EFFECTS OF CLIMATE CHANGE ON GLOBAL SEAWEED COMMUNITIES

30 years revisit survey for long-term changes in the Antarctic subtidal algal assemblage

A long-term change of a subtidal macroalgal assemblage has been investigated in Maxwell Bay, King George Island (KGI) of the Antarctic coast by a revisit survey after 30 years. Field surveys were done by SCUBA diving at six sites in 2016–2018 to directly compare with the previous survey conducted in 1988–1993 at the same sites. The total number of macroalgal species was similar between the previous and the present survey, 25 and 27 species respectively. However, the macroalgal assemblage changed substantially with the average similarity of 48.2% between the two surveys. Also, the species-level abundance showed a high variability between surveys. On the other hand, over the 30 years interval there was little overall change at the between-site level hierarchical structure in the subtidal communities of Maxwell Bay. The sites near the penguin rookery consistently showed the highest biodiversity, indicating the importance of land-based nutrients input in Antarctic coastal habitats. A noticeable pattern change over 30 years was the increase of Desmarestia complex and Plocamium cartilagineum and the decrease of Himantothallus grandifolius. Both groups are still dominant, but the shift from Himantothallus to Desmarestia-Plocamium may reflects temperature rise on the Maxwell Bay coast compared to the past.

Nitrogen sufficiency enhances thermal tolerance in habitat-forming kelp: implications for acclimation under thermal stress

Local and global changes associated with anthropogenic activities are impacting marine and terrestrial ecosystems. Macroalgae, especially habitat-forming species like kelp, play critical roles in temperate coastal ecosystems. However, their abundance and distribution patterns have been negatively affected by warming in many regions around the globe. Along with global change, coastal ecosystems are also impacted by local drivers such as eutrophication. The interaction between global and local drivers might modulate kelp responses to environmental change. This study examines the regulatory effect of NO₃⁻ on the thermal plasticity of the giant kelp Macrocystis pyrifera. To do this, thermal performance curves (TPCs) of key temperature-dependant traits–growth, photosynthesis, NO₃⁻ assimilation and chlorophyll a fluorescence–were examined under nitrate replete and deplete conditions in a short-term incubation. We found that thermal plasticity was modulated by NO₃⁻ but different thermal responses were observed among traits. Our study reveals that nitrogen, a local driver, modulates kelp responses to high seawater temperatures, ameliorating the negative impacts on physiological performance (i.e. growth and photosynthesis). However, this effect might be species-specific and vary among biogeographic regions – thus, further work is needed to determine the generality of our findings to other key temperate macroalgae that are experiencing temperatures close to their thermal tolerance due to climate change.

Macroalgal germplasm banking for conservation, food security, and industry

Ex situ seed banking was first conceptualized and implemented in the early 20th century to maintain and protect crop lines. Today, ex situ seed banking is important for the preservation of heirloom strains, biodiversity conservation and ecosystem restoration, and diverse research applications. However, these efforts primarily target microalgae and terrestrial plants. Although some collections include macroalgae (i.e., seaweeds), they are relatively few and have yet to be connected via any international, coordinated initiative. In this piece, we provide a brief introduction to macroalgal germplasm banking and its application to conservation, industry, and mariculture. We argue that concerted effort should be made globally in germline preservation of marine algal species via germplasm banking with an overview of the technical advances for feasibility and ensured success.

Seaweed germplasm banking is an important resource for biodiversity conservation, human food security, and industry innovation. This Perspective article maintains that an international, coordinative initiative is needed to fully develop and capitalize on this resource.

Photosynthetic Responses of Turf-forming Red Macroalgae to High CO2 Conditions

Seaweeds are important components of near-shore ecosystems as primary producers, foundation species, and biogeochemical engineers. Seaweed communities are likely to alter under predicted climate change scenarios. We tested the physiological responses of three perennial, turf-building, intertidal rhodophytes, Mastocarpus stellatus, Osmundea pinnatifida, and the calcified Ellisolandia elongata, to elevated pCO₂ over 6 weeks. Responses varied between these three species. E. elongata was strongly affected by high pCO₂ , whereas non-calcified species were not. Elevated pCO₂ did not induce consistent responses of photosynthesis and respiration across these three species. While baseline photophysiology differed significantly between species, we found few clear effects of elevated pCO₂ on this aspect of macroalgal physiology. We found effects of within-species variation in elevated pCO₂ response in M. stellatus, but not in the other species. Overall, our data confirm the sensitivity of calcified macroalgae to elevated pCO₂ , but we found no evidence suggesting that elevated pCO₂ conditions will have a strong positive or negative impact on photosynthetic parameters in non-calcified macroalgae.

Impacts of ocean warming on kelp forest ecosystems

Kelp forests represent some of the most diverse and productive habitats on Earth, and provide a range of ecosystem goods and services on which human populations depend. As the distribution and ecophysiology of kelp species is strongly influenced by temperature, recent warming trends in many regions have been linked with concurrent changes in kelp populations, communities and ecosystems. Over the past decade, the number of reports of ocean warming impacts on kelp forests has risen sharply. Here, I synthesise recent studies to highlight general patterns and trends. While kelp responses to climate change vary greatly between ocean basins, regions and species, there is compelling evidence to show that ocean warming poses an unequivocal threat to the persistence and integrity of kelp forest ecosystems in coming decades.

Gene regulatory response to hyposalinity in the brown seaweed Fucus vesiculosus

BACKGROUND

Rockweeds are among the most important foundation species of temperate rocky littoral shores. In the Baltic Sea, the rockweed Fucus vesiculosus is distributed along a decreasing salinity gradient from the North Atlantic entrance to the low-salinity regions in the north-eastern margins, thus, demonstrating a remarkable tolerance to hyposalinity. The underlying mechanisms for this tolerance are still poorly understood. Here, we exposed F. vesiculosus from two range-margin populations to the hyposaline (2.5 PSU - practical salinity unit) conditions that are projected to occur in the region by the end of this century as a result of climate change. We used transcriptome analysis (RNA-seq) to determine the gene expression patterns associated with hyposalinity acclimation, and examined the variation in these patterns between the sampled populations.

RESULTS

Hyposalinity induced different responses in the two populations: in one, only 26 genes were differentially expressed between salinity treatments, while the other population demonstrated up- or downregulation in 3072 genes. In the latter population, the projected future hyposalinity induced an acute response in terms of antioxidant production. Genes associated with membrane composition and structure were also heavily involved, with the upregulation of fatty acid and actin production, and the downregulation of ion channels and alginate pathways. Changes in gene expression patterns clearly indicated an inhibition of the photosynthetic machinery, with a consequent downregulation of carbohydrate production. Simultaneously, energy consumption increased, as revealed by the upregulation of genes associated with respiration and ATP synthesis. Overall, the genes that demonstrated the largest increase in expression were ribosomal proteins involved in translation pathways. The fixation rate of SNP:s was higher within genes responding to hyposalinity than elsewhere in the transcriptome.

CONCLUSIONS

The high fixation rate in the genes coding for salinity acclimation mechanisms implies strong selection for them. The among-population differentiation that we observed in the transcriptomic response to hyposalinity stress suggests that populations of F. vesiculosus may differ in their tolerance to future desalination, possibly as a result of local adaptation to salinity conditions within the Baltic Sea. These results emphasise the importance of considering interspecific genetic variation when evaluating the consequences of environmental change.

Health Functionality and Quality Control of Laver (Porphyra, Pyropia): Current Issues and Future Perspectives as an Edible Seaweed

The growing interest in laver as a food product and as a source of substances beneficial to health has led to global consumer demand for laver produced in a limited area of northeastern Asia. Here we review research into the benefits of laver consumption and discuss future perspectives on the improvement of laver product quality. Variation in nutritional/functional values among product types (raw and processed (dried, roasted, or seasoned) laver) makes product-specific nutritional analysis a prerequisite for accurate prediction of health benefits. The effects of drying, roasting, and seasoning on the contents of both beneficial and harmful substances highlight the importance of managing laver processing conditions. Most research into health benefits has focused on substances present at high concentrations in laver (porphyran, Vitamin B12, taurine), with assessment of the expected effects of laver consumption. Mitigation of chemical/microbiological risks and the adoption of novel technologies to exploit under-reported biochemical characteristics of lavers are suggested as key strategies for the further improvement of laver product quality. Comprehensive analysis of the literature regarding laver as a food product and as a source of biomedical compounds highlights the possibilities and challenges for application of laver products.

Thermal plasticity is independent of environmental history in an intertidal seaweed

Organisms inhabiting the intertidal zone have been used to study natural ecophysiological responses and adaptations to thermal stress because these organisms are routinely exposed to high-temperature conditions for hours at a time. While intertidal organisms may be inherently better at withstanding temperature stress due to regular exposure and acclimation, they could be more vulnerable to temperature stress, already living near the edge of their thermal limits. Strong gradients in thermal stress across the intertidal zone present an opportunity to test whether thermal tolerance is a plastic or canalized trait in intertidal organisms. Here, we studied the intertidal pool-dwelling calcified alga, Ellisolandia elongata, under near-future temperature regimes, and the dependence of its thermal acclimatization response on environmental history. Two timescales of environmental history were tested during this experiment. The intertidal pool of origin was representative of long-term environmental history over the alga's life (including settlement and development), while the pool it was transplanted into accounted for recent environmental history (acclimation over many months). Unexpectedly, neither long-term nor short-term environmental history, nor ambient conditions, affected photosynthetic rates in E. elongata. Individuals were plastic in their photosynthetic response to laboratory temperature treatments (mean 13.2°C, 15.7°C, and 17.7°C). Further, replicate ramets from the same individual were not always consistent in their photosynthetic performance from one experimental time point to another or between treatments and exhibited no clear trend in variability over experimental time. High variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level over time.

Cellular Responses of Gelidium floridanum (Gelidiales, Rhodophyta) Tetraspores Under Heat Wave and Copper Pollution

Spore settlement and development are bottlenecks for resilience of habitat-forming macroalgal species. These processes are directly related to temperature, a global stressor protagonist of ocean warming. The toxic effects of local pollutants such as copper may be worsened under a global warming scenario. Therefore, in this paper, we investigated the effects of increased temperature combined with elevated concentrations of copper on the viability, photosynthetic pigments, and ultrastructure of Gelidium floridanum tetraspores. Tetraspores were cultivated on slides with sterilized seawater or seawater enriched with CuCl₂ , and incubated under 24°C or 30°C for 24 h. Tetraspores cultivated with copper 3.0 μM under 30°C had lower viability. Both temperature and copper had a significant effect on phycocyanin and phycoerythrin concentrations. Samples cultivated with copper under 30°C presented a heavily altered cellular structure, with vesicles throughout the cytoplasm, chloroplasts with altered structure and cells with degenerated cytoplasm and cell walls. Our findings show that temperature and copper significantly affect the viability, photosynthetic pigments, and ultrastructure of G. floridanum tetraspores, presenting an additive interaction for the physiology of this seaweed's early stages.

The Screening and Evaluation of Fucus serratus and Fucus vesiculosus Extracts against Current Strains of MRSA Isolated from a Clinical Hospital Setting

Antimicrobial resistant strains of infection are afflicting clinical settings, driving the search for novel antimicrobial compounds. Naturally sourced bioactives, for instance those from seaweeds, have the potential to ameliorate this issue. As such, solvent extracts from the edible Irish seaweeds Fucus serratus and Fucus vesiculosus were screened for antimicrobial activity against 28 clinically isolated strains of MRSA, including one GISA (glycopeptide intermediate S. aureus) and two mecC gene containing strains. The water extract of F. vesiculosus was the most promising extract went on to be tested for biofilm prevention and disruption activity. The disk diffusion method was used to investigate the inhibition of the bacterial pathogens tested while MIC, MBC and biofilm disruption and prevention analyses were performed spectroscopically and by plate counts, respectively. Solvent extracts were found to have a wide array of antimicrobial activity against the strains tested, with the water extract from Fucus vesiculosus being the most promising. This extract was also found to both prevent and disrupt MRSA biofilms indicating the potential extract as new antimicrobials, and raising the possibility of their possible use in therapeutics.

Current Trends on Seaweeds: Looking at Chemical Composition, Phytopharmacology, and Cosmetic Applications

Seaweeds have received huge interest in recent years given their promising potentialities. Their antioxidant, anti-inflammatory, antitumor, hypolipemic, and anticoagulant effects are among the most renowned and studied bioactivities so far, and these effects have been increasingly associated with their content and richness in both primary and secondary metabolites. Although primary metabolites have a pivotal importance such as their content in polysaccharides (fucoidans, agars, carragenans, ulvans, alginates, and laminarin), recent data have shown that the content in some secondary metabolites largely determines the effective bioactive potential of seaweeds. Among these secondary metabolites, phenolic compounds feature prominently. The present review provides the most remarkable insights into seaweed research, specifically addressing its chemical composition, phytopharmacology, and cosmetic applications.

Unexpected nutrient influence on the thermal ecophysiology of seaweeds that recently followed opposite abundance shifts

World's oceans are warming, and recent studies suggest that the Iberian upwelling system may be weakening. To understand the potential consequences of both trends, six intertidal seaweeds that recently followed opposite upward and downward abundance shifts in the Iberian upwelling region were exposed for six weeks to conditions simulating present and warmed scenarios, combined with nutrient treatments emulating the influence and absence of the upwelling. Unlike expectations, a high nutrient supply did not ameliorate the effects of warming. Instead, warming slowed down growth in four seaweeds and accelerated the photosynthesis of downward seaweeds only if nutrients were abundant. In a weakened upwelling scenario, nutrient limitation might more strongly influence the performance of both upward and downward seaweeds than warming. With a normally functioning upwelling, warming might be more detrimental to the performance of some downward seaweeds as they might would lose their ability to benefit from the extra nutrient input.

Ecological feedbacks stabilize a turf-dominated ecosystem at the southern extent of kelp forests in the Northwest Atlantic

Temperate marine ecosystems globally are undergoing regime shifts from dominance by habitat-forming kelps to dominance by opportunistic algal turfs. While the environmental drivers of shifts to turf are generally well-documented, the feedback mechanisms that stabilize novel turf-dominated ecosystems remain poorly resolved. Here, we document a decline of kelp Saccharina latissima between 1980 and 2018 at sites at the southernmost extent of kelp forests in the Northwest Atlantic and their replacement by algal turf. We examined the drivers of a shift to turf and feedback mechanisms that stabilize turf reefs. Kelp replacement by turf was linked to a significant multi-decadal increase in sea temperature above an upper thermal threshold for kelp survival. In the turf-dominated ecosystem, 45% of S. latissima were attached to algal turf rather than rocky substrate due to preemption of space. Turf-attached kelp required significantly (2 to 4 times) less force to detach from the substrate, with an attendant pattern of lower survival following 2 major wave events as compared to rock-attached kelp. Turf-attached kelp allocated a significantly greater percentage of their biomass to the anchoring structure (holdfast), with a consequent energetic trade-off of slower growth. The results indicate a shift in community dominance from kelp to turf driven by thermal stress and stabilized by ecological feedbacks of lower survival and slower growth of kelp recruited to turf.

Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming

Ocean acidification and warming represent major environmental threats to kelp mariculture. In this study, sporophytic photochemical efficiency and gametophytic growth of Saccharina japonica and Undaria pinnatifida were evaluated under different pCO2 levels (360, 720, and 980 ppmv) and temperatures (5, 10, 15, and 20 °C for sporophytes; 15 and 20 °C for gametophytes). Sporophytic photochemical efficiencies of both kelps were significantly greater at 720 ppmv than at 360 and 980 ppmv. Female gametophytes of both kelps grew significantly better at 360 ppmv than at higher pCO2 levels. The growth of U. pinnatifida gametophytes was significantly greater at 20 °C than at 15 °C, while no significant difference was observed for the growth of S. japonica. These results indicate that increased pCO2 stimulated sporophytic photochemical efficiency while inhibited gametophytic growth of these kelps, which might negatively affect their seedling cultivation. U. pinnatifida exhibited higher productivity in warmer ocean than S. japonica.

Environmental modulation of the proteomic profiles from closely phylogenetically related populations of the red seaweed Plocamium brasiliense

The genus Plocamium encompasses seaweeds that are widely distributed throughout the world’s oceans, with Plocamium brasiliense found along the tropical and subtropical coasts of the Western Atlantic. This wide distribution can lead to structured populations due to environmental differences (e.g., light levels or temperature), restricted gene flow, and the presence of cryptic species. Abiotic variation can also affect gene expression, which consequently leads to differences in the seaweeds protein profile. This study aimed to analyze the genetic and proteomic profiles of P. brasiliense sampled in two geographically distinct sites on the coastline of Rio de Janeiro state, Brazil: Arraial do Cabo (P1) and Búzios (P2). The genetic profiles of macroalgal specimens from these two sites were indistinguishable as assessed by the markers UPA/23S, rbcL, and COI-5P; however, the protein profiles varied significantly between populations from the two sites. At both sites the ribulose-1,5-biphosphate carboxylase/oxygenase was the most abundant protein found in P. brasiliense specimens. The number of phycobiliproteins differed between both sites with the highest numbers being found at P1, possibly due to water depth. The differences in proteomic profiles of the two nearly identical populations of P. brasiliense suggest that environmental parameters such as light availability and desiccation might induce distinct protein expression, probably as a result of the phenotypic plasticity within this population of seaweed.

Individuality in seaweeds and why we need to care

Documenting the causes and consequences of intraspecific variation forms the foundation of much of evolutionary ecology. In this Perspectives piece, we review the importance of individual variation in ecology and evolution, argue that contemporary phycology often overlooks this foundational biological unit, and highlight how this lack of attention has potentially constrained our understanding of seaweeds. We then provide some suggestions of promising but underrepresented approaches, for instance: conducting more studies and analyses at the level of the individual; designing studies to evaluate heritability and genetic regulation of traits; and measuring associations between individual variation in functional traits and ecological outcomes. We close by highlighting areas of phycological research (e.g., population biology, ecology, aquaculture, climate change management) that could benefit immediately from including a focus on individual variation. Algae, for their part, provide us with a powerful and diverse set of ecological and evolutionary traits to explore these topics. There is much to be discovered.

Negative effects of warming on seagrass seedlings are not exacerbated by invasive algae

The observed and projected rise in sea surface temperature challenges marine biodiversity worldwide, and particularly in temperate ecosystems dealing with the arrival of novel species of tropical provenance. When the impacted biota are early life stages of ecosystem engineers, the effects of those impacts are of major concern for ecologists and coastal managers. We experimentally examined the individual and potential additive effects of seawater warming and the presence of the invasive algae on the development of seedlings of the seagrass Posidonia oceanica in a three-month mesocosm experiment. Whereas the presence of the invasive algae (Caulerpa cylindracea and Lophocladia lallemandii) did not result in detrimental effects on seedlings, warming negatively affected seedling development. Interestingly, the presence of both invasive algae may ameliorate the negative effects of warming.

Seasonal and spatial variation in photosynthetic response of the kelp Ecklonia radiata across a turbidity gradient

Understanding the photoacclimation response of macroalgae across broad spatial and temporal scales is necessary for predicting their vulnerability to environmental changes and quantifying their contribution to coastal primary production. This study investigated how the photosynthesis-irradiance response and photosynthetic pigment content of the kelp Ecklonia radiata varies both spatially and seasonally among seven sites located across a turbidity gradient in the Hauraki Gulf, north-eastern New Zealand. Photosynthesis-irradiance curves were derived under laboratory conditions for whole adult E. radiata using photorespirometry chambers. Lab-derived photosynthesis-irradiance curves in summer were also compared with in situ measurements made on kelp at each of the seven study sites. Photosynthetic parameters and pigments showed clear seasonal patterns across all sites as demonstrated by higher photosynthetic pigment levels and photosynthetic efficiency occurring in autumn and winter, and higher maximum rates of photosynthesis and respiration occurring in summer. Lamina biomass was similar across sites, yet thalli exhibited a clear photokinetic response to increasing turbidity. At turbid sites photosynthetic pigment levels and photosynthetic efficiency was higher, and respiration and saturation and compensation irradiances lower, compared to high-light sites. The results presented here further our understanding of low-light acclimation strategies in kelp and highlight the degree of seasonality in photosynthetic parameters. Though E. radiata demonstrates a clear capacity to photoacclimate to a degrading light environment, further research is needed to investigate the extent to which the observed acclimation can offset the likely negative effects of increasing turbidity on kelp forest primary production.

Phylogeographic diversification and postglacial range dynamics shed light on the conservation of the kelp Saccharina japonica

Studies of postglacial range shifts could enhance our understanding of seaweed species' responses to climate change and hence facilitate the conservation of natural resources. However, the distribution dynamics and phylogeographic diversification of the commercially and ecologically important kelp Saccharina japonica in the Northwest Pacific (NWP) are still poorly surveyed. In this study, we analyzed the evolutionary history of S. japonica using two mitochondrial markers and 24 nuclear microsatellites. A STRUCTURE analysis revealed two partially isolated lineages: lineage H, which is scattered along the coast of Japan; and lineage P, which occurs along the west coast of the Japan Sea. Ecological niche modeling projections to the Last Glacial Maximum (LGM) revealed that the southern coasts of the Japan Sea and the Pacific side of the Oshima and Honshu Peninsulas provided the most suitable habitats for S. japonica, implying that these regions served as ancient refugia during the LGM. Ancient isolation in different refugia may explain the observed divergence between lineages P and H. An approximate Bayesian computation analysis indicated that the two lineages experienced post-LGM range expansion and that postglacial secondary contact occurred in Sakhalin. Model projections into the year 2,100 predicted that S. japonica will shift northwards and lose its genetic diversity center on the Oshima Peninsula in Hokkaido and Shimokita Peninsula in Honshu. The range shifts and evolutionary history of S. japonica improve our understanding of how climate change impacted the distribution range and diversity of this species and provide useful information for the conservation of natural resources under ongoing environmental change in the NWP.

Removal of intertidal grazers by human harvesting leads to alteration of species interactions, community structure and resilience to climate change

Extreme fluctuations in abiotic conditions can induce a biological stress response (e.g. bleaching) detrimental to an organism's health. In some instances, organisms can recover if conditions are alleviated, such as through co-occurrence with other species that confer protection. Biodiverse, multitrophic communities are increasingly recognised as important promoters of species persistence and resilience under environmental change. On intertidal shores, the role of grazers as top-down determinants of algal community structure is well recognised. Similarly, the harvesting of grazers for human consumption is increasingly prevalent with potential to greatly alter the community dynamics. Here, we assess how differences in harvesting pressure of grazers under three management regimes (no-take; managed access; open-access) alters the trophic interactions between grazers, and algal communities. Grazer density and body size frequencies were different among regimes leading to changes in the photosynthetic performance and recovery of crustose coralline algae (CCA) post-bleaching, as well as their presence altering the strength of interactions between species. The exclusion of grazers from patches using cages led to different emergent communities and reduced negative correlations between taxa. The absence of larger grazers (>9 cm) at the managed access site led to macroalgal overgrowth of bleached CCA negatively affecting its recovery, whereas no-take or open-access led to a moderated algal growth and a shift from competitive to facilitative interactions between algal species. Given that CCA play an important role in the population growth and development of other species, the choice of management measure should be carefully considered before implementation, depending on objectives.

Recruitment tolerance to increased temperature present across multiple kelp clades

Kelp systems dominate nearshore marine environments in upwelling zones characterized by cold temperatures and high nutrients. Worldwide, kelp population persistence and recruitment success generally decreases with rising water temperatures coupled with low nutrients, making kelp populations vulnerable to impending warming of the oceans. This response to climate change at a global scale, however, may vary due to regional differences in temperature variability, acclimation, and differential responses of kelp species to changing conditions. Culture experiments were conducted on 12 eastern Pacific kelp taxa across geographic regions (British Columbia, central California, and southern California) under three nitrate levels (1, 5, and 10 μmol/L) and two temperatures (12°C and 18°C) to determine sporophyte production (i.e., recruitment success). For all taxa from all locations, sporophytes were always present in the 12°C treatment and when recruitment failure was observed, it always occurred at 18°C, regardless of nitrate level, indicating that temperature is the driving factor limiting recruitment, not nitrate. Rising ocean temperatures will undoubtedly cause recruitment failure for many kelp species; however, the ability of species to acclimatize or adapt to increased temperatures at the warmer edge of their species range may promote a resiliency of kelp systems to climate change at a global scale.

In a squeeze: Epibiosis may affect the distribution of kelp forests

The processes limiting the population recovery of the kelp Saccharina latissima after recent large-scale loss from the south coast of Norway are poorly understood. Previous investigations do, however, suggest that the impacts of biotic interactions (epibiosis and competition) and increased water turbidity are important. We investigated the depth-related patterns of growth, epibiosis, and mortality in two sample populations of kelp, from the south and the southwest coast of Norway. The investigations were performed over a period of seven months, in a crossed translocational study, where kelps were mounted on rigs at six depths (1, 3, 6, 9, 15, and 24 m). In a second experiment, the amounts of light blocked by different epibiont layers growing on the kelp frond were investigated. While growth decreased with depth in spring and summer, the kelp grew faster at 15 m than at shallower depths in fall. Survival was low both in shallow water and below 15 m depth. Epibionts covered the kelp growing at depths from 1 to 9 m, and the laboratory study showed that the coverage may have deprived the individuals of as much as 90% of the available light. Although the depth-related results we present apply-in the strictest sense-only to kelp translocated on rigs, we argue that the relative patterns are relevant for natural populations. Growth and survival of S. latissima is likely to be reduced by heavy loads of epibionts, while depths where epibionts are sparse may be close to the lower limit of the kelps depth distribution along the south coast of Norway. This suggests that a vertical squeeze, or narrowing of the distribution range of kelp forests may be occurring in Norway.

Mechanical properties of the wave-swept kelp Egregia menziesii change with season, growth rate and herbivore wounds

The resistance of macroalgae to damage by hydrodynamic forces depends on the mechanical properties of their tissues. Although factors such as water-flow environment, algal growth rate and damage by herbivores have been shown to influence various material properties of macroalgal tissues, the interplay of these factors as they change seasonally and affect algal mechanical performance has not been worked out. We used the perennial kelp Egregia menziesii to study how the material properties of the rachis supporting a frond changed seasonally over a 2 year period, and how those changes correlated with seasonal patterns of the environment, growth rate and herbivore load. Rachis tissue became stiffer, stronger and less extensible with age (distance from the meristem). Thus, slowly growing rachises were stiffer, stronger and tougher than rapidly growing ones. Growth rates were highest in spring and summer when upwelling and long periods of daylight occurred. Therefore, rachis tissue was most resistant to damage in the winter, when waves were large as a result of seasonal storms. Herbivory was greatest during summer, when rachis growth rates were high. Unlike other macroalgae, E. menziesii did not respond to herbivore damage by increasing rachis tissue strength, but rather by growing in width so that the cross-sectional area of the wounded rachis was increased. The relative timing of environmental factors that affect growth rates (e.g. upwelling supply of nutrients, daylight duration) and of those that can damage macroalgae (e.g. winter storms, summer herbivore outbreaks) can influence the material properties and thus the mechanical performance of macroalgae.

Future climate change is predicted to affect the microbiome and condition of habitat-forming kelp

Climate change is driving global declines of marine habitat-forming species through physiological effects and through changes to ecological interactions, with projected trajectories for ocean warming and acidification likely to exacerbate such impacts in coming decades. Interactions between habitat-formers and their microbiomes are fundamental for host functioning and resilience, but how such relationships will change in future conditions is largely unknown. We investigated independent and interactive effects of warming and acidification on a large brown seaweed, the kelp Ecklonia radiata, and its associated microbiome in experimental mesocosms. Microbial communities were affected by warming and, during the first week, by acidification. During the second week, kelp developed disease-like symptoms previously observed in the field. The tissue of some kelp blistered, bleached and eventually degraded, particularly under the acidification treatments, affecting photosynthetic efficiency. Microbial communities differed between blistered and healthy kelp for all treatments, except for those under future conditions of warming and acidification, which after two weeks resembled assemblages associated with healthy hosts. This indicates that changes in the microbiome were not easily predictable as the severity of future climate scenarios increased. Future ocean conditions can change kelp microbiomes and may lead to host disease, with potentially cascading impacts on associated ecosystems.

Ecophysiological implications of UV radiation in the interspecific interaction of Pyropia acanthophora and Grateloupia turuturu (Rhodophyta)

Radiation, both photosynthetic active radiation (PAR, l = 400-700 nm) and Ultraviolet (UVR, l = 280-400 nm) is one of the key factors regulating algal distribution in aquatic environments. Pyropia acanthophora and Grateloupia turuturu have been found over upper rocky shore areas in Southern Brazil, occupying the same niche space. The first species is native and the second one is exotic and considered a potential invader of South Atlantic. The aim of the present study was to evaluate the effects of radiation on physiological responses of both species and infer mechanisms that allow their niche competition in the environment. Samples were cultured in the following conditions: associated or separated, and with an addition of PAR, PAR + UVA (PA) and PAR + UVA + UVB (PAB), totalizing six factorial treatments during 5 days of exposure. Photosynthetic responses of F_v/F_m and ETR were daily evaluated. At the beginning and at the end of the experiment, samples were analyzed for pigment content (chlorophyll a and phycobiliproteins), and mycosporine-like amino acids (MAAs), while oxygen evolution was evaluated at the end of the experiment. As the main results, G. turuturu died when cultivated in PAB conditions. P. acanthophora presented higher amounts of chlorophyll a than G. turuturu during the whole experiment. Phycoerythrin and F_v/F_m remained constant in P. acanthophora but diminished for G. turuturu in UV treatments. ETR was higher for samples that were cultivated in associative treatment. The presence of G. turuturu in the same flask enhanced MAA synthesis in P. acanthophora, regardless of radiation condition. In addition, UV radiation can be a factor controlling species distribution and could counteract the spreading of invasive species, like G. turuturu, allowing P. acanthophora survival in upper rocky shore zones of the natural ecological distribution area.

Bayesian inference of environmental effects on seaweed production in Japan via a production-environmental suitability model

BACKGROUND

Both natural and human-induced disturbances are commonly responsible for an overall decrease of the world's seaweed. Along Japan's coastal areas, edible seaweed production has been decreasing for decades. In this study, a production-environmental suitability model to estimate the impacts of environmental factors on seaweed production was developed. The developed model not only estimates human-induced disturbances but also quantifies the impacts of environmental factors responsible for the decline of annual seaweed production. The model estimated the temporal variation in human-induced disturbances and the effects of environmental factors (i.e., rainfall, CO2 concentrations, temperature, typhoons, solar radiation, water nutrient levels, and water quality) on edible seaweeds in Japan from 1985 to 2012.

RESULTS

The environmental suitability for seaweed production in Japan was about 4.6 times greater in 1992 than in 2011, meanwhile as a result of human activities, human-induced disturbances of seaweed increased at a rate of 4.9 times faster during the period of 1998-2012 than the period of 1985-1997. The ratio of decreased production to decreased environmental suitability for seaweed production in Japan increased by 15.2% during the study years, which means that seaweed production has become more sensitive to environmental disturbances, including climatic factors and human activities in 1998-2012.

CONCLUSIONS

The results are novel in demonstrating temporal variations in the level of environmental suitability to seaweed production by using a simple mathematical model. The production-environmental suitability model successfully predicted seaweed production by reflecting the 28-year temporal variation of the observed seaweed production in Japan.

Phylogeography and genetic connectivity of the marine macro-alga Sargassum ilicifolium (Phaeophyceae, Ochrophyta) in the northwestern Pacific1

The evolutionary influences of historical and contemporary factors on the population connectivity and phylogeographic structure of a brown seaweed, Sargassum ilicifolium, were elucidated using the nuclear ITS2 and mitochondrial COI markers for the collections newly sampled within its distribution range in the northwestern Pacific (NWP). Significant genetic structure at variable levels was identified between populations (pairwise FST ) and among populations grouped by geographical proximity (ΦCT among regions). The adjacent groups of populations with moderate structure revealed from AMOVA appeared to have high genetic connectivity. However, a lack of genealogical concordance with the geographic distribution was uncovered for S. ilicifolium from the NWP. Such genetic homogeneity is interpreted as a result of the interaction between postglacial recolonization and dynamic oceanic current regimes in the region. Two separated glacial refugia, the South China Sea and the Okinawa Trough, in the marginal seas of east China were recognized based on the presence of endemic haplotypes and high haplotype diversity in the populations at southern China and northeast of Taiwan. Populations persisting in these refugia may have served as the source for recolonization in the NWP with the rise of sea level during the warmer interglacial periods. The role of oceanic currents in maintaining genetic connectivity of S. ilicifolium in the region was further corroborated by the coherence between the direction of oceanic currents and that of gene flow, especially along the eastern coast of Taiwan. This study underlines the interaction between historical postglacial recolonization and contemporary coastal hydrodynamics in contributing to population connectivity and distribution for this tropical seaweed in the NWP.

Ocean change within shoreline communities: from biomechanics to behaviour and beyond

Humans are changing the physical properties of Earth. In marine systems, elevated carbon dioxide concentrations are driving notable shifts in temperature and seawater chemistry. Here, we consider consequences of such perturbations for organism biomechanics and linkages amongst species within communities. In particular, we examine case examples of altered morphologies and material properties, disrupted consumer-prey behaviours, and the potential for modulated positive (i.e. facilitative) interactions amongst taxa, as incurred through increasing ocean acidity and rising temperatures. We focus on intertidal rocky shores of temperate seas as model systems, acknowledging the longstanding role of these communities in deciphering ecological principles. Our survey illustrates the broad capacity for biomechanical and behavioural shifts in organisms to influence the ecology of a transforming world.

Effects of ocean acidification on the levels of primary and secondary metabolites in the brown macroalga Sargassum vulgare at different time scales

Most of the studies regarding the impact of ocean acidification on macroalgae have been carried out for short-term periods, in controlled laboratory conditions, thus hampering the possibility to scale up the effects on long-term. In the present study, the volcanic CO2 vents off Ischia Island were used as a natural laboratory to investigate the metabolic response of the brown alga Sargassum vulgare to acidification at different time scales. For long-term effects, algal populations naturally growing at acidified and control sites were compared. For short-term responses, in situ reciprocal transplants from control to acidified site and vice-versa were performed. Changes in the levels of sugars, fatty acids (FAs), amino acids (AAs), antioxidants, and phenolic compounds were examined. Our main finding includes variable metabolic response of this alga at different time scales to natural acidification. The levels of sugars, FAs, and some secondary metabolites were lower in the natural population at the acidified site, whereas the majority of AAs were higher than those detected in thalli growing at control site. Moreover, in algae transplanted from control to acidified site, soluble sugars (glucose and mannose), majority of AAs, and FAs increased in comparison to control plants transplanted within the same site. The differences in the response of the macroalga suggest that the metabolic changes observed in transplants may be due to acclimation that supports algae to cope with acidification, thus leading to adaptation to lowered pH in long time scale.

Combined effects of warming and nutrients on marine communities are moderated by predators and vary across functional groups

Warming, nutrient enrichment and biodiversity modification are among the most pervasive components of human-induced global environmental change. We know little about their cumulative effects on ecosystems; however, even though this knowledge is fundamental to predicting and managing their consequences in a changing world. Here, we show that shifts in predator species composition can moderate both the individual and combined effects of warming and nutrient enrichment in marine systems. However, all three aspects of global change also acted independently to alter different functional groups in our flow-through marine rock-pool mesocosms. Specifically, warming reduced macroalgal biomass and assemblage productivity, whereas enrichment led to increased abundance of meso-invertebrate consumers, and loss of predator species led to increased gastropod grazer biomass. This disparity in responses, both across trophic levels (macroalgae and intermediate consumers), and between detecting additive effects on aggregate measures of ecosystem functioning, yet interactive effects on community composition, illustrates that our forecasting ability depends strongly on the level of ecological complexity incorporated within global change experiments. We conclude that biodiversity change-and loss of predator species in particular-plays a critical and overarching role in determining how ecological communities respond to stressors.

Ocean warming and copper pollution: implications for metabolic compounds of the agarophyte Gelidium floridanum (Gelidiales, Rhodophyta)

Ocean warming is increasing and scientific predictions suggest a rise of up to 4°C in sea water temperatures. The combination of a polluted and warmer environment may be detrimental for aquatic species, especially for primary producers such as seaweeds. This study investigated the potential for interactive effects of an increased seawater temperature in a copper-rich environment on the photosynthetic pigments and metabolic compounds of the red seaweed Gelidium floridanum. Seaweed samples were cultivated in a factorial design with temperature (24°C and 30°C), copper (0 and 3 μM), and time (7 and 14 d). The exposure of G. floridanum to copper and 30°C for 7 d resulted in a lower concentration of chlorophyll a, smaller phycobiliprotein rods and lower concentration of soluble sugars. After 14 d of cultivation, a higher concentration of chlorophyll a and soluble sugars could be observed on seaweeds cultivated under 30°C. The accumulation of carotenoids and the release of phenolic compounds indicated specific protective mechanisms against temperature and copper, respectively. Overall, seaweeds grew less when exposed to copper 3 μM at 30°C.

Tolerance to climate change of the clonally reproducing endemic Baltic seaweed, Fucus radicans: is phenotypic plasticity enough?

To predict the effects of climate change, we first need information on both the current tolerance ranges of species and their future adaptive potential. Adaptive responses may originate either in genetic variation or in phenotypic plasticity, but the relative importance of these factors is poorly understood. Here, we tested the tolerance of Fucus radicans to the combination of hyposalinity and warming projected by climate models for 2070-2099. We measured the growth and survival responses of thalli in both current and future conditions, focusing on variations in tolerance among and within different clonal lineages. Survival was 32% lower in future than in current conditions, but the weight and length of the thalli which survived was respectively 267% and 178% higher when exposed to future conditions. The relatively high tolerance to the future conditions suggests that F. radicans is likely to persist in its current distributional range, which is limited to the Gulf of Bothia and Estonian coast in the Baltic Sea. Furthermore, this species may be able to expand its distribution southward and replace its congener F. vesiculosus, which, in previous studies, has not tolerated the future conditions as well. In addition, we discovered variation in tolerance to future conditions within one of the clonal lineages, which have been hitherto presumed to lack adaptive variation. The discovery of intra-clonal phenotypic plasticity means that this alga has the potential for adaptive responses to climate change, which may be the key to the future persistence of F. radicans in the Baltic Sea.

Physiological and biochemical responses of a coralline alga and a sea urchin to climate change: Implications for herbivory

Direct responses to rising temperatures and ocean acidification are increasingly well known for many single species, yet recent reviews have highlighted the need for climate change research to consider a broader range of species, how stressors may interact, and how stressors may affect species interactions. The latter point is important in the context of plant-herbivore interactions, as increasing evidence shows that increasing seawater temperature and/or acidification can alter algal traits that dictate their susceptibility to herbivores, and subsequently, community and ecosystem properties. To better understand how marine rocky shore environments will be affected by a changing ocean, in the present study we investigated the direct effects of short-term, co-occurring increased temperature and ocean acidification on a coralline alga (Jania rubens) and a sea urchin herbivore (Echinometra lucunter) and assessed the indirect effects of these factors on the algal-herbivore interaction. A 21-day mesocosm experiment was conducted with both algae and sea urchins exposed to ambient (24 °C, Low CO₂), high-temperature (28 °C, Low CO₂), acidified (24 °C, High CO₂), or high-temperature plus acidified (28 °C, High CO₂) conditions. Algal photosynthesis, respiration, and phenolic content were unaffected by increased temperature and CO₂, but calcium carbonate content was reduced under high CO₂ treatments in both temperatures, while total sugar content of the algae was reduced under acidified, lower temperature conditions. Metabolic rates of the sea urchin were elevated in the lower temperature, high CO₂ treatment, and feeding assays showed that consumption rates also increased in this treatment. Despite some changes to algal chemical composition, it appears that at least under short-term exposure to climate change conditions, direct effects on herbivore metabolism dictated herbivory rates, while indirect effects caused by changes in algal palatability seemed to be of minor importance.

Biodiversity of Kelp Forests and Coralline Algae Habitats in Southwestern Greenland

All marine communities in Greenland are experiencing rapid environmental change, and to understand the effects on those structured by seaweeds, baseline records are vital. The kelp and coralline algae habitats along Greenland’s coastlines are rarely studied, and we fill this knowledge gap for the area around Nuuk, west Greenland. Using subtidal swath surveys, photo-quadrats, and grab samples, we characterised the diversity of floral and faunal assemblages in kelp forests and coralline algae beds. The most abundant herbivore assemblages and the most diverse communities occur in the interstitial habitats of rhodolith beds. In kelp forests, species diversity is higher in epi-benthic (photo-quadrat) and mid-water (swath) surveys. These habitats are not mutually exclusive; Agarum clathratum is prominent in coralline algal habitats, while crustose coralline algae cover the bedrock under kelp holdfasts. Overall, the suite of surveys used capture the diverse communities within kelp forests and coralline algae in Greenland and their differing role in the life history of the inhabitants. Furthermore, coralline algae beds are an important carbonate store, with CaCO3 concentrations ranging from 28.06 to 103.73 g·m−3. Our research sets the baseline for continued investigations and monitoring of these important habitats and their supported fisheries.

Copper pollution exacerbates the effects of ocean acidification and warming on kelp microscopic early life stages

Ocean warming (OW), ocean acidification (OA) and their interaction with local drivers, e.g., copper pollution, may negatively affect macroalgae and their microscopic life stages. We evaluated meiospore development of the kelps Macrocystis pyrifera and Undaria pinnatifida exposed to a factorial combination of current and 2100-predicted temperature (12 and 16 °C, respectively), pH (8.16 and 7.65, respectively), and two copper levels (no-added-copper and species-specific germination Cu-EC50). Meiospore germination for both species declined by 5-18% under OA and ambient temperature/OA conditions, irrespective of copper exposure. Germling growth rate declined by >40%·day-1, and gametophyte development was inhibited under Cu-EC50 exposure, compared to the no-added-copper treatment, irrespective of pH and temperature. Following the removal of copper and 9-day recovery under respective pH and temperature treatments, germling growth rates increased by 8-18%·day-1. The exception was U. pinnatifida under OW/OA, where growth rate remained at 10%·day-1 before and after copper exposure. Copper-binding ligand concentrations were higher in copper-exposed cultures of both species, suggesting that ligands may act as a defence mechanism of kelp early life stages against copper toxicity. Our study demonstrated that copper pollution is more important than global climate drivers in controlling meiospore development in kelps as it disrupts the completion of their life cycle.

Forecast climate change conditions sustain growth and physiology but hamper reproduction in range-margin populations of a foundation rockweed species

Intensifying environmental changes due to climate change affect marine species worldwide. Herein, we experimentally tested if the combination of forecasted warming and hyposalinity adversely affected growth, receptacle formation, and photosynthesis of three marginal populations of the brown alga Fucus from the northern Baltic Sea. Growth was not impaired by the projected consequences of climate change but genotypes varied in their responses, suggesting existence of genetic variation in phenotypic plasticity. Climate change further prevented receptacle formation, implying that Fucus fail to reproduce sexually. Photosynthesis was not affected by climate change but varied among populations. Our results show that Fucus populations photosynthesized, grew, and survived well under the projected climate change but their sexual reproduction ceased. This suggests that the marginal populations tested herein are resilient to future conditions but only if asexual reproduction enables them to proliferate.

Effects of ocean acidification on algae growth and feeding rates of juvenile sea urchins

The recent decrease in seawater pH has stimulated a great deal of research on the effects of ocean acidification on various organisms. Most of these studies have mainly focused on the direct effects of acidification on organisms. However, the effects on ecological interactions have been poorly studied. In this paper we have focused on determining the effects of acidification on feeding rates of two species of sea urchins, Paracentrotus lividus and Diadema africanum through laboratory experiments. Nine algae species were reared under two pH treatmens (ph = 8.1 vs. pH = 7.6) for 10 days. We evaluated possible changes in calcification rates, growth and internal structure. Then these algae were offered to juvenile sea urchins for 7 days, evaluating the consumption rates of juvenile sea urchins under these different pH conditions. The algae reared in the control treatment showed higher growth rates and concentration of calcium carbonate, however no internal structural changes were observed in any algae. Juvenile Paracentrotus lividus showed higher consumption rates on algae previously subjected to pH 7.6 than on algae reared under control conditions and between algae species in low pH.The algae most consumed were C. liebetruthii, C. abies-marina and C. elongata by P. lividus juveniles from low pH treatment. However in D. africanum the feeding rates were similar between treatments. This study demonstrated the negative effects of low pH on various species of algae in growth, and indirectly the increase in herbivory rates of juvenile sea urchins on algae reared under low pH.

Seaweed assemblages under a climate change scenario: Functional responses to temperature of eight intertidal seaweeds match recent abundance shifts

Field evidence is essential to assess the consequences of climate change but a solid causal link often requires additional information obtained under controlled laboratory conditions. Additionally, the functional response to temperature may also help to discriminate species potentially more vulnerable to warming. Using a highly resolved temperature gradient, we examined the temperature dependence of photosynthesis and respiration in eight intertidal seaweeds that recently followed opposite abundance trends in NW Iberia. The temperature dependence of photosynthesis was consistently different between the macroalgae that increased and those that decreased their abundance in the last decade and a half, with photosynthesis twice more sensitive in the upward group. Unlike photosynthesis, the temperature dependence of respiration was unrelated to the abundance trend group, implying that the net metabolic scaling with temperature varied between the two groups of seaweeds. Overall, our results provide experimental support to the role of temperate as a likely driver of the changes in abundance recorded by field-monitoring studies. They also suggest that the temperature dependence of photosynthesis and respiration assessed in short-term experiments may serve as a biomarker of the potential vulnerability of some seaweed to the consequences of water warming.

Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts

While changes in the abundance of keystone predators can have cascading effects resulting in regime shifts, the role of mesopredators in these processes remains underexplored. We conducted annual surveys of rocky reef communities that varied in the recovery of a keystone predator (sea otter, Enhydra lutris) and the mass mortality of a mesopredator (sunflower sea star, Pycnopodia helianthoides) due to an infectious wasting disease. By fitting a population model to empirical data, we show that sea otters had the greatest impact on the mortality of large sea urchins, but that Pycnopodia decline corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities. Our results reveal that predator complementarity in size-selective prey consumption strengthens top-down control on urchins, affecting the resilience of alternative reef states by reinforcing the resilience of kelp forests and eroding the resilience of urchin barrens. We reveal previously underappreciated species interactions within a 'classic' trophic cascade and regime shift, highlighting the critical role of middle-level predators in mediating rocky reef state transitions.

Increased food supply mitigates ocean acidification effects on calcification but exacerbates effects on growth

Because many of the negative effects of ocean acidification on marine life may result from underlying energetic short-falls associated with increased metabolic demands, several studies have hypothesized that negative responses to high CO₂ could be reduced by energy input. Although this hypothesis was supported by a recent meta-analysis, we believe that the meta-analytic calculation used was not appropriate to test the stated hypothesis. Here, we first clarify the hypothesis put forward, the crux being that the effects of increased food supply and CO₂ interact statistically. We then test this hypothesis by examining the available data in a more appropriate analytical framework. Using factorial meta-analysis, we confirm that food addition has a positive effect and CO₂ has a negative effect on both growth and calcification. For calcification, food addition did indeed reduce CO₂ impacts. Surprisingly, however, we found that food addition actually exacerbated the effects of acidification on growth, perhaps due to increased scope upon which CO₂ effects can act in food-replete situations. These interactive effects were undetectable using a multilevel meta-analytic approach. Ongoing changes in food supply and carbonate chemistry, coupled with under-described, poorly understood, and potentially surprising interactive outcomes for these two variables, suggest that the role of food should remain a priority in ocean acidification research.

Arising from: L. Ramajo et al., Sci. Rep. 6: 19374 (2016).

Decadal stability in genetic variation and structure in the intertidal seaweed Fucus serratus (Heterokontophyta: Fucaceae)

BACKGROUND

The spatial distribution of genetic diversity and structure has important implications for conservation as it reveals a species' strong and weak points with regard to stability and evolutionary capacity. Temporal genetic stability is rarely tested in marine species other than commercially important fishes, but is crucial for the utility of temporal snapshots in conservation management. High and stable diversity can help to mitigate the predicted northward range shift of seaweeds under the impact of climate change. Given the key ecological role of fucoid seaweeds along rocky shores, the positive effect of genetic diversity may reach beyond the species level to stabilize the entire intertidal ecosystem along the temperate North Atlantic. In this study, we estimated the effective population size, as well as temporal changes in genetic structure and diversity of the seaweed F. serratus using 22 microsatellite markers. Samples were taken across latitudes and a range of temperature regimes at seven locations with decadal sampling (2000 and 2010).

RESULTS

Across latitudes, genetic structure and diversity remained stable over 5-10 generations. Stable small-scale structure enhanced regional diversity throughout the species' range. In accordance with its biogeographic history, effective population size and diversity peaked in the species' mid-range in Brittany (France), and declined towards its leading and trailing edge to the north and south. At the species' southern edge, multi-locus-heterozygosity displayed a strong decline from 1999 to 2010.

CONCLUSION

Temporally stable genetic structure over small spatial scales is a potential driver for local adaptation and species radiation in the genus Fucus. Survival and adaptation of the low-diversity leading edge of F. serratus may be enhanced by regional gene flow and 'surfing' of favorable mutations or impaired by the accumulation of deleterious mutations. Our results have clear implications for the conservation of F. serratus at its genetically unique southern edge in Northwest Iberia, where increasing temperatures are likely the major cause for the decline not only of F. serratus, but also other intertidal and subtidal macroalgae. We expect that F. serratus will disappear from Northwest Iberia by 2100 if genetic rescue is not induced by the influx of genetic variation from Brittany.