Exotic species invasions often result in native biodiversity loss, i.e. a lower taxonomic diversity, but current knowledge on invasions effects underlined a potential increase of functional diversity. We thus explored the connections between functional diversity and exotic species invasions, while accounting for their environmental drivers, using a fine-resolution large dataset of Mediterranean stream fish communities. While functional diversity of native and exotic species responded similarly to most environmental constraints, we found significant differences in the effects of altitude and in the different ranking of constraints. These differences suggest that invasion dynamics could play a role in overriding some major environmental drivers. Our results also showed that a lower diversity of ecological traits in communities (about half of less disturbed communities) corresponded to a high invasion degree, and that the exotic component of communities had typically less diverse ecological traits than the native one, even when accounting for stream order and species richness. Overall, our results suggest that possible outcomes of severe exotic species invasions could include a reduced functional diversity of invaded communities, but analyzing data with finer ecological, temporal and spatial resolutions would be needed to pinpoint the causal relationship between invasions and functional diversity.

Motivation: Here, we make available a second version of the BioTIME database, which compiles records of abundance estimates for species in sample events of ecological assemblages through time. The updated version expands version 1.0 of the database by doubling the number of studies and includes substantial additional curation to the taxonomic accuracy of the records, as well as the metadata. Moreover, we now provide an R package (BioTIMEr) to facilitate use of the database.Main Types of Variables Included: The database is composed of one main data table containing the abundance records and 11 metadata tables. The data are organised in a hierarchy of scales where 11,989,233 records are nested in 1,603,067 sample events, from 553,253 sampling locations, which are nested in 708 studies. A study is defined as a sampling methodology applied to an assemblage for a minimum of 2 years.Spatial Location and Grain: Sampling locations in BioTIME are distributed across the planet, including marine, terrestrial and freshwater realms. Spatial grain size and extent vary across studies depending on sampling methodology. We recommend gridding of sampling locations into areas of consistent size.Time Period and Grain: The earliest time series in BioTIME start in 1874, and the most recent records are from 2023. Temporal grain and duration vary across studies. We recommend doing sample‐level rarefaction to ensure consistent sampling effort through time before calculating any diversity metric.Major Taxa and Level of Measurement: The database includes any eukaryotic taxa, with a combined total of 56,400 taxa.Software Format: csv and. SQL.

Introduction: Non-native species are widely recognized as threats to biodiversity, ecosystems, and the services they provide to humans. The Mediterranean Sea has a high biodiversity of endemic species and is a hot spot of biological invasions. One of the most recent threats to Mediterranean ecosystems is the invasion of the Atlantic blue crab Callinectes sapidus.Methods: The occurrences of the crab throughout the Mediterranean coastline were indexed from citizen science through the Global Biodiversity Information Facility. Using spatial analysis and linear mixed models, we investigated geomorphology (i.e., water depth and coastal wetlands extension), water physical variables (i.e., salinity and winter and summer water temperature), water quality variables (i.e., chlorophyll-a, nitrate and orthophosphate) and anthropogenic factors (i.e., ship density and population size) potentially affecting the blue crab occurrence along the coast.Results: Our results showed that nitrate, as an indicator of riverine nutrient loading, and water depth, as an indicator of slope of the bottom, were the most influential variables in explaining the occurrences of blue crabs. Water temperature and salinity had lesser impacts; anthropogenic factors, such as the density of commercial marine traffic and human population size had no effect on blue crab occurrence.Discussion: These results sug gest that benthic primary production and shallow water drive blue crab occurrences along the Mediterranean coasts. Even considering data limitations and gaps, our large-scale findings contribute to a broader understanding of the factors that drive blue crab invasion success which, in turn, can inform management actions and outline research needs.

Protected areas (PAs) are the cornerstones of global biodiversity conservation efforts, but to fulfil this role they must be effective at conserving both habitat and species. Among protected taxa, freshwater fish are exposed to multiple disturbances and are considered one of the most endangered. The Natura 2000 reserves network was established with the aim of preserving biodiversity across Europe, but few assessments have been made on its effectiveness on the conservation of freshwater fish species. We tested the hypothesis that fish community is exposed to less anthropogenic pressures within the Natura 2000 sites than outside, hosting a higher number of native species and maintain lower number of non-native species. We tested these hypotheses considering 3,777 sampling sites, found across the entire Italian territory. Results showed that PAs did not guarantee less anthropogenic impacts and higher fish species richness than outside PAs, suggesting that PAs are not a panacea for anthropogenic pressures and safeguarding fish diversity. Nevertheless, more caution should be applied to the management measures and the design of new PAs due to the limitations of the protection of a single stretch within a whole river ecosystem. Moreover, the impossibility to operate any management of invasive fish species on the broad scale of a whole river basin is likely the most limiting factor to fish biodiversity conservation in Italy. Finally, it is also necessary to extend the analysis to other basins and Natura 2000 sites in Europe.

An increase in water temperature is one of the main factors that can potentially modify biogeochemical dynamics in lowland rivers, such as the removal and recycling of nitrogen (N). This effect of climate change on N processing deserves attention, as it may have unexpected impacts on eutrophication in the coastal zones. Intact sediment cores were collected seasonally at the closing section of the Po River, the largest Italian river and one of the main N inputs to the Mediterranean Sea. Benthic oxygen fluxes, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) rates were measured using laboratory dark incubations. Different temperature treatments were set up for each season based on historical data and future predictions. Higher water temperatures enhanced sediment oxygen demand and the extent of hypoxic conditions in the benthic compartment, favoring anaerobic metabolism. Indeed, warming water temperature stimulated nitrate (NO₃⁻) reduction processes, although NO₃⁻ and organic matter availability were found to be the main controlling factors shaping the rates between seasons. Denitrification was the main process responsible for NO₃⁻ removal, mainly supported by NO₃⁻ diffusion from the water column into the sediments, and much more important than N recycling via DNRA. The predicted increase in the water temperature of the Po River due to climate change may exert an unexpected negative feedback on eutrophication by strongly controlling denitrification and contributing to partial buffering of N export in the lagoons and coastal areas, especially in spring. Graphical Abstract

The introduction of the Atlantic blue crab (Callinectes sapidus) in the Mediterranean Sea dates back to the 1900s; however, the species has recently spread in the region resulting in negative impacts on the structure and functions of invaded ecosystems and local fisheries. This study investigated the covariation between spatiotemporal dynamics of the Atlantic blue crab fishery landings (catch-per-unit-area; CPUE) and environmental explanatory variables (i.e., salinity, water temperature, nitrate and chlorophyll-a used as a proxy of primary productivity) over a four-year period (2020-2023) in four key lagoonal ecosystems of the North Adriatic Sea. Our results showed that the marked increase in Atlantic blue crab CPUE in all studied lagoons since 2020 was strongly related with local primary productivity which likely supports a greater abundance of food resources for the suspension feeding Manila clam (Ruditapes philippinarum), a key prey for blue crabs and one of the most important fisheries in the region. Conversely, salinity and water temperature, two key parameters regulating blue crab biology, i.e., mating and subsequent larval spawning, did not significantly influence CPUE in the studied lagoons. These results suggest that primary production in the lagoons, which directly influences food availability (e.g., Manila clams) for the Atlantic blue crab, is the primary factor driving its apparent invasion success in the study area. Our results provide new insights into understanding the environmental factors that promote its invasion and spread, allowing for targeted control measures such as managed fisheries and water quality.