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Este artículo contiene 19 páginas, 4 figuras, 2 tablas., The extent and impacts of biological invasions on biodiversity are largely shaped by an array of socio-economic and environmental factors, which exhibit high variation among countries. Yet, a global analysis of how these factors vary across countries is currently lacking. Here, we investigate how five broad, country-specific socio-economic and environmental indices (Governance, Trade, Environmental Performance, Lifestyle and Education, Innovation) explain country-level (1) established alien species (EAS) richness of eight taxonomic groups, and (2) proactive or reactive capacity to prevent and manage biological invasions and their impacts. These indices underpin many aspects of the invasion process, including the introduction, establishment, spread and management of alien species. They are also general enough to enable a global comparison across countries, and are therefore essential for defining future scenarios for biological invasions. Models including Trade, Governance, Lifestyle and Education, or a combination of these, best explained EAS richness across taxonomic groups and national proactive or reactive capacity. Historical (1996 or averaged over 1996–2015) levels of Governance and Trade better explained both EAS richness and the capacity of countries to manage invasions than more recent (2015) levels, revealing a historical legacy with important implications for the future of biological invasions. Using Governance and Trade to define a two-dimensional socio-economic space in which the position of a country captures its capacity to address issues of biological invasions, we identified four main clusters of countries in 2015. Most countries had an increase in Trade over the past 25 years, but trajectories were more geographically heterogeneous for Governance. Declines in levels of Governance are concerning as they may be responsible for larger levels of invasions in the future. By identifying the factors influencing EAS richness and the regions most susceptible to changes in these factors, our results provide novel insights to integrate biological invasions into scenarios of biodiversity change to better inform decision-making for policy and the management of biological invasions., This research was funded through the 2017-2018 Belmont Forum and BiodivERsA joint call for research proposals, under the BiodivScen ERA-Net COFUND programme, and with the funding organisations FWF (project no I 4011-B32–GL, BeL, SD, DM, FE), MCIN/AEI/https:// doi. org/ 10. 13039/ 50110 00110 33 (PCI2018-092966– NRP, CPG, EC), BMBF (16LC1807C–MG, IK; 16LC1807A–HS; 16LC1807B–JMJ) and ANR (NR-18-EBI4-0004–FC, CB, CD, AT).

Este artículo contiene 10 páginas, 5 figuras, 1 tabla., The process of site selection and spatial planning has received scarce attention in the scientific literature dealing with marine restoration, suggesting the need to better address how spatial planning tools could guide restoration interventions. In this study, for the first time, the consequences of adopting different restoration targets and criteria on spatial restoration prioritization have been assessed at a regional scale, including the consideration of climate changes. We applied the decision-support tool Marxan, widely used in systematic conservation planning on Mediterranean macroalgal forests. The loss of this habitat has been largely documented, with limited evidences of natural recovery. Spatial priorities were identified under six planning scenarios, considering three main restoration targets to reflect the objectives of the EU Biodiversity Strategy for 2030. Results show that the number of suitable sites for restoration is very limited at basin scale, and targets are only achieved when the recovery of 10% of regressing and extinct macroalgal forests is planned. Increasing targets translates into including unsuitable areas for restoration in Marxan solutions, amplifying the risk of ineffective interventions. Our analysis supports macroalgal forests restoration and provides guiding principles and criteria to strengthen the effectiveness of restoration actions across habitats. The constraints in finding suitable areas for restoration are discussed, and recommendations to guide planning to support future restoration interventions are also included., This study was funded by the EASME–EMFF (Sustainable Blue Economy) Project AFRIMED (http://afrimed-project.eu/, grant agreement N. 789059), supported by the European Community.

Este artículo contiene 18 páginas, 4 figuras., Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015–2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change., This paper was supported by Euromarine. Joaquim Garrabou acknowledges the funding by the “Severo Ochoa Centre of Excellence” (CEX2019-000928-S), the MCIU/AEI/FEDER [HEATMED; RTI2018-095346-B-I00], Interreg-Med Programme MPA-Engage (1MED15_3.2_M2_337), the European Union Horizon 2020 research and innovation programme (Futuremares SEP-210597628). Nuria Teixido acknowledges the French National Research Agency (4Oceans-MOPGA grant, ANR-17-MPGA-0001) and internal funds from the Stazione Zoologica Anton Dohrn. Gil Rilov was supported by the Israel Ministry of Environmental Protection. Hocein Bazairi, Free Spinosa, and Vasilis Gerovasileiou acknowledge the funding by the MAVA Fondation (MedKeyHabitats I Project) and the European Commission (Ecap-MED II Project; projects implemented by UNEP/MAP-RAC/SPA). Alfonso Ramos was supported the CIESM “Tropical Signals,” Stelios Katsanevakis and Maria Sini were supported by the Project “Coastal Environment Observatory and Risk Management in Island Regions AEGIS+” (MIS 5047038), implemented within the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020), co-financed by the Hellenic Government (Ministry of Development and Investments) and the European Union (European Regional Development Fund, Cohesion Fund), Stelios Katsanevakis, Maria Sini and Vasilis Gerovasileiou acknowledge the support of the MARISCA Project, co-funded by 85% by the EEA GRANTS, 2009–2014, and 15% by the Public Investments Programme (PIP) of the Hellenic Republic. Ivan Guala and Daniele Grech thanks thank the support of the project “Pinna nobilis—ricerca per la sopravvivenza: un'iniziativa di Citizen Science per tracciare la mortalità di massa di Pinna nobilis in Sardegna” project and the L/7 grant (CUP 87G17000070002) funded by the Regione Autonoma Sardegna. Jean-Baptiste Ledoux was funded by an assistant researcher contract framework of the RD Unit—UID/Multi/04423/2019—Interdisciplinary Centre of Marine and Environmental Research—financed by the European Regional Development Fund (ERDF) through COMPETE2020—Operational Program for Competitiveness and Internationalization (POCI) and national funds through FCT/MCTES (PIDDAC). This research was supported by the Strategic Funding UIDB/04423/2020 and UIDP/04423/2020 through national funds provided by the FCT—Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the program PT2020. Bernat Hereu and Cristina Linares acknowledge the support of the long-term monitoring programme of the catalan Natural Parks, funded by the Departament de Territori i Sostenibilitat of the Generalitat de Catalunya. Cristina Linares acknowledges the support of the ICREA Academia programme. David Díaz acknowledges the support the research grant CTM2016-77027-R of the Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad and Program of Marines Strategies of Spain funded by MITERD. Jamila Ben Soussi was partially funded by the Fondation Albert 2 Monaco (MIMOSA Project) and the Tropical Signals Program of CIESM. Giovanni Chimienti was supported by the Italian Ministry of Education, University and Research (PON 2014–2020, AIM 1807508–1, Linea 1), by the Ente Parco Nazionale del Gargano (Research agreement with CoNISMa N. 21/2018), and by the National Geographic Society (Grant EC-176R-18). Nathaniel Bensoussan acknowledges financial support from the European Commission through the programme “Caroline Herschell” in the context of the action “Developing Downstream applications and services on BIO-PHYsical characterization of the seascape for COASTal management” (BIOPHYCOAST). Monica Montefalcone and Annalissa Azzola collected some of their data on MMEs in the frame of the project “Mare Caldo” funded by Greenpeace Italy. Núria Marbà acknowledges financial support from the Spanish Ministries of Economy and Competitiveness (CTM2012-32603, CGL2015-71809-P) and Ministerio de Ciencia, Innovación y Universidades (RTI2018-095441-B-C21). Diego K. Kersting acknowledges support by the postdoctoral fellowship programme Beatriu de Pinós funded by the Secretary of Universities and Research (Government of Catalonia) and the Horizon 2020 programme of research and innovation of the European Union under the Marie Sklodowska-Curie grant agreement No 801370.

Este artículo contiene 11 páginas, 2 figuras, 2 tablas., Local, regional and global targets have been set to halt marine biodiversity loss. Europe has set its own policy targets to achieve Good Environmental Status (GES) of marine ecosystems by implementing the Marine Strategy Framework Directive (MSFD) across member states. We combined an extensive dataset across five Mediterranean ecoregions including 26 Marine Protected Areas (MPAs), their reference unprotected areas, and a no-trawl case study. Our aim was to assess if MPAs reach GES, if their effects are local or can be detected at ecoregion level or up to a Mediterranean scale, and which are the ecosystem components driving GES achievement. This was undertaken by using the analytical tool NEAT (Nested Environmental status Assessment Tool), which allows an integrated assessment of the status of marine systems. We adopted an ecosystem approach by integrating data from several ecosystem components: the seagrass Posidonia oceanica, macroalgae, sea urchins and fish. Thresholds to define the GES were set by dedicated workshops and literature review. In the Western Mediterranean, most MPAs are in good/high status, with P. oceanica and fish driving this result within MPAs. However, GES is achieved only at a local level, and the Mediterranean Sea, as a whole, results in a moderate environmental status. Macroalgal forests are overall in bad condition, confirming their status at risk. The results are significantly affected by the assumption that discrete observations over small spatial scales are representative of the total extension investigated. This calls for large-scale, dedicated assessments to realistically detect environmental status changes under different conditions. Understanding MPAs effectiveness in reaching GES is crucial to assess their role as sentinel observatories of marine systems. MPAs and trawling bans can locally contribute to the attainment of GES and to the fulfillment of the MSFD objectives. Building confidence in setting thresholds between GES and non-GES, investing in long-term monitoring, increasing the spatial extent of sampling areas, rethinking and broadening the scope of complementary tools of protection (e.g., Natura 2000 Sites), are indicated as solutions to ameliorate the status of the basin., This article was undertaken within the COST Action 15121 MarCons (http://www.marcons-cost.eu, European Cooperation in Science and Technology), the Interreg MED AMAre Plus (Ref: 8022) and the project PO FEAMP 2014-2020 Innovazione, sviluppo e sostenibilita ` nel settore della pesca e dell’acquacoltura per la Regione Campania (ISSPA 2.51). M.C.U., A.B. have been funded by the project MEDREGION (European Commission DG ENV/MSFD, 2018 call, Grant Agreement 110661/ 2018/794286/SUB/ENV.C2). Aegean Sea data were retrieved from the project PROTOMEDEA (www.protomedea.eu), funded by DG for Marine Affairs and Fisheries of the EC, under Grant Agreement SI2.721917. JB acknowledges support from the Spanish Ministry of Science and Innovation (Juan de la Cierva fellowship FJC 2018-035566-I)., With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S).

Este artículo contiene 1 página, 1 figura., Early detection of invasive species is critical to their successful management because control methods can be enacted before the invaders become established. But what happens when an invasive species escapes early discovery because it closely resembles a native species? Marine algae in the genus Caulerpa are prolific invaders of tropical, subtropical, and temperate coasts, where they substantially disrupt ecosystem functioning. Caulerpa species including Caulerpa cylindracea are easily discernable by their characteristic rhizoids, stolon, and fronds (Figure 1a). However, a previously undescribed form of C cylindracea (Figure 1b) displays features that are atypical of the species: namely, an unbranched habit and the presence of long, vertical filaments, 10 times as thin as those typically seen in this taxon. These filaments are nearly impossible to identify visually in the field and, when detected, can be easily misidentified as native species in genera such as Derbesia or Chlorodesmis. Genetic analyses confirm that these filaments are C cylindracea, which is likely the most rapidly proliferating invasive macroalga in the Mediterranean Sea. What promotes such morphological divergence within a species? Preliminary lab-based experiments suggest that it may be a response to stressful conditions. It is unclear if other invasive Caulerpa species exhibit the same degree of morphological flexibility and whether individuals displaying the uncharacteristic filamentous morphology could revert to the regular branching morphology; although both morphological forms have been simultaneously observed at the same location in the field, the reversion process has yet to be observed under controlled laboratory settings. What is clear, however, is that this novel form can disperse widely, as its filaments break easily and can float over long distances to colonize new areas. Managing invasive flora is already challenging, and is only further complicated when they may hide in plain sight among native flora.

Este artículo contiene 10 páginas, 2 tablas, 2 figuras., Herbivory has long been considered an important component of biotic resistance against macroalgae invasions in marine habitats. However, most of the studies on herbivory of invasive algae refer only to consumption by strictly herbivorous organisms, whereas consumption by omnivorous species has been largely ignored and rarely quantified. In this study, we assess whether the commonest omnivorous sparid species in the Mediterranean Sea are consuming the highly invasive alga, Caulerpa cylindracea, and determine both, its importance in their diet and their electivity toward it as a source of food. Our results confirm that three of the four fish species studied regularly consume C. cylindracea, but in most cases, the importance of C. cylindracea in the diet is low. Indeed, the low electivity values indicate that all species avoid feeding on the invasive alga and that it is probably consumed accidentally. However, despite animals and detritus being the main food for these sparid species, several individual specimens were found to have consumed high amounts of C. cylindracea. This suggests a potential role that these fish species, being really abundant in shallow rocky bottoms, may play in controlling, to some extent, the abundance of the invader., Funding for this project was obtained from the Spanish Ministry Project ANIMA (CGL2016-76341-R, MINECO/FEDER, UE), the Spanish Autonomous Organism of National Parks through the project BIGPARK (project 2017-2462), and the Padi Foundation to FT (CGA App #: 5134). JS has received funding from “La Caixa” Foundation (ID 100010434), under agreement LCF/BQ/DE17/11600001.

Herbivory has long been considered an important component of biotic resistance against macroalgae invasions in marine habitats. However, most of the studies on herbivory of invasive algae refer only to consumption by strictly herbivorous organisms, whereas consumption by omnivorous organisms has been largely ignored and rarely quantified. In this study, we assess whether the commonest omnivorous sparid species in the Mediterranean Sea are consuming the highly invasive alga, Caulerpa cylindracea, and determine its importance in their diet and their electivity towards it as a source of food. Our results confirm that three of the four fish species we studied do, in fact, consume C. cylindracea, but in most cases, the importance of C. cylindracea in the diet was low. Indeed, the low electivity values confirm that all four fish species avoid feeding on the invasive alga and that it is probably consumed accidentally. However, despite animals and detritus being the main food for these sea bream species, several individual specimens were found to have consumed high amounts of C. cylindracea. This suggests a potential role that these fish species may play in controlling, to some extent, the abundance of the invader. We suggest that herbivory by omnivorous fish might complement the higher impact exerted by the strict herbivores, and together, they might contribute to the overall biotic resistance against the invader.

Este artículo contiene 14 páginas, 8 figuras,5 tablas., Morphological plasticity can enable algae to adapt to environmental change and increase their invasibility when introduced into new habitats. Nevertheless, there is still a lack of knowledge on how such plasticity can affect the invasion process of an invasive species. In this context, the high plasticity in the genus Caulerpa is well documented. However, after an extremely hot summer, a previously unreported filamentous morphology of Caulerpa cylindracea was detected; indeed, this morphology could only be confirmed taxonomically after in-depth morphological characterization and molecular analysis with the genetic marker tufA. We describe an ex situ culture experiment which showed that stressful conditions, such as high temperatures, can trigger this morphological change. Almost all of the thalli maintained at a constant extreme temperature of 29°C died, but after being returned to optimum temperature conditions, the filamentous morphology began to develop from the surviving microscopic tissue. In contrast, thalli at a control temperature of 21°C maintained the regular morphology throughout the experiment. When C. cylindracea develops this filamentous morphology, it may act as a cryptic invader because it is difficult to detect in the field. Furthermore, the filaments likely improve C. cylindracea’s invasive capabilities with regard to resistance, persistence and dispersion and may have an important role in the re-colonization process, after a population disappears following a period of stressful conditions. Possibly, C. cylindracea’s ability to respond plastically to stressful conditions might explain its remarkable success as an invasive species., This project was funded by the Spanish Ministry of Science, Innovation and Universities (project ANIMA, ref. CGL2016-76341-R). JS received the support of a fellowship from “La Caixa” Foundation (ID 100010434) with code (LCF/BQ/DE17/11600001). RG benefited from a pre-doctoral fellowship from the Spanish Ministry of Science (ref. BES-2017- 079907).

The extent and impacts of biological invasions on biodiversity are largely shaped by an array of socio-ecological predictors, which exhibit high variation among countries. Yet a global synthetic perspective of how these factors vary across countries is currently lacking. Here, we investigate how a set of five socio-ecological predictors (Governance, Trade, Environmental Performance, Lifestyle and Education, Innovation) explain i) country-level established alien species (EAS) richness of eight taxonomic groups, and ii) country capacity to prevent and manage biological invasions and their impacts. Trade and Governance together best predicted the average EAS richness, increasing variance explained by up to 54% compared to models based on climatic and spatial variables only. Country-level EAS richness increased strongly with Trade, whereas high level of Governance resulted in lower EAS richness. Historical (1996) levels of Governance and Trade better explained response variables than current (2015) levels. Thus, our results reveal a historical legacy of these two predictors with profound implications for the future of biological invasions. We therefore used Governance and Trade to define a two-dimensional socio-economic space in which the position of a country captures its capacity to address issues of biological invasions. Our results provide novel insights into the complex relationship between socio-ecological predictors and biological invasions. Further, we highlight the need for designing better policies and management measures for alien species, and for integrating biological invasions in global environmental scenarios.

Invasive species pose a major threat to global diversity, and once they are well established their eradication typically becomes unfeasible. However, certain natural mechanisms can increase the resistance of native communities to invaders and can be used to guide effective management policies. Both competition and herbivory have been identified as potential biotic resistance mechanisms that can limit plant invasiveness, but it is still under debate to what extent they might be effective against well-established invaders. Surprisingly, whereas biotic mechanisms are known to interact strongly, most studies to date have examined single biotic mechanisms separately, which likely influences our understanding of the strength and effectiveness of biotic resistance against invaders. Here we use long-term field data, benthic assemblage sampling, and exclusion experiments to assess the effect of native assemblage complexity and herbivory on the invasion dynamics of a successful invasive species, the alga Caulerpa cylindracea. A higher complexity of the native algal assemblage limited C. cylindracea invasion, probably through competition by canopy-forming and erect algae. Additionally, high herbivory pressure by the fish Sarpa salpa reduced C. cylindracea abundance by more than four times. However, long-term data of the invasion reflects that biotic resistance strength can vary across the invasion process and it is only where high assemblage complexity is concomitant with high herbivory pressure, that the most significant limitation is observed (synergistic effect). Overall, the findings reported in this study highlight that neglecting the interactions between biotic mechanisms during invasive processes and restricting the studied time scales may lead to underestimations of the true capacity of native assemblages to develop resistance to invaders., Funding for this project was obtained from the Spanish Ministry Project ANIMA (CGL2016-76341-R, MINECO/FEDER, UE), the European Union’s EMFS Program, AFRIMED (EASME/EMFF/2017/1.2.1.12/S4/01/SI2.789059), the Spanish Autonomous Organism of National Parks through the project BIGPARK (project 2017-2462), and the Padi Foundation to FT (CGA App: 5134). JS received the support of a fellowship from “La Caixa” Foundation (ID 100010434) with code (LCF/BQ/DE17/11600001).

Este artículo contiene 9 páginas, 4 figuras, 2 tablas., Understanding the interactions between various stressors, and the resulting cumulative impacts they exert, is essential in order to predict the potential resilience of marine habitats to climate change. Crustose coralline algae (CCA) are a major calcifying component of marine habitats, from tropical to polar oceans, and play a central role as ecosystem engineers in many rocky reefs. These species are increasingly threatened by the stress of climate change. However, the effects of other stressors linked to global change, such as invasive species, have scarcely been addressed. We have studied the interactive effects of invasive algae and global warming on CCA, combining observational and experimental approaches. CCA sensitivity to invasive algae is heightened when they are concurrently exposed to elevated seawater temperature, and the interaction between these two stressors triggers drastic synergistic effects on CCA. The reduction and eventual disappearance of these “ecosystem foundation species” may undermine ecological functioning, leading to the disappearance and/or fragmentation of the communities associated with them., Financial support has been provided by European Union's Horizon 2020 - Research and Innovation Framework Programme, MERCES Project (No. 689518), the European Union's EMFS Program, AFRIMED (No. EASME/EMFF/2017/1.2.1.12/S4/01/SI2.789059) and the Spanish Ministry Project ANIMA (No. CGL2016-76341-R, MINECO/FEDER, UE) and FoRestA (No PID2020-112985GB-I00). CL gratefully acknowledges the financial support by ICREA under the ICREA Academia programme., With the institutional support of the ‘Severo OchoaCentre of Excellence’ accreditation (CEX2019-000928-S).

Este artículo contiene 16 páginas, 7 figuras., 1. Gradual climate change and discrete extreme climatic events have driven shifts in the structure of populations and the distribution of species in many marine ecosystems. The most profound impacts of recent warming trends have been generally observed at species' warm edges and on large conspicuous species. However, given that different species and populations exhibit different responses to warming, and that responses are highly variable at regional scales, there is a need to broaden the evidence to include less conspicuous species and to focus on both local-and regional-scale processes. 2. We examined the population dynamics of canopy-forming seaweed populations situated at the core range of their distribution during a regional marine heatwave (MHW) event that occurred in the Mediterranean Sea in 2015, to determine between-site variability in relation to the intensity of the MHW. We combined field observations with a thermo-tolerance experiment to elucidate mechanisms underlying observed responses. 3. Despite our study populations are located in the species core range, the MHW was concomitant with a high mortality and structural shifts in only one of the two surveyed populations, most likely due to differences in habitat characteristics between sites (e.g. degree of shelter and seawater transfer). The experiment showed high mortalities at temperatures of 28°C, having the most severe implications for early life stages and fertility, which is consistent with warming being the cause of population changes in the field. Crucially, the regional-scale quantification of the MHW (as described by satellite-derived SSTs) did not capture local-scale variation in MHW conditions at the study sites, which likely explained variation in population-level responses to warming. 4. Synthesis. Enclosed and semi-enclosed seas, such as the Mediterranean Sea, often highly impacted by human perturbations, are also global hotspots for ocean warming and are highly susceptible to future MHWs. Our findings highlight that local-scale variability in the magnitude of extreme climatic events can lead to local extinctions of already fragmented populations of habitat-forming seaweeds, even towards the species' core range. However, our results highlight the potential for local-scale climatic refugia, which could be identified and managed to safeguard the persistence of canopy-forming seaweeds., Ministerio de Economía, Industria y Competitividad, Gobierno de España, Grant/ Award Number: CGL2016-76341- R and FPI (BES-2017- 079907); European Maritime and Fisheries Fund EMFF, Grant/Award Number: EASME/EMFF/2017/1.2.1.12/ S4/01/SI2.789059; UK Research and Innovation, Grant/Award Number: MR/ S032827/1; Horizon 2020 Framework Programme, Grant/Award Number: 689518; Generalitat de Catalunya, Grant/Award Number: 2017 SGR 1521; Universitat de Girona, Grant/Award Number: IFUdG-2016 and MPCUdG2016/097; European Regional Development Fund, Grant/Award Number: CGL2016-76341- R; “la Caixa” Foundation, Grant/Award Number: LCF/BQ/ ES17/11600001

Global change is striking harder and faster in the Mediterranean Sea than elsewhere, where high levels of human pressure and proneness to climate change interact in modifying the structure and disrupting regulative mechanisms of marine ecosystems. Rocky reefs are particularly exposed to such environmental changes with ongoing trends of degradation being impressive. Due to the variety of habitat types and associated marine biodiversity, rocky reefs are critical for the functioning of marine ecosystems, and their decline could profoundly affect the provision of essential goods and services which human populations in coastal areas rely upon. Here, we provide an up-to-date overview of the status of rocky reefs, trends in human-driven changes undermining their integrity, and current and upcoming management and conservation strategies, attempting a projection on what could be the future of this essential component of Mediterranean marine ecosystems.

Este artículo contiene 13 páginas, 1 tabla, 5 figuras., Climate change threatens coastal benthic communities on a global scale. However, the potential effects of ongoing warming on mesophotic temperate reefs at the community level remain poorly understood. Investigating how different members of these communities will respond to the future expected environmental conditions is, therefore, key to anticipating their future trajectories and developing specific management and conservation strategies. Here, we examined the responses of some of the main components of the highly diverse Mediterranean coralligenous assemblages to thermal stress. We performed thermotolerance experiments with different temperature treatments (from 26 to 29°C) with 10 species from different phyla (three anthozoans, six sponges and one ascidian) and different structural roles. Overall, we observed species‐specific contrasting responses to warming regardless of phyla or growth form. Moreover, the responses ranged from highly resistant species to sensitive species and were mostly in agreement with previous field observations from mass mortality events (MMEs) linked to Mediterranean marine heat waves. Our results unravel the diversity of responses to warming in coralligenous outcrops and suggest the presence of potential winners and losers in the face of climate change. Finally, this study highlights the importance of accounting for species‐specific vulnerabilities and response diversity when forecasting the future trajectories of temperate benthic communities in a warming ocean., the funding support of Organismo Autónomo Parques Nacionales (CORCLIM 759S/2012 and 766S/2012), the TOTAL foundation (CLIMCARES project), the Prince Albert II de Monaco Foundation (MIMOSA project n° 1983), the MPA‐ADAPT project, the Interreg MED Program (European Regional Development Fund), and the European Union's Horizon 2020 research and innovation program under grant agreement No 689518 (MERCES). D.G.G. was supported by an FPU grant (FPU15/05457) from the Spanish Ministry of Education, M.P.E. by an APIF‐2016 and I.M.S. by an FPI grant (BES‐2013‐066150). The authors are part of the Marine Conservation research group (www. medrecover.org) (2017 SGR 1521) from the Generalitat de Catalunya.

Este artículo contiene 12 páginas, 3 tablas, 7 figuras., Marine forests dominated by macroalgae have experienced noticeable regression along some temperate and subpolar rocky shores. Along continuously disturbed shores, where natural recovery is extremely difficult, these forests are often permanently replaced by less structured assemblages. Thus, implementation of an active restoration plan emerges as an option to ensure their conservation. To date, active transplantation of individuals from natural and healthy populations has been proposed as a prime vehicle for restoring habitat-forming species. However, given the threatened and critical conservation status of many populations, less invasive techniques are required. Some authors have experimentally explored the applicability of several non-destructive techniques based on recruitment enhancement for macroalgae restoration; however, these techniques have not been effectively applied to restore forest-forming fucoids. Here, for the first time, we successfully restored four populations of Cystoseira barbata (i.e., they established self-maintaining populations of roughly 25 m2) in areas from which they had completely disappeared at least 50 years ago using recruitment-enhancement techniques. We compared the feasibility and costs of active macroalgal restoration by means of in situ (wild-collected zygotes and recruits) and ex situ (provisioning of lab-cultured recruits) techniques. Mid/long-term monitoring of the restored and reference populations allowed us to define the best indicators of success for the different restoration phases. After 6 years, the densities and size structure distributions of the restored populations were similar and comparable to those of the natural reference populations. However, the costs of the in situ recruitment technique were considerably lower than those of the ex situ technique. The restoration method, monitoring and success indicators proposed here may have applicability for other macroalgal species, especially those that produce rapidly sinking zygotes. Recruitment enhancement should become an essential tool for preserving Cystoseira forests and their associated biodiversity., This project has received funding from the Horizon 2020 EU Research and Innovation Program under grant agreement No. 689518 (MERCES), the Fundación Biodiversidad under the framework of the project: “Conservación y restauración de poblaciones de especies amenazadas del género Cystoseira” and the Spanish Ministry Project ANIMA (CGL2016-76341-R, MINECO/FEDER, UE). This project has also been funded by Dirección General de Innovación e Investigación (Govern Illes Balears) and European Regional Development Fund (FEDER). JV has been funded by a IFUdG-2016 grant.

Este artículo contiene 18 páginas, 4 figuras., Good datasets of geo-referenced records of alien species are a prerequisite for assessing the spatio-temporal dynamics of biological invasions, their invasive potential, and the magnitude of their impacts. However, with the exception of first records on a country level or wider regions, observations of species presence tend to remain unpublished, buried in scattered repositories or in the personal databases of experts. Through an initiative to collect, harmonize and make such unpublished data for marine alien and cryptogenic species in the Mediterranean Sea available, a large dataset comprising 5376 records was created. It includes records of 239 alien or cryptogenic taxa (192 Animalia, 24 Plantae, 23 Chromista) from 19 countries surrounding the Mediterranean Sea. In terms of records, the most reported Phyla in descending order were Chordata, Mollusca, Chlorophyta, Arthropoda, and Rhodophyta. The most recorded species was Caulerpa cylindracea, followed by Siganus luridus, Magallana sp. (cf. gigas or angulata) and Pterois miles. The dataset includes records from 1972 to 2020, with the highest number of records observed in 2018. Among the records of the dataset, Dictyota acutiloba is a first record for the Mediterranean Sea. Nine first country records are also included: the alga Caulerpa taxifolia var. distichophylla, the cube boxfish Ostracion cubicus, and the cleaner shrimp Urocaridella pulchella from Israel; the sponge Paraleucilla magna from Libya and Slovenia; the lumpfish Cyclopterus lumpus from Cyprus; the bryozoan Celleporaria vermiformis and the polychaetes Prionospio depauperata and Notomastus aberans from Malta., The publication of this article is supported by the Open Access Publishing Fund of the International Association for Open Knowledge on Invasive Alien Species (INVASIVESNET; www.invasivesnet.org). Stelios Katsanevakis, Maria Sini and Konstantinos Tsirintanis were supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: HFRI-FM17-1597). Enalia Physis acknowledges Pantelis Patsalou for his support with field-logistics and links with fishers. Fiona Tomas would like to acknowledge funding from FECYT FCT- 14-9319 (¡OJO A LAS INVASORAS! BIODIVERSIDAD Y ESPECIES INVASORAS DEL MEDITERRÁNEO BALEAR). Vasilis Gerovasileiou, Thanos Dailianis and Maria Sini acknowledge the support by the MARISCA project (www.marisca.eu), co-funded (85%) by EEA GRANTS, 2009–2014, and the Public Investments Program (PIP) of the Hellenic Republic (15%). Razy Hoffman acknowledges funding by Yad-Hanadiv foundation, through the Israel Society of Ecology and Environmental Sciences and Israel Nature and Parks Authority (An integrated program for establishing biological baselines and monitoring protocols for marine reserves in the Israeli Mediterranean Sea). Argyro Zenetos and Paraskevi K. Karachle would like to thank the citizenscientists collaborating with the Ellenic Network on Aquatic Invasive Species (ELNAIS – elnais.hcmr.gr). Nikolaos Doumpas, Ioannis Giovos, Periklis Kleirou and Francesco Tiralongo would like to thank all the citizen-scientists that contributed with their shared records and data in the citizen-science project “Is it alien to you? Share it!!!” (https://www.facebook.com/ groups/104915386661854/). Data from Gyaros Island marine reserve were collected under the “GyarosMPA” project, funded by “MAVA Fondation pour la Nature”. Data from Corsica coastline were mainly collected in the framework of the “Corsica Alien Network” initiated by “Office de l’Environnement de la Corse”. Carla Morri and Carlo Nike Bianchi received financial support from FFARB (funds for basic research activities) by the Italian Ministry of Education, University and Research. Ergün Taşkın has been supported by TÜBİTAK, Ankara, Turkey (Project Number: 114Y238). The Slovenian authors would like to acknowledge their financial support from the Slovenian Research Agency (research core funding No. P1-0237) and the Ministry of Agriculture, Forestry and Food of the Republic of Slovenia. Mehmet Fatih Huseyinoglu thanks University of Kyrenia’s Scientific Research Project numbered GRN-20191-004. Fabio Crocetta was funded by the COST (European Cooperation in Science and Technology) Action TD1209 Alien Challenge project. The FRI (HAO DEMETER) team is very grateful to the Marine Strategy Project for financial support. Records of NIS in Jbel Moussa, the National Park of Al Hoceima and Cap des Trois Fourches sites from Morocco were obtained during surveys conducted within the framework of the MedKeyHabitats and the MedMPAnet Projects implemented by UNEP/MAP-RAC/SPA in close collaboration with the Haut Commissariat aux Eaux et Forêts et à la Lutte Contre la Désertification (HCEFLCD) and financially supported by RAC/SPA, Tunisia and the MAVA Foundation, Switzerland (MedKeyHabitats Project) and the European Commission (EC), the Spanish Agency for International Cooperation to Development (AECID), and the French Global Environment Facility (MedMPAnet Project). Jamila Ben Souissi was partially funded by BiodivMex /Chantier MISTRALS. Konstantinos Tsiamis sampling records were retrieved during his post in the Hellenic Centre for Marine Research, which he would like to thank for. Periklis Kleitou and Demetris Kletou were supported by the LIFE financial instrument of the European Union – RELIONMED project [Grant Agreement LIFE16 NAT/ CY/000832]. Some of the data included in the dataset were obtained through the marine citizen science platform Observadores del Mar www.observadoresdelmar.es with the support of FECYT FCT-17-12469, LIFE IP Intemares and Fundació Marilles, and through the citizen science site of the Italian Marine Protected Area of “Regno di Nettuno” (islands of Ischia, Procida and Vivara): www.citizensciencerdn.org. Most data from Lebanon were retrieved from social media dedicated to citizen science (Facebook group: Sea Lebanon https://www.facebook.com/ groups/109615625861815/) or fishers and scuba divers WhatsApp groups). Jamila Rizgalla wishes to thank the administration of Regatta for granting a free pass to conduct field surveys and the security personnel for providing a safe environment. Anna Occhipinti-Ambrogi was supported by European Community’s Seventh Framework Program VECTORS (Vectors of Change in Oceans and Seas Marine Life, Impact on Economic Sectors). The long lasting collaboration with the ICES Working Group on Introductions and Transfer of Marine Organisms (WGITMO) has been a good forum where many information and ideas could be exchanged within some of the authors (Anna Occhipinti-Ambrogi, Argyro Zenetos, Agnese Marchini, and a wider community of scientists working on biological invasions). A. Rosso and R. Sanfilippo received grants from the Catania University Research Plan 2016/2018. Data from Kuriat island were collected under the “Kuriat project”, funded by “MAVA Fondation pour la Nature” executed by SPA/RAC in partnership with the Coastal Protection and Management Agency (APAL) and Notre Grand Bleu (NGB) NGO. The AIS/ERA (Environment and Resources Authority) Maltese data were obtained from the EU funded project EMFF 8.3.1 under the European Maritime and Fisheries Fund 2014–2020 with a total cost of €1.6 million in public eligible EMFF funds (75% EU 25% MT), managed by AIS/ERA (Environment and Resources Authority). The ultimate goals of this European Maritime and Fisheries Fund (EMFF 2014–2020) project are to devise a holistic approach towards marine monitoring and develop a comprehensive database of data collected about the Maltese waters., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Este artículo contiene 11 páginas, 8 figuras., Marine macroalgal forests are highly productive and iconic ecosystems, which are seriously threatened by number of factors such as habitat destruction, overgrazing, ocean warming, and pollution. The effect of chronic, but low levels of pollutants on the long-term survival of the canopy-forming algae is not well understood. Here we test the effects of low concentrations (found in good quality water-bodies) of nitrates, heavy metals copper (Cu) and lead (Pb), and herbicides (glyphosate) on both adults and recruits of Carpodesmia crinita, a Mediterranean canopy forming macroalga. We show that although adult biomass, height and photosynthetic yield remain almost unaffected in all the assays, low Cu levels of 30 µg/L completely suppress adult fertility. In addition, all the assays have a strong and negative impact on the survival and growth of recruits; in particular, glyphosate concentrations above 1 µg/L almost totally inhibit their survival. These results suggest that the long-term viability of C. crinita may be severely compromised by low pollutant levels that are not affecting adult specimens. Our results provide important data for a better understanding of the present-day threats to marine canopy-forming macroalgae and for the design of future management actions aimed at preserving macroalgal forests., This project has received funding from the Horizon 2020 EU Research and Innovation Program (MERCES; No. 689518) the European Union’s EMFF program, AFRIMED (EASME/EMFF/2017/1.2.1.12/S4/01/SI2.789059) and the Spanish Ministry Project ANIMA (CGL2016-76341-R, MINECO/FEDER, UE). SC, JV, AV and EC are members of the Catalan Government’s consolidated research group 2017 SGR 1521 MedRecover.

Este artículo contiene 14 páginas, 5 figuras, 2 tablas.-- Special Issue: Environmental DNA for Biodiversity and Ecosystem Monitoring., In the marine realm, biomonitoring using environmental DNA (eDNA) of benthic communities requires destructive direct sampling or the setting-up of settlement structures. Comparatively much less effort is required to sample the water column, which can be accessed remotely. In this study we assess the feasibility of obtaining information from the eukaryotic benthic communities by sampling the adjacent water layer. We studied two different rocky-substrate benthic communities with a technique based on quadrat sampling. We also took replicate water samples at four distances (0, 0.5, 1.5, and 20 m) from the benthic habitat. Using broad range primers to amplify a ca. 313 bp fragment of the cytochrome oxidase subunit I gene, we obtained a total of 3,543 molecular operational taxonomic units (MOTUs). The structure obtained in the two environments was markedly different, with Metazoa, Archaeplastida and Stramenopiles being the most diverse groups in benthic samples, and Hacrobia, Metazoa and Alveolata in the water. Only 265 MOTUs (7.5%) were shared between benthos and water samples and, of these, 180 (5.1%) were identified as benthic taxa that left their DNA in the water. Most of them were found immediately adjacent to the benthos, and their number decreased as we moved apart from the benthic habitat. It was concluded that water eDNA, even in the close vicinity of the benthos, was a poor proxy for the analysis of benthic structure, and that direct sampling methods are required for monitoring these complex communities via metabarcoding., This research has been funded by project BIGPARK of the Spanish Autonomous Organism of National Parks (OAPN, project 2017- 2462), and by projects PopCOmics (CTM2017-88080, MINECO/ AEI/FEDER,UE) and ANIMA (CGL2016-76341-R, MINECO/AEI/ FEDER,UE) of the Spanish Government. AA was funded by a predoctoral FPI contract of the Spanish Government. This is a contribution from the Consolidated Research Group “Benthic Biology and Ecology” SGR2017-1120 (Catalan Government).

Este artículo contiene 12 páginas, 5 figuras., 1. Understanding the combined effects of global and local stressors is crucial for conservation and management, yet challenging due to the different scales at which these stressors operate. Here, we examine the effects of one of the most pervasive threats to marine biodiversity, ocean warming, on the early life stages of the habitat‐forming macroalga Cystoseira zosteroides, its long‐term consequences for population resilience, and its combined effect with physical stressors. 2. First, we performed a controlled laboratory experiment exploring the impacts of warming on early life stages. Settlement and survival of germlings were measured at 16°C (control), 20°C, and 24°C, and both processes were affected by increased temperatures. Then, we integrated this information into stochastic, density‐dependent integral projection models. 3. Recovery time after a major disturbance significantly increased in warmer scenarios. The stochastic population growth rate (λs) was not strongly affected by warming alone, as high adult survival compensated for thermal‐induced recruitment failure. Nevertheless, warming coupled with recurrent physical disturbances had a strong impact on λs and population viability. 4. Synthesis. The impact of warming effects on early stages may significantly decrease the natural ability of habitat‐forming algae to rebound after major disturbances. These findings highlight that, in a global warming context, populations of deep‐water macroalgae will become more vulnerable to further disturbances, and stress the need to incorporate abiotic interactions into demographic models., This work was supported by an FI‐DRG grant from the Secretaria d’Universitats i Recerca from the Economy and Knowledge Department of the Generalitat de Catalunya to P. Capdevila and by a Ramon y Cajal Research Contract (RyC‐2011‐08134) to C. Linares, and by the Ministerio de Economía y Competitividad Smart project (CGL2012‐32194). Funding was also provided by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 689518 (MERCES). This output reflects only the author’s view and the European Union cannot be held responsible for any use that may be made of the information contained therein. Most authors are part of the Marine Biodiversity Conservation Research Group (2014SGR1297, www. medrecover.org) from Generalitat de Catalunya. R. Salguero‐Gómez was supported by an NERC IRF (NE/M018458/1).

Este artículo contiene 8 páginas, 2 figuras, 1 tabla., Managing invasive alien species is particularly challenging in the ocean mainly because marine ecosystems are highly connected across broad spatial scales. Eradication of marine invasive species has only been achieved when species were detected early, and management responded rapidly. Generalized approaches, transferable across marine regions, for prioritizing actions to control invasive populations are currently lacking. Here, expert knowledge was elicited to prioritize 11 management actions for controlling 12 model species, distinguished by differences in dispersion capacity, distribution in the area to be managed, and taxonomic identity. Each action was assessed using five criteria (effectiveness, feasibility, acceptability, impacts on native communities, and cost), which were combined in an ‘applicability’ metric. Raising public awareness and encouraging the commercial use of invasive species were highly prioritized, whereas biological control actions were considered the least applicable. Our findings can guide rapid decision-making on prioritizing management options for the control of invasive species especially at early stages of invasion, when reducing managers' response time is critical., This work is a contribution of the ANR project “PAVIS: Assessing the relationships between marine protected areas and invasive species” (ANR-16-ACHN-0016-01) and the COST Action 15121 “MarCons: Advancingmarine conservation in the European and contiguous seas” supported by the European Cooperation in Science and Technology (CA15121).

Este artículo contiene 10 páginas, 10 figuras., As habitat mapping is crucially important for developing effective management and restoration plans, the aim of this work was to produce a census of available map resources at the European scale focusing on: a) key marine habitats; b) degraded habitats; c) human activities and pressures acting on degraded habitats, and d) the restoration potential of degraded habitats. Almost half of the 580 map records were derived from grey literature and web resources but contained no georeferenced files for download, thus limiting further use of the data. Biogeographical heterogeneity was observed and varied between the type and quality of information provided. This variability was mainly related to differences in research efforts and stakeholder focus. Habitat degradation was assessed in only 28% of the map records and was mostly carried out in a qualitative manner. Less than half of the map records included assessments on the recovery/restoration potential of the degraded habitats, with passive restoration by removal of human activities being the most commonly recommended measure. The current work has identified several gaps and challenges both in the thematic and geographic coverage of the available map resources, as well as in the approaches implemented for the harmonized assessment of habitat degradation. These should guide future mapping initiatives in order to more comprehensively support and advise the marine habitat restoration agenda for better meeting the objectives set in relevant policy documents and legislative acts in Europe., This research has received funding from the European Union’s Horizon 2020, research and innovation programme under grant agreement No 689518 (MERCES: Marine Ecosystem Restoration in Changing European Seas). TM was supported by Program Investigador FCT, Portugal (IF/01194/2013).

Active restoration is considered a profitable strategy to return ecosystems to their predisturbance state, in a reasonable time frame. However, ecological restoration of marine ecosystems is still in its infancy if compared to the terrestrial context. A review of 498 studies published in the last 25 years was carried out within the MERCES H2020 EU project to understand the effects of marine restoration actions across coastal habitats at global scale. Here, an overview focused on the Mediterranean Sea was carried out to identify both contextual and methodological determinants of restoration success in the basin. Results show that restoration efforts across habitats are increasing, especially in seagrasses and saltmarshes, but never approached at ecosystem level. Targets, methods, response variables and standards are still very heterogeneous. Short project duration (one-two years), small restoration areas (< 1 ha), lack of controls and knowledge of baselines are still a limit for deriving generalities. Finally, restorations rarely consider future challenges linked to global change, thus impairing long- term success stories. Marine restoration is a promising approach to counteract habitat loss in coastal areas. However, restoration science needs more robust approaches leading to the development of best practices (e.g. protocols, monitoring of the effects, reasons for failure) to be applied at spatial and temporal scales so as to answer to present and future disturbance regimes.

Este artículo contiene 11 páginas, 7 figuras, 2 tablas., Stochastic perturbations can trigger major ecosystem shifts. Marine systems have been severely affected in recent years by mass mortality events related to positive thermal anomalies. Although the immediate effects in the species demography affected by mortality events are well known, information on the mid- to long-term effects at the community level is much less documented. Here, we show how an extreme warming event replaces a structurally complex habitat, dominated by long-lived species, by a simplified habitat (lower species diversity and richness) dominated by turf-forming species. On the basis of a study involving the experimental manipulation of the presence of the gorgonian Paramuricea clavata, we observed that its presence mitigated the effects of warming by maintaining the original assemblage dominated by macroinvertebrates and delaying the proliferation and spread of the invasive alga Caulerpa cylindracea. However, due to the increase of sediment and turf-forming species after the mortality event we hypothesize a further degradation of the whole assemblage as both factors decrease the recruitment of P.clavata, decrease the survival of encrusting coralligenous-dwelling macroinvertebrates and facilitate the spreading of C. cylindracea., Financial support has been provided by a Spanish Ministry Project ANIMA (CGL2016-76341-R), OAPN project (CORCLIM 759S/2012 and 766S/2012) and European Union’s Horizon 2020 (grant agreement No. 689518) MERCES Project. This output reflects only the authors’ view and the European Union cannot be held responsible for any use that may be made of the information contained therein. J.V. has been funded by a IFUdG2016 grant. Managers of ACNP are acknowledged for sampling permissions. We also thank to David Díaz, Eneko Aspillaga, Pol Capdevila, Bernat Hereu and Fiona Tomas for their collaboration in fieldwork. J.V., C.L. and E.C. are members of the Marine Conservation Research Group (www.medrecover.org; 2017 SGR 1521) and R.C. is part of the Marine Biogeochemistry and Global Change Research Group (2017SGR1011) from the Generalitat de Catalunya.

13 páginas, 7 figuras, 1 tabla., The differential response of marine populations to climate change remains poorly understood. Here, we combine common garden thermotolerance experiments in aquaria and population genetics to disentangle the factors driving the population response to thermal stress in a temperate habitatforming species: the octocoral Paramuricea clavata. Using eight populations separated from tens of meters to hundreds of kilometers, which were differentially impacted by recent mortality events, we identify 25°C as a critical thermal threshold. After one week of exposure at this temperature, seven of the eight populations were affected by tissue necrosis and after 30 days of exposure at this temperature, the mean % of affected colonies increased gradually from 3 to 97%. We then demonstrate the weak relation between the observed differential phenotypic responses and the local temperature regimes experienced by each population. A significant correlation was observed between these responses and the extent of genetic drift impacting each population. Local adaptation may thus be hindered by genetic drift, which seems to be the main driver of the differential response. Accordingly, conservation measures should promote connectivity and control density erosion in order to limit the impact of genetic drift on marine populations facing climate change., The authors gratefully acknowledge the funding support given by the Alan Program (CC Doctoral Fellowship), by CSIC-Uruguay (Call Programa de pasantías en el exterior 2015) and by the Portuguese Foundation for Science and Technology (Fundação para a Ciència e a Tecnologia; FCT) which funded JBL Postdoctoral grant (SFRH/ BPD/74400/2010). Authors are also grateful to the MEDCHANGE project funded by the Agence Nationale pour la Recherche (ANR) and to the Spanish Ministry of Economy and Competitivity (http://www.mineco.gob.es) through the Biorock (CTM2009-08045), Smart (CGL2012-32194) and CSI-Coral (CGL2013-43106-R). Temperature data series data is part of the regional temperature observation network T-MEDNet (www.t-mednet.org); we thank J.M. Dominici for providing the data for the Réserve Naturelle de Scandola. The authors also thank the staff of Experimental Aquarium Facilities at the Institute of Marine Sciences E. Martinez and M. Delgado for the technical support provided. EC, JG, CL, PL and NT are part of the Marine Conservation research group MEDRECOVER www.medrecover.org (2009 SGR 1174) while RC and MR are part of the Marine Biogeochemistry and Global Change Research group (2014SGR1029) from the Generalitat de Catalunya.

Macroalgal forests have gone missing from most temperate rocky shores during the last decades, triggering an important biodiversity loss. Cystoseira species are some of the main marine habitat-forming species on shallow water Mediterranean rocky bottoms and follow the same tendency, mainly related to habitat destruction and pollution. However, here we suggest that anormal positive thermal events may contribute to this widespread Cystoseira decline. Monitoring thorough natural populations showed a drastic decline on a natural and relict C. crinita population in terms of density and structure coinciding with anormal high temperatures experienced during a summer period. Additionally, we experimentally test in the laboratory the cause-effect of those temperatures and UV radiation conditions experienced in the field on C. crinita populations. Although, C. crinita is able to resist high temperature picks, usually reached in Mediterranean summers, exceptional and maintained periods as those experienced during extreme events (28ºC) lead to the death of all individuals, compromising the viability and conservation of these forest-forming populations. We show how climate change may seriously compromise algal populations and synergically act with historical drivers of macroalgal decline (pollution, habitat destruction and herbivorism). Financial support from EU2020 (R+I) under grant agreement No 689518 (MERCES), MINECO (CGL2016-76341-R) and from University of Girona under congress assistance fellowship program for PhD and master students.