Invasion genomics of lionfish in the Mediterranean Sea

The rate of biological invasions is steadily increasing, with major ecological and economic impacts accounting for billions of dollars in damage as a result. One spectacular example is the western Atlantic invasion by lionfishes. In the Mediterranean Sea, invasions from the Red Sea via the Suez Canal (termed Lessepsian invasions) comprise more than 100 fish species, including a recent invasion by lionfish. In light of the devastating effects of lionfish in the Caribbean Sea, understanding the dynamics of Mediterranean lionfish invasion is crucial. The Lessepsian lionfish invasion started in 2012, and rapidly spread to the central Mediterranean. Here, we used thousands of RAD seq genomic markers to study the population dynamics of this invasion. While we did not find a reduction in genetic diversity between source (Red Sea) and invasive (Mediterranean) populations (i.e., bottleneck effects), we found evidence of population structure within the invasive range in the Mediterranean Sea. We found that loci that are potentially under selection may play an important role in invasion success (in particular, genes involved in osmoregulation and fin spine sizes). Genomic approaches proved powerful in examining the ecological and evolutionary patterns of successful invaders and may be used as tools to understand and potentially mitigate future invasions.

Crowding in the middle of marine food webs: A focus on Raja asterias and other mediterranean batoids

The Mediterranean Sea is among the three biodiversity hotspots of the world where elasmobranchs are severely threatened. Elasmobranchs act as apex or meso-predators within marine food webs and the loss/decline of apex predators determines the mesopredator release, leading in turn to increased predation on smaller prey. However, also several mesopredators (including rays, skates and small sharks) are intensively fished, being of commercial interest, or by-caught, and thus mesopredators increase could not be so evident. We analysed the trophic ecology of an endemic Mediterranean ray, the starry ray Raja asterias, at a seasonal scale from the Adriatic basin, one of the most intensively exploited area of the Mediterranean, by means of stomach contents and stable isotopes analyses. Our results evidenced that starry rays rely on benthic sources including species of local commercial values, such as swimming crabs, small cephalopods, and stomatopods and share the same trophic position with other elasmobranchs (rays, skates, and small sharks) and other mesopredators (e.g., common soles, Norway lobsters and mullets). As all mesopredators are overexploited, as well as their benthic prey are affected by intense trawl-fishing, the whole food webs are disrupted and neither the classical trophic cascade nor the mesopredator release hypothesis could be verified. Conservation measures for these species, such as the release after capture or the application of exclusion grids to the net, should be applied in areas where populations are strongly impacted by trawling.

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.

Marine heatwaves drive recurrent mass mortalities in the Mediterranean Sea

Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015-2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change.

Seasonal trophic ecology of the invasive crab Percnon gibbesi (Brachyura, Plagusiidae) in the southwestern mediterranean: Insights from stomach contents and stable isotope analyses

The invasive sally lightfoot crab Percnon gibbesi (H. Milne Edwards, 1853) has spread among the coasts of the Mediterranean Sea, including the coasts of Annaba Gulf (Algeria). Investigating the trophic position of the species and looking for the seasonal variations in the diet of this alien decapod was the aim of this study. To do this, samples of P. gibbesi were collected along Annaba coasts within a year. The traditional stomach content analysis (SCA) was integrated to the stable isotope analysis (SIA) of nitrogen and carbon to provide a comprehensive evaluation of the feeding ecology of P. gibbesi, and its within-year variability. Results highlighted, for the first time, significant seasonal variation in P. gibbesi diet, improving our understanding of its trophic plasticity and potential dietary overlaps with other herbivore species. Its feeding plasticity is an asset in the successful expansion of its distribution. Relating its diet composition through the different seasons with the interactions with native herbivores will be essential to fully appreciate the impact of the spread of P. gibbesi in the Mediterranean Sea.

Right out of the gate: the genomics of Lessepsian invaders in the vicinity of the Suez Canal

Marine organisms that enter the Mediterranean from the Red Sea via the Suez Canal are known as Lessepsian bioinvaders. In general, genetic studies of Lessepsian fishes have shown little structure between Red Sea and Mediterranean populations. Yet notable exceptions suggest the importance of life-history factors that may influence patterns of spatial genetic variation. In this study, by sampling two invasive fishes with different life histories (the rabbitfish Siganus rivulatus and the filefish Stephanolepis diaspros), we looked at evidence of population structure and selection at the boundary between the Red Sea and the Mediterranean (the Suez Canal), using thousands of molecular markers. Results illustrate two divergent patterns of genetic patterns, with little genetic structure in S. rivulatus and strong population structure in S. diaspros, even at such small spatial scale. We discuss differences in ecological characteristics between the two species to account for such differences. In addition, we report that in the face of both high (S. rivulatus) and low (S. diaspros) gene flow, loci under selection were uncovered, and some protein coding genes were identified as being involved with osmoregulation, which seems to be an important feature of individuals crossing the salinity-variable Suez Canal. The presence of genes under selection in populations near the Suez Canal supports the idea that selection may be active and essential for successful invasions right out of the gate.

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.

Habitat suitability, niche unfilling and the potential spread of Pterois miles in the Mediterranean Sea

The common lionfish Pterois miles has rapidly spread across the eastern Mediterranean Sea. We compiled occurrence data from both native and invaded range under the framework of Species Distribution Modelling (SDM). Through a construction of an environmental suitability model and estimation of spread rates we investigated the lionfish climate niche in both its native and invaded domains, this latter represented by the Mediterranean region. Model projections allowed to identify suitable areas for lionfish establishment in the Mediterranean. Spread analysis suggested that a further geographical expansion in this basin could be completed within the next years. Our results did not provide evidence for niche expansion but highlighted a high degree of niche unfilling thus prospecting a likely spread of Mediterranean lionfish invasion beyond the predictions of current SDMs. These findings provide novel inputs to forecast the future geographical evolution of the lionfish in the Mediterranean Sea and asses the related risk of invasion.

Management priorities for marine invasive species

Managing invasive alien species is particularly challenging in the ocean mainly because marine ecosystems are highly connected across broad spatial scales. Eradication of marine invasive species has only been achieved when species were detected early, and management responded rapidly. Generalized approaches, transferable across marine regions, for prioritizing actions to control invasive populations are currently lacking. Here, expert knowledge was elicited to prioritize 11 management actions for controlling 12 model species, distinguished by differences in dispersion capacity, distribution in the area to be managed, and taxonomic identity. Each action was assessed using five criteria (effectiveness, feasibility, acceptability, impacts on native communities, and cost), which were combined in an 'applicability' metric. Raising public awareness and encouraging the commercial use of invasive species were highly prioritized, whereas biological control actions were considered the least applicable. Our findings can guide rapid decision-making on prioritizing management options for the control of invasive species especially at early stages of invasion, when reducing managers' response time is critical.

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.

Climate change, biological invasions, and the shifting distribution of Mediterranean fishes: A large-scale survey based on local ecological knowledge

Climate change and biological invasions are rapidly reshuffling species distribution, restructuring the biological communities of many ecosystems worldwide. Tracking these transformations in the marine environment is crucial, but our understanding of climate change effects and invasive species dynamics is often hampered by the practical challenge of surveying large geographical areas. Here, we focus on the Mediterranean Sea, a hot spot for climate change and biological invasions to investigate recent spatiotemporal changes in fish abundances and distribution. To this end, we accessed the local ecological knowledge (LEK) of small-scale and recreational fishers, reconstructing the dynamics of fish perceived as "new" or increasing in different fishing areas. Over 500 fishers across 95 locations and nine different countries were interviewed, and semiquantitative information on yearly changes in species abundance was collected. Overall, 75 species were mentioned by the respondents, mostly warm-adapted species of both native and exotic origin. Respondents belonging to the same biogeographic sectors described coherent spatial and temporal patterns, and gradients along latitudinal and longitudinal axes were revealed. This information provides a more complete understanding of the shifting distribution of Mediterranean fishes and it also demonstrates that adequately structured LEK methodology might be applied successfully beyond the local scale, across national borders and jurisdictions. Acknowledging this potential through macroregional coordination could pave the way for future large-scale aggregations of individual observations, increasing our potential for integrated monitoring and conservation planning at the regional or even global level. This might help local communities to better understand, manage, and adapt to the ongoing biotic transformations driven by climate change and biological invaders.

Annual rhythms of temporal niche partitioning in the Sparidae family are correlated to different environmental variables

The seasonal timing of recurring biological processes is essential for organisms living in temperate regions. While ample knowledge of these processes exists for terrestrial environments, seasonal timing in the marine environment is relatively understudied. Here, we characterized the annual rhythm of habitat use in six fish species belonging to the Sparidae family, highlighting the main environmental variables that correlate to such rhythms. The study was conducted at a coastal artificial reef through a cabled observatory system, which allowed gathering underwater time-lapse images every 30 minutes consecutively over 3 years. Rhythms of fish counts had a significant annual periodicity in four out of the six studied species. Species-specific temporal patterns were found, demonstrating a clear annual temporal niche partitioning within the studied family. Temperature was the most important environmental variable correlated with fish counts in the proximity of the artificial reef, while daily photoperiod and salinity were not important. In a scenario of human-induced rapid environmental change, tracking phenological shifts may provide key indications about the effects of climate change at both species and ecosystem level. Our study reinforces the efficacy of underwater cabled video-observatories as a reliable tool for long-term monitoring of phenological events.

Warming-related shifts in the distribution of two competing coastal wrasses

Warming induces organisms to adapt or to move to track thermal optima, driving novel interspecific interactions or altering pre-existing ones. We investigated how rising temperatures can affect the distribution of two antagonist Mediterranean wrasses: the 'warm-water' Thalassoma pavo and the 'cool-water' Coris julis. Using field surveys and an extensive database of depth-related patterns of distribution of wrasses across 346 sites, last-decade and projected patterns of distribution for the middle (2040-2059) and the end of century (2080-2099) were analysed by a multivariate model-based framework. Results show that T. pavo dominates shallow waters at warmest locations, where C. julis locates deeper. The northernmost shallow locations are dominated by C. julis where T. pavo abundance is low. Projections suggest that the W-Mediterranean will become more suitable for T. pavo whilst large sectors of the E-Mediterranean will be unsuitable for C. julis, progressively restricting its distribution range. These shifts might result in fish communities' re-arrangement and novel functional responses throughout the food-web.

Predicting future thermal habitat suitability of competing native and invasive fish species: from metabolic scope to oceanographic modelling

Global increase in sea temperatures has been suggested to facilitate the incoming and spread of tropical invaders. The increasing success of these species may be related to their higher physiological performance compared with indigenous ones. Here, we determined the effect of temperature on the aerobic metabolic scope (MS) of two herbivorous fish species that occupy a similar ecological niche in the Mediterranean Sea: the native salema (Sarpa salpa) and the invasive marbled spinefoot (Siganus rivulatus). Our results demonstrate a large difference in the optimal temperature for aerobic scope between the salema (21.8°C) and the marbled spinefoot (29.1°C), highlighting the importance of temperature in determining the energy availability and, potentially, the distribution patterns of the two species. A modelling approach based on a present-day projection and a future scenario for oceanographic conditions was used to make predictions about the thermal habitat suitability (THS, an index based on the relationship between MS and temperature) of the two species, both at the basin level (the whole Mediterranean Sea) and at the regional level (the Sicilian Channel, a key area for the inflow of invasive species from the Eastern to the Western Mediterranean Sea). For the present-day projection, our basin-scale model shows higher THS of the marbled spinefoot than the salema in the Eastern compared with the Western Mediterranean Sea. However, by 2050, the THS of the marbled spinefoot is predicted to increase throughout the whole Mediterranean Sea, causing its westward expansion. Nevertheless, the regional-scale model suggests that the future thermal conditions of Western Sicily will remain relatively unsuitable for the invasive species and could act as a barrier for its spread westward. We suggest that metabolic scope can be used as a tool to evaluate the potential invasiveness of alien species and the resilience to global warming of native species.

External morphology explains the success of biological invasions

Biological invasions have become major players in the current biodiversity crisis, but realistic tools to predict which species will establish successful populations are still unavailable. Here we present a novel approach that requires only a morphometric characterisation of the species. Using fish invasions of the Mediterranean, we show that the abundance of non-indigenous fishes correlates with the location and relative size of occupied morphological space within the receiving pool of species. Those invaders that established abundant populations tended to be added outside or at the margins of the receiving morphospace, whereas non-indigenous species morphologically similar to resident ones failed to develop large populations or even to establish themselves, probably because the available ecological niches were already occupied. Accepting that morphology is a proxy for a species' ecological position in a community, our findings are consistent with ideas advanced since Darwin's naturalisation hypothesis and provide a new warning signal to identify invaders and to recognise vulnerable communities.

Genetics of a Lessepsian sprinter: the bluespotted cornetfish, Fistularia commersonii

Our current understanding of the mechanisms that lead to successful biological invasions is limited. Although local adaptation plays a central role in biological invasions, genetic studies have failed to produce a unified theory so far. The bluespotted cornetfish, a recent invader of the Mediterranean Sea from the Red Sea via the Suez Canal, provides an ideal case study to research the mechanisms of invasive genetics. Previous genetic work based on mitochondrial markers has shown the genetic diversity of the Mediterranean population was greatly reduced in comparison to the natural population in the Red Sea. In the current study, we expand upon these studies by adding mitochondrial and nuclear markers. Mitochondrial results confirm previous findings. The nuclear marker, however, does not show evidence of reduction in diversity. We interpret these results as either a differential dispersal capability in males and females, or the presence of selection on the invading Mediterranean population.

First record of the Atlantic bumper Chloroscombrus chrysurus (Teleostei: Carangidae) in the Mediterranean Sea

In December 1997, one specimen of the Atlantic bumper, Chloroscombrus chrysurus was recorded for the first time in the Mediterranean Sea, off Almuñécar (Granada, Spain: 36° 43' 26″ N; 3° 41' 39″ W). This species probably entered the Mediterranean Sea via the Strait of Gibraltar.

Conservation physiology of marine fishes: advancing the predictive capacity of models

At the end of May, 17 scientists involved in an EU COST Action on Conservation Physiology of Marine Fishes met in Oristano, Sardinia, to discuss how physiology can be better used in modelling tools to aid in management of marine ecosystems. Current modelling approaches incorporate physiology to different extents, ranging from no explicit consideration to detailed physiological mechanisms, and across scales from a single fish to global fishery resources. Biologists from different sub-disciplines are collaborating to rise to the challenge of projecting future changes in distribution and productivity, assessing risks for local populations, or predicting and mitigating the spread of invasive species.

Food partitioning and diet temporal variation in two coexisting sparids, Pagellus erythrinus and Pagellus acarne

Resource partitioning in two congeneric sparids, pandora Pagellus erythrinus and axillary seabream Pagellus acarne, was investigated using stomach content analysis integrated with data on stable isotopes (δ(15) N and δ(13) C). The study was carried out on coastal muddy bottoms in the Gulf of Castellammare (southern Tyrrhenian Sea, western Mediterranean Sea) in seasons (autumn, November 2004; winter, March 2005; spring, early June 2005), at depths between 50 and 100 m. Stomach content analysis suggested low trophic niche overlap between the two species. Pagellus erythrinus mainly preyed on strictly benthic organisms (polychaetes, brachyuran crabs and benthic crustaceans). Although it consumed benthic prey, P. acarne preferred suprabenthic prey such as peracarid crustaceans from the benthic boundary layer a few metres above the bottom. The two species showed different isotopic values, with P. erythrinus exhibiting higher δ(15) N and more enriched δ(13) C than P. acarne, in accordance with its marked benthic behaviour and high predation on carnivore polychaetes. Significant temporal variability in both diet and isotopic values caused trophic differences between the two species. The autumn and winter diet differed from the spring diet and the trophic levels of both species increased from autumn and winter to spring, in accordance with variations in food availability and changes in prey δ(15) N and δ(13) C. These temporal variations may be linked to an increase in energy requirements for reproduction, together with the differing availability of preferred prey throughout the year. Significantly, lower δ(13) C was recorded in fishes collected in winter (March), suggesting the influence of river inputs as a source of particulate organic matter in this zone after the flooding season. In conclusion, these sympatric congeneric fish species displayed clear food partitioning throughout the temporal scale analysed.

Sewage pollution impact on Mediterranean rocky-reef fish assemblages

The effects of sewage outfalls on subtidal fish assemblages were studied along the NW coasts of Malta (Sicily channel, Mediterranean Sea) by means of underwater visual census. The presence of two spatially distinct outfalls discharging untreated wastewaters allowed to use a balanced symmetrical after control/impact (ACI) design that consisted of two putatively impacted locations and two controls, with four sites nested in each location. Surveys were performed in 2006 at two random dates. The study highlighted significant changes at both assemblage and individual species levels. Fish assemblages structures were different between controls and sewages, where total abundance of fish were higher. The responses of individual species to sewage pollution were mostly related to an anomalous increase of two small opportunistic species i.e. Gobius bucchichii and Parablennius rouxi and to a decrease of species of the genus Symphodus, particularly S. roissali and S. ocellatus. Moreover in correspondence of the outfalls, significant changes of the fish size distribution were detected for several species. These results support the use of fish assemblages as biological indicators for marine coastal waters and demonstrated the possibility to obtain sharp signals of environmental impact from some individual fish species.

Genetic bottlenecks and successful biological invasions: the case of a recent Lessepsian migrant

Our current understanding of the mechanisms that lead to successful biological invasions is limited. Although adaptations play a central role in biological invasions, genetic studies have so far failed to produce a unified theory. The bluespotted cornetfish, a recent Red Sea invader in the Mediterranean Sea via the Suez Canal, provides an ideal case study for research in the mechanisms of invasive genetics. In this study, we show that the invading bluespotted cornetfish underwent a severe population bottleneck that reduced the genetic diversity of this immigrant to only two mitochondrial haplotypes. Although loss of genetic diversity is considered detrimental to the need to adapt to new environments, bluespotted cornetfish experienced an unprecedented success and rapid spread across the Mediterranean.

Molecular systematics, zoogeography, and evolutionary ecology of the atlantic parrotfish genus Sparisoma

Parrotfishes of the genus Sparisoma (Scaridae) are ecologically important tropical reef fishes restricted to the Atlantic Ocean. We investigated phylogenetic relationships among the eight extant species within this genus using mitochondrially encoded 12S and 16S ribosomal genes. Our molecular data support the view that (i) Sparisoma originated approximately 14-35 million years ago (mya), probably in the tropical western Atlantic, off Brazil; (ii) there have been at least four discrete bouts of cladogenesis within the genus, with the most recent one ( approximately 2.8-5.6 mya) involving four events in both the east and the west Atlantic and across the Atlantic; and (iii) the genus invaded the eastern Atlantic on two different occasions, probably by at least two different routes. The data also offer support for Bellwood's ideas concerning the evolutionary changes in adult feeding patterns and habitat use within Scarids. Specifically, they support the evolutionary position of the ecological traits of Sparisoma as intermediate within the family.