Accurate species monitoring is foundational for understanding and assessing species extinction risk. Environmental DNA (eDNA) based species detection methods have been proposed as fast and powerful biodiversity monitoring tools. Yet, these methods are susceptible to errors that might hinder the assessment of species extinction risk. Samples may contain low DNA concentrations of the target taxa and/or exhibit high levels of PCR inhibitors, which can yield false negatives. We investigated how adjusting the input sample volume in the eDNA‐based molecular assay improves detection of an endangered fish, Anaecypris hispanica, in highly eutrophic streams. Water samples were filtered and tested using a real‐time PCR (qPCR) assay varying the input volume of eDNA samples (i.e., 0.5X, 1X and 3.3X). From the positive detections obtained with different eDNA input volumes, we built species occurrence maps and estimated geographic range metrics used in species extinction risk assessment. Although the number of sites with positive detections was similar among the input eDNA sample volumes tested, positive detections were not spatially redundant. When comparing the pooled results from all eDNA‐based trials to a fixed 1X eDNA volume, there was a nearly 75% increase in the number of sites with detections, consequently leading to increases in all geographic range metrics (i.e., extent of occurrence, area of occupancy number of locations). Our results highlight that false negatives in eDNA‐based surveys are not to be overlooked. The success of species detection will likely vary on a case‐by‐case basis, depending on the DNA concentration of the target taxa and the concentration of potential inhibitors in bulk eDNA samples, both of which are generally unknown. Improved species detection may be achieved by running, in parallel, qPCR assays with different input volumes of bulk eDNA samples. As interest grows in integrating eDNA‐based tools into species monitoring practices, it is essential to continuously refine protocols and carefully consider study design decisions to ensure robust results, advancing species management and conservation.

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.

The introduction of non-native species poses a critical threat to biodiversity in Mediterranean freshwater ecosystems. This study documents the first record of non-native Squalius hybrids in the Ave River (Iberian Peninsula), combining morphological and molecular data to confirm their presence and assess their potential origin. The specimens exhibit hybrid characteristics, with most morphological and meristic traits overlapping those of both S. cephalus and S. squalus. Almost all individuals analysed showed an admixed genomic background for both species, suggesting a hybrid origin likely within the species’ native range before their introduction into Portugal through human-mediated activities, likely related to recreational fishing. Furthermore, molecular data also supports hybridization with the native S. carolitertii, raising conservation concerns given the negative impacts associated with hybridization with non-native species. By combining data from social media and citizen science platforms, we were able to map the rapid expansion of this invasive chub in the Ave River from 2018 until now. Our findings emphasize the urgent need for population control measures, while enhancing monitoring, genetic studies, and increased public awareness to mitigate the impacts of invasive species on Iberian freshwater biodiversity.

Invasive species can trigger profound effects on recipient ecosystems, namely through the food web. Despite being recognized as one of the worst invasive species, little is known about the feeding ecology of the Mozambique tilapia Oreochromis mossambicus. To understand how this invasive species might impact food webs, we applied metabarcoding to analyze its diet’s composition in two African mangroves, in the Obô Natural Park in the oceanic island of São Tomé. Given the particular importance of mangroves as fish nurseries, we specifically aimed to determine if this invader might predate on other fish species. However, we found that tilapia were mostly phytoplanktivorous and indication on predation of other fish was very limited. Instead, due to their local high densities, tilapia may impact basal trophic levels and nutrient availability with the potential to cascade through the food web by means of bottom-up disruption. In addition, we recorded important changes in the taxonomic composition of the diet, linked to locations and life stages, suggesting that its opportunistic feeding associated with its aggressive territorial behavior may result in resource competition with native species with which it has overlapping dietary niches.