually. Further research is needed to understand the impacts of ice scouring and subsequent algal retention on ecosystem functioning in this rapidly changing polar environment.

The ability of organisms to detect, locate and navigate to resource patches is modified by the surrounding landscape. Green sea urchins Strongylocentrotus droebachiensis in barren grounds exist in a food-limited state and are subject to intense competition. Rapid detection and consumption of resource patches, particularly pieces of macroalgae from adjacent algal beds, are key in determining individual growth, survival and reproductive success. Detection and movement to resource patches requires moving through a heterogeneous benthic seascape composed of rocky and sandy patches, presenting different degrees of resistance to movement. We used time-lapse photography to describe the foraging behaviour of urchins in relation to the presence of a key resource subsidy (drift kelp) and different benthic seascapes. We demonstrated that urchins could detect the presence of drift kelp in barren-ground habitats and alter their movement behaviour in response, but did not exhibit the ability to directionally navigate towards kelp in field conditions. Seascapes with increased proportions of rocky substrata facilitated increased movement in response to the presence of drift. Moreover, urchin foraging behaviour was temporally variable, with no response to the presence of drift in early spring (May). This indicates not only that interpretations of observations of urchin behaviour must take intrinsic and extrinsic seasonal dynamics into account, but that extrapolating results to explain larger-scale patterns and processes must include both spatially explicit subtidal seascapes and temporal dynamics. In many temperate and boreal regions, this indicates the need for increased subtidal benthic research in the fall and winter.

The establishment of non-indigenous species in the Antarctic, an ecosystem isolated for millions of years, could dramatically alter its unique and endemic biota. In coastal waters, calcified species (e.g., echinoderms, gastropods, bivalves) of benthic communities will be particularly vulnerable to shell-crushing (i.e., durophagous) predators such as crabs. The magnitude of changes in the community structure of shallow Antarctic waters potentially produced by such non-indigenous predators will depend on the innate vulnerability of these species (e.g., shell characteristics) and their potential to respond to novel threats (e.g., behavior, shell thickening). This study aims to evaluate the potential interaction between shell-crushing predators and the limpet Nacella concinna, an endemic Antarctic species and one of the most abundant and conspicuous gastropods in intertidal and shallow subtidal zones of the Antarctic. First, we showed that the king crab Lithodes santolla, a representative species of a group of crabs likely to invade Antarctic waters, was able to break the shell of N. concinna and consume it in the laboratory. We then assessed the shell-breaking force of N. concinna living in four Antarctic habitats (two intertidal and two subtidal) and found wide variation in this trait. Finally, we examined shell-breaking force of a subantarctic congener, N. deurata, which naturally coexists with shell-crushing predators in its native range, and found its shell-breaking force to be similar to the strongest populations of the Antarctic species. Taking into account the crushing claw force of crabs and their high consumption rate of limpets, N. concinna will be highly vulnerable to this kind of durophagous predators and may have limited reaction norms for increasing any inducible defenses such as the thickening and hardening of the shell or changes in their behavior in the face of the almost inevitable invasion of shell-crushing predators into the Antarctic marine ecosystem.

The design of anthropogenic marine structures can have unintended consequences for ecological communities. We describe differences in biofouling assemblages between two primary anthropogenic habitats—pontoons and pilings—in a marina in British Columbia, Canada, using multiple measures of diversity (i.e., richness, evenness, and Shannon indices) and multiple metrics of variability in taxonomic composition (i.e., Jaccard and modified Gower methods) using two complementary surveys. First, a video-transect survey revealed abundances of crawling benthic predators to be 19 times greater on pilings than on pontoons. Second, a photo-quadrat survey of sessile invertebrates revealed moderate differences in diversity but differences of 86% in taxonomic composition and 88% in non-indigenous species (NIS), owing largely to the dominance of mussels (Mytilus species complex) on pontoons and their absence on pilings. We discuss several environmental factors associated with the design of anthropogenic infrastructure and propose that contact with the seafloor is the key driver of observed differences between the biofouling assemblages at this site. Contact with the seafloor permits access to crawling predators and thereby drives the abundances of ecosystem-engineering taxa. Patterns of taxonomic composition and assemblage dispersion indicate that biofouling organisms are affected by these phenomena according to their roles either as prey or as competitors with mussels and not whether they are native or NIS. Finally, we consider how the growing body of ecological studies on biofouling communities such as ours can inform the implementation of infrastructure for the purposes of enhancing biotic diversity and resilience.

Kelp ecosystems provide habitat to many ecologically and commercially important species. They are declining globally but trends are highly variable at small geographic and temporal scales. Understanding what constrains kelp distribution at a scale relevant to management efforts is thus fundamental. Here, we examined the abiotic correlates of the distribution of two dominant kelp species ( Alaria esculenta and Saccharina latissima ) in the Sept-Iles region (50.21°N, 66.38°W), Canada, in 2017 and 2018. We surveyed kelp distribution, measured abiotic conditions in two contrasting habitats (bay and outlying islands), and conducted a transplant experiment of both species between these habitats to examine kelp performance. Saccharina latissima inhabited both habitats while A. esculenta was absent from the bay. While wave exposure was similar between the bay and islands, other abiotic factors varied between habitats, potentially driving the differing kelp distributions: temperature, turbidity and sedimentation were greater in the bay, while light availability and salinity were greater around the islands. Temperature and salinity across habitats were within the tolerance limits for both species, while irradiance was near or below sub-optimal levels in the bay, suggesting that light, turbidity and sedimentation might be the main factors limiting the distribution of A. esculenta . Both transplanted kelp species grew and survived better around the islands than in the bay, suggesting that the island habitat offers better conditions. A. esculenta survived and grew in the bay, indicating that its local-scale distribution is not constrained at the early adult stage. Our results provide an understanding of current kelp distribution and possible changes related to future abiotic conditions.

Spatially concentrated resources result in patch-based foraging, wherein the detection and choice of patches as well as the process of locating and exploiting resource patches involve moving through an explicit landscape composed of both resources and barriers to movement. An understanding of behavioral responses to resources and barriers is key to interpreting observed ecological patterns. We examined the process of resource discovery in the context of a heterogeneous seascape using sea urchins and drift kelp in urchin barrens as a model system. Under field conditions, we manipulated both the presence of a highly valuable resource (drift kelp) and a barrier to movement (sandy substratum) to test the interacting influence of these two factors on the process of resource discovery in barren grounds by urchins. We removed all foraging urchins (Strongylocentrotus droebachiensis) from replicate areas and monitored urchin recolonization and kelp consumption. We tested two hypotheses: (1) unstable substratum is a barrier to urchin movement and (2) the movement behavior of sea urchins is modified by the presence of drift kelp. Very few urchins were found on sand, sand was a permeable barrier to urchin movement, and the permeability of this barrier varied between sites. In general, partial recolonization occurred strikingly rapidly, but sand slowed the consumption of drift kelp by limiting the number of urchins. Differences in the permeability of sand barriers between sites could be driven by differences in the size structure of urchin populations, indicating size-specific environmental effects on foraging behavior. We demonstrate the influence of patchy seascapes in modulating grazing intensity in barren grounds through modifications of foraging behavior. Behavioral processes modified by environmental barriers play an important role in determining grazing pressure, the existence of refuges for new algal recruits, and ultimately the dynamics of urchin-algal interactions in barren grounds.

The coastal zone of the Canadian Arctic represents 10% of the world’s coastline and is one of the most rapidly changing marine regions on the planet. To predict the consequences of these environmental changes, a better understanding of how environmental gradients shape coastal habitat structure in this area is required. We quantified the abundance and diversity of canopy forming seaweeds throughout the nearshore zone (5–15 m) of the Eastern Canadian Arctic using diving surveys and benthic collections at 55 sites distributed over 3,000 km of coastline. Kelp forests were found throughout, covering on average 40.4% (±29.9 SD) of the seafloor across all sites and depths, despite thick sea ice and scarce hard substrata in some areas. Total standing macroalgal biomass ranged from 0 to 32 kg m–2 wet weight and averaged 3.7 kg m–2 (±0.6 SD) across all sites and depths. Kelps were less abundant at depths of 5 m compared to 10 or 15 m and distinct regional assemblages were related to sea ice cover, substratum type, and nutrient availability. The most common community configuration was a mixed assemblage of four species: Agarum clathratum (14.9% benthic cover ± 12.0 SD), Saccharina latissima (13% ± 14.7 SD), Alaria esculenta (5.4% ± 1.2 SD), and Laminaria solidungula (3.7% ± 4.9 SD). A. clathratum dominated northernmost regions and S. latissima and L. solidungula occurred at high abundance in regions with more open water days. In southeastern areas along the coast of northern Labrador, the coastal zone was mainly sea urchin barrens, with little vegetation. We found positive relationships between open water days (days without sea ice) and kelp biomass and seaweed diversity, suggesting kelp biomass could increase, and the species composition of kelp forests could shift, as sea ice diminishes in some areas of the Eastern Canadian Arctic. Our findings demonstrate the high potential productivity of this extensive coastal zone and highlight the need to better understand the ecology of this system and the services it provides.

Kelp habitats contribute to marine productivity and diversity, making understanding the constraints on their distribution important. In the Gulf of St. Lawrence, Alaria esculenta occupies a subset of Saccharina latissima's range. Since tolerance to sedimentation by early life stages was suggested to cause this contrasting distribution, we tested the influence of sediment levels on spore attachment and development. For both species, the proportion of attached spores that developed decreased with increasing sediment. However, spore attachment and gametophyte density increased with sediment concentration but only for Saccharina. At the maximum sediment level examined, spore attachment and gametophyte densities of the two species were similar, contrary to the idea that sediment effects on early life stages explain differences in adult distribution. Further investigation, particularly with higher sediment loads, is required to confirm this conclusion. As turbidity is increasing globally, understanding the mechanisms underpinning changes in seaweed distribution will facilitate appropriate local-scale management.

Cycling of organic carbon in the ocean has the potential to mitigate or exacerbate global climate change, but major questions remain about the environmental controls on organic carbon flux in the coastal zone. Here, we used a field experiment distributed across 28° of latitude, and the entire range of 2 dominant kelp species in the northern hemisphere, to measure decomposition rates of kelp detritus on the seafloor in relation to local environmental factors. Detritus decomposition in both species were strongly related to ocean temperature and initial carbon content, with higher rates of biomass loss at lower latitudes with warmer temperatures. Our experiment showed slow overall decomposition and turnover of kelp detritus and modeling of coastal residence times at our study sites revealed that a significant portion of this production can remain intact long enough to reach deep marine sinks. The results suggest that decomposition of these kelp species could accelerate with ocean warming and that low-latitude kelp forests could experience the greatest increase in remineralization with a 9% to 42% reduced potential for transport to long-term ocean sinks under short-term (RCP4.5) and long-term (RCP8.5) warming scenarios. However, slow decomposition at high latitudes, where kelp abundance is predicted to expand, indicates potential for increasing kelp-carbon sinks in cooler (northern) regions. Our findings reveal an important latitudinal gradient in coastal ecosystem function that provides an improved capacity to predict the implications of ocean warming on carbon cycling. Broad-scale patterns in organic carbon decomposition revealed here can be used to identify hotspots of carbon sequestration potential and resolve relationships between carbon cycling processes and ocean climate at a global scale.

Ports play a central role in our society, but they entail potential environmental risks and stressors that may cause detrimental impacts to both neighboring natural ecosystems and human health. Port managers face multiple challenges to mitigate risks and avoid ecosystem impacts and should recognize that ports are embedded in the wider regional coastal ecosystem. Cumulative impacts of anthropogenic stressors have the potential to further burden the existing suite of natural stressors, particularly where ports are located in embayments and estuaries. Environmental monitoring in ports should thus develop a comprehensive, holistic, multilayered approach integrated in the wider ecosystem that will help managers better achieve sustainable development, a major goal of the United Nations’ 2030 agenda and Decade of Ocean Science for Sustainable Development (2021–2030). This practice bridge showcases the experience of the second Canadian Healthy Ocean Network (CHONe2) in Baie des Sept Îles (BSI, Quebec; the fourth largest industrial port in Canada) laying the foundations of holistic environmental monitoring in ports. We describe the partnership model (i.e., engaging scientists, local authorities, an independent organization, and local industries), synthesize the multidisciplinary studies that turned environmental monitoring into a systemic investigation of the biological and physical components of BSI, integrate the developed scientific knowledge into a social–ecological–environmental system, present an innovative near real-time monitoring approach, and discuss implications for management and policy. The CHONe2 experience in BSI aligns with the decade’s road map for sustainable development and provides elements that could be adapted to other commercial ports. By suggesting a set of best practices (e.g., multidisciplinarity, transparency, inclusivity, participatory modeling), we hope to spark new interest in environmental monitoring as a path to conciliate development and sustainability of ports and other high-use marine areas.

The choice of the duration and frequency of sampling to detect relevant patterns in field experiments or for environmental monitoring is always challenging since time and material resources are limited. In practice, duration and frequency of sampling are often chosen based on logistical constraints, experience, or practices described in published works but are rarely justified and almost never optimized before initiating sampling. Settlement plates are commonly used as a passive sampling tool to study recruitment patterns of fouling organisms (including non-indigenous species) and their deployment is amenable to experimentation with respect to manipulating duration and frequency of sampling. This study aimed to determine the optimal sampling strategy to detect rare species (e.g., a non-indigenous species early in the invasion process when its population size is still small). To do so, we deployed a series of settlement plates of various durations (1–32 days) and sampling frequencies (daily to biweekly) during the seasonal onset of recruitment, when larval supply was low, a situation that mimics the low propagule pressure of the early stages of the invasion process. We demonstrated that a combination of longer sampling duration and higher sampling frequency was the best strategy to maximize taxonomic richness. However, we found that an intermediate sampling duration of 1–2 weeks was optimal for detecting most species. These results can guide species-specific and assemblage-level sampling strategies using settlement plates. Additionally, this study can serve as a practical template for optimizing sampling of other taxonomic groups that were not examined in the present study as well as for the use of other methods.

Latitudinal diversity gradients have provided many insights into species differentiation and community processes. In the well‐studied intertidal zone, however, little is known about latitudinal diversity in microbiomes associated with habitat‐forming hosts. We investigated microbiomes of Fucus vesiculosus because of deep understanding of this model system and its latitudinally large, cross‐Atlantic range. Given multiple effects of photoperiod, we predicted that cross‐Atlantic microbiomes of the Fucus microbiome would be similar at similar latitudes and correlate with environmental factors. We found that community structure and individual amplicon sequencing variants (ASVs) showed distinctive latitudinal distributions, but alpha diversity did not. Latitudinal differentiation was mostly driven by ASVs that were more abundant in cold temperate to subarctic (e.g., Granulosicoccus_t3260, Burkholderia/Caballeronia/Paraburkholderia_t8371) or warm temperate (Pleurocapsa_t10392) latitudes. Their latitudinal distributions correlated with different humidity, tidal heights, and air/sea temperatures, but rarely with irradiance or photoperiod. Many ASVs in potentially symbiotic genera displayed novel phylogenetic biodiversity with differential distributions among tissues and regions, including closely related ASVs with differing north‐south distributions that correlated with Fucus phylogeography. An apparent southern range contraction of F. vesiculosus in the NW Atlantic on the North Carolina coast mimics that recently observed in the NE Atlantic. We suggest cross‐Atlantic microbial structure of F. vesiculosus is related to a combination of past (glacial‐cycle) and contemporary environmental drivers.

Kelp habitats are threatened across the globe, and because of their ecological importance, active conservation and restoration solutions are needed. The use of man-made structures as artificial reefs is one way to enhance kelp habitat by providing suitable substrata, but in the past the ecology of artificial structures has been investigated mainly in contrast to natural coastal habitats, not as elements integrated into the seascape. Indeed, it is now emerging that structuring processes, including ecological interactions (e.g., herbivory), can depend on properties of the surrounding seascape. In Eastern Canada, grazing by the green sea urchin can jeopardize the success of artificial reefs for kelp enhancement. Urchin activity is, however, likely to be influenced by the bottom composition, and thus a seascape approach is needed to integrate urchin behavior and habitat heterogeneity. Adopting a spatially explicit framework, we investigated whether the seascape creates areas of differential grazing risk for kelp by affecting urchin habitat use. Specifically, we transplanted kelp onto modules of artificial substrata distributed on a heterogeneous area that we mapped for bottom type and algal cover. After following kelp survival and urchin distribution over time, we modeled kelp survival as function of urchin metrics and coupled it to urchin use of the habitat models to map grazing risk in the area. Kelp survival was a function of the frequency of the urchins presence. Urchins avoided sandy patches, while bottom composition and algal cover modulated the within-patch urchin use of the habitat, creating heterogeneity in grazing risk. Discrete seascape features (boulders) also increased the grazing risk locally. The heterogeneity of coastal seafloor can thus play a major role in determining the ecological outcomes on artificial structures. Incorporating this information when planning artificial reefs could minimize the detrimental grazing risk, thereby increasing the success of artificial reefs for kelp habitat enhancement.

Climate change is transforming marine ecosystems through the expansion and contraction of species’ ranges. Sea ice loss and warming temperatures are expected to expand habitat availability for macroalgae along long stretches of Arctic coastlines. To better understand the current distribution of kelp forests in the Eastern Canadian Arctic, kelps were sampled along the coasts for species identifications and percent cover. The sampling effort was supplemented with occurrence records from global biodiversity databases, searches in the literature, and museum records. Environmental information and occurrence records were used to develop ensemble models for predicting habitat suitability and a Random Forest model to predict kelp cover for the dominant kelp species in the region – Agarum clathratum, Alaria esculenta, and Laminariaceae species (Laminaria solidungula and Saccharina latissima). Ice thickness, sea temperature and salinity explained the highest percentage of kelp distribution. Both modeling approaches showed that the current extent of arctic kelps is potentially much greater than the available records suggest. These modeling approaches were projected into the future using predicted environmental data for 2050 and 2100 based on the most extreme emission scenario (RCP 8.5). The models agreed that predicted distribution of kelp in the Eastern Canadian Arctic is likely to expand to more northern locations under future emissions scenarios, with the exception of the endemic arctic kelp L. solidungula, which is more likely to lose a significant proportion of suitable habitat. However, there were differences among species regarding predicted cover for both current and future projections. Notwithstanding model-specific variation, it is evident that kelps are widespread throughout the area and likely contribute significantly to the functioning of current Arctic ecosystems. Our results emphasize the importance of kelp in Arctic ecosystems and the underestimation of their potential distribution there.

Sea stars often function as keystone predators in food webs of intertidal and subtidal communities, especially in temperate and sub-polar regions. In South America the sea star Cosmasterias lurida is distributed along both the Atlantic and Pacific coasts of Patagonia and is one of the most conspicuous and abundant benthic predators in the shallow subtidal zone (<25 m). Its feeding strategy and prey selection are, however, still poorly known. This study describes the feeding behavior of C. lurida at a site in the Seno del Reloncaví (Chile), assessing its abundance, size and prey selection in the field relative to observed prey abundance and size along a bathymetric gradient. We hypothesized that C. lurida is a generalist predator, feeding on suitable prey according to their availability. However, we found that this predator only consumed a limited number (7 of 48) of potential prey species, primarily the slipper limpets Crepipatella spp. and the mussels Aulacomya ater and Mytilus chilensis . Electivity analysis revealed a clear preference for one mussel ( A. ater ) but not the other ( M. chilensis ) as well as depth-dependent selectivity for the slipper limpets, which changed from avoidance to preference with increasing depth. Sea star densities varied with depth, peaking between depths of 5 and 10 m, but the size of sea stars and the size of their prey did not vary significantly along a depth gradient. No significant correlations were found with the most commonly selected prey. These results would indicate that while this predator may be a generalist–opportunist, its feeding behavior is context-dependent and its high selectivity for certain species suggests that this sea star plays a key role structuring subtidal benthic communities in Patagonia.