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Extreme climatic events (ECEs), such as marine heatwaves (MHWs), are a major threat to biodiversity. Understanding the variability in ecological responses to recurrent ECEs within species and underlying drivers arise as a key issue owing to their implications for conservation and population recovery. Yet, our knowledge on such ecological responses is limited since it has been frequently gathered following "single‐event approaches" focused on one particular event. These approaches provide snapshots of ecological responses but fall short of capturing heterogeneity patterns that may occur among recurrent ECEs, questioning current predictions regarding biodiversity trends. Here, we adopt a "multiple events" perspective to characterize the effects of recurrent ECEs on the ecological responses in Paramuricea clavata, a Mediterranean temperate coral threatened by MHWs. Through a common‐garden experiment repeated three consecutive years with the same individuals from three populations, we assessed the respective roles of environmental (year effect), genetic (population effect), and phenotypic (population‐by‐environment interactions effect) components in the ecological response to recurrent heat stress. The environmental component (year) was the main driver underlying the responses of P. clavata colonies across experiments. To build on this result, we showed that: (i) the ecological responses were not related to population (genetic isolation) and individual (multilocus heterozygosity) genetic make‐up, (ii) while all the individuals were characterized by a high environmental sensitivity (genotype‐by‐environment interactions) likely driven by in situ summer thermal regime. We confront our experimental results to in situ monitoring of the same individuals conducted in 2022 following two MHWs (2018, 2022). This confirms that the targeted populations harbor limited adaptive and plastic capacities to on‐going recurrent ECEs and that P. clavata might face unavoidable population collapses in shallow Mediterranean waters. Overall, we underscore the need to consider the recurrence of ECEs to assess threats to biodiversity and to forecast its evolution. [ABSTRACT FROM AUTHOR]

• Diving impacts on the density, recruitment, survival, and size of the colonies. • Bryozoan recruitment events are stochastic showing inter-annual variation. • Higher growth and lower necrosis rates were found during the colder months. • Bryozoan densities on non-frequented locations have increased since the 1990s. • Pentapora fascialis showed a fast population dynamics with high capacity of recovery. Marine Protected Areas (MPAs) have been recognized as effective management and conservation tools to protect marine coastal ecosystems. However, due to an increasing interest in marine ecosystems, recreational activities such as scuba diving are rapidly growing in these areas, highlighting the need to implement adaptive management strategies based on continuous monitoring and evaluation of protected areas. To date, several studies have quantified the impact of diving using benthic species as indicators, such as bryozoans, but usually ignoring their population dynamics. Here, we studied the population dynamics of the abundant and common bryozoan Pentapora fascialis on a Mediterranean MPA with high levels of diving activity. Specifically, we monitored eight different localities with two different levels of diving frequentation (non-frequented versus frequented) from October 2015 to October 2018, accounting for the demographic parameters before and after the summer. Our results showed the impact of diving on the density, recruitment, survival, and size of colonies, reaching higher values on non-frequented localities. In addition, we detected two peaks of recruitment during July 2016 and July 2018, suggesting that bryozoan recruitment events are stochastic, with a high inter-annual variation. Contrastingly, regardless of the diver frequentation level, we found higher growth rates during the colder months and higher necrosis rates after the summer in all the studied localities. Besides the aforementioned differences, the densities observed in this study were much higher compared to previous studies performed in the same area during the 1990s. Taken together, these results suggested rapid population dynamics of P. fascialis , with fast growth rates and a high capacity to recover from perturbations. Despite the quantified effects of diving on our studied species, their abundance in frequented sites remained very low over the whole study period, compromising the use of P. fascialis as an optimal indicator of diving impact for adaptive management of temperate benthic populations. Overall, our results highlight the importance of continuous monitoring programs to unravel the population dynamics of indicator species to effectively manage marine populations and evaluate the impact of human activities on marine protected areas. [ABSTRACT FROM AUTHOR]

Climate change is impacting ecosystems worldwide, and the Mediterranean Sea is no exception. Extreme climatic events, such as marine heat waves (MHWs), are increasing in frequency, extent and intensity during the last decades, which has been associated with an increase in mass mortality events for multiple species. Coralligenous assemblages, where the octocoral Paramuricea clavata lives, are strongly affected by MHWs. The Medes Islands Marine Reserve (NW Mediterranean) was considered a climate refugia for P. clavata, as their populations were showing some resilience to these changing conditions. In this study, we assessed the impacts of the MHWs that occurred between 2016 and 2022 in seven shallow populations of the octocoral P. clavata from a Mediterranean Marine Protected Area. The years that the mortality rates increased significantly were associated with the ones with strong MHWs, 2022 being the one with higher mortalities. In 2022, with 50 MHW days, the proportion of total affected colonies was almost 70%, with a proportion of the injured surface of almost 40%, reaching levels never attained in our study site since the monitoring was started. We also found spatial variability between the monitored populations. Whereas few of them showed low levels of mortality, others lost around 75% of their biomass. The significant impacts documented here raise concerns about the future of shallow P. clavata populations across the Mediterranean, suggesting that the resilience of this species may not be maintained to sustain these populations face the ongoing warming trends. [ABSTRACT FROM AUTHOR]

Climate change threatens the structure and function of marine ecosystems, highlighting the importance of understanding the response of species to changing environmental conditions. However, thermal tolerance determining the vulnerability to warming of many abundant marine species is still poorly understood. In this study, we quantified in the field the effects of a temperature anomaly recorded in the Mediterranean Sea during the summer of 2015 on populations of two common sympatric bryozoans, Myriapora truncata and Pentapora fascialis. Then, we experimentally assessed their thermal tolerances in aquaria as well as different sublethal responses to warming. Differences between species were found in survival patterns in natural populations, P. fascialis showing significantly lower survival rates than M. truncata. The thermotolerance experiments supported field observations: P. fascialis started to show signs of necrosis when the temperature was raised to 25-26 °C and completely died between 28-29 °C, coinciding with the temperature when we observed first signs of necrosis in M. truncata. The results from this study reflect different responses to warming between these two co-occurring species, highlighting the importance of combining multiple approaches to assess the vulnerability of benthic species in a changing climate world. [ABSTRACT FROM AUTHOR]

Aim: Intraspecific genetic diversity is one of the pillars of biodiversity, supporting the resilience and evolutionary potential of populations. Yet, our knowledge regarding the patterns of genetic diversity at macroecological scales, so‐called macrogenetic patterns, remains scarce, particularly in marine species. Marine habitat‐forming (MHF) species are key species in some of the most diverse but also most impacted marine ecosystems, such as coral reefs and marine forests. We characterize the patterns and drivers of genetic diversity in MHF species and provide a macrogenetic baseline, which can be used for conservation planning and for future genetic monitoring programmes. Location: Global. Time period: Contemporary. Major taxa studied: Bryozoans, hexacorals, hydrozoans, octocorals, seagrasses, seaweeds, sponges. Methods: We analysed a database including genetic diversity estimates based on microsatellites in more than 9,000 georeferenced populations from 140 species, which belong to seven animal and plant taxa. Focusing on expected heterozygosity, we used generalized additive models to test the effect of latitude, taxon, and conservation status. We tested the correlation between the species richness and the genetic diversity. Results: We reveal a significant but complex biogeographic pattern characterized by a bimodal latitudinal trend influenced by taxonomy. We also report a positive species genetic diversity correlation at the scale of the ecoregions. The difference in genetic diversity between protected and unprotected areas was not significant. Main conclusions: The contrasting results between MHF animals and plants suggest that the latitudinal genetic diversity patterns observed in MHF species are idiosyncratic, as reported in terrestrial species. Our results support the existence of shared drivers between genetic and species diversities, which remain to be formally identified. Concerning, these macrogenetic patterns are not aligned from the existing network of marine protected areas. Providing the first macrogenetic baseline in MHF species, this study echoes the call regarding the need to consider genetic diversity in biodiversity assessments and management. [ABSTRACT FROM AUTHOR]

Canopy‐forming algae play a key role in temperate coastal ecosystems sustaining complex habitats that provide food and refuge for rich associated biotic communities. These macroalgae are in decline in many coastal areas, where overgrazing by herbivores can lead to the loss of these highly structured and diverse habitats toward less complex sea urchin barren grounds. Once established, low productive barren grounds are considered stable states maintained by several positive feedback mechanisms that prevent the recovery of marine forests. To revert this global decline, restoration efforts and measures are being encouraged by EU regulations and local actions. Here, we tested the success of active revegetation techniques as a tool to promote functional and productive Treptacantha elegans forests in sea urchin barren grounds under different restoration strategies (active, and combined active with passive strategies). Active revegetation was performed in 6 barren grounds, 3 located inside a Mediterranean No‐Take marine reserve (active and passive strategy) and 3 outside (active strategy alone), following a three‐step protocol: (1) sea urchin population eradication, (2) seeding with Treptacantha elegans, and (3) enhancement of T. elegans recruitment. Revegetation success was assessed 1 year later in the six barren grounds, but was only achieved after combining active with passive restoration strategies. Our results encourage revegetation of barren grounds to shift from less productive habitats to complex T. elegans forests, highlight the potential of the combined passive and active restoration strategies, as well as the important role of marine reserves not only in conservation but also in ecological restoration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Understanding how no-take zones (NTZs) shape the population dynamics of key herbivores is crucial for the conservation and management of temperate benthic communities. Here, we examine the recovery patterns of sea urchin populations following a high-intensity storm under contrasting protection regimes in the NW Mediterranean Sea. We found significant differences in the recovery trends of Paracentrotus lividus abundance and biomass in the five years following the storm. The P. lividus populations outside the NTZ recovered faster than the populations inside the NTZ, revealing that predation was the main factor controlling the sea urchin populations inside the NTZ during the study period. Arbacia lixula reached the highest abundance and biomass values ever observed outside the NTZ in 2016. Our findings reveal that predation can control the establishment of new sea urchin populations and emphasize top-down control in NTZs, confirming the important role of fully protected areas in the structure of benthic communities. Highlights • Top-down controls are the main force controlling the recovery of depleted herbivorous populations. • Fully protected areas have an important role in the recovery patterns of sea urchin populations. • Well-designed long-term monitoring is key for a better understanding of the natural dynamics of benthic populations. [ABSTRACT FROM AUTHOR]

During the last two decades, several Marine Heatwaves (MHWs) have affected coralligenous assemblages in the Mediterranean Sea, causing catastrophic mass mortalities of several habitat-forming species such as gorgonians, corals, and sponges. Even though Marine Protected Areas (MPAs) are contributing to effectively protect marine ecosystems, the impacts associated to extreme climatic events within MPAs are jeopardizing their protective role. Therefore, minimizing local stressors within MPAs is crucial to minimize interactive effects with global, more difficult to manage, stressors. To address this, we assessed to what extent the regulation of diving frequentation can support more effective protection to climate change, focusing on the case study of the Medes Islands, which has recently suffered the impacts of different global stressors and is one of the most visited MPAs in the Mediterranean Sea. We combined 6 years of demographic data of the red gorgonian Paramuricea clavata with population modelling tools, to explore the long-term viability of this species to different managing schemes and mass mortality events scenarios. Overall, our results show that climate-adaptive management of the recreational diving activity under climate change can enhance the long-term viability of this key Mediterranean habitat-forming octocoral, which is otherwise predicted to go locally extinct at shallow depths (<25 m) within the next 20 years. This study provides one of the few attempts to quantify to what extent an adaptive management scheme may help delay climate change impacts in a Marine Protected Area. • Marine heatwaves are severely impacting key Mediterranean octocorals. • Over-frequentation by divers can be detrimental in no-take marine protected areas. • Interactions between local and global stressors can be synergistic. • Adaptive management on local impacts gives borrowed time to face climate change. • Long-term monitoring and modelling are key to design adaptive management schemes. [ABSTRACT FROM AUTHOR]

The widespread decline of canopy-forming macroalgal assemblages has been documented in many regions during the last decades. This pattern is often followed by the replacement of structurally complex algal canopies by more simplified habitats (e.g., turfs or sea urchin barren grounds). Against all odds, the fucoid Treptacantha elegans, a large Mediterranean brown macroalga, broadened its depth range to deeper and exposed environments and displayed an unexpected range expansion along the northern coast of Catalonia over the last two decades. Here, we reconstruct the spread of T. elegans in time and space and unravel ecological and demographic traits such as population dynamics and genetic patterns to provide a comprehensive and integrated view of the current status and geographical expansion for this species. Fast-growing dynamics, early fertile maturity, and high turnover rate are the main competitive advantages that allow the exposed populations of T. elegans to colonize available substrata and maintain dense and patchy populations. We also provided evidence that the deeper and exposed populations of T. elegans constitute a single group across the Catalan coast, with little genetic differentiation among populations. This seems to support the hypothesis of a unique source of spread in the last decades from the Medes Islands No-Take Zone towards both southern and northern waters. [ABSTRACT FROM AUTHOR]

Macroalgal communities have an essential role in the shallow benthic habitats of temperate seas, where changes in their composition can resonate through entire coastal ecosystems. As all major ecosystems on Earth, algal beds have already been affected by multiple disturbances. Passive conservation tools, such as marine protected areas or No-take zones, have the potential to reduce some of the anthropogenic impacts by limiting human activity. However, without a good knowledge of the natural community dynamics, it is not easy to discern between changes fruit of the intrinsic variability of biological communities and the ones caused by human-related stressors. In this study, we evaluated the natural variability of macroalgal communities' composition inside and outside a Mediterranean No-Take marine reserve during 15 years. We described their temporal dynamics considering their main drivers and we tested the effect of protection in seaweed beds. We did not find differences either in the composition of the macroalgal assemblages or the total algal cover between protected and non-protected locations over the fifteen years of study. Nevertheless, we observed a positive effect of the protection increasing the cover of some specific species, such as the canopy-forming Treptacantha elegans. Our results highlight the importance of obtaining long-term data in ecological studies to better understand the natural variability of marine communities. Accordingly, a robust understanding of the community dynamics would help us to avoid misinterpretations between 'impacted' or 'in-recovery' communities when recovery times are longer than the study periods. • Long-term stability of macroalgal assemblages. • Marine protection does not affect the most representative macroalgal species. • Long-term monitoring is key for a better understanding of the natural dynamics of benthic populations. • A current and unique baseline of the rocky-shallow infralittoral macroalgal assemblages in the NW Mediterranean Sea. [ABSTRACT FROM AUTHOR]