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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]

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]

Marine ecosystems are highly affected by several human stressors. In this context, beyond passive restoration measures such as the creation of marine protected areas, it is urgent that we explore active restoration measures to enhance and accelerate the recovery of sessile marine species.Bryozoans are among the most common sessile invertebrates in rocky bottom ecosystems and are considered habitat‐forming species that are highly vulnerable to physical disturbances, such as recreational diving, ghost fishing nets, and global warming, which makes them highly vulnerable to other impacts. Despite their ecological importance and vulnerability, to date restoration actions for bryozoans have rarely been explored.In this study, different restoration techniques were developed and tested, with a focus on two types of effective methodologies previously applied to other marine invertebrates: recruitment enhancement and the transplantation of adult colonies, in both cases using the Mediterranean bryozoan Pentapora fascialis as a model species.First, different types of artificial surfaces were installed in different coralligenous habitats to test the enhancement of recruitment, concluding that plastic grids are the best substrate in terms of facilitating the recruitment of new bryozoan colonies.Second, different methodologies were tested for adult transplantation. The most successful was to fix colonies to a suitable substrate with a nylon thread attached to the colony ex situ (i.e. on the boat).Using this technique a trial restoration programme was undertaken, involving transplanting adult colonies collected from a ghost fishing net trapped on the bottom, which showed a high survival rate of ~50% after 6 months.The low economic cost of the implementation of the proposed techniques as well as the successful results obtained highlight the viability of restoring bryozoan populations over long temporal and spatial scales. [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]

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]