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.

Eutrophication remains a critical threat affecting estuarine and coastal lagoon ecosystems, largely driven by intensified anthropogenic pressures and exacerbated by climate change. Understanding the impacts of eutrophic processes on biological communities is essential to ensure effective conservation and management of these vulnerable environments. This study investigates the ecological consequences of eutrophication-induced algal blooms and hypoxia-mediated mass mortality events on fish communities in the Mar Menor coastal lagoon (Western Mediterranean Sea). We assessed temporal changes in fish assemblage structure and composition across three different periods: a baseline reference period (2002-2004), an algal bloom period (2018-2019), and a mass mortalities period (2020-2021). For that purpose, multiple community metrics were assessed, including species richness, abundance, biomass, β-diversity, functional guilds, and species dominance. Significant disturbances in fish abundance and biomass in response to critical eutrophic events were found, though species richness remained stable. Community similarity decreased during warmer seasons of eutrophic periods, but β-diversity values remained constant. Species-specific responses highlighted a marked decline of benthic taxa closely associated with bottom habitats, while zooplanktivores and planktivores became dominant, suggesting the emergence of top-down trophic control mechanisms. Additionally, during hypoxic events, large macrobenthivorous species appeared to seek refuge in shallow and more oxygenated areas, thus leading to evident shifts in fish assemblage composition. These findings provide robust evidence of structural and functional disruption in fish assemblages under eutrophic stress conditions. Our study underscores the relevance of long-term biological monitoring and adaptive management strategies in transitional systems, particularly under future climate and nutrient enrichment scenarios.

Over the past decades, intensive agriculture has expanded worldwide in response to the rising human demand for food. Intensive farming practices commonly involve the application of pesticides and other agrochemical compounds, contributing to the global decline in farmland bird populations, particularly aerial insectivores. Moreover, the increased mechanization of agricultural operations (e.g., grass cutting, tree pruning, and brush chipping) may destroy nests and reduce the breeding success of ground‐nesting bird species. Here, we used a ground‐nesting insectivorous bird, the Red‐necked Nightjar (Caprimulgus ruficollis), as a model to test for the effects of organic vs. intensive farming practices on breeding performance. We used data from 191 nightjar nests monitored over a 4‐year period in a highly cultivated landscape of SE Spain. Four breeding parameters (clutch size, hatching success, fledging success, and overall breeding success) were compared between two adjacent farms under organic and conventional intensive management. Additionally, we compared four population‐level attributes (breeding phenology, breeding density, age structure of breeders, and foraging range size) considered to be important determinants of breeding performance. Nightjars breeding in the organic and in the intensive farms had a moderate breeding performance comparable to that reported in other, more extensive agricultural landscapes (e.g., vineyards). All breeding parameters and two out of the four measured population‐level attributes were statistically not different between the organic and the intensive farm. However, nest aggregation was higher in the organic farm, and space use analyses revealed that GPS‐tracked nightjars nesting within the intensive farm traveled to foraging areas outside the farm more often than those from the organic farm. This suggests that plasticity in foraging behavior (e.g., the use of alternative foraging sites) may buffer the potential negative effects of intensive farming practices (e.g., decreased prey availability) on the breeding performance of nightjars. Our study underlines the potential role of landscape complementation and ecological plasticity in space‐use behaviors as determinants of breeding performance in farmland birds, enabling these species to (partly) compensate for the impacts of intensive agriculture.