Seafloor primary production in a changing Arctic Ocean.

Phytoplankton and sea ice algae are traditionally considered to be the main primary producers in the Arctic Ocean. In this Perspective, we explore the importance of benthic primary producers (BPPs) encompassing microalgae, macroalgae, and seagrasses, which represent a poorly quantified source of Arctic marine primary production. Despite scarce observations, models predict that BPPs are widespread, colonizing ~3 million km2 of the extensive Arctic coastal and shelf seas. Using a synthesis of published data and a novel model, we estimate that BPPs currently contribute ~77 Tg C y-1 of primary production to the Arctic, equivalent to ~20 to 35% of annual phytoplankton production. Macroalgae contribute ~43 Tg C y-1, seagrasses contribute ~23 Tg C y-1, and microalgae-dominated shelf habitats contribute ~11 to 16 Tg C y-1. Since 2003, the Arctic seafloor area exposed to sunlight has increased by ~47,000 km2 y-1, expanding the realm of BPPs in a warming Arctic. Increased macrophyte abundance and productivity is expected along Arctic coastlines with continued ocean warming and sea ice loss. However, microalgal benthic primary production has increased in only a few shelf regions despite substantial sea ice loss over the past 20 y, as higher solar irradiance in the ice-free ocean is counterbalanced by reduced water transparency. This suggests complex impacts of climate change on Arctic light availability and marine primary production. Despite significant knowledge gaps on Arctic BPPs, their widespread presence and obvious contribution to coastal and shelf ecosystem production call for further investigation and for their inclusion in Arctic ecosystem models and carbon budgets.

Kelp carbon sink potential decreases with warming due to accelerating decomposition.

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.

Temperature sensitivity of detrital photosynthesis.

BACKGROUND AND AIMS: Kelp forests are increasingly considered blue carbon habitats for ocean-based biological carbon dioxide removal, but knowledge gaps remain in our understanding of their carbon cycle. Of particular interest is the remineralization of detritus, which can remain photosynthetically active. Here, we study a widespread, thermotolerant kelp (Ecklonia radiata) to explore detrital photosynthesis as a mechanism underlying temperature and light as two key drivers of remineralization. METHODS: We used meta-analysis to constrain the thermal optimum (Topt) of E. radiata. Temperature and light were subsequently controlled over a 119-day ex situ decomposition experiment. Flow-through experimental tanks were kept in darkness at 15 °C or under a subcompensating maximal irradiance of 8 µmol photons m-2 s-1 at 15, 20 or 25 °C. Photosynthesis of laterals (analogues to leaves) was estimated using closed-chamber oxygen evolution in darkness and under a saturating irradiance of 420 µmol photons m-2 s-1. KEY RESULTS: T opt of E. radiata is 18 °C across performance variables (photosynthesis, growth, abundance, size, mass and fertility), life stages (gametophyte and sporophyte) and populations. Our models predict that a temperature of >15 °C reduces the potential for E. radiata detritus to be photosynthetically viable, hence detrital Topt ≤ 15 °C. Detritus is viable under subcompensating irradiance, where it performs better than in darkness. Comparison of net and gross photosynthesis indicates that elevated temperature primarily decreases detrital photosynthesis, whereas darkness primarily increases detrital respiration compared with optimal experimental conditions, in which detrital photosynthesis can persist for ≥119 days. CONCLUSIONS: T opt of kelp detritus is ≥3 °C colder than that of the intact plant. Given that E. radiata is one of the most temperature-tolerant kelps, this suggests that photosynthesis is generally more thermosensitive in the detrital phase, which partly explains the enhancing effect of temperature on remineralization. In contrast to darkness, even subcompensating irradiance maintains detrital viability, elucidating the accelerating effect of depth and its concomitant light reduction on remineralization to some extent. Detrital photosynthesis is a meaningful mechanism underlying at least two drivers of remineralization, even below the photoenvironment inhabited by the attached alga.

Marine protected areas can be useful but are not a silver bullet for kelp conservation.

Kelp forests are among the most valuable ecosystems on Earth, but they are increasingly being degraded and lost due to a range of human-related stressors, leading to recent calls for their improved management and conservation. One of the primary tools to conserve marine species and biodiversity is the establishment of marine protected areas (MPAs). International commitments to protect 30% of the world's ecosystems are gaining momentum, offering a promising avenue to secure kelp forests into the Anthropocene. However, a clear understanding of the efficacy of MPAs for conserving kelp forests in a changing ocean is lacking. In this perspective, we question whether strengthened global protection will create meaningful conservation outcomes for kelp forests. We explore the benefits of MPAs for kelp conservation under a suite of different stressors, focusing on empirical evidence from protected kelp forests. We show that MPAs can be effective against some drivers of kelp loss (e.g., overgrazing, kelp harvesting), particularly when they are maintained in the long-term and enforced as no-take areas. There is also some evidence that MPAs can reduce impacts of climate change through building resilience in multi-stressor situations. However, MPAs also often fail to provide protection against ocean warming, marine heatwaves, coastal darkening, and pollution, which have emerged as dominant drivers of kelp forest loss globally. Although well-enforced MPAs should remain an important tool to protect kelp forests, successful kelp conservation will require implementing an additional suite of management solutions that target these accelerating threats.

Whole genome population structure of North Atlantic kelp confirms high-latitude glacial refugia.

Coastal refugia during the Last Glacial Maximum (~21,000 years ago) have been hypothesized at high latitudes in the North Atlantic, suggesting marine populations persisted through cycles of glaciation and are potentially adapted to local environments. Here, whole-genome sequencing was used to test whether North Atlantic marine coastal populations of the kelp Alaria esculenta survived in the area of southwestern Greenland during the Last Glacial Maximum. We present the first annotated genome for A. esculenta and call variant positions in 54 individuals from populations in Atlantic Canada, Greenland, Faroe Islands, Norway and Ireland. Differentiation across populations was reflected in ~1.9 million single nucleotide polymorphisms, which further revealed mixed ancestry in the Faroe Islands individuals between putative Greenlandic and European lineages. Time-calibrated organellar phylogenies suggested Greenlandic populations were established during the last interglacial period more than 100,000 years ago, and that the Faroe Islands population was probably established following the Last Glacial Maximum. Patterns in population statistics, including nucleotide diversity, minor allele frequencies, heterozygosity and linkage disequilibrium decay, nonetheless suggested glaciation reduced Canadian Atlantic and Greenlandic populations to small effective sizes during the most recent glaciation. Functional differentiation was further reflected in exon read coverage, which revealed expansions unique to Greenland in 337 exons representing 162 genes, and a modest degree of exon loss (103 exons from 56 genes). Altogether, our genomic results provide strong evidence that A. esculenta populations were resilient to past climatic fluctuations related to glaciations and that high-latitude populations are potentially already adapted to local conditions as a result.

Arctic marine forest distribution models showcase potentially severe habitat losses for cryophilic species under climate change.

The Arctic is among the fastest-warming areas of the globe. Understanding the impact of climate change on foundational Arctic marine species is needed to provide insight on ecological resilience at high latitudes. Marine forests, the underwater seascapes formed by seaweeds, are predicted to expand their ranges further north in the Arctic in a warmer climate. Here, we investigated whether northern habitat gains will compensate for losses at the southern range edge by modelling marine forest distributions according to three distribution categories: cryophilic (species restricted to the Arctic environment), cryotolerant (species with broad environmental preferences inclusive but not limited to the Arctic environment), and cryophobic (species restricted to temperate conditions) marine forests. Using stacked MaxEnt models, we predicted the current extent of suitable habitat for contemporary and future marine forests under Representative Concentration Pathway Scenarios of increasing emissions (2.6, 4.5, 6.0, and 8.5). Our analyses indicate that cryophilic marine forests are already ubiquitous in the north, and thus cannot expand their range under climate change, resulting in an overall loss of habitat due to severe southern range contractions. The extent of marine forests within the Arctic basin, however, is predicted to remain largely stable under climate change with notable exceptions in some areas, particularly in the Canadian Archipelago. Succession may occur where cryophilic and cryotolerant species are extirpated at their southern range edge, resulting in ecosystem shifts towards temperate regimes at mid to high latitudes, though many aspects of these shifts, such as total biomass and depth range, remain to be field validated. Our results provide the first global synthesis of predicted changes to pan-Arctic coastal marine forest ecosystems under climate change and suggest ecosystem transitions are unavoidable now for some areas.

Habitat configurations shape the trophic and energetic dynamics of reef fishes in a tropical-temperate transition zone: implications under a warming future.

Understanding the extent to which species' traits mediate patterns of community assembly is key to predict the effect of natural and anthropogenic disturbances on ecosystem functioning. Here, we apply a trait-based community assembly framework to understand how four different habitat configurations (kelp forests, Sargassum spp. beds, hard corals, and turfs) shape the trophic and energetic dynamics of reef fish assemblages in a tropical-temperate transition zone. Specifically, we tested (i) the degree of trait divergence and convergence in each habitat, (ii) which traits explained variation in species' abundances, and (iii) differences in standing biomass (kg ha-1), secondary productivity (kg ha-1 day-1) and turnover (% day-1). Fish assemblages in coral and kelp habitats displayed greater evidence of trait convergence, while turf and Sargassum spp. habitats displayed a higher degree of trait divergence, a pattern that was mostly driven by traits related to resource use and thermal affinity. This filtering effect had an imprint on the trophic and energetic dynamics of reef fishes, with turf habitats supporting higher fish biomass and productivity. However, these gains were strongly dependent on trophic guild, with herbivores/detritivores disproportionately contributing to among-habitat differences. Despite these perceived overall gains, turnover was decoupled for fishes that act as conduit of energy to higher trophic levels (i.e. microinvertivores), with coral habitats displaying higher rates of fish biomass replenishment than turf despite their lower productivity. This has important implications for biodiversity conservation and fisheries management, questioning the long-term sustainability of ecological processes and fisheries yields in increasingly altered marine habitats.

Leveraging the blue economy to transform marine forest restoration.

The UN Decade of Ecosystem Restoration is a response to the urgent need to substantially accelerate and upscale ecological restoration to secure Earth's sustainable future. Globally, restoration commitments have focused overwhelmingly on terrestrial forests. In contrast, despite a strong value proposition, efforts to restore seaweed forests lag far behind other major ecosystems and continue to be dominated by small-scale, short-term academic experiments. However, seaweed forest restoration can match the scale of damage and threat if moved from academia into the hands of community groups, industry, and restoration practitioners. Connecting two rapidly growing sectors in the Blue Economy-seaweed cultivation and the restoration industry-can transform marine forest restoration into a commercial-scale enterprise that can make a significant contribution to global restoration efforts.

Homogenization and miniaturization of habitat structure in temperate marine forests.

Humans are rapidly transforming the structural configuration of the planet's ecosystems, but these changes and their ecological consequences remain poorly quantified in underwater habitats. Here, we show that the loss of forest-forming seaweeds and the rise of ground-covering 'turfs' across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Globally, turf seascapes occupied a smaller architectural trait space and were structurally more similar across regions than marine forests, evidencing habitat homogenization. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat architecture, as well as across disparate drivers of marine forest decline. Turf seascapes contained high sediment loads, with the miniaturization of habitat across 100s of km in mid-Western Australia resulting in reefs retaining an additional ~242 million tons of sediment (four orders of magnitude more than the sediments delivered fluvially annually). Together, this work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs.

Local flexibility in feeding behaviour and contrasting microhabitat use of an omnivore across latitudes.

As the environment is getting warmer and species are redistributed, consumers can be forced to adjust their interactions with available prey, and this could have cascading effects within food webs. To better understand the capacity for foraging flexibility, our study aimed to determine the diet variability of an ectotherm omnivore inhabiting kelp forests, the sea urchin Echinus esculentus, along its entire latitudinal distribution in the northeast Atlantic. Using a combination of gut content and stable isotope analyses, we determined the diet and trophic position of sea urchins at sites in Portugal (42° N), France (49° N), southern Norway (63° N), and northern Norway (70° N), and related these results to the local abundance and distribution of putative food items. With mean estimated trophic levels ranging from 2.4 to 4.6, omnivory and diet varied substantially within and between sites but not across latitudes. Diet composition generally reflected prey availability within epiphyte or understorey assemblages, with local affinities demonstrating that the sea urchin adjusts its foraging to match the small-scale distribution of food items. A net "preference" for epiphytic food sources was found in northern Norway, where understorey food was limited compared to other regions. We conclude that diet change may occur in response to food source redistribution at multiple spatial scales (microhabitats, sites, regions). Across these scales, the way that key consumers alter their foraging in response to food availability can have important implication for food web dynamics and ecosystem functions along current and future environmental gradients.

Whole-genome sequencing reveals forgotten lineages and recurrent hybridizations within the kelp genus Alaria (Phaeophyceae).

The genomic era continues to revolutionize our understanding of the evolution of biodiversity. In phycology, emphasis remains on assembling nuclear and organellar genomes, leaving the full potential of genomic datasets to answer long-standing questions about the evolution of biodiversity largely unexplored. Here, we used whole-genome sequencing (WGS) datasets to survey species diversity in the kelp genus Alaria, compare phylogenetic signals across organellar and nuclear genomes, and specifically test whether phylogenies behave like trees or networks. Genomes were sequenced from across the global distribution of Alaria (including Alaria crassifolia, A. praelonga, A. crispa, A. marginata, and A. esculenta), representing over 550 GB of data and over 2.2 billion paired reads. Genomic datasets retrieved 3,814 and 4,536 single-nucleotide polymorphisms (SNPs) for mitochondrial and chloroplast genomes, respectively, and upwards of 148,542 high-quality nuclear SNPs. WGS revealed an Arctic lineage of Alaria, which we hypothesize represents the synonymized taxon A. grandifolia. The SNP datasets also revealed inconsistent topologies across genomic compartments, and hybridization (i.e., phylogenetic networks) between Pacific A. praelonga, A. crispa, and putative A. grandifolia, and between some lineages of the A. marginata complex. Our analysis demonstrates the potential for WGS data to advance our understanding of evolution and biodiversity beyond amplicon sequencing, and that hybridization is potentially an important mechanism contributing to novel lineages within Alaria. We also emphasize the importance of surveying phylogenetic signals across organellar and nuclear genomes, such that models of mixed ancestry become integrated into our evolutionary and taxonomic understanding.

Carbon export is facilitated by sea urchins transforming kelp detritus.

With the increasing imperative for societies to act to curb climate change by increasing carbon stores and sinks, it has become critical to understand how organic carbon is produced, released, transformed, transported, and sequestered within and across ecosystems. In freshwater and open-ocean systems, shredders play a significant and well-known role in transforming and mobilizing carbon, but their role in the carbon cycle of coastal ecosystems is largely unknown. Marine plants such as kelps produce vast amounts of detritus, which can be captured and consumed by shedders as it traverses the seafloor. We measured capture and consumption rates of kelp detritus by sea urchins across four sampling periods and over a range of kelp detritus production rates and sea urchin densities, in northern Norway. When sea urchin densities exceeded 4 m-2, the sea urchins captured and consumed a high percentage (ca. 80%) of kelp detritus on shallow reefs. We calculated that between 1.3 and 10.8 kg of kelp m-2 are shredded annually from these reefs. We used a hydrodynamic dispersal model to show that transformation of kelp blades to sea urchin feces increased its export distance fourfold. Our findings show that sea urchins can accelerate and extend the export of carbon to neighboring areas. This collector-shredder pathway could represent a significant flow of small particulate carbon from kelp forests to deep-sea areas, where it can subsidize benthic communities or contribute to the global carbon sink.

Detrital carbon production and export in high latitude kelp forests.

The production and fate of seaweed detritus is a major unknown in the global C-budget. Knowing the quantity of detritus produced, the form it takes (size) and its timing of delivery are key to understanding its role as a resource subsidy to secondary production and/or its potential contribution to C-sequestration. We quantified the production and release of detritus from 10 Laminaria hyperborea sites in northern Norway (69.6° N). Kelp biomass averaged 770 ± 100 g C m-2 while net production reached 499 ± 50 g C m-2 year-1, with most taking place in spring when new blades were formed. Production of biomass was balanced by a similar formation of detritus (478 ± 41 g C m-2 year-1), and both were unrelated to wave exposure when compared across sites. Distal blade erosion accounted for 23% of the total detritus production and was highest during autumn and winter, while dislodgment of whole individuals and/or whole blades corresponded to 24% of the detritus production. Detachment of old blades constituted the largest source of kelp detritus, accounting for > 50% of the total detrital production. Almost 80% of the detritus from L. hyperborea was thus in the form of whole plants or blades and > 60% of that was delivered as a large pulse within 1-2 months in spring. The discrete nature of the delivery suggests that the detritus cannot be retained and consumed locally and that some is exported to adjacent deep areas where it may subsidize secondary production or become buried into deep marine sediments as blue carbon.

Movement of pulsed resource subsidies from kelp forests to deep fjords.

Resource subsidies in the form of allochthonous primary production drive secondary production in many ecosystems, often sustaining diversity and overall productivity. Despite their importance in structuring marine communities, there is little understanding of how subsidies move through juxtaposed habitats and into recipient communities. We investigated the transport of detritus from kelp forests to a deep Arctic fjord (northern Norway). We quantified the seasonal abundance and size structure of kelp detritus in shallow subtidal (0‒12 m), deep subtidal (12‒85 m), and deep fjord (400‒450 m) habitats using a combination of camera surveys, dive observations, and detritus collections over 1 year. Detritus formed dense accumulations in habitats adjacent to kelp forests, and the timing of depositions coincided with the discrete loss of whole kelp blades during spring. We tracked these blades through the deep subtidal and into the deep fjord, and showed they act as a short-term resource pulse transported over several weeks. In deep subtidal regions, detritus consisted mostly of fragments and its depth distribution was similar across seasons (50% of total observations). Tagged pieces of detritus moved slowly out of kelp forests (displaced 4‒50 m (mean 11.8 m ± 8.5 SD) in 11‒17 days, based on minimum estimates from recovered pieces), and most (75%) variability in the rate of export was related to wave exposure and substrate. Tight resource coupling between kelp forests and deep fjords indicate that changes in kelp abundance would propagate through to deep fjord ecosystems, with likely consequences for the ecosystem functioning and services they provide.

The present is the key to the past: linking regime shifts in kelp beds to the distribution of deep-living sea urchins.

Understanding processes that drive sudden shifts in ecosystem structure and function has become an important research focus for coastal management. In kelp bed ecosystems, regime shifts occur when high densities of sea urchins destructively graze kelp and create coralline algal barrens. While the importance of predation and disease in mediating shifts between kelp beds and barrens on shallow rocky reefs has been well documented, little is known about the role of deep-living urchins in these alternative stable-state dynamics. In this study, we test the hypothesis that deep-living urchins along the central Atlantic coast of Nova Scotia move onshore and trigger shifts from kelp beds to barrens on shallow rocky reefs. We documented urchin distribution and abundance using tow-camera surveys down to 140 m depth and spanning 140 km of coast and created a predictive species-distribution model using these observations and spatial data on environmental factors that likely delineate suitable habitat for urchins. We used a random forest model to generate our predictions, which correctly classified 91% of observations into a positive or negative occurrence of urchins. Sea urchins predominantly occurred within 1.5 km of shore, in depressions and flat habitats between 40 and 85 m depth. We found that shallow regions where destructive grazing fronts have been documented over the past four decades were closer to deep-living sea urchin habitats compared to regions that remained in a kelp bed state during the same period. This supports our prediction that deep-living urchins play an important role in driving shallow regime shift dynamics, and indicates that their distribution can help identify areas of coast that are most vulnerable to a collapse to barrens.

Carbon removal and climate change mitigation by seaweed farming: A state of knowledge review.

The pressing need to mitigate the effects of climate change is driving the development of novel approaches for carbon dioxide removal (CDR) from the atmosphere, with the ocean playing a central role in the portfolio of solutions. The expansion of seaweed farming is increasingly considered as one of the potential CDR avenues among government and private sectors. Yet, comprehensive assessments examining whether farming can lead to tangible climate change mitigation remain limited. Here we examine the results of over 100 publications to synthesize evidence regarding the CDR capacity of seaweed farms and review the different interventions through which an expansion of seaweed farming may contribute to climate change mitigation. We find that presently, the majority of the carbon fixed by seaweeds is stored in short-term carbon reservoirs (e.g., seaweed products) and that only a minority of the carbon ends up in long-term reservoirs that are likely to fit within existing international accounting frameworks (e.g., marine sediments). Additionally, the tiny global area cultivated to date (0.06 % of the estimated wild seaweed extent) limits the global role of seaweed farming in climate change mitigation in the present and mid-term future. A first-order estimate using the best available data suggests that, at present, even in a low emissions scenario, any carbon removal capacity provided by seaweed farms globally is likely to be offset by their emissions (median global balance net emitter: -0.11 Tg C yr-1; range -2.07-1.95 Tg C yr-1), as most of a seaweed farms' energy and materials currently depend on fossil fuels. Enhancing any potential CDR though seaweed farming will thus require decarbonizing of supply chains, directing harvested biomass to long-term carbon storage products, expanding farming outside traditional cultivation areas, and developing robust models tracing the fate of seaweed carbon. This will present novel scientific (e.g., verifying permanence of seaweed carbon), engineering (e.g., developing farms in wave exposed areas), and economic challenges (e.g., increase market demand, lower costs, decarbonize at scale), many of which are only beginning to be addressed.

Substantial kelp detritus exported beyond the continental shelf by dense shelf water transport.

Kelp forests may contribute substantially to ocean carbon sequestration, mainly through transporting kelp carbon away from the coast and into the deep sea. However, it is not clear if and how kelp detritus is transported across the continental shelf. Dense shelf water transport (DSWT) is associated with offshore flows along the seabed and provides an effective mechanism for cross-shelf transport. In this study, we determine how effective DSWT is in exporting kelp detritus beyond the continental shelf edge, by considering the transport of simulated sinking kelp detritus from a region of Australia's Great Southern Reef. We show that DSWT is the main mechanism that transports simulated kelp detritus past the continental shelf edge, and that export is negligible when DSWT does not occur. We find that 51% per year of simulated kelp detritus is transported past the continental shelf edge, or 17-29% when accounting for decomposition while in transit across the shelf. This is substantially more than initial global estimates. Because DSWT occurs in many mid-latitude locations around the world, where kelp forests are also most productive, export of kelp carbon from the coast could be considerably larger than initially expected.

Impacts of Climate Change on Marine Foundation Species.

Marine foundation species are the biotic basis for many of the world's coastal ecosystems, providing structural habitat, food, and protection for myriad plants and animals as well as many ecosystem services. However, climate change poses a significant threat to foundation species and the ecosystems they support. We review the impacts of climate change on common marine foundation species, including corals, kelps, seagrasses, salt marsh plants, mangroves, and bivalves. It is evident that marine foundation species have already been severely impacted by several climate change drivers, often through interactive effects with other human stressors, such as pollution, overfishing, and coastal development. Despite considerable variation in geographical, environmental, and ecological contexts, direct and indirect effects of gradual warming and subsequent heatwaves have emerged as the most pervasive drivers of observed impact and potent threat across all marine foundation species, but effects from sea level rise, ocean acidification, and increased storminess are expected to increase. Documented impacts include changes in the genetic structures, physiology, abundance, and distribution of the foundation species themselves and changes to their interactions with other species, with flow-on effects to associated communities, biodiversity, and ecosystem functioning. We discuss strategies to support marine foundation species into the Anthropocene, in order to increase their resilience and ensure the persistence of the ecosystem services they provide.

Global impacts of marine heatwaves on coastal foundation species.

With increasingly intense marine heatwaves affecting nearshore regions, foundation species are coming under increasing stress. To better understand their impacts, we examine responses of critical, habitat-forming foundation species (macroalgae, seagrass, corals) to marine heatwaves in 1322 shallow coastal areas located across 85 marine ecoregions. We find compelling evidence that intense, summer marine heatwaves play a significant role in the decline of foundation species globally. Critically, detrimental effects increase towards species warm-range edges and over time. We also identify several ecoregions where foundation species don't respond to marine heatwaves, suggestive of some resilience to warming events. Cumulative marine heatwave intensity, absolute temperature, and location within a species' range are key factors mediating impacts. Our results suggest many coastal ecosystems are losing foundation species, potentially impacting associated biodiversity, ecological function, and ecosystem services provision. Understanding relationships between marine heatwaves and foundation species offers the potential to predict impacts that are critical for developing management and adaptation approaches.