Aquatic ecosystems are particularly vulnerable to the introduction of non-indigenous species (NIS), leading to multi-faceted ecological, economic and health impacts worldwide. The Iberian Peninsula comprises an exceptionally biodiverse Mediterranean region with a high number of threatened and endemic aquatic species, most of them strongly impacted by biological invasions. Following a structured approach that combines a systematic review of available information and expert opinion, we provide a comprehensive and updated multi-taxa inventory of aquatic NIS (fungi, macroalgae, vascular plants, invertebrates and vertebrates) in Iberian inland waters. Moreover, we assess overall patterns in the establishment status, introduction pathways, native range and temporal introduction trends of listed NIS. In addition, we discuss the legal coverage provided by both national (Spanish and Portuguese) and European NIS regulations. We inventoried 326 aquatic NIS in Iberian inland waters, including 215 established, 96 with uncertain establishment status and 15 cryptogenic taxa. Invertebrates (54.6%) and vertebrates (24.5%) were the groups with the highest number of NIS, with Arthropoda, Mollusca, and Chordata being the most represented phyla. Recorded NIS originated from diverse geographic regions, with North and South America being the most frequent. Vertebrates and vascular plants were mostly introduced through intentional pathways (i.e. release and escape), whereas invertebrates and macroalgae arrived mostly through unintentional ways (i.e. contaminant or stowaway). Most of the recorded NIS were introduced in Iberian inland waters over the second half of the 20^th century, with a high number of NIS introductions being reported in the 2000s. While only 8% of the recorded NIS appear in the European Union list of Invasive Alien Species of Union concern, around 25% are listed in the Spanish and Portuguese NIS regulations. This study provides the most updated checklist of Iberian aquatic NIS, meeting the requirements set by the EU regulation and providing a baseline for the evaluation of its application. We point out the need for coordinated transnational strategies to properly tackle aquatic invasions across borders of the EU members.

The blue crab (Callinectes sapidus) has rapidly invaded several coastal lagoons along the Western Mediterranean. However, there are still no comprehensive assessments of its population biology, habitat use and trapping efficiency in critical habitats. A two-year study (November 2021 – September 2023) was conducted in a natural corridor zone placed between the hypersaline Mar Menor coastal lagoon and the Mediterranean Sea. Our main goal was to assess the population structure, habitat use and trapping efficiency (four types of traps) of the blue crab. The blue crab shows a population dynamic and structure that reflects its full settlement and reproductive movements across the study area. Most captures corresponded to adults and subadults, peaking in summer, and largest crabs were recorded in November. A significant relationship was found between crab size, habitat type (Cymodocea nodosa meadows, Caulerpa prolifera meadows and bare substrates) and trap effectiveness. Trapping efficiency varied with both habitat characteristics and crab size, showing a positive relationship of juveniles and adults with muddy substrates, while water depth had a negative influence on juveniles and subadults. However, results supported great plasticity at the microhabitat scale. Fyke nets were identified as the most effective trapping method. Trap type significantly affected the number of captures as a function of crab size and sex, with subadults and females being predominantly captured in fyke nets. These findings provide novel insights into the species’ population biology in invaded regions and cost-efficient control methods, enabling the design of priority management strategies in shallow waters to minimize impacts from crab invasions and to ensure ecological integrity.

Introduction: Long-term ecological monitoring is essential to understand the responses of fish communities to global change in transitional ecosystems. Coastal lagoons are particularly vulnerable to eutrophication, which can trigger abrupt regime shifts, mass mortality events, and loss of ecological functions. The Mar Menor coastal lagoon (SE Spain) represents one of the most impacted Mediterranean systems, providing a unique opportunity to assess long-term ecological responses of fish assemblages to sustained anthropogenic pressure. Objetives: This study aims to synthesize long-term monitoring data to evaluate structural, functional, and population-level responses of fish assemblages to eutrophication processes, and to identify critical habitats and mechanisms supporting resilience. Methodology: We integrated multiple datasets derived from long-term monitoring programs (2002–2004 as and 2018–2025), including community structure, functional diversity, population dynamics of resident species, and habitat-based indicators. Analyses encompassed pre-impact, eutrophication, and post-disturbance phases, allowing for a multi-scale assessment of ecological responses. Results: Eutrophication-driven disturbances caused major shifts in fish assemblages, including declines in biomass and abundance, species-specific responses, and increased dominance of opportunistic trophic groups. Functional diversity analyses revealed strong homogenization processes and loss of specialist traits, indicating reduced ecosystem functionality. Population dynamics of resident species reflected habitat degradation, highlighting their value as ecological indicators. Despite these impacts, shallow coastal habitats acted as critical refuges, buffering hypoxic conditions and enabling partial persistence and recovery of fish communities. Conclusions: Our results demonstrate that long-term monitoring provides essential insights into the mechanisms driving fish community responses to eutrophication. The identification of functional changes and refuge habitats is key for adaptive management. Protecting and restoring critical habitats, particularly shallow areas, is crucial to enhance resilience and guide conservation strategies in Mediterranean coastal lagoons under global change.

Introduction: The Iberian killifish (Apricaphanius iberus), an endemic cyprinodontid of the Spanish Mediterranean coast, is a key conservation species due to its restricted distribution, high sensitivity to habitat alteration and invasive fish, and ecological role in saline wetlands. Classified as Endangered by national administration and listed in Annex II of the EU Habitats Directive, its populations have undergone severe declines across its native range. Coastal salt pans have become critical refuges for the persistence of this species, often supporting some of the highest population densities recorded. However, the conservation value of these anthropogenic systems strongly depends on hydrological management, which directly influences habitat stability and suitability. Objectives: This study aims to assess the long-term population responses of A. iberus under contrasting hydrological management regimes in coastal salt pans. Methodology: We analysed ten years of monitoring data across five salt pan circuits in the perimeter area of the Mar Menor coastal lagoon (SE Spain), covering a salinity gradient and three management regimes: economic exploitation (EE), preventive management (PM), and non-management (NM). Population metrics (occurrence, abundance and breeder proportion) were evaluated. Results: Population performance differed markedly among management regimes. EE circuits showed consistently high occurrence and abundance, including in hypersaline ponds, high breeder proportions, low interannual variability, and weak dependence on meteorological conditions and ephemeral prey. PM circuits displayed intermediate patterns. In contrast, NM circuits exhibited low occurrence and abundance, low breeder proportions, high temporal fluctuations, and strong dependence on meteorological variability. Conclusions: Hydrological management is a key determinant of A. iberus population stability in coastal salt pans. Maintaining or restoring traditional management practices enhances habitat suitability, buffers environmental variability, and supports conservation actions such as reintroduction. These findings highlight the critical role of managed anthropogenic wetlands as refuges for endangered fishes and provide a transferable framework for conservation under global change.

Introduction: Freshwater fish communities in Mediterranean basins have undergone profound changes over recent decades due to biological invasions, habitat alteration, and hydrological regulation. The Segura River basin (SE Spain), particularly in the Region of Murcia, represents a paradigmatic case of these transformations, with increasing pressures on native ichthyofauna and growing relevance for recreational fisheries. Objective: This study aims to provide an updated inventory of fish communities in the rivers and reservoirs of the Region of Murcia, assessing current composition, relative abundance, and conservation status. Methodology: Fish assemblages were surveyed during sampling campaigns conducted in autumn 2023, 2024 and 2025. Sampling sites included representative reservoirs and river reaches within the middle sector of the Segura River basin, focusing on areas of interest for recreational fishing. Passive fishing gears were used in reservoirs, while electrofishing was conducted in riverine habitats. Presence and relative abundance data were recorded for all detected taxa. Results: A total of 15 taxa were identified (8 in reservoirs and 15 in river reaches). Reservoir communities were almost entirely dominated by non-native invasive species, including Cyprinus carpio, Alburnus alburnus, Sander lucioperca, Micropterus salmoides, Lepomis gibbosus, and Gambusia holbrooki, with Luciobarbus sclateri as the only native species. Riverine sections of the main channel also showed a strong dominance of exotic taxa, with additional species such as Esox lucius, Oncorhynchus mykiss, Gobio lozanoi, and Pseudochondrostoma polylepis. Native species detected included L. sclateri (dominant), Anguilla anguilla, and Salariopsis fluviatilis, the latter showing a recent expansion likely linked to human-mediated introduction. Isolated tributaries hosted the most valuable assemblages, including populations of L. sclateri, Squalius tartessicus, and the endangered Valencia hispanica (recently unauthorized translocations into the Segura river basin). Conclusions: Current fish communities in the Region of Murcia reflect a marked ecological degradation compared to historical conditions, driven by the proliferation of non-native species and habitat alteration. Changes over the last 30 years have been particularly pronounced in reservoirs and regulated sections of the main river channel, where local extinction of the native S. tartessicus has also been detected. Only the headwaters of certain tributaries retain fish assemblages of notable conservation interest, highlighting their priority for management and protection.