Disentangling causation from correlation is the foundation of the scientific method. Yet, growing evidence suggests that much observational ecology research has not correctly made this distinction due to inappropriate statistical modelling and unappreciated time-delays. Here, we apply time-lagged causal inference techniques to assess the drivers of seabird declines, using multi-decadal North Atlantic seabird data across the behaviour, mass, survival, reproduction and population size of two species' ecology (Atlantic puffin, Fratercula arctica, and black-legged kittiwake, Rissa tridactyla). We demonstrate that both climate and anthropogenic activity can suppress breeding success and cause population declines. Moreover, population size is specifically impacted by delayed recruitment effects where both species decline after a lag corresponding to their estimated age of first reproduction. These North Atlantic seabirds are therefore at risk from future environmental and anthropogenic changes, as time-delays may result in populations already on an extinction trajectory prior to changes being detectable in their abundance.

Island biota is currently threatened by global anthropogenic pressures. The limited ability of island species to track suitable conditions and their inherent sensitivity to anthropogenic changes make insular biota highly vulnerable to global threats. Although vulnerability assessments of species to single threats individually have been conducted, the vulnerability of island faunas to multiple global change drivers has not. We evaluated the relative vulnerability of 266 insular bird and mammal species from 45 islands in six well-studied archipelagos to multiple threats. We first quantified the current exposure of islands to climate change, land-use change, and biological invasions. We then calculated insular assemblage sensitivity based on species' ecological characteristics, such as diet and habitat specialization, generation length, and geographical rarity. To assess the adaptive capacity of insular species in response to these threats, we examined biotic and abiotic features, such as species' dispersal ability, terrain heterogeneity, and proportion of protected area. Exposure and adaptive capacity markers varied greatly among the six archipelagos, but the mean sensitivity of assemblages was similar across islands. Hawai'i, the Azores, and the Mascarenes had high vulnerability scores. Climate change and biological invasions were dominant threats in Hawai'i, and land-use change was the dominant threat in the Mascarenes, Azores, and Canaries. Assemblages from the Galapagos and Tristan da Cunha had lower vulnerability to current threats. The differences in vulnerability among island assemblages, mostly arising from differences in exposure and adaptive capacity, mean these islands' conservation needs differ. Our results delineate the mechanisms behind the vulnerability of insular biota under global change, a necessary step to effectively preserve island biodiversity and its associated human benefits.

Anthropogenic disturbances are degrading nature at a rate that exceeds its capacity to recover. While considerable research has focused on understanding ecosystem impacts, recovery processes remain comparatively overlooked, particularly in marine ecosystems, where long-term data on how highly complex systems respond to disturbances are scarce. In this context, we provide decadal insights into recovery patterns in Mediterranean coralligenous assemblages by revisiting a site that had lost 60% of its benthic cover due to an extreme storm in 2008, and comparing it with a nearby, non-impacted reference site. Using a community trait-based approach, we evaluated whether, after 14 years, the storm-impacted site achieved functional recovery, defined as a return to pre-disturbance levels of trait diversity and dominance. Our results show an initial recovery during the first four years, driven by the intermediate recolonization of local species and nearing pre-storm values in terms of species size and longevity. However, a decade later, recovery has stagnated, resulting in a more autotrophic and less structurally complex community, with potential consequences for ecosystem functioning. Notably, both the storm-impacted and reference sites exhibited a similar shift in trait dominance, accompanied by an increase in functional divergence, suggesting that marine heatwaves and global warming are reshaping community structure. These changes may be altering the recovery trajectory of the storm-impacted site and exacerbating its recovery debt. Overall, our findings provide new insights into how coralligenous assemblages may respond to acute extreme events in the current context of climate change, while highlighting the role of ongoing global pressures in deepening the functional deficits of recovering systems.

Animal migrations move biomass, nutrients and energy in seasonal pulses that sustain productivity, trophic networks and carbon cycling across oceans, rivers and terrestrial landscapes. Yet the loss of these flows remains poorly quantified because most biodiversity assessments track abundance rather than the biomass flows that sustain ecosystem function, and are anchored to baselines that already reflect centuries of exploitation. Using data for 5,654 species, we identified mass migrations as those comprising over 90% of total migratory biomass and reconstructed their long-term trajectories across major taxonomic groups in marine, freshwater and terrestrial realms. Migratory biomass declined by 41.9% since 1950 and by 95.2% since 1800, with losses dominated by marine fish, marine mammals and terrestrial mammals. These declines shortened migration distances, eroded trophic function and disrupted nutrient redistribution, connectivity and carbon transport across major biomes. Apparent recoveries are systematically overestimated. Species assessed as recovering against recent 1950 benchmarks frequently remain below 1% of pre-industrial 1800 levels, and mean annualised recovery rates are three orders of magnitude lower when assessed against pre-disturbance rather than recent baselines. We identify priority systems for conservation and rewilding and show that restoring migratory function requires transboundary, movement-centred frameworks anchored to historical baselines and biomass-based metrics rather than static species distributions.

Marine heatwaves (MHWs) are driving mass mortalities of coastal foundation species globally, threatening their persistence and the ecosystems they support. However, long-term demographic evidence of these impacts at regional scales is scarce. Accordingly, whether ongoing conservation actions, mainly marine protected areas (MPAs), mitigate the impact of MHWs is still an open question. Here, we address these gaps by analysing over two decades of demographic monitoring data from 49 shallow (< 40 m depth) populations of the foundation gorgonian Paramuricea clavata paired with in situ temperature records across the north-western Mediterranean (38°-43° N, 0°-8° E). Using hierarchical Bayesian models, we estimated regional-scale trends and assessed the combined influence of MHW exposure and protection status. We found that increasingly frequent extreme thermal events have caused widespread mass mortality, resulting in a 45% median decline in biomass at the regional scale over the past two decades. Within this context of extensive decline, protection temporarily buffered MHW impacts by sustaining higher overall biomass, despite protected populations experiencing greater absolute losses. Taken together, these findings indicate that local protection alone cannot offset climate-driven mortality and underscore the urgent need to integrate conservation measures with global climate action to preserve shallow marine ecosystems.

Islands are at the forefront of global environmental change. Biological invasions, land-use change, and climate change are driving population declines and causing irreversible losses in island ecosystems. Although global threat exposure maps have been developed in recent years, they are mostly designed for coarse-grained, continental-extent analyses, often overlooking islands. Here, we assessed the cumulative exposure to biological invasion, land-use change, and climate change by 2050, for more than 16,000 islands worldwide using multiple threat markers. Climate change emerged as a ubiquitous threat, being the dominant threat for 65% of all islands, followed by land-use change (22%) and biological invasions (13%). Islands with the highest cumulative exposure were more likely to be isolated, without historical connection with the mainland. Small and low-elevation islands at low latitudes exhibited greater exposure to climate change, whereas larger, high-elevation islands tended to be more exposed to land-use change. Certain countries and subdivisions, such as Seychelles, Bangladesh, China, French Polynesia, and Micronesia, harbored statistically disproportionate numbers of highly exposed islands, highlighting geographic hotspots of cumulative exposure where conservation efforts might be particularly urgent. Our study indicates that by 2050, most islands will be simultaneously exposed to a triple threat arising from the combined impacts of land-use change, climate change, and biological invasions. This study provides robust quantification of island cumulative exposure to three key drivers of biodiversity loss, making a crucial step toward assessing global biodiversity vulnerability.

Global warming is profoundly reshaping biodiversity. Until now, most research has focused on the impacts of extreme temperature events. However, in many ecosystems, it is becoming increasingly apparent that climate change is accelerating the onset of spring warming conditions. These advanced warming conditions can significantly disrupt critical biological processes such as reproduction, which is key for population persistence. While interest in phenological shifts has increased in recent years, their effects on marine foundation species, such as corals, remain poorly understood. Here, we combined observational and experimental approaches to assess the effects of advanced spring warming conditions driven by climate change on the reproduction of the Mediterranean octocoral Paramuricea clavata , a foundation species. Our findings reveal that a 2°C warming leads to a 2-week advancement in P. clavata spawning, as evidenced by both field observations, and ex-situ experiments. These results underscore the role of advanced spring warming as a significant driver of phenological shifts in coastal marine ecosystems. Furthermore, we show that this phenological shift lead to a reduction in the number of spawning events, as well as decreases in larval biomass, survival rates, and settlement success. These findings highlight the urgent necessity to monitor phenological changes in foundational marine species, as such shifts can undermine the long-term viability of coral populations and contribute to substantial decline in associated biodiversity. Consequently, the increased vulnerability of species caused by phenological responses driven by seasonal changes may lead to more dramatic consequences of ocean warming than previously anticipated.

Conservation policies aiming to halt biodiversity loss often focus on globally prevalent threats like habitat loss and exploitation, yet direct and interactive effects of multiple threats remain poorly quantified. Here, we go beyond prior meta-analyses or species-level studies by providing a global, population-level empirical analysis of threat interactions by examining 3129 vertebrate population time series worldwide with documented exposure to single and multiple threats. Populations affected solely by habitat loss or exploitation do not exhibit the steepest declines; instead, disease, invasive species, pollution, and climate change are associated with faster declines. Interactive threats contribute more to population declines than temporal or spatial variation. Counterfactual analyses reveal that mitigating multiple threats is essential to achieving nonnegative vertebrate population trends and halting biodiversity loss.

The European eel (Anguilla anguilla) is a critically endangered and declining species. Information from traditional fisheries and a fish monitoring scheme in the Ebro Delta reflect the widely reported eel decline onset in the late 1970s and also a recent, sharp and ongoing decline of similar magnitude (> 80%). This recent trend arises from both fishery and monitoring data, is solidly described by time-series analyses and agrees with patterns reported in other areas. Decline drivers could be related to emergent invasions and/or to the exploitation of the already depleted eel stock. There is an urgent need to re-evaluate eel status and associated management strategies.

As the climate crisis unfolds, marine heatwaves (MHWs), defined as discrete periods of anomalously high seawater temperatures, are emerging as one of the most pervasive threats to marine biodiversity worldwide. From coastal shallow waters to the deep sea, increasingly frequent and intense MHWs are reshaping ocean life at all levels of ecological organisation, undermining ecosystem resilience and compromising the provision of essential ecosystem services to human societies. This growing environmental challenge has rendered a new scientific discipline-marine heatwave ecology-which aims to advance our understanding, forecasting capacity and mitigation of MHW impacts on ecological systems. These priorities are central to marine science and conservation. Yet, despite increasing scientific attention, many critical research questions remain unresolved. In this cross-journal Special Feature, published across the Journal of Animal Ecology, Journal of Ecology and Functional Ecology, we present a collection of 13 studies that address some of the most pressing knowledge gaps in MHW ecology. These studies were conducted across diverse ocean basins and encompass a wide range of marine taxa, such as corals, macroalgae, seagrasses, molluscs, fish and plankton, among others. They span multiple levels of ecological organisation, from individual organisms to entire ecosystems, and employ a variety of methodologies and approaches. Collectively, the contributions to this special feature demonstrate how MHWs erode ecosystem resilience, reveal previously hidden biological and ecological impacts and show that vulnerability not only depends on thermal tolerance but also on environmental context. The studies also explore how MHW effects cascade up and down across levels of ecological organisation and reinforce the importance of applying ecological frameworks to better categorise and understand MHW dynamics. Finally, we have identified remaining knowledge gaps to guide future research, essential to further develop the MHW ecology field and to inform more effective conservation and management strategies. This will be especially urgent in the context of a rapidly warming ocean, where strong and recurrent MHWs are becoming the new normal.

Marine habitat-forming species provide crucial ecosystem functions and services worldwide. Still, the individual and combined long-term effects of ocean acidification and warming on bryozoan populations, structures, and microbiomes remain unexplored. Here, we investigate the skeletal properties, microbiome shifts, and population trends of two bryozoan species living inside and outside a volcanic CO2 vent, a natural analog to future ocean acidification conditions. We show that bryozoans can acclimatize to acidification by adjusting skeletal properties and maintaining stable microbiomes. However, we document a decrease in microbial genera playing essential functions under acidified conditions. Moreover, we show that ocean acidification exacerbates bryozoan cover loss and mortality caused by ocean warming. The observed shifts in the microbiome and cover suggest that, despite their morphological plasticity, bryozoan species will be heavily impacted by future ocean conditions, posing a threat to many benthic ecosystems in which they play a pivotal role.

Anthropogenic threats are reshaping Earth's biodiversity at an unprecedented rate and scale. Conservation policies often prioritise threats like habitat loss and exploitation based on their global prevalence. However, these assessments rarely quantify the impacts of individual or interacting threats, potential masking the true effects of the Anthropocene. Here, we quantitatively analyse the trends of 3,129 vertebrate populations worldwide with documented exposure to specific and multiple threats. Populations impacted solely by habitat loss or exploitation, the most prevalent threats, do not show the fastest declines. Rather, populations exposed to disease, invasive species, pollution, and climate change decline more rapidly. However, habitat loss and exploitation, along with climate change, do act as additive interactive threats, amplifying population declines. Notably, these interactive threats contribute to population declines, more than temporal or spatial sources of variation. Finally, counterfactual scenarios show that to achieve global non-negative vertebrate population trends, we need to mitigate the effects of multiple threats. These findings underscore the urgency of addressing the compounding effects of multiple threats to halt biodiversity loss and suggest that the local-scale impacts of climate change may be more severe than previously recognized. ### Competing Interest Statement The authors have declared no competing interest.

Establishing operational approaches to assess and forecast resilience is critical for understanding ecosystem responses to global change. Current methods fall short when applied to water-driven transitional ecosystems, which undergo periodic shifts between aquatic and terrestrial phases. These ecosystems are highly sensitive to changes in historical wet-dry regimes, yet existing approaches often neglect the interconnection and compensatory dynamics between phases, yielding unreliable resilience estimates. We propose a holistic approach that integrates the entire wet-dry cycle and treats aquatic and terrestrial phases as interconnected components of a scalable meta-ecosystem. This perspective captures key resilience mechanisms-species turnover and functional redundancy driving compensatory effects-that sustain biodiversity and functioning across phases. By framing resilience as an emergent ecosystem property, our system-wide approach identifies essential elements for reliable assessments and provides a functional pathway to make resilience evaluations more actionable, with broad implications for managing water-driven transitional ecosystems under global change.

The majority of vulnerability assessments of biodiversity to global changes have so far been applied to, and designed for, mainland systems, overlooking islands. However, islands harbour unique biodiversity and are epicentres of ongoing extinctions. We thus introduce a specific framework for quantifying the vulnerability of terrestrial insular biota to multiple threats. This framework uses markers of exposure, sensitivity, and adaptive capacity to account for the unique characteristics of island biodiversity. Our assessment framework involves five steps: (1) defining the scope of the vulnerability assessment, (2) selecting the most appropriate markers, (3) computing the vulnerability metric, (4) evaluating uncertainties, and (5) providing recommendations for conservation. The development of this vulnerability framework tailored for island systems is part of a larger initiative to meet international policy targets that better integrate biodiversity threats and dimensions. We thus discuss the need and urgency for applying this framework to guide evidence-based decisions for the conservation of insular biodiversity, and for increased attention to insular biota at the science-policy interface.

The IPCC predicts that events at the extreme tail of the probability distribution will increase at a higher rate relative to less severe but still abnormal events. Such outlier events are of particular concern due to nonlinear physiological and demographic responses to climatic exposure, meaning that these events are expected to have disproportionate impacts on populations over the next decades (so called low-likelihood, high-impact events -LLHI). Because such events are historically rare, forecasting how biodiversity will respond requires mechanistic models that integrate the fundamental processes driving biological responses to our changing climate. Here we built a matrix population model (MPM) from long-term monitored populations of an insect model species in a Mediterranean area. The model simultaneously integrates the effects of extreme microclimatic heat exposure and drought-induced host-plant scarcity on early life stages, a key methodological step forward because these understudied life stages are usually very susceptible to climatic events. This model for the first time allowed us to forecast the demographic impacts that LLHI events will have on a well-known insect considering their whole life cycle. We found that juveniles were the life stage with the largest relative contribution to population dynamics. In line with field observations, simulated population rates in current climatic regimes were importantly determined by drought impacts, producing a regional mosaic of non-declining and declining populations. The simulations also indicated that in future, climate scenarios not meeting the Paris Agreement, LLHI heat extremes triggered regionally widespread and severe declines in this currently abundant species. Our results suggest that LLHI events could thus emerge as a critical new -but overlooked- driver of the declines in insect populations, risking the crucial ecosystem functions they perform. We suggest that process-based and whole-cycle modelling approaches are a fundamental tool with which to understand the true impacts of climate change.

Understanding species population trends is key for assessing their conservation status and proposing measures to ensure their future persistence amid recent biodiversity loss. However, studies are reporting contrasting biodiversity trends over time. These discrepancies can be partly attributed to biases in global datasets, which might not capture the representativeness of local processes. Here, we aimed to address this gap of knowledge by complementing data included in the Living Planet Database (LPD), one of the largest repositories of population time-series, with locally sourced data from the Iberian Peninsula. The study aim: (i) to assess the state of wildlife Iberian vertebrates using population time-series across taxonomic groups and (ii) to determine differences between locally sourced data and LPD (evaluating also the differences between data sources). To supplement LPD, we conducted a review, analysing over 6000 peer-reviewed manuscripts and grey literature documents. We obtained 999 population time-series for 294 vertebrate species compiled in an Iberian Vertebrate (IbeV) database, two times the number of populations as the LPD includes. Our results indicate contrasting population trends across taxonomic groups, with freshwater amphibians and bony fishes showing steep declines. Moreover, the LPD shows a positive trend and IbeV indicates no net change over time. Threatened species did not exhibit net changes in population trends, while non-threatened species showed positive trends. We showed that local databases can provide distinct population trends compared to global databases. This approach highlights the need to bridge the gap between global and local datasets, to support context-specific management and conservation programmes.

Global ocean warming and acidification are two of the major threats to many marine calcifying habitat-forming species, potentially affecting entire ecosystems. Consequently, the need for a better understanding and predicting the response of marine calcifiers has never been more pressing. Paradoxically, the individual and combined long-term effects of these stressors on bryozoans have remained largely unexplored, despite their great abundance and diversity globally. Here, we first evaluate the changes in skeletal structure and mineralogy, and the associated microbiome composition on the populations of Pentapora ottomuelleriana (encrusting) and Myriapora truncata (erect) bryozoan species living inside and outside a volcanic CO2 vent in Ischia Island. We then examine the effects of a long-term exposure to elevated p CO2 and its combined effects of ocean warming on the proportion of cover of populations of the encrusting species through time after summer. Both bryozoan species show indicators of acclimatization by adjusting skeletal properties and having stable microbial communities under acidification conditions. However, we document novel patterns about microbiome shifts in response to future ocean acidification in bryozoans for the first time. Microbial genera known to have essential functions to the host such as biosynthesis of defense compounds or thermal protection were depleted at the acidified site, which suggest early warnings of potential deterioration of bryozoan health under near future ocean conditions. The proportion of cover of the encrusting species also decreased from 2016 to 2020 in both studied sites, with faster declines at the acidified ones. Our model suggests that the increasing seawater temperature drove a decline in the bryozoan cover although the combined effects with acidification accelerated its mortality rates in the CO2 vent. More multidisciplinary research combining both environmental stressors on a wider range of calcifying species is needed to better understand the adaptive capacity of the holobiont to a changing environment. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes

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.