Lag times in Lessepsian fish invasion

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.

Harnessing Fishers' local knowledge and their perceptions: Opportunities to improve management of coastal fishing in Mediterranean marine protected areas

To contribute to the sustainable management of the coastal fishing in the future Marine Protected Area (MPA) of "Taza" (Algeria, SW Mediterranean), the aim of this study was to evaluate the Local Knowledge (LK) of fishers operating near the forthcoming MPA and to understand their conservation-oriented attitudes. Data were collected through interviews and participatory mapping. To this end, 30 face-to-face semi-structured interviews were conducted between June and September 2017 with fishers, collecting socioeconomic, biological, and ecological information in the fishing harbor of Ziama (Jijel, NE Algeria). The case study focuses on both professional and recreational coastal fisheries. This fishing harbor is located in the eastern part of the Gulf of Béjaia, a Bay located within the area of this future MPA, but outside its boundaries. Based on fishers' LK, cartography of fishing grounds within the MPA perimeter was obtained, while the perceived healthy bottom habitats and polluted areas in the Gulf were mapped by the use of a hard copy map. The results show that fishers present detailed knowledge that is consistent with literature about different target species and their breeding seasons, showing awareness about the reserve effects 'spillover' in enhancing local fisheries. Overall, the fishers noted that the good management of the MPA relies on limiting trawling in coastal areas and avoiding land-based pollution within the Gulf. Some of such management measures are already included in the proposed zoning plan, but lack of enforcement is a perceived constraint. Given the gap observed between the two shores of the Mediterranean Sea in terms of both financial resources and MPA coverage, the use of local knowledge system (e.g., fishers' LK and their perceptions) can enable the implementation of a cost-effective method to encourage the creation of new MPAs in the Southern shore for more ecological representativeness systems of MPAs at a Mediterranean scale. Therefore, this work offers management opportunities that may be used for addressing the lack of scientific knowledge in managing coastal fishing and valuing MPAs in Southern Mediterranean low-income countries characterized by a data-poor context.

The evolutionary process of invasion in the fall armyworm (Spodoptera frugiperda)

The fall armyworm (FAW; Spodoptera frugiperda) is one of the major agricultural pest insects. FAW is native to the Americas, and its invasion was first reported in West Africa in 2016. Then it quickly spread through Africa, Asia, and Oceania, becoming one of the main threats to corn production. We analyzed whole genome sequences of 177 FAW individuals from 12 locations on four continents to infer evolutionary processes of invasion. Principal component analysis from the TPI gene and whole genome sequences shows that invasive FAW populations originated from the corn strain. Ancestry coefficient and phylogenetic analyses from the nuclear genome indicate that invasive populations are derived from a single ancestry, distinct from native populations, while the mitochondrial phylogenetic tree supports the hypothesis of multiple introductions. Adaptive evolution specific to invasive populations was observed in detoxification, chemosensory, and digestion genes. We concluded that extant invasive FAW populations originated from the corn strain with potential contributions of adaptive evolution.

Unwanted Guest Continues its Northern Journey in the Aegean Sea: Pterois miles (Bennett, 1828)

Pterois miles (Bennett, 1828), one of the most destructive marine invaders, was reported from the Mediterranean in 1991. It has invaded most parts of the Mediterranean from 2013, when it was reported for the second time, until today. On 7th October 2020, a single specimen of P. miles was collected by the bottom trawl from the Edremit Bay (Northern Aegean Sea). COI barcode region was used for the molecular identification of the specimen. DNA barcode data suggest that the specimen used in the present study is P. miles with a 99.69% probability. The current study is presented by providing the northernmost occurrence of the P. miles from the Aegean Sea with molecular confirmation.

Spatio-temporal dynamics of exotic fish species in the Mediterranean Sea: Over a century of invasion reconstructed

With over a thousand of introduced species, the Mediterranean is the most heavily invaded marine region in the world. Yet, the spatio-temporal dynamics of this bioinvasion has never been analysed. Examination of a comprehensive dataset of 4015 georeferenced observations, extracted from the scientific literature, allowed (i) reconstructing the invasion and the introduction and post-introduction dynamics of exotic fish species, (ii) calculating introduction and spread rates, and (iii) investigating the time correlates since introduction. Our analysis encompasses 188 fish species that entered the Mediterranean from 1896 to 2020, including 25 Atlantic species that naturally expanded their range through the Strait of Gibraltar. Cumulative occurrences, reported in 264 distribution maps, documented the progressive expansion of the most represented species and the spatio-temporal patterns associated with three introduction routes: the Suez Canal (CAN); other human-mediated vectors (HM) and the Strait of Gibraltar (NRE). The arrival rate of the species introduced through all three routes increased steeply after 1990, without a sign of saturation. Data analysis highlighted some temporal and geographical patterns, such as the effect and eventual weakening of the biogeographical barriers represented by the Strait of Sicily and the North Aegean Sea and the asymmetrical distribution of occurrences along the northern and southern Mediterranean coasts. Finally, there was an exponential increase in the secondary spread rates of CAN and NRE immigrants, as the more recent introductions achieved the fastest geographical expansions. Our findings provide a detailed and spatially explicit summary of a massive invasion that has changed the history of the Mediterranean biota and represent a remarkable example of rapid biotic homogenization in the global ocean.

A Risk Screening of Potential Invasiveness of Alien and Neonative Marine Fishes in the Mediterranean Sea: Implications for Sustainable Management

Biological invasions have posed a major threat to global and regional biodiversity. The Mediterranean Sea, one of the major biodiversity hotspots in the world, has long suffered multiple and frequent invasion events. This paper represents the screening results of the potential invasiveness of 23 introduced marine fish species, which are classified as neonative and alien. To predict the invasiveness potential of species under current and predicted climate conditions, the Aquatic Species Invasiveness Screening Kit (AS-ISK) is applied. Thresholds have been constituted to classify low, medium and high-risk species by receiver operative characteristic curve analysis (ROC). The calibrated basic and climate-change threshold assessment scores used to classify species from low, to medium to high risk were computed between 27.5 and 33.0 respectively. Based on these thresholds, under current climatic conditions, 15 species were high risk, while the remaining species were medium risk, and the Chaetodipterus faber and the Holocentrus adscensionis switched from the medium-risk to the high-risk group under future climatic conditions. The highest score belonged to Fistularia petimba, followed by Siganus fuscescens, Abudefduf spp., Acanthurus monroviae and Lutjanus argentimaculatus. This study focused on the species that have not been assessed for their invasiveness potential, and the results can provide important insights into their sustainable management in the future.

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.

Meta-analysis on the ecological impacts of widely spread non-indigenous species in the Baltic Sea

The introduction of non-indigenous species (NIS) is a major driver for global change in species biogeography, often associated with significant consequences for recipient ecosystems and services they provide for humans. Despite mandated by several high-level international legislative instruments, comprehensive quantitative evaluation on ecosystem impacts of marine NIS is scarce and lack a robust and data-driven assessment framework. The current study is aiming at fulfilling this gap, through quantitative assessment on the effects of the widespread NIS of the Baltic Sea on multiple ecosystem features and components including direct food-web effects. The outcomes of this study allowed identifying the most impacting widespread NIS, together with defining the processes underlying the most significant changes and outlined major sources of uncertainty. Lack and/or bias in the availability of evidence of impacts was recorded for several (both recent and early) introductions. Realizing a sophisticated, data and information-hungry framework for the evaluation of ecosystem impacts of NIS is not pragmatic for management purposes in the foreseeable future. Instead, simple approaches, such as application of common statistical parameters like absolute effect size, are more likely to result in tangible outcomes. As bearing no unit, effect sizes can be later easily aggregated across taxa, affected ecosystem features or spatial scales. The proposed approach enables performing systematic comparisons on the severity of impacts of different NIS along different study disciplines and ecosystems.

Who’s Next? Non-Indigenous Cnidarian and Ctenophoran Species Approaching to the Italian Waters

The aims of the present paper were to review the knowledge about the Mediterranean non-indigenous species of the taxa Cnidaria and Ctenophora (CC NIS), to screen the risk of 98 species for their potential invasiveness in the Mediterranean Sea and their approach to the Italian waters. Of these, 38% are well established in the basin, 4% are known for their invasiveness, 44% are casual, 11% have a taxonomic status unresolved, and 3% are included in the category ”cryptogenic”. The biodiversity CC NIS of the Mediterranean Sea has changed considerably in the last two decades and 27 out of 98 Mediterranean CC NIS are present in the Italian waters. Fifteen CC NIS, some equipped with high invasive potential, should be regarded as good candidates to become future immigrants of the Italian waters. Anticipatory NIS forecast based on biogeographical and ecological analyses may provide a useful tool for targeted management of the CC NIS issue and for the assessment of the second descriptor of Good Environmental Status. On the other hand, conservation and management of marine ecosystem should be based on the conservation of the essential environmental conditions for the functioning of these ecosystems instead of the contamination or eradication of alien species.

Using molecular data to monitor the post-establishment evolution of the invasive skeleton shrimp Caprella scaura

The study aims to monitor the post-establishment success of the invasive skeleton shrimp Caprella scaura in the Atlantic-Mediterranean transition zone and understand its connectivity with other world areas, providing new information on the status of the introduced population and its global distribution. By using mitochondrial markers (16S and COI) we examined the temporal variation of populations in Cadiz Bay, Spain (hotspot for introductions in Europe) in between 2010 and 2017; as well as their linkage with foreign populations in its native and introduced distribution ranges. Cadiz Bay populations exhibited a connection with several European introduced populations (Iberian Peninsula, Canary Islands, Mediterranean Sea and The Netherlands), eastern USA, Sea of Japan and Australia. We found no evidence to support a Brazilian origin (one potential native area) of the Iberian Peninsula populations. We identified a progressive decrease in haplotype diversity and a low connectivity at the end of the monitoring period in one of the stations. Human-mediated changes in propagule pressure, and unfavorable environmental fluctuations are probably responsible for this. Meanwhile, populations in Cadiz Bay count on numerous foreign donors that could easily refuel the propagule input by exchanging gene flow. This implies that a vector regulation strategy has the potential of compromising the success of established non-native populations, which usually undergo vulnerability periods due to the challenging conditions of marinas. The use of molecular tools in a time series approach is then useful to identify the ideal time window to put in action management measures so that they are cost-effective.

Possible implications of sea level changes for species migration through the Suez Canal

The Mediterranean and Red Sea, which were connected via the Suez Canal during the 19th century after eons of separation, host two distinctive ecosystems. Species invasion through the Suez Canal from the Red Sea vastly influences the ecology of the Mediterranean, but the level of reverse migration is assumed to be negligible. We present the first reconstructed flow transport record through the canal during the period 1923-2016. According to this reconstruction, the flow intensity and direction through the canal are strongly influenced by seasonal and long-term sea-level changes, which could also play a role in the characteristics of species migration through it. Our record not only supports previous observations of the unidirectional invasion until the 1980s and the accelerated species migration rates to the Mediterranean ever since, but also suggest that southward migration could have become possible since the early 1980s. The southward flow was primarily enhanced by Indian Ocean cooling and the Eastern Mediterranean Transition in deep water formation during the period 1980-2000. It was then gradually reduced by accelerated sea-level rise in the northern Indian Ocean.

Trends in the detection of aquatic non-indigenous species across global marine, estuarine and freshwater ecosystems: A 50-year perspective

Aim:

The introduction of aquatic non-indigenous species (ANS) has become a major driver for global changes in species biogeography. We examined spatial patterns and temporal trends of ANS detections since 1965 to inform conservation policy and management.

Location:

Global.

Methods:

We assembled an extensive dataset of first records of detection of ANS (1965–2015) across 49 aquatic ecosystems, including the (a) year of first collection, (b) population status and (c) potential pathway(s) of introduction. Data were analysed at global and regional levels to assess patterns of detection rate, richness and transport pathways.

Results:

An annual mean of 43 (±16 SD) primary detections of ANS occurred–one new detection every 8.4 days for 50 years. The global rate of detections was relatively stable during 1965–1995, but increased rapidly after this time, peaking at roughly 66 primary detections per year during 2005–2010 and then declining marginally. Detection rates were variable within and across regions through time. Arthropods, molluscs and fishes were the most frequently reported ANS. Most ANS were likely introduced as stowaways in ships’ ballast water or biofouling, although direct evidence is typically absent.

Main conclusions:

This synthesis highlights the magnitude of recent ANS detections, yet almost certainly represents an underestimate as many ANS go unreported due to limited search effort and diminishing taxonomic expertise. Temporal rates of detection are also confounded by reporting lags, likely contributing to the lower detection rate observed in recent years. There is a critical need to implement standardized, repeated methods across regions and taxa to improve the quality of global-scale comparisons and sustain core measures over longer time-scales. It will be fundamental to fill in knowledge gaps given that invasion data representing broad regions of the world's oceans are not yet readily available and to maintain knowledge pipelines for adaptive management.

Using online questionnaires to assess marine bio-invasions: A demonstration with recreational fishers and the Atlantic blue crab Callinectes sapidus (Rathbun, 1986) along three Mediterranean countries

Marine bioinvasions require integrating monitoring tools with other complementary strategies. In this study, we collected information about the invasive alien crab Callinectes sapidus in Italy, Croatia and Montenegro, by means of online questionnaires administered to recreational fishers (n = 797). Our records matched the current distribution of the species: C. sapidus resulted far more common in the Adriatic/Ionian than in the Tyrrhenian/Ligurian sector. Most respondents rated the species as 'occasional' or 'rare'. Moreover, the more C. sapidus was considered to be abundant, the more fishers tended to perceive it as a negative disturbance over fisheries and the environment. Our findings suggest that C. sapidus is more common than previously thought in most of the study area, and it could have reached the levels of a true invasions in the south-eastern Adriatic Sea. This experience demonstrates that online questionnaires can be appropriate tools to effectively engage stakeholders in alien species monitoring.

Trade-offs between morphology and thermal niches mediate adaptation in response to competing selective pressures

The effects of climate change-such as increased temperature variability and novel predators-rarely happen in isolation, but it is unclear how organisms cope with multiple stressors simultaneously. To explore this, we grew replicate Paramecium caudatum populations in either constant or variable temperatures and exposed half to predation. We then fit thermal performance curves (TPCs) of intrinsic growth rate (r max) for each replicate population (N = 12) across seven temperatures (10°C-38°C). TPCs of P. caudatum exposed to both temperature variability and predation responded only to one or the other (but not both), resulting in unpredictable outcomes. These changes in TPCs were accompanied by changes in cell morphology. Although cell volume was conserved across treatments, cells became narrower in response to temperature variability and rounder in response to predation. Our findings suggest that predation and temperature variability produce conflicting pressures on both thermal performance and cell morphology. Lastly, we found a strong correlation between changes in cell morphology and TPC parameters in response to predation, suggesting that responses to opposing selective pressures could be constrained by trade-offs. Our results shed new light on how environmental and ecological pressures interact to elicit changes in characteristics at both the individual and population levels. We further suggest that morphological responses to interactive environmental forces may modulate population-level responses, making prediction of long-term responses to environmental change challenging.

Detecting the occurrence of indigenous and non-indigenous megafauna through fishermen knowledge: A complementary tool to coastal and port surveys

Marine bioinvasions and other rapid biodiversity changes require today integrating existing monitoring tools with other complementary detection strategies to provide a more efficient management. Here we explored the efficacy of fishermen observations and traditional port surveys to effectively track the occurrence of both indigenous and non-indigenous megafauna in the Adriatic Sea. This consisted mainly of mobile taxa such as fishes, crustaceans and molluscs. Port surveys using traps and nets within 10 major Adriatic harbours, were compared with the information obtained from 153 interviews with local fishermen. Information gathered by traps and nets varied significantly and generally resulted of limited efficacy in exotic species detection. Interviews allowed tracking the occurrence of new species through time and space, providing complementary knowledge at the low cost. This combined approach improves our capability of being informed on the arrival of species of different origin, providing a more rational, improved basis for environmental management and decision making.

Exploring the relationships between marine protected areas and invasive fish in the world's most invaded sea

Marine Protected Areas (MPAs) are an essential tool for marine biodiversity conservation. Yet, their effectiveness in protecting marine ecosystems from global stressors is debated. Biological invasions are a major driver of global change, causing biodiversity loss and altering ecosystem functioning. Here, we explored the relationships between MPAs and alien/native range-expanding fishes in the Mediterranean Sea, the world's most invaded sea. We surveyed fish and benthic communities in nine MPAs and adjacent unprotected areas across six countries. In the South and Eastern Mediterranean MPAs, the biomass of alien and native range-expanding fishes often exceeded 50% of the total fish biomass. Conversely, in the North and Western Mediterranean, alien fishes were absent. A negative relationship was found between native and alien species richness. Average and minimum sea surface temperature (SST) over six consecutive years were positively correlated with the total biomass of alien species; no alien fishes were recorded below 20.5°C average SST and 13.8°C minimum SST. We also found a negative relationship between alien fishes' biomass and the distance from the Suez Canal, which is the main pathway for the introduction of alien fish in the Mediterranean Sea. The biomass of alien and native range-expanding fishes was found to be higher in the South and Eastern Mediterranean MPAs than in adjacent unprotected areas. The association of barrens (rocky reefs deprived of vegetation) and invasive herbivores was observed at all eastern sites, regardless of protection status. Currently, the level of fishing pressure exerted on alien and native range-expanding fishes seems to be the most influential factor determining the lower biomass of invasive fishes at unprotected sites compared to MPAs. Our findings suggest that complementary management actions, such as species-targeted removals, should be taken in MPAs to effectively control invasive fish populations.

Thermal affinity as the dominant factor changing Mediterranean fish abundances

Recent decades have seen profound changes in species abundance and community composition. In the marine environment, the major anthropogenic drivers of change comprise exploitation, invasion by nonindigenous species, and climate change. However, the magnitude of these stressors has been widely debated and we lack empirical estimates of their relative importance. In this study, we focused on Eastern Mediterranean, a region exposed to an invasion of species of Red Sea origin, extreme climate change, and high fishing pressure. We estimated changes in fish abundance using two fish trawl surveys spanning a 20-year period, and correlated these changes with estimated sensitivity of species to the different stressors. We estimated sensitivity to invasion using the trait similarity between indigenous and nonindigenous species; sensitivity to fishing using a published composite index based on the species' life-history; and sensitivity to climate change using species climatic affinity based on occurrence data. Using both a meta-analytical method and random forest analysis, we found that for shallow-water species the most important driver of population size changes is sensitivity to climate change. Species with an affinity to warm climates increased in relative abundance and species with an affinity to cold climates decreased suggesting a strong response to warming local sea temperatures over recent decades. This decrease in the abundance of cold-water-associated species at the trailing "warm" end of their distribution has been rarely documented. Despite the immense biomass of nonindigenous species and the presumed high fishing pressure, these two latter factors seem to have only a minor role in explaining abundance changes. The decline in abundance of indigenous species of cold-water origin indicates a future major restructuring of fish communities in the Mediterranean in response to the ongoing warming, with unknown impacts on ecosystem function.

Remarkable size-spectra stability in a marine system undergoing massive invasion

The Mediterranean Sea is an invasion hotspot, with non-indigenous species suspected to be a major driver behind community changes. We used size spectra, a reliable index of food web structure, to examine how the influx of Red Sea fishes into the Mediterranean Sea has impacted the indigenous species community. This is the first attempt to use changes in the size spectra to reveal the effect of biological invasions. We used data from trawl catches along Israel's shoreline spanning 20 years to estimate changes in the community size spectra of both indigenous and non-indigenous species. We found that the relative biomass of non-indigenous species increased over the 20 years, especially for small and large species, leading to a convergence with the indigenous species size spectra. Hence, the biomass of indigenous and non-indigenous species has become identical for all size classes, suggesting similar energetic constraints and sensitivities to fishing. However, over this time period the size spectrum of indigenous species has remained remarkably constant. This suggests that the wide-scale invasion of non-indigenous species into the Mediterranean may have had little impact on the community structure of indigenous species.