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.

Nutrient conditions determine the strength of herbivore-mediated stabilizing feedbacks in barrens.

Abiotic environmental conditions can significantly influence the way species interact. In particular, plant-herbivore interactions can be substantially dependent on temperature and nutrients. The overall product of these relationships is critical for the fate and stability of vegetated ecosystems like marine forests. The last few decades have seen a rapid spread of barrens on temperate rocky reefs mainly as a result of overgrazing. The ecological feedbacks that characterize the barren state involve a different set of interactions than those occurring in vegetated habitats. Reversing these trends requires a proper understanding of the novel feedbacks and the conditions under which they operate. Here, we explored the role of a secondary herbivore in reinforcing the stability of barrens formed by sea urchin overgrazing under different nutrient conditions. Combining comparative and experimental studies in two Mediterranean regions characterized by contrasting nutrient conditions, we assessed: (i) if the creation of barren areas enhances limpet abundance, (ii) the size-specific grazing impact by limpets, and (iii) the ability of limpets alone to maintain barrens. Our results show that urchin overgrazing enhanced limpet abundance. The effects of limpet grazing varied with nutrient conditions, being up to five times more intense under oligotrophic conditions. Limpets were able to maintain barrens in the absence of sea urchins only under low-nutrient conditions, enhancing the stability of the depauperate state. Overall, our study suggests a greater vulnerability of subtidal forests in oligotrophic regions of the Mediterranean and demonstrates the importance of environment conditions in regulating feedbacks mediated by plant-herbivore interactions.

Resilience of seagrass populations to thermal stress does not reflect regional differences in ocean climate.

The prevalence of local adaptation and phenotypic plasticity among populations is critical to accurately predicting when and where climate change impacts will occur. Currently, comparisons of thermal performance between populations are untested for most marine species or overlooked by models predicting the thermal sensitivity of species to extirpation. Here we compared the ecological response and recovery of seagrass populations (Posidonia oceanica) to thermal stress throughout a year-long translocation experiment across a 2800-km gradient in ocean climate. Transplants in central and warm-edge locations experienced temperatures > 29°C, representing thermal anomalies > 5°C above long-term maxima for cool-edge populations, 1.5°C for central and < 1°C for warm-edge populations. Cool-edge, central and warm-edge populations differed in thermal performance when grown under common conditions, but patterns contrasted with expectations based on thermal geography. Cool-edge populations did not differ from warm-edge populations under common conditions and performed significantly better than central populations in growth and survival. Our findings reveal that thermal performance does not necessarily reflect the thermal geography of a species. We demonstrate that warm-edge populations can be less sensitive to thermal stress than cooler, central populations suggesting that Mediterranean seagrasses have greater resilience to warming than current paradigms suggest.

Reproductive dynamics of the invasive lionfish (Pterois miles) in the Eastern Mediterranean Sea.

The lionfish Pterois miles invaded the Mediterranean Sea in 2012 and spread fast to the entire eastern basin. This study provides evidence of successful spawning and the first detailed analysis of P. miles ovarian dynamics in the Mediterranean Sea. The ovarian reproductive phases of mature females collected from Cyprus (eastern Mediterranean) between September 2017 and August 2018 were analysed, both macroscopically and histologically. The results suggested a prolonged oocyte recruitment and development season, and a spawning season that primarily occurred during summertime, even though spawning-capable females were caught also in autumn. A year-round spawning activity may have been inhibited due to seasonal variations in water temperature. Multiple oocyte developmental stages co-occurred in females at different reproductive phases, indicating that more than one oocyte batches were released per spawning season. The analysis of the spawning batch formation enabled the batch fecundity estimation at 3225-63149 oocytes. The oocyte development pattern described in this study shared characteristics with the indeterminate fecundity type, where new oocytes are recruited to the secondary growth phase in parallel with spawning activity. Climate change is likely to extend the spawning season of lionfish in the Mediterranean Sea and further favour its invasion. The information provided in this study is vital for the design of strategic and effective management plans to restrain the expansion of this highly invasive fish.

The role of social media in compensating for the lack of field studies: Five new fish species for Mediterranean Egypt.

In the Mediterranean Sea, where biological invasions constitute a serious threat, the combination of citizen science and social networks amplified the power of proper field studies, recording species that would have otherwise presumably passed unnoticed. Based on data collected on several Facebook groups, we hereby first report the presence of five fish taxa (Kyphosus sp., Heniochus intermedius, Pomacanthus imperator, Pomacanthus maculosus and Abudefduf sp.) new for the Mediterranean Egypt, revise their distribution in the Mediterranean Sea and discuss their possible introduction pathways. Finally, we provide some considerations on the potentiality of social media for citizen science projects.

Fishery reforms for the management of non-indigenous species.

Marine ecosystems are undergoing major transformations due to the establishment and spread of Non-Indigenous Species (NIS). Some of these organisms have adverse effects, for example by reducing biodiversity and causing ecosystem shifts. Others have upsides, such as benefits to fisheries or replacing lost ecological functions and strengthening biogenic complexity. Stopping the spread of NIS is virtually impossible and so the societal challenge is how to limit the socioeconomic, health, and ecological risks, and sustainably exploit the benefits provided by these organisms. We propose a move away from the notion that NIS have only negative effects, and suggest a turn towards an Ecosystem-Based Fishery Management approach for NIS (EBFM-NIS) in the Mediterranean Sea, the world's most invaded marine region. A structured, iterative, and adaptive framework that considers the range of costs and benefits to ecosystems, ecosystem services, and fisheries is set out to determine whether NIS stocks should be managed using sustainable or unsustainable exploitation. We propose fishery reforms such as multiannual plans, annual catch limits, technical measures for sustainable exploitation, and legitimization of unlimited fishing of selected NIS and introduction of a radical new license for NIS fishing for unsustainable exploitation. Depending on local conditions, investment strategies can be included within the EBFM-NIS framework to protect/enhance natural assets to improve ecosystem resilience against NIS, as well as fishery assets to improve the performance of NIS fisheries. Examples of the former include the enhancement of Marine Protected Areas, harvesting of invasive NIS within MPAs, and protection of overfished predators and key species. Examples of the latter include market promotion and valorisation of NIS products, development of novel NIS products, and innovative/alternative NIS fishing such as fishery-related tourism ('pescatourism'). The application of the suggested EBFM-NIS would create jobs, protect and enhance ecosystem services, and help to meet the United Nations Sustainable Development Goal 14: Conserve and sustainably use the oceans, seas, and marine resources for sustainable development.

The bastard grunt Pomadasys incisus (Bowdich, 1825) (Teleostei: Haemulidae) in Cyprus (eastern Mediterranean Sea) - a late arrival or just a neglected species?

Pomadasys incisus is a thermophilous coastal subtropical fish species belonging to the family Haemulidae. Originally described from Gambia, this species is widely distributed in the Eastern Atlantic from Galicia to South Africa. It has also been recorded in the Mediterranean Sea since 1840, presumably expanding its distribution in the next decades, although the species could have been already present in the basin, but simply overlooked until the mid XIX century. In this study, we first record P. incisus from Cyprus (eastern Mediterranean Sea), based on two opportunistic observations obtained through a citizen-science project and review the distribution of this species in the Mediterranean Sea. The present sighting raises the question on whether this species is a late arrival in the country or its presence has just been neglected until now. Based on present data, the most likely hypothesis is the latter one, with P. incisus occurring in low densities and being overlooked due to the absence of field studies. Whatever is true, some intrinsic or extrinsic factors may have played a role in limiting its spread or wide establishment in the above-mentioned country.

They are here to stay: the biology and ecology of lionfish (Pterois miles) in the Mediterranean Sea.

The lionfish, Pterois miles, is one of the most recent Lessepsian immigrants into the Mediterranean Sea, and it poses a serious threat to marine ecosystems in the region. This study assesses the basic biology and ecology of lionfish in the Mediterranean, examining morphometrics, reproduction and diet as well as population structure and distribution. The population density of lionfish has increased dramatically in Cyprus since the first sighting in late 2012; by 2018 aggregations of up to 70 lionfish were found on rocky grounds with complex reefs and artificial reefs in depths of 0-50 m. Lionfish in Cyprus become mature within a year, and adults are capable of spawning year-round, with peak spawning in summer when the sea-surface temperature reaches 28.4°C. The Cypriot lionfish grow faster and bigger than in their native range, and females are more common than males. Lionfish are generalist predators in these waters, as also found in their native range, consuming a range of teleost and crustacean prey, some of which are of high economic value (e.g., Spicara smaris and Sparisoma cretense) or have an important role in local trophic webs (e.g., Chromis chromis). Overall, the reproductive patterns, the presence of juveniles and adults throughout the year, the rapid growth rates and the generalist diet indicate that lionfish are thriving and are now already well established in the region and could potentially become the serious nuisance that they are in their temperate and tropical western Atlantic-invasive range.

Seagrass recovery after fish farm relocation in the eastern Mediterranean.

Finfish aquaculture has damaged seagrass meadows worldwide as wastes from the farms can kill these habitat-forming plants. In Cyprus, the Mediterranean endemic Posidonia oceanica is at its upper thermal limits yet forms extensive meadows all around the island. Understanding this under-studied isolated population may be important for the long-term survival of the species given that the region is warming rapidly. When fish farming began around Cyprus in the mid-nineties, cages were moored above seagrass beds, but as production expanded they were moved into deeper water further away from the meadows. Here, we monitored the deepest edge of meadows near fish farms that had been moved into deeper waters as well as at a decommissioned farm site. Four P. oceanica monitoring systems were set up using methods developed by the Posidonia Monitoring Network. Seagrass % coverage, shoot density, % of plagiotropic rhizomes, shoot exposure, leaf morphometry, and sediment organic matter content and grain size were monitored at 11 fixed plots within each system, in 2012-2014 and in 2017. Expansion at the lower depth limit of seagrass meadows was recorded at all monitoring sites. Most other P. oceanica descriptors either did not change significantly or declined. Declines were most pronounced at a site that was far from mariculture activities but close to other anthropogenic pressures. The most important predictor affecting P. oceanica was depth. Monitoring using fixed plots allowed direct comparisons of descriptors over time, removes patchiness and intra-meadow variability increasing our understanding of seagrass dynamics and ecosystem integrity. It seems that moving fish farms away from P. oceanica has helped ensure meadow recovery at the deepest margins of their distribution, an important success story given that these meadows are at the upper thermal limits of the species.

Genetics reveal the identity and origin of the lionfish invasion in the Mediterranean Sea.

Following aquarium releases, invasive lionfishes have colonized large areas of the Caribbean and western Atlantic, resulting in an immense ecological damage. The early stages of that invasion are poorly known. Indeed, a lag of time between the introduction and detection often preclude genetic characterization of that crucial phase. With elevated awareness, the recent invasion of Pterois miles was quickly detected in the Mediterranean Sea. We hereby show that the very first individuals establishing populations in the Mediterranean Sea display haplotypes that nest within the large genetic diversity of Red Sea individuals, thus indicating an invasion via the Suez Canal. We also show that only two haplotypes are detected in the Mediterranean Sea, suggesting that few individuals may have been involved in the invasion. Thus, we conclude that the Mediterranean invasion is the result of a movement of individuals from the Red Sea, rather than from other means, and that low genetic diversity does not seem to have a negative effect on the success and spread of lionfish into the Mediterranean Sea.