Decoding the spread of non-indigenous fishes in the Mediterranean Sea.

The ocean is dynamically changing due to the influence of climate processes and human activities. The construction of the Suez Canal in the late nineteenth century opened the Pandora's box by facilitating the dispersal of Red Sea species in the Mediterranean Sea. In this study, we developed an open-source spatio-temporal numerical analysis framework to decodify the complex spread of Mediterranean non-indigenous fish species (NIS) that entered through the Suez Canal. We utilized 772 historical detection records of 130 NIS to disentangle their dynamic spread through space and time. The results indicated that species follow a north-westward trajectory with an average expansion time step of 2.5 years. Additionally, we estimated the overall time for a NIS to reach the Central Mediterranean Sea from the Suez Canal at approximately 22 years. Based on the analysis, more than half of the introduced fishes have been established in less than 10 years. Finally, we proceeded in the cross-validation of our results using actual spread patterns of invasive fishes of the Mediterranean Sea, resulting up to 90% of temporal and spatial agreement. The methodology and the findings presented herein may contribute to management initiatives in highly invaded regions around the globe.

Cumulative Negative Impacts of Invasive Alien Species on Marine Ecosystems of the Aegean Sea.

Biological invasions are a human-induced environmental disturbance that can cause major changes in ecosystem structure and functioning. Located in the northeastern Mediterranean basin, the Aegean Sea is a hotspot of biological invasions. Although the presence of alien species in the Aegean has been studied and monitored, no assessment has been conducted on their cumulative impacts on native biodiversity. To address this gap, we applied the CIMPAL index, a framework developed for mapping the cumulative impacts of invasive species, to identify the most affected areas and habitat types and determine the most invasive species in the region. Coastal areas showed stronger impacts than the open sea. The highest CIMPAL scores were four times more frequent in the South than in the North Aegean. Shallow (0-60 m) hard substrates were the most heavily impacted habitat type, followed by shallow soft substrates and seagrass meadows. We identified Caulerpa cylindracea, Lophocladia lallemandii, Siganus luridus, Siganus rivulatus, and Womersleyella setacea as the most impactful species across their range of occurrence in the Aegean but rankings varied depending on the habitat type and impact indicator applied. Our assessment can support marine managers in prioritizing decisions and actions to control biological invasions and mitigate their impacts.

Can Biological Traits Serve as Predictors for Fishes' Introductions, Establishment, and Interactions? The Mediterranean Sea as a Case Study.

The Mediterranean Sea (MED) is prone to species' introductions, induced by human activities and/or climate change. Recent studies focus on the biological traits that result in such introductions, yet on a single-area-type approach. Here, we used, analyzed, and compared biological traits derived from FishBase for MED, non-indigenous (NIS) and neonative (NEO) in the Mediterranean, and adjacent Atlantic (ATL) and Red Sea (RS) species. A quantitative trait-based analysis was performed using random forest to determine the importance of traits in the successful establishment in the Mediterranean. MED fishes were mainly demersal, slow growing and small-medium sized, preferring intermediate temperatures. Conversely, ATL were mainly deep-dwelling species, preferring low temperatures. RS and NIS were predominantly reef-associated, thermophilus, and stenothermic. NEO species were stenothermic with preference to intermediate-high temperatures. Omnivores with preference to animals was the most common trophic group among regions. MED species exhibited higher phylogenetic uniqueness (PD50) compared to RS and NIS, indicating that they have long ancestral branches and few descendants. Preferred temperature, habitat type preference and maximum reported length (Lmax) and infinite length (Linf) were the most important predictors in the establishment process. Overall, the results presented here could serve as a baseline for future research, especially by using more refined and/or additional biological trail estimates.

Improving predictions of invasive fish ranges combining functional and ecological traits with environmental suitability under climate change scenarios.

Biological invasions represent one of the main threats to marine biodiversity. From a conservation perspective, especially in the context of increasing sea warming, it is critical to examine the suitability potential of geographical areas for the arrival of Range-Expanding Introduced and Native Species (REINS), and hence anticipate the risk of such species to become invasive in their new distribution areas. Here, we developed an empirical index, based on functional and bio-ecological traits, that estimates the Invasive Potential (IP; i.e. the potential success in transport, introduction and population establishment) for a set of 13 fishes that are expanding their distributional range into the Mediterranean Sea, the most invaded sea in the world. The IP index showed significant correlation with the observed spreading of REINS. For the six species characterized by the highest IP, we calculated contemporary and future projections of their Environmental Suitability Index (ESI). By using an ensemble modelling approach, we estimated the geographical areas that are likely to be the most impacted by REINS spreading under climate change. Our results demonstrated the importance of functional traits related to reproduction for determining high invasion potential. For most species, we found high contemporary ESI values in the South-eastern Mediterranean Sea and low to intermediate contemporary ESI values in the Adriatic Sea and North-western Mediterranean sector. Moreover, we highlighted a major potential future expansion of high ESI values, and thus REINS IP, towards the northern Mediterranean, especially in the northern Adriatic Sea. This potential future northward expansion highlights the risk associated with climate-induced impacts on ecosystem conservation and fish stock management throughout the entire Mediterranean Sea.

A global occurrence database of the Atlantic blue crab Callinectes sapidus.

The Atlantic blue crab Callinectes sapidus is a portunid native to the western Atlantic, from New England to Uruguay. The species was introduced in Europe in 1901 where it has become invasive; additionally, a significant northward expansion has been emphasized in its native range. Here we present a harmonized global compilation of C. sapidus occurrences from native and non-native distribution ranges derived from online databases (GBIF, BISON, OBIS, and iNaturalist) as well as from unpublished and published sources. The dataset consists of 40,388 geo-referenced occurrences, 39,824 from native and 564 from non-native ranges, recorded in 53 countries. The implementation of quality controls imposed a severe reduction, in particular from online databases, of the records selected for inclusion in the dataset. In addition, a technical validation procedure was used to flag entries showing identical coordinates but different year of record, in-land occurrences and those located close to the coast. Similarly, a flagging system identified entries outside the known distribution of the species, or associated with unsuccessful introductions.

Non-indigenous species refined national baseline inventories: A synthesis in the context of the European Union's Marine Strategy Framework Directive.

Refined baseline inventories of non-indigenous species (NIS) are set per European Union Member State (MS), in the context of the Marine Strategy Framework Directive (MSFD). The inventories are based on the initial assessment of the MSFD (2012) and the updated data of the European Alien Species Information Network, in collaboration with NIS experts appointed by the MSs. The analysis revealed that a large number of NIS was not reported from the initial assessments. Moreover, several NIS initially listed are currently considered as native in Europe or were proven to be historical misreportings. The refined baseline inventories constitute a milestone for the MSFD Descriptor 2 implementation, providing an improved basis for reporting new NIS introductions, facilitating the MSFD D2 assessment. In addition, the inventories can help MSs in the establishment of monitoring systems of targeted NIS, and foster cooperation on monitoring of NIS across or within shared marine subregions.

Developing a list of invasive alien species likely to threaten biodiversity and ecosystems in the European Union.

The European Union (EU) has recently published its first list of invasive alien species (IAS) of EU concern to which current legislation must apply. The list comprises species known to pose great threats to biodiversity and needs to be maintained and updated. Horizon scanning is seen as critical to identify the most threatening potential IAS that do not yet occur in Europe to be subsequently risk assessed for future listing. Accordingly, we present a systematic consensus horizon scanning procedure to derive a ranked list of potential IAS likely to arrive, establish, spread and have an impact on biodiversity in the region over the next decade. The approach is unique in the continental scale examined, the breadth of taxonomic groups and environments considered, and the methods and data sources used. International experts were brought together to address five broad thematic groups of potential IAS. For each thematic group the experts first independently assembled lists of potential IAS not yet established in the EU but potentially threatening biodiversity if introduced. Experts were asked to score the species within their thematic group for their separate likelihoods of i) arrival, ii) establishment, iii) spread, and iv) magnitude of the potential negative impact on biodiversity within the EU. Experts then convened for a 2-day workshop applying consensus methods to compile a ranked list of potential IAS. From an initial working list of 329 species, a list of 66 species not yet established in the EU that were considered to be very high (8 species), high (40 species) or medium (18 species) risk species was derived. Here, we present these species highlighting the potential negative impacts and the most likely biogeographic regions to be affected by these potential IAS.

Ecoregion-based conservation planning in the Mediterranean: dealing with large-scale heterogeneity.

Spatial priorities for the conservation of three key Mediterranean habitats, i.e. seagrass Posidonia oceanica meadows, coralligenous formations, and marine caves, were determined through a systematic planning approach. Available information on the distribution of these habitats across the entire Mediterranean Sea was compiled to produce basin-scale distribution maps. Conservation targets for each habitat type were set according to European Union guidelines. Surrogates were used to estimate the spatial variation of opportunity cost for commercial, non-commercial fishing, and aquaculture. Marxan conservation planning software was used to evaluate the comparative utility of two planning scenarios: (a) a whole-basin scenario, referring to selection of priority areas across the whole Mediterranean Sea, and (b) an ecoregional scenario, in which priority areas were selected within eight predefined ecoregions. Although both scenarios required approximately the same total area to be protected in order to achieve conservation targets, the opportunity cost differed between them. The whole-basin scenario yielded a lower opportunity cost, but the Alboran Sea ecoregion was not represented and priority areas were predominantly located in the Ionian, Aegean, and Adriatic Seas. In comparison, the ecoregional scenario resulted in a higher representation of ecoregions and a more even distribution of priority areas, albeit with a higher opportunity cost. We suggest that planning at the ecoregional level ensures better representativeness of the selected conservation features and adequate protection of species, functional, and genetic diversity across the basin. While there are several initiatives that identify priority areas in the Mediterranean Sea, our approach is novel as it combines three issues: (a) it is based on the distribution of habitats and not species, which was rarely the case in previous efforts, (b) it considers spatial variability of cost throughout this socioeconomically heterogeneous basin, and (c) it adopts ecoregions as the most appropriate level for large-scale planning.

Evaluation of online information sources on alien species in Europe: the need of harmonization and integration.

Europe is severely affected by alien invasions, which impact biodiversity, ecosystem services, economy, and human health. A large number of national, regional, and global online databases provide information on the distribution, pathways of introduction, and impacts of alien species. The sufficiency and efficiency of the current online information systems to assist the European policy on alien species was investigated by a comparative analysis of occurrence data across 43 online databases. Large differences among databases were found which are partially explained by variations in their taxonomical, environmental, and geographical scopes but also by the variable efforts for continuous updates and by inconsistencies on the definition of "alien" or "invasive" species. No single database covered all European environments, countries, and taxonomic groups. In many European countries national databases do not exist, which greatly affects the quality of reported information. To be operational and useful to scientists, managers, and policy makers, online information systems need to be regularly updated through continuous monitoring on a country or regional level. We propose the creation of a network of online interoperable web services through which information in distributed resources can be accessed, aggregated and then used for reporting and further analysis at different geographical and political scales, as an efficient approach to increase the accessibility of information. Harmonization, standardization, conformity on international standards for nomenclature, and agreement on common definitions of alien and invasive species are among the necessary prerequisites.

Ecological quality status of coastal benthic ecosystems in the Sea of Marmara.

The macrofauna in the north Marmara Sea were identified and evaluated with univariate measures and biotic indices (BENTIX, AMBI). As expected, the diversity and species' variety decreased as the sediments became muddier and as the stress increased. The AMBI index failed to detect the spatial differentiation of the EcoQ between the sites whereas, the BENTIX index succeeded (in 70% of the cases) in producing an ecologically relevant classification reflecting the environmental pressures. Results suggested that risks of reduced species' richness and diversity from organic loading and other associated stressors in sediments should be relatively low at TOC concentrations < about 6 mg/g, high at concentrations>about 22 mg/g, and intermediate at concentrations in-between. It is suggested that these TOC critical points may be used as a general screening-level indicator for assessing the EcoQ in association with reduced biodiversity over coastal areas receiving organic wastes and other pollutants from human activities. It is further suggested that both assignment of species to ecological groups and classification scales for biotic indices (AMBI, BENTIX) for sites in the Mediterranean Sea should be readjusted so as to be closer related to environmental variables.

Analysis of Benthic Communities in the Cyclades Plateau (Aegean Sea) Using Ecological and Paleoecological Data Sets.

In the Cyclades plateau (Aegean Sea), a qualitative and quantitative analysis of macro-benthic fauna was carried out in 1986. Standard multivariate analysis techniques were applied to both ecological (living benthic fauna) and paleoecological data sets in order to distinguish distribution patterns. Results showed that caution must prevail in drawing conclusions from a limited data set. The clearest classification was obtained using total living fauna, while the dead molluscan fauna gave a similar pattern; this indicates similar response to the environmental conditions of the area. In the analysis of the living molluscan fauna, the groups failed to show any clusters, probably as an effect of some impoverished sites. In the two groups delineated, depth seems to be the major factor in the distribution of species. The fact that two distinct data sets (subfossil assemblages and living communities), when treated separately, produce similar grouping indicates that the subfossil assemblages could be reliably used as a first approach for determination of the living communities' distribution patterns.