No abstract is provided for an Editorial Paper.

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.

The early detection of invasive species in aquatic ecosystems is particularly challenging with most records of new species made years after their initial invasion, by which time they are already widespread. Recently, early detection tools such as citizen science and environmental DNA have emerged, significantly improving early warnings in aquatic ecosystems. However, there is limited understanding of how these new tools complement each other and how consistent they are. In this study, we present a case study combining social media data mining and environmental DNA (eDNA) to detect new records of the invasive European perch (Perca fluviatilis) in mainland Portugal. From 2021 to 2024, we analyzed online angling groups to identify potential new areas of invasion. Later, water samples were collected from several reservoirs and tested for the European perch presence using real-time quantitative PCR. This combined approach detected four new locations of European perch. Moreover, eDNA analysis revealed three new potential populations, while data mining appears to offer near real-time tracking of the species’ spread. This work showcases the improved efficiency and early detection benefits of this integrated approach for monitoring freshwater invasive fish, with broader applicability to other invasive species.

Sea level rise is having major impacts on estuaries due to salinity intrusion. These changes in stress profiles have ripple effects in ecosystems, including altering the invasibility of these wetlands depending on the salt tolerance of the invading species. Alternanthera philoxeroides Mart. (Griseb.) (alligator weed), native to South America and long recognized as one of the world’s worst freshwater aquatic weeds, recently invaded tidal wetlands in California’s San Francisco Bay–Delta Estuary. Generally considered a freshwater-limited glycophyte, observations suggested this invasive macrophyte may have some degree of salinity tolerance, though its degree of tolerance and capacity to spread with increased salinity intrusion were unknown. In two full-factorial greenhouse experiments, we assessed responses of emergent (soil-rooted) and free-floating growth forms of A. philoxeroides to four salinity concentrations (freshwater to euhaline) at the whole-plant (growth, biomass production and allocation, fitness), physiological, and biochemical levels. We also conducted a third experiment exploring the recovery potential of free-floating A. philoxeroides in freshwater following extended exposure to mesohaline to euhaline aqueous salinity. Although sensitivity of A. philoxeroides to increasing salinity was documented, the survival of both growth forms in the full range of salinity treatments was notable and unexpected. Our results indicate A. philoxeroides is a facultative halophyte well adapted to oligohaline–mesohaline salinity levels. Results also revealed the invasive weed’s multiple strategies to survive salinity-induced physiological stress, supporting its survival even at elevated polyhaline to euhaline conditions. The macrophyte expressed functional trait responses spanning stress tolerance, avoidance, and escape strategies that may sustain its spread as estuarine salinity intrusion increases with sea level rise.

Since the opening of the Suez Canal in 1869, hundreds of Indo-Pacific species have rapidly colonised the Mediterranean. Understanding the spatial and temporal patterns of this biological invasion is crucial for assessing its ecological impact. A notable example is the non-indigenous oyster Dendostrea sp., first discovered in Türkiye in 1998 and later found throughout the easternmost Mediterranean, though its identity remained uncertain. This study clarifies the taxonomic identity and the introduction pathways of Dendostrea sp. using molecular analyses. Over 100 specimens from 25 sites in the eastern Mediterranean, as well as Île d’Ambre and Rodrigues in the Mauritius Archipelago (the native range), were sequenced for mitochondrial DNA (COI) and compared to 422 sequences from GenBank. Phylogenetic and species delimitation analyses identified the Mediterranean oysters as D. cf. crenulifera, conspecific with oysters from Rodrigues. The Mediterranean populations exhibited high genetic diversity, lack of phylogeographic structure and showed no evidence of a founder effect. These findings suggest that D. cf. crenulifera entered the Mediterranean over two decades ago through multiple shipping-mediated introductions from its native range and successfully established, likely aided by the decline of native biodiversity. The observed genetic diversity pattern across the Mediterranean indicates high propagule pressure driving the species’ invasion history, which likely underpins its establishment success by reducing the deleterious consequences of population bottlenecks and overcoming the so-called genetic paradox. This study underscores the value of molecular surveys in identifying taxonomically challenging non-indigenous species and uncovering their invasion histories.

The construction of the Suez Canal initiated a profound marine biogeographic rearrangement by connecting two marine regions that had been separated for about 16 million years. To date, more than 100 fish species native to the Indo-West Pacific Ocean have crossed the Suez Canal and become established in the Mediterranean Sea. The purpose of this study is to identify the major factors that influence how fish species of Indo-Pacific origin (FSIPO) spread within the Mediterranean. We analyzed Mediterranean records of 136 FSIPOs, divided the Mediterranean Sea into polygons, and examined how sea currents, shipping, environmental variables, and species characteristics affect the probability that an FSIPO record is found in a polygon. Our analysis showed that any particular FSIPO is more likely to colonize regions that receive currents from the entrance of the Suez Canal, as well as regions that are close to – or receive currents or cargo ships from – other regions already occupied by the same species. Higher salinity is linked to increased colonization rates, and colonization rates overall show a significant increase over time. In addition, colonization due to spatial proximity to occupied regions and due to shipping increased significantly over time. Comparisons between simulated and observed rates of spread showed that there is additional variation among fish species that our analysis did not capture.

Predator-prey relationships underpin the stability of ecosystems but can be perturbed by numerous factors, such as biological invasions. Crayfish readily colonize new ecosystems and their impacts can modify food webs or ecosystem functioning. However, while crayfish exert high levels of predation pressure handling prey with their claws, claw loss is also common in their populations, which could mediate prey selection pressures. Here, we investigate how the number of claws in the marbled crayfish Procambarus virginalis modulates its preferences for two different available prey: Chironomus plumosus and Gammarus fossarum. We showed that the food preference of P. virginalis was mainly for soft, less mobile prey, such as C. plumosus, with significantly fewer G. fossarum (harder, more mobile prey) being killed. This preference was largely independent of claw presence but depended on the availability of prey, with fewer G. fossarum being targeted as the number of claws decreased. Our results highlight the complexity of predator-prey ecological relationships in invaded freshwater ecosystems and show that some biotic factors, such as the quantity and type of prey available, need to be taken into account in order to better understand their role in ecosystem dynamics.

Recent declines in the population size and habitat of the native European Impatiens noli-tangere have led to its observed disappearance. The spread of the North American I. capensis in Europe presents a potential additional threat. However, comparative studies on natural populations of the two species are still lacking. Our research aimed to elucidate the determinants of potential habitat segregation between the two Impatiens species in the natural environment and to identify key factors influencing variations in their growth and reproduction traits. Fine spatial scale studies allowed for a detailed description of microhabitat conditions and demonstrated the high explanatory power of our multidimensional models. The two species have overlapping environmental distributions, but the range of habitats supporting I. noli-tangere is narrower than that of I. capensis. The contrasting patterns in species traits result from different responses of each Impatiens species to environmental factors. A comparison of RDA results showed the environmental factors to explain 86.4% of the trait variability in I. noli-tangere, the soil Pb content (56%) and habitat fertility (21%) being most influential, followed by shading and the soil pH and Ca content. In I. capensis, environmental variables accounted for 70.7% of the variability, with shading being the most significant (29%), followed by anthropogenic pressure, aphid presence, soil pH, and moisture content. Our findings suggest no strong habitat barriers preventing I. capensis from entering habitats occupied by I. noli-tangere. While I. capensis invasion in Poland is still in the early stages and no co-occurrence of both species has been reported in European forests, I. capensis may eventually colonize forest habitats, given its preference for understory conditions in its native range. The higher sensitivity of I. noli-tangere to environmental changes and its weaker performance raise concerns about its ability to persist if I. capensis continues to spread.

There is increasing concern that the effects of biological invasions may be magnified by other human-induced global changes. Here, we compare the non-consumptive effects imposed by invasive vs. native predators and how these (differential) responses to both predator types depend on warming and prey latitude. We raised damselfly larvae from central- and high-latitudes in incubators under two temperatures (current [20 °C] and warming [24 °C]) and further exposed them to one of three predator cues: noble (native), signal (invasive at both latitudes) and spiny-cheek (invasive at central- but absent at high latitudes) crayfish. Growth rate increased in central-latitude but decreased in high-latitude prey in response to both noble and signal crayfish. The spiny-cheek crayfish only reduced growth rate in high-latitude prey. Cues from all three crayfish species generally caused a higher net energy budget, but only under warming. Our results demonstrated that high-latitude prey were able to recognize a novel invasive predator (spiny-cheek crayfish) cue, and revealed differential growth responses of central- and high-latitude prey toward the shared invasive predator (signal crayfish). Our data provide rare support for the concern that global change factors may magnify the impact of both native and novel invasive predators.

Individual variation assessments are essential to better understand population and community dynamics, as well ecosystem functioning. Although researchers have long recognized this aspect, only recently has evidence accumulated about the ecological importance of variation within species. The incorporation of individual variation provides an even more complete description of the effects a species may have on ecosystems and this detailed ecological knowledge can be especially important in the context of biological invasions. In this study, we used an invasion gradient of the signal crayfish Pacifastacus leniusculus in the Rabaçal River (NE Portugal) to assess possible intrapopulation differences in key biological traits and evaluate possible changes in ecological impacts. For this, we collected individuals from the core and front of an invasion gradient to characterize several traits such as abundance, size, sex-ratio, body condition, behaviour (i.e. boldness), and trophic niche. In addition, we performed two laboratory experiments to assess possible differences regarding the consumption of prey (gastropods), leaf mass loss, and nutrients release. Signal crayfish from the front of the invasion gradient have lower abundance, are larger, predominantly male, have better body condition in both sexes, exhibit increased boldness, and have higher δ15N and lower δ13C values. In addition, in experimental conditions, signal crayfish from the front of the invasion gradient consumed more gastropods and leaves and increased the concentration of nitrates and phosphates in the water. Overall, the signal crayfish has different biological traits and distinct ecological impacts along the invasion gradient in the studied river. Our study demonstrates the relevance of assessing biological traits and impacts of invasive species at the intrapopulation level. Graphical abstract