FACETS

Coastal forests are increasingly threatened by saturated soil and elevated salinity levels resulting from sea level rise, saltwater intrusion, and storm surges. In response to rising salinization and flooding, healthy coastal forests that rely on freshwater (both wetland forests and low-elevation upland forests) are transitioning into landscapes dominated by dead or dying trees, known as ghost forests. Situated among salt-tolerant shrubs and grasses, ghost forests eventually become marshes or open water. Here, our main objective was to quantify the dynamics and pathways of these forest landscape conversions, as well as the factors contributing to the changes, which is vital for understanding the progression of coastal ecosystem degradation and forecasting future changes. We focused first on identifying the best method to track forest landscape change by exploring the role of multiple remote sensing indices (i.e., multispectral, bi-seasonal, topographical, and phenological metrics) in enhancing the performance of deep learning models (convolutional neural networks, CNNs) for land cover classification in the coastal plain of North Carolina using surface reflectance of Landsat 8 and Sentinel-2 images. Then, we used the best available data (Landsat 8) to understand long-term change and identify patterns of land cover change from 1985 to 2021. Our study reveals that incorporating phenology and topographical indices enhances the separability of the ghost forests class from all other vegetation classes. In our assessment, the higher-resolution Sentinel-2 data (F1 Score = 96.3) outperformed Landsat images (F1 score = 93.4) for the 2021 co-available year. However, Landsat remains an important tool used due to its long-term data record. Therefore, we used Landsat to determine that 21% of forests were lost between 1985 and 2021, and that the rate of loss is increasing. Between 2010 and 2021, 23,876 ha of forest were converted to marsh, ghost forest, and shrub, which is 1.5 times higher than the 16,968 ha lost between 1985 and 2010. These conversions from forest to ghost forest and marshes were driven primarily by proximity to the channel, salinity, and the increasing rate of relative sea level rise (RSLR), which are the key environmental drivers of observed changes. By quantifying these changes, we highlight regions most vulnerable to environmental stressors, providing a basis for targeted conservation strategies.

Here, we report the first genetic confirmation of golden mussels (Limnoperna fortunei) in North America, and the subsequent development, optimization, and deployment of golden mussel eDNA monitoring procedures. Aquatic species invasions are economically costly, disrupt ecosystem functionality, and impact native aquatic communities. Early detection of new invasive species enables rapid response via implementation of effective eradication or control measures and is key for reducing harmful outcomes. Initial species detection and taxonomic identification can be aided by genetic methods that have high detection sensitivity and accuracy. Genetic methods such as environmental DNA (eDNA) sampling can be used to detect invasive species before they become established in new systems, providing an early alert system to inform resource managers. Golden mussels were first detected in North America in October 2024 near the Port of Stockton in the San Francisco Estuary (SFE). The SFE is particularly vulnerable to invasion due to the access and connectivity provided by the presence of engineering infrastructure and shipping lanes. Collaborative efforts between public agencies and academic institutions are underway to develop a coordinated detection and response plan. Early detection followed by a rapid response is the best defense against prolific invasive species, such as the golden mussel.

AimSeamounts are key components of deep-sea ecosystems. Yet, their biodiversity patterns and conservation needs remain poorly understood, presenting a critical knowledge gap as they face multiple environmental stressors. Here, we aim to characterize benthic community structure across multiple seamounts along the Kyushu-Palau Ridge (KPR) and identify conservation priorities. LocationPhilippine Sea in the Western Pacific. Major taxa studiedDeep-sea benthos. MethodsWe surveyed six transects (13.3{degrees}N-22.9{degrees}N; 614-5,055 m depth; 165 kilometers in total length) using a towed camera system, yielding 31,342 images and 14,218 identified individuals. Community structure was assessed through species depth-range overlap analysis to distinguish nestedness versus turnover patterns. {beta}-diversity was partitioned into local contributions (LCBD) and species contributions (SCBD) to evaluate site-level uniqueness and species-level influence. Generalized linear mixed models were used to relate LCBD and SCBD to depth, slope, aspect, bathymetric position, and functional traits. ResultsCommunity structures varied among slopes and seamounts. Western, steeper slopes were dominated by nestedness, whereas gentler eastern slopes showed mixed patterns of nestedness and gradual turnover. Sessile species largely exhibited nestedness, while mobile taxa showed mixed structures. LCBD declined with depth overall but increased on north-facing slopes and sites with higher broad-scale bathymetric position. Wide-ranging generalist species, particularly among Echinoidea and Holothuroidea, contributed disproportionately to {beta}-diversity. Main conclusionsSeamount benthic communities along the KPR are structured by interactions between depth, geomorphology, and species ecological breadth. The dominance of nestedness on western slopes suggests that protecting shallow, species-rich habitats could capture much of the biodiversity therein. In contrast, the mixed structures on eastern slopes indicate the need for a hybrid conservation approach that includes both shallow summits and deeper, compositionally distinct zones. Our findings highlight the importance of slope-specific, depth-informed strategies to conserve these vulnerable marine ecosystems.

Artificial intelligence (AI) development is concentrated within private firms, yet their participation in scientific publishing remains poorly understood. We conducted a bibliometric analysis of all 317 AI unicorn startups (1998-2025). Only 1,389 eligible peer-reviewed publications and 688 preprints involving some leading startup contributions were identified. More than half of startups (52.4%) produced no qualifying scientific output, and only 24 firms (7.6%) produced any highly cited papers ([≥]200 citations). Scientific influence was highly concentrated: the top 10% of firms accounted for 96.8% of citations, while three startups accounted for 92 of 134 firm-attributed highly cited papers. Firm valuation was not associated with publication productivity or highly cited output, whereas funding raised showed weak associations. Overall, participation in formal scientific communication among AI unicorn startups is negligible, comprising only 0.1% of the overall AI literature in 2025. Most leading developers of AI technology do not engage with the scientific literature, raising concerns for the transparency, reproducibility, and accountability of this rapidly moving innovation frontier.

Chinstrap penguins (Pygoscelis antarcticus) in the Antarctic Peninsula and Scotia Arc regions (CCAMLR subareas 48.1 and 48.2) have experienced substantial declines, yet uncertainty remains about regional variation and conservation priorities. We applied a Bayesian hierarchical model to 1,072 nest counts from 194 colonies (1970 to 2024) to quantify population trends, estimate probabilities of exceeding IUCN Red List thresholds, and assess compensation potential across four locations. The regional population declined by 41.9% over three generations, with 91.4% probability of exceeding the 30% Vulnerable threshold but only 9.2% probability of exceeding the 50% Endangered threshold. Declines were spatially heterogeneous: South Shetland Islands (40.2% of regional population) declined by 74.7% with near-certainty of exceeding both thresholds, while South Orkney Islands showed stability with high uncertainty (median -5%, 95% CI: -31.5% to +36.8%). The probability of increasing colonies compensating for regional losses was only 7%. These results support a three-zone conservation strategy for CCAMLR's proposed Marine Protected Area: urgent protection for the South Shetland Islands, enhanced monitoring for South Orkney and Elephant Islands, and adaptive management for the Antarctic Peninsula. Our uncertainty-quantified framework provides evidence-based guidance for balancing krill fishery access with predator protection in a rapidly changing Southern Ocean.

Freshwater ecosystems in Scotland are increasingly threatened by multiple interacting stressors, including pollution, hydrological alteration, land use change, and climate-driven pressures. Scotland's rivers are amongst the most physically diverse and dynamic in the UK, contributing significantly to the country-s economy and natural heritage. Monitoring 125,000 km of waterways presents an issue, with limited funding and capacity of environmental agencies creating an environmental monitoring deficit at a time when robust data are essential for delivering national and global biodiversity targets. Citizen science offers a scalable, community driven approach to strengthening environmental evidence. This study evaluates the development, implementation, and outcomes of Guardians of our Rivers (GooR), a nationwide citizen science programme using macroinvertebrate-based river health assessments based on the Anglers' Riverfly Monitoring Initiative (RMI) established by the Riverfly Partnership. Between 2022 and 2025, GooR trained more than 850 volunteers, established 123 monitoring sites across Scotland, and generated over 860 surveys-surpassing the previous 16 years of aquatic invertebrate monitoring efforts. Standardised field training, full equipment provision, and structured support enabled high-quality data collection across diverse catchments. The establishment of nationally applied trigger and target thresholds created a consistent mechanism for detecting ecological deterioration and ensured that verified trigger breaches (n = 39 in 2025) resulted in formal investigation or follow-up. Analysis of national abundance patterns revealed ecological and biogeographic trends across the eight RMI taxa, confirming data sensitivity to habitat differences, water quality, and regional pressures. A detailed case study of the Lothian Esk catchment demonstrated the programme's capacity to detect seasonal macroinvertebrate dynamics and site level ecological trajectories over time. Overall, GooR illustrates how well-designed and well-supported citizen science can deliver high resolution spatiotemporal datasets, enhance early warning systems, empower communities, and make a meaningful contribution to promoting river health. Importantly, GooR forged a working partnership with Scottish Environmental Protection Agency (SEPA) that allowed communities to not only gather data but also transformed the way citizen science is recognized as contributing to freshwater conservation. Continued investment and long-term support will be essential to sustain these gains and realise the full potential of citizen-driven freshwater stewardship.

Background: Canadian biomedical core facilities (BCFs) provide researchers with access to advanced tools and unique technical expertise, essential for research. However, their role, sustainability, and impact remain poorly understood. We report on the evolution of model and existing state of Canadas 205 BCFs, examining challenges and benefits. Methods: Cross referencing of national databases by the Canadian Innovation Fund (CFI), and from data collected by the Canadian Network of Scientific Platforms (CNSP) allowed he identification of BCFs. Hand curation of these lists validated that cores are operational. To ensure cores not listed by CFI/CNSP were captured, research intensive institutions in Canada were independently searched to identify active cores. Results: There are currently 205 active and operational BCFs located across 9 provinces, which can be further stratified into 9 technical domains that describe the nature of services they provide. Quebec (80 cores) and Ontario (75 cores) have the highest confluence of BCFs, with Quebec having a higher ratio of cores per capita. Conclusions: While our data establishes the ubiquity of Canadian BCFs, we highlight substantial challenges including sustainability, governance, evaluation and the recognition of support for core scientists. Here, we establish a framework to address these challenges and to inform best practice, to optimize creation of impactful, accessible and functional biomedical core facilities.

The southern sea otter (Enhydra lutris nereis) population at San Nicolas Island, California, has been monitored annually since the translocation of 140 sea otters to the island was completed in 1990. Monitoring efforts have varied in frequency and method across years. In 2017, in accordance with the National Defense Authorization Act for Fiscal Year 2016, the U.S. Navy and the U.S. Fish and Wildlife Service formally initiated a sea otter monitoring and research plan to determine the effects of military readiness activities on the growth or decline of the southern sea otter population at San Nicolas Island. The monitoring program, at its basic level, includes quarterly seasonal surveys of population abundance, distribution, and foraging activity. This report presents data from the program with a focus on the recent three years from winter 2023 through winter (February) 2026. From 2023 to 2026, we measured an 8.1-percent per annum decrease in population abundance (95-percent confidence interval =1.1-14.6 percent), with 106 total individuals counted as of February 2026. Historically, sea otter habitat usage at San Nicolas Island was concentrated on the west end of the island. Between 2017 and 2019, we observed increased seasonal usage of the north and south sides of the island, and in 2020-2022, a large (approximately 30-40 individuals) group of sea otters (raft) took up residence off the east end. During 2023-2026 the east end raft disappeared, and sea otters returned to their historical habitat usage patterns at the west end of the island. Foraging data were collected from summer 2023 to winter 2026 on a total of 461 foraging dives in 32 foraging bouts, and the majority of identified prey on successful dives (n=325) were sea urchins (124) followed by snails (48), bivalves (41) and crabs (23). One lobster and one octopus were also identified among the sea otter prey items. We combined these data with data from 2020-2022 to estimate overall energy intake rates that averaged 7.7 kilocalories per minute (95-percent credible interval =6.6-9.1 kilocalories per minute). These results can be useful to the planning of future monitoring and research of sea otters at San Nicolas Island.

Deep-sea abyssal plains harbour extensive biodiversity, much of which remains undocumented. Polymetallic nodules in the abyssal plains of the Clarion-Clipperton Zone (CCZ), Central Pacific, harbour diverse meiofaunal communities within their crevices, representing an understudied habitat. Given their high concentrations of nickel, copper, and cobalt, nodules are currently one of the primary targets for the extraction of deep-sea mineral resources. Here, we characterise the physical properties of polymetallic nodules, quantify their meiofaunal crevice communities, and compare them to those from the nearby sediments. We show that nodules contain internal cracks and microfossils, that their crevices harbour meiofaunal communities dominated by nematodes and copepods, and that faunal abundance increases significantly with nodule volume. Nodule-crevice nematode and copepod abundances were equivalent to approximately 10% and 25%, respectively, of those recorded in nearby sediments across the two exploration contract areas in the eastern CCZ. Based on 18S rRNA data, nematode and copepod assemblages recovered from nodule crevices differed from those recovered from nearby sediments collected during the same expedition and within the same exploration contract areas. Our findings, therefore, point to the possibility of nodule-associated crevice meiofauna communities and the consequent risk of biodiversity loss associated with nodule removal through potential future commercial mining.

Benthic algae integrate catchment-and reach-scale pressures in streams. We assessed land-use effects on benthic algal assemblage structure, chlorophyll-a, ash-free dry mass (AFDM), and autotrophic index across 24 headwater streams in the Sondu-Miriu River basin, Kenya, and explored wet-dry patterns in two monitoring streams. We sampled across four land-use categories: natural forest (NF), tea and tree plantations (TTP), smallholder agriculture (SHA), and smallholder tea (SHT). Synoptic sampling occurred in August 2025, and one NF stream and one SHA stream were sampled five times between November 2024 and May 2025. Shannon and Simpson diversity were highest in NF streams and lowest in SHT streams. Chlorophyll-a and AFDM were highest in SHA streams; chlorophyll-a was lowest in SHT, while AFDM and autotrophic index were lowest in NF. Relative abundance patterns showed that SHA streams were dominated by Lyngbya and Stigeoclonium, whereas SHT streams were dominated mainly by Stigeoclonium; NF streams supported persistent diatom-rich assemblages. Non-metric multidimensional scaling showed land-use separation of benthic algal assemblages, while redundancy analysis indicated weak, non-significant evidence of environmental associations in the synoptic dataset. Composition and biomass metrics tracked land-use gradients and wet-dry patterns, supporting periphyton-based bioassessment for monitoring disturbance in Afrotropical headwater streams.

1. Sandy beaches along urbanized coasts are increasingly managed through beach nourishment and hard infrastructure, yet these interventions often constrain natural dune-building processes. Along the Belgian coast, where much of the beach-dune interface is bordered by dikes, promenades and intensive recreation, strandline vegetation may provide an overlooked mechanism for retaining sand and initiating embryo dune development. 2. We assessed the potential for four pioneer dune plant species (Cakile maritima, Calamagrostis arenaria, Elymus farctus and Salsola kali) to establish, develop vegetation cover and contribute to sand accumulation along the Belgian coast. Using field surveys from 2017-2023, LiDAR-derived beach elevation and annual sediment dynamics, we modelled species occurrence and abundance/cover in low-disturbance reference zones and projected these relationships across the wider coastline. 3. Occurrence models identified where abiotic conditions allow plants to establish and persist until the late growing season, whereas zero-inflated abundance/cover models estimated expected vegetation development across environmental gradients. Predicted occurrence was widespread for several species, suggesting that the abiotic gradients modelled here are not the primary constraints on potential establishment across large parts of the coast. In contrast, expected abundance/cover showed stronger species-specific responses, particularly to sand accretion, indicating that sediment dynamics mainly affect post-establishment vegetation development rather than occurrence alone. 4. Independent field measurements of embryo dunes showed positive relationships between vegetation cover and local sand accumulation for all four species. When scaled using spatial predictions of potential abundance/cover, pioneer vegetation could retain substantial volumes of sand, with Cakile maritima contributing the largest share, followed by Salsola kali, Elymus farctus and Calamagrostis arenaria. Estimated volumes depended on assumptions about whether vegetation occurs as dispersed units or aggregated patches. 5. Synthesis and applications. Our results show that, even along a heavily urbanized and nourished coastline, abiotic conditions can support strandline vegetation and embryo dune initiation where disturbance is reduced. Management actions such as limiting trampling, adapting beach cleaning and protecting strandline vegetation could enhance the retention of nourished sand and support nature-based coastal defense. Rather than replacing engineered interventions, strandline vegetation may increase the efficiency with which available sediment is retained within the beach-dune system.

Quagga mussels (Dreissena rostriformis bugensis) are ecosystem engineers that can alter nutrient cycling, benthic-pelagic coupling, and food-web structure in deep lakes. Although their invasion trajectories are well documented in the Laurentian Great Lakes in North America, depth-specific population dynamics remain poorly resolved in recently invaded European perialpine lakes. We analyzed five annual lake-wide surveys (2021-2025) from 54 stations spanning 2.4-253 m depth in Lake Constance to quantify changes in quagga mussel density, biomass, and shell-length distribution. Contrary to expectations of lake-wide exponential growth, shallow-water populations (< 20 m) showed no significant increase during the study period and appear to have reached carrying capacity before monitoring began. In contrast, densities increased monotonically at intermediate depths (40-125 m), indicating ongoing expansion into deeper strata. Mean shell length declined with depth, and size distributions in shallow waters shifted toward larger individuals, consistent with a transition from active recruitment to somatic growth of established mussels. Compared with the Laurentian Great Lakes, Lake Constance already has substantially higher shallow-water biomass, whereas deeper invasion trajectories are broadly similar. These results show that quagga mussel invasion in deep European lakes can combine rapid littoral saturation with slower profundal expansion, complicating direct transfer of predictions from the Great Lakes. Continued depth-stratified monitoring will be essential for anticipating future ecosystem effects in perialpine lakes.

Businesses are increasingly encouraged to disclose their nature-related dependencies, impacts, risks and opportunities. A common component of sustainability reporting is screening operational sites for ecologically sensitivity to identify locations for further evaluation and action. However, with 600+ biodiversity metrics available, selecting and interpreting appropriate metrics remains challenging for business. We developed a simple screening framework informed by the Taskforce for Nature-Related Financial Disclosures guidance, grouping eleven widely used global biodiversity metrics into four complementary [&prime]baskets[&prime], representing different aspects of biodiversity. We created hypothetical but realistic mining, onshore wind energy and agricultural companies, to assess how metric choice, buffer size, scoring approach and sensitivity thresholds influence screening outcomes. Our basket framework consistently identified similar high-priority sites across metric combinations, but site rankings varied with methodological choices. We recommend clearer guidance on metric selection and application, alongside greater transparency from business regarding assumptions, methods and limitations when screening sites for ecological sensitivity.

The tidal wetlands of Louisiana comprise about 25% of those found throughout the conterminous United States yet estimates of wetland loss rates in the region between 1932 and 2016 have exceeded 60 km2 yr-1. To mitigate further degradation and wetland loss in the region, a globally unprecedented $50B, 50-year plan for coastal Louisiana is driving restoration efforts, and demand exists from multiple stakeholders for regularly updated, regional-scale, accurate land cover information. We used machine learning (random forests; RF) and cloud computing to develop a new Landsat-based, marsh vegetation community geospatial dataset. The dataset depicts wetland vegetation community types defined in a previous study at annual (1985-2025) time steps at 30-m resolution. An RF algorithm was used to integrate training samples with feature variables derived from Landsat imagery, and the resulting geospatial data product achieved an overall correct classification rate of 78%. The approach for development of the land cover dataset presented here has potential for application in other coastal wetland habitats throughout the world.

Blue Economy models position aquaculture as a key pathway to securing global food security. Species selected for aquaculture typically show rapid growth, high stress tolerance and fast biomass accumulation, but these same traits may increase their potential to become invasive when introduced beyond their native range. We investigated the invasion history and current status of the commercially important red seaweed Kappaphycus alvarezii in the Palk Bay-Gulf of Mannar region of India. This is one of the worlds largest cultivation hubs, a climatically vulnerable marine biodiversity hotspot, and one of the three regions to report invasion. We combined in-water surveys, interviews with wild seaweed collectors, and a review of published literature to reconstruct the history of invasion and assess current status. Invasion has declined substantially, with interviews indicating that the disappearance of invasive populations began around 2014. We discuss several non-mutually exclusive explanations for this decline, including climate change, loss of coral substrate, herbivory, and reduced vitality of the seaweed. Although the decline in invasion is encouraging for coral reefs, our findings raise questions about the ecological and socioeconomic consequences of introducing non-native aquaculture species under Blue Economy initiatives, particularly in ecologically sensitive regions vulnerable to climate change.

Capelin (Mallotus villosus), a key forage fish in the Northwest Atlantic, links zooplankton to predators including commercial fishes, seabirds, and marine mammals, yet its life-cycle movements in the Gulf of St. Lawrence (GSL) remain poorly understood. Between 2022 and 2024, otoliths from 927 individuals collected during and after spawning were analysed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Building on previous work on regional structuring, seven trace elements (Li, B, Mg, K, Zn, Sr, Ba) were used to discriminate three regions. Early-life regional signatures were inferred through an edge-to-core approach, assigning otolith core chemistry to one of these regions using quadratic discriminant analysis. The core was treated as an integrated early-life signal (late-larval to early juvenile period) rather than a strictly natal signature. Spatial variation in core chemistry was consistent across cohorts, mirroring the stability documented on the otolith edge. Results revealed widespread dispersal alongside partial regional residency: individuals with northeastern early-life signatures showed the strongest correspondence between early-life and capture regions, whereas other regions were more connected. Fish sampled during spawning were more often reassigned to their inferred early-life region than post-spawning fish, a regional-scale homing-like pattern consistent with regional spawning fidelity. This coexistence of dispersive and resident strategies likely generates a portfolio effect buffering the population against environmental variability and localised reproductive failures.

Registered Reports are a publication format designed to reduce publication bias by guaranteeing publication before results are known. This guarantee is considered attractive in the prevailing publish or perish culture. But would researchers always prefer such a low-risk option? When strong results allow publication in prestigious journals, the results-dependent nature of standard publications can actually be an advantage for authors. Given this trade-off, the choice between publication formats represents decision making under risk, and researchers may not always be risk-averse. To better understand under which circumstances Registered Reports are likely to be popular, we draw on risk-sensitivity theory from behavioural ecology and develop an agent-based model that explores how four factors shape publication strategies: whether additional publications yield diminishing or increasing career returns, the pace at which studies are completed, publication targets, and competition. We find that many realistic configurations lead researchers to avoid Registered Reports, even when Registered Reports are nearly as valuable as the best possible standard publication. Intense competition and low empirical pace can make the format unviable, while high empirical pace attenuates most other effects. Given prevailing career incentives in many fields, these results suggest that the market share of Registered Reports may remain trivially low without additional incentives or interventions.

Knowledge regarding variation in habitat use among individuals is crucial for understanding population dynamics and for management and conservation measures. This is especially important for diadromous fishes that shift between habitats, being affected by external pressures and environmental change in different habitats over ontogeny. Herer, we assessed individual variation in habitat use of European eel along a salinity gradient, ranging from fully marine to freshwater in northern Europe, using otolith microchemistry data from >3600 eel together with established time-series segmentation and clustering methods. We show that eel display high degree of individual variation in habitat use. Assigned life-histories included coastal resident, freshwater resident, and coastal and freshwater habitat shifting individuals. Coastal resident eels were observed in a large range of salinities. Given the widespread occurrence of migration barriers in freshwater, it is unknown whether the coastal resident eel preferred that habitat, or if it was the only available habitat for them. Our findings nonetheless highlight the need to include coastal habitats when assessing population development and silver eel production of the critically endangered European eel.

The management of Atlantic bluefin tuna (Thunnus thynnus) is currently defined by a long-standing life-history paradox: a stark divergence in maturation schedules between the Eastern and Western stocks. While the Mediterranean contingent matures at approximately 104 cm straight fork length (SFL; age 3-5), the western stock has long been characterized as a late-maturing, at [~]190 cm SFL (age 8+), and as late as age 15.8, based on size-at-catch data in the presumed exclusive spawning areas of the Gulf of Mexico. This discrepancy defies maturity states confirmed by endocrine hormones as well as established life-history principles that link metabolic energetics to reproductive biology. To resolve this critical issue in stock assessment, we present a sensitivity analysis based on the first histological evidence of spawning- capable individuals from 42 bluefin females (97-244 cm curved fork length or [~]95- 236 cm SFL) sampled in June 2025 within the Slope Sea, Northwest Atlantic. This historically overlooked, temperate spawning ground must be recognized and past estimates of stock productivity reevaluated. Our data provide a conservative estimate of length-at-50% maturity, L50 for females at 123.3 cm SFL, effectively reconciling the reproductive parameters of the two stocks based on histology. Our findings align established bluefin tuna metabolic and evolutionary symmetries in life history, irrespective of management boundaries. Incorporating this previously unrecognized spawning group (i.e., smaller, younger fish) calls for a substantial upward revision of Western spawning stock biomass (SSB). This biomass represents an intrinsic biological buffer that could contribute to the Atlantic bluefins adaptation and resilience. Appreciating demographic diversity is critical to accurately diagnosing stock vulnerability, ensuring that management frameworks protect long-term population stability in the face of climate-driven oceanographic shifts and ongoing exploitation pressure.

Environmental DNA (eDNA) metabarcoding has become a cornerstone of marine biodiversity monitoring, yet it recovers genetic material irrespective of organism viability and may therefore conflate historical and contemporary community signals. Environmental RNA (eRNA), derived from less stable ribonucleic acid, is hypothesized to be biased toward metabolically active organisms and may provide a more temporally resolved snapshot of living communities. Here we present a paired eDNA/eRNA metabarcoding comparison across a tropical marine seascape, analyzing 19 co-sampled sites spanning coral reefs, mangroves, a seagrass bed, shipwrecks, a cenote, and coastal infrastructure around San Andres Island, Colombia. To our knowledge this is the first in situ, ecosystem-scale paired eDNA/eRNA survey of the broad eukaryotic community across multiple natural habitat types in a tropical marine system, extending mesocosm and freshwater work (e.g., Giroux et al., 2022) to a field setting. Using COI-region amplicon sequencing processed by NatureMetrics, we recovered 1,944 operational taxonomic units (OTUs) across the 19 paired sites. Of these, 1,015 (52.2%) were detected by both approaches, 305 (15.7%) were unique to eDNA, and 624 (32.1%) were unique to eRNA. The eRNA-unique fraction was taxonomically enriched for groups including diatoms (class Bacillariophyceae, phylum Ochrophyta), ciliates, and other protists. Paired Wilcoxon signed-rank tests showed that eRNA recovered significantly higher OTU richness (median 239 vs. 207; W = 36, p = 0.016) and Shannon diversity (median 3.64 vs. 3.38; W = 40, p = 0.026) than eDNA. The mean per-site Jaccard similarity between paired samples was 0.40, indicating substantial turnover in the rare-taxon composition recovered by each method. Principal coordinates analysis of Bray-Curtis dissimilarity showed that habitat type structured abundance-weighted community composition (PERMANOVA F = 2.49, p = 0.001) whereas molecular method did not (F = 1.37, p = 0.107). A PERMDISP test found homogeneous multivariate dispersion between methods (F = 0.01, p = 0.92), reinforcing the absence of a method effect, but significant dispersion heterogeneity among habitats (F = 24.0, p < 0.01), so the habitat result is interpreted with caution. Indicator species analysis identified 73 OTUs significantly associated with one template: eDNA indicators were dominated by dinoflagellates (Dinophyceae) and eRNA indicators by diatoms (Bacillariophyceae) and fungi, consistent with an eRNA bias toward metabolically active microbial eukaryotes. A read-weighted overlap analysis showed that although eRNA-unique OTUs outnumbered eDNA-unique OTUs roughly two to one, the large majority of reads (>95%) fell in shared OTUs, so method-unique detections are predominantly rare taxa. We discuss the complementary value of eRNA for marine monitoring, with the seagrass habitat -- where eRNA reduced masking by terrestrial plant material -- as the clearest use case, and propose, rather than prescribe, the integration of eRNA into routine programs.