Alien animal introductions in Iberian inland waters: An update and analysis

Identification of potential invasive alien species in Spain through horizon scanning

Invasive alien species have widespread impacts on native biodiversity and ecosystem services. Since the number of introductions worldwide is continuously rising, it is essential to prevent the entry, establishment and spread of new alien species through a systematic examination of future potential threats. Applying a three-step horizon scanning consensus method, we evaluated non-established alien species that could potentially arrive, establish and cause major ecological impact in Spain within the next 10 years. Overall, we identified 47 species with a very high risk (e.g. Oreochromis niloticus, Popillia japonica, Hemidactylus frenatus, Crassula helmsii or Halophila stipulacea), 61 with high risk, 93 with moderate risk, and 732 species with low risk. Many of the species categorized as very high or high risk to Spanish biodiversity are either already present in Europe and neighbouring countries or have a long invasive history elsewhere. This study provides an updated list of potential invasive alien species useful for prioritizing efforts and resources against their introduction. Compared to previous horizon scanning exercises in Spain, the current study screens potential invaders from a wider range of terrestrial, freshwater, and marine organisms, and can serve as a basis for more comprehensive risk analyses to improve management and increase the efficiency of the early warning and rapid response framework for invasive alien species. We also stress the usefulness of measuring agreement and consistency as two different properties of the reliability of expert scores, in order to more easily elaborate consensus ranked lists of potential invasive alien species.

The challenge of managing threatened invasive species at a continental scale

The European Union's (EU) environmental legislation establishes common measures to prevent the entry and spread of invasive non-native species and to minimize their impacts. However, species that are native to at least one member state but non-native and potentially invasive in others (NPIS) are in limbo because they are neither legally regulated at the EU level nor in most member states. We used the Communication and Information Resource Centre for Administrations, Businesses and Citizens (CIRCABC) raw data on NPIS (317 taxa) to analyze their distribution across the EU and identify which biogeographical regions are the main sources of invasions. We additionally evaluated the conservation challenge posed by NPIS that are threatened within their native ranges. We performed a pairwise analysis summarizing the number of species that are native to a given member state but non-native to another and vice versa. Although distribution patterns of NPIS varied across taxa groups, overall, southern and central EU countries were both donors and recipients of NPIS. Eastern countries were mainly a source, and western and northern countries mostly received NPIS. Around 27% of NPIS were threatened in some of their EU native ranges, which is a challenge for conservation and management because some of them have serious negative effects on European biodiversity, but hitherto remain outside the scope of the EU regulation of invasive non-native species. This highlights an unresolved paradox because efforts to manage species as invasive conflict with efforts to protect them as threatened within the same territory.

Non-indigenous aquatic fauna in transitional waters from the Spanish Mediterranean coast: A comprehensive assessment

Understanding drivers of spatial variation in non-indigenous species (NIS) is a key goal in invasion biology, but comprehensive assessments providing high-resolution data are extremely scarce. Anthropogenic modifications to transitional waters facilitate the invasion of NIS where they cause both ecological and economic important damage. By screening validated data sources, we conducted a comprehensive assessment of non-indigenous aquatic fauna in Spanish Mediterranean transitional waters (30 sites), as well as assessed introduction pathways, native regions, NIS assemblage patterns and temporal introduction rate. One hundred and twenty-nine NIS were inventoried, with 72 % established and more than half listed before 1980. Two intentional (release, escape) and two unintentional (contaminant, stowaway) introduction pathways were dominant. Recorded NIS originated mostly from North America and Asia. A clear nested pattern in NIS assemblages was observed across sites, suggesting secondary spread from the most invaded waters placed in the northern regions. Our updated inventory should be pivotal for designing prevention protocols and informing specific management plans on non-indigenous fauna in transitional waters.

A horizon scan exercise for aquatic invasive alien species in Iberian inland waters

As the number of introduced species keeps increasing unabatedly, identifying and prioritising current and potential Invasive Alien Species (IAS) has become essential to manage them. Horizon Scanning (HS), defined as an exploration of potential threats, is considered a fundamental component of IAS management. By combining scientific knowledge on taxa with expert opinion, we identified the most relevant aquatic IAS in the Iberian Peninsula, i.e., those with the greatest geographic extent (or probability of introduction), severe ecological, economic and human health impacts, greatest difficulty and acceptability of management. We highlighted the 126 most relevant IAS already present in Iberian inland waters (i.e., Concern list) and 89 with a high probability of being introduced in the near future (i.e., Alert list), of which 24 and 10 IAS, respectively, were considered as a management priority after receiving the highest scores in the expert assessment (i.e., top-ranked IAS). In both lists, aquatic IAS belonging to the four thematic groups (plants, freshwater invertebrates, estuarine invertebrates, and vertebrates) were identified as having been introduced through various pathways from different regions of the world and classified according to their main functional feeding groups. Also, the latest update of the list of IAS of Union concern pursuant to Regulation (EU) No 1143/2014 includes only 12 top-ranked IAS identified for the Iberian Peninsula, while the national lists incorporate the vast majority of them. This fact underlines the great importance of taxa prioritisation exercises at biogeographical scales as a step prior to risk analyses and their inclusion in national lists. This HS provides a robust assessment and a cost-effective strategy for decision-makers and stakeholders to prioritise the use of limited resources for IAS prevention and management. Although applied at a transnational level in a European biodiversity hotspot, this approach is designed for potential application at any geographical or administrative scale, including the continental one.

Perceptions and risk behaviors regarding biological invasions in inland aquatic ecosystems

Public engagement is vital to effectively manage Invasive Alien Species (IAS) and biosecurity campaigns directed to stakeholders are decisive to raise awareness regarding IAS regulations and problems. To design and implement adequate communication plans, stakeholders' perceptions and risk behaviors regarding IAS need to be monitored by surveys. IAS do not recognize borders and most countries are not biogeographically isolated. Therefore, international information and consensus are necessary when applying measures at a biogeographic scale. Our bilingual survey was performed at the Iberian Peninsula, targeting the general public, decision-makers and other stakeholders, covering all taxa associated to inland aquatic ecosystems. We found differences in IAS' awareness between countries, and between different stakeholder groups. Results showed that the awareness of socioeconomic and human health impacts is substantially lower when compared with impacts on biodiversity. We found that the perception regarding the predation impacts is consistent across groups and countries, while other perceptions differ. The negative socioeconomic impact on angling due to IAS introductions is widely recognized. However, angling is also the activity most referred as positively impacted by IAS due to fish introductions. Most responders knew what IAS are, providing correct species examples. For all three awareness types (Biodiversity, Socio-economic and Human health) the model regressions showed that the most important predictor was the country of provenance of the respondent, followed by Education level for the socio-economic and biodiversity regressions and the stakeholder group in the Human health regression. We can conclude that in Portugal and Spain the general public and other key target-groups have reduced understanding of some threats posed by IAS. We highlight that raising awareness about IAS impacts on humans, namely on socio-economic aspects and human health, may be more effective and it is certainly needed in education campaigns towards IAS.

Management of invasive alien species in Spain: A bibliometric review

Scientific and grey literature on invasive alien species (IAS) is conditioned by social, economic and political priorities, editorial preferences and species and ecosystem characteristics. This leads to knowledge gaps and mismatches between scientific research interests and management needs. We reviewed the literature on IAS management in Spain found in Scopus, Web of Science, Google Scholar and Dialnet to identify key deficiencies and priority research areas. The collected literature was classified, employing features describing formal aspects and content. We used bibliometric and keyword co-occurrence network analyses to assess the relationship between features and reveal the existence of additional topics. Most of the compiled documents (n = 388) were focused on terrestrial ecosystems and inland waters, whereas marine and urban ecosystems were under-represented. The literature was largely generic and not species-specific, focusing on raising awareness and proposing changes on current regulation as prominent approaches to prevent further introductions. The compiled authors exhibited many clear publishing preferences (e.g. language or document type), but less regarding target taxa. In addition, there was a strong association between species and the different features considered, especially between the methodological approach (e.g. review, field experiment) and the primary emphasis of study (i.e. basic/theoretical, applied or interdisciplinary). This indicates that research on IAS has had a strong species-specific focus. References about terrestrial species focused mainly on vascular plants, whereas references about inland waters were mostly on fishes and the giant reed (Arundo donax), which has been managed with partial success. Animal culling and plant removal were the most frequent eradication and small-scale control treatments, whereas the documents addressing wider spatial scales were largely theoretical. Consequently, the success of described treatments was largely uncertain. Spanish invasion science research has been occasionally innovative, incorporating novel technologies (e.g. species distribution modelling) and engaging society with citizen-science approaches. However, the ratio between basic/theoretical and applied studies indicates that more applied research/management is needed, especially in inland waters and marine ecosystems. We call for increasing effort in the effective dissemination of experience in IAS management to enhance current practical knowledge, including that of schemes undertaken by public agencies.

Plasticity in Reproductive Traits, Condition and Energy Allocation of the Non-Native Pyrenean Gudgeon Gobio lozanoi in a Highly Regulated Mediterranean River Basin

The invasion success of non-native fish, such as Pyrenean gudgeon Gobio lozanoi in several Iberian rivers, is often explained by the expression of its life history traits. This study provides the first insights into the reproductive traits, fish condition, and energy allocation (protein and lipid contents of tissues) of this species, along a longitudinal gradient in one of the most regulated river basins in the Iberian Peninsula, the Segura river. Larger sizes of first maturity, higher fecundity and larger oocytes were found in fluvial sectors with the most natural flow regimes, characterised by a low base flow with high flow peaks in spring and autumn. A delay in the reproductive period, lower fish condition and no differences in sex-ratio were observed in fluvial sectors with a high increase in base flow and notable inversion in the seasonal pattern of flow regime. Lipid contents in the liver and gonads were stable during the reproductive cycle and decreases in muscle were noted, whereas ovarian and liver proteins increased. In relation to energy allocation for G. lozanoi, an intermediate energy strategy was observed between income and capital breeding. Our results support the hypothesis that the high plasticity of G. lozanoi population traits plays a significant role in its success in a highly regulated Mediterranean river basin. Understanding the mechanisms by which flow regulation shapes fish populations in Mediterranean type-rivers could inform management actions.

Defining non-indigenous fish assemblage types in Mediterranean rivers: Network analysis and management implications

The design and implementation of appropriate management actions to tackle the spread and negative impacts of non-indigenous fish species (NIFS) in freshwater ecosystems still remains a complex task. In an effort to address the limitations of current managerial approaches, our study develops and applies a classification framework to define non-indigenous fish assemblage types (FATs) in Mediterranean riverine ecosystems and identifies the linkage with various regional, local, biotic and abiotic environmental factors. This framework contributes to a pre-invasion stage screening and to the design of effective type-specific post-invasion management actions dealing with specific NIFS assemblages. A network analysis was applied in order to extract NIFS community level information from 393 samples obtained from 51 river basins of Greece, while a multivariate ordination analysis was conducted to detect the factors best explaining the structure and distribution of FATs. The association patterns of the study's inputs and outcomes are illustrated through an alluvial diagram, providing insights across different spatial scales. In total, five FATs were generated where the major NIFS contributors of average similarity within each modularity class revealed the key indicator species (Gambusia-FAT; Carassius/Lepomis-FAT; Pseudorasbora-FAT; Salmonids-FAT and Carp-FAT). Overall, the identified FATs varied spatially, indicating different community structure, mainly based on the diverse habitat preferences and life-history traits of indicator species. Alien FATs were mainly distributed within large and transboundary rivers, while Translocated and Salmonids FATs mostly occupied ecoregions with relatively depauperate faunas and often in biodiversity hotspots. The results of this study can identify conservation priorities within FATs, inform specific-type post-invasion management actions tackling NIFS, while in addition may provide valuable information for protecting high-priority water bodies before invasion.

Projecting the continental accumulation of alien species through to 2050

Biological invasions have steadily increased over recent centuries. However, we still lack a clear expectation about future trends in alien species numbers. In particular, we do not know whether alien species will continue to accumulate in regional floras and faunas, or whether the pace of accumulation will decrease due to the depletion of native source pools. Here, we apply a new model to simulate future numbers of alien species based on estimated sizes of source pools and dynamics of historical invasions, assuming a continuation of processes in the future as observed in the past (a business-as-usual scenario). We first validated performance of different model versions by conducting a back-casting approach, therefore fitting the model to alien species numbers until 1950 and validating predictions on trends from 1950 to 2005. In a second step, we selected the best performing model that provided the most robust predictions to project trajectories of alien species numbers until 2050. Altogether, this resulted in 3,790 stochastic simulation runs for 38 taxon-continent combinations. We provide the first quantitative projections of future trajectories of alien species numbers for seven major taxonomic groups in eight continents, accounting for variation in sampling intensity and uncertainty in projections. Overall, established alien species numbers per continent were predicted to increase from 2005 to 2050 by 36%. Particularly, strong increases were projected for Europe in absolute (+2,543 ± 237 alien species) and relative terms, followed by Temperate Asia (+1,597 ± 197), Northern America (1,484 ± 74) and Southern America (1,391 ± 258). Among individual taxonomic groups, especially strong increases were projected for invertebrates globally. Declining (but still positive) rates were projected only for Australasia. Our projections provide a first baseline for the assessment of future developments of biological invasions, which will help to inform policies to contain the spread of alien species.