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Cold-water corals (CWCs) are bioengineering species that can increase habitat heterogeneity and improve the deep sea’s biological diversity and ecosystem functioning. Knowledge of their distribution provides a critical baseline for assessing the effect of natural and anthropogenic impacts on these important deep-sea habitats. The aims of this study are: i) provide new data on the spatial distribution of six CWCs species in the Strait of Sicily, ii) describe the principal environmental and anthropogenic variables that play a role in shaping their distribution, iii) identify hotspots in which individuals belonging to the various species co-occur. Presence-only data of six CWCs species, ten environmental variables (depth, slope, rugosity, aspect, flowdir, temperature, salinity, north bottom current, east bottom current, chlorophyll-a), and one variable relating to bottom trawling effort (Automatic Information System – AIS) were used to predict the suitable habitats. We used Maximum Entropy modelling (MaxEnt) approach and used the AUC (area under the receiver operating characteristic curve) and TSS (true skill statistics) to evaluate the model performance. The results showed excellent AUC, TSS and AUC’s standard deviation mean values for all six species. The validation show high predictive performance. MaxEnt identified slope, depth, and rugosity as the most important predictors, showing the highest percentage contribution for all six species considered. Throughout the study area, highlyinterspecific persistent density hotspot of CWCs co-occurrence were discovered, with a total extension of 4.05 km2 where all species co-occur. Although studies on the effect of environmental and anthropogenic factors that impact the distribution of these species of conservation interest remain scarce, the results of this study offer useful guidance for decision-makers to develop necessary conservation measures.

Marine protected areas are proposed to protect elasmobranchs (sharks, skates, and rays) but the fishing impact from small-scale fisheries in these areas is unknown. From 1256 fishing operations carried out in partially protected and unprotected areas in six Mediterranean countries, this study shows that catches were higher in partially protected areas than in unprotected areas, indicating poor small-scale fisheries management as a threat for these species.

Discards remain among the main negative impacts of fishing activities, and their reductions are strengthened by the European Common Fisheries Policy (European Regulation 1380/2013). Trammel net fisheries appear more sustainable compared with other fishing techniques, especially from an ecological viewpoint. Despite this, reports show that trammel net fisheries deliver discard quantities between 10% and 43% of the total catch biomass. To supplement existing information, this current work attempts to address the discard reduction using guarding net in the small-scale fisheries of Egadi Islands MPA (Western Sicily, Central Mediterranean Sea). To assess the reduction of unwanted catches, 48 experimental fishing trials were conducted within a 6-month period. The experimental fishing trial employed a trammel net made up of 20 panels alternated with two different net configurations. The control panels (CN) held a large outer (180 mm) and small inner (31.25 mm) meshes. The test panels (GN) with guarding net constituted a three-mesh-high (50-mm mesh size) net placed between trammel net panels and a lead line. A total of 3,310 individuals belonging to 106 taxa and nine phyla were caught. Crustaceans were the most abundant unwanted catches in the control panels, whereas bioconstructions occurred in the guarding net panels. The discard ratios of CN and GN panels were statistically different (t-value = –2.55; p< 0.05). The analysis of catch per unit effort showed higher catches of CN panels for both commercial and discard fractions (p< 0.05). Moreover, the guarding net panels caught the main discarded species at 20% lower compared with the control. The overall value of the catch at the CN panels (€ 3,366.90) was higher than the total income (€ 2,043.70) generated using the GN panels, which suggests a significant commercial loss of 40% (p< 0.05).

Knowledge of the reproductive strategy is a key prerequisite to predict population dynamics and potential invasiveness of both native and non-indigenous outbreak-forming species. In 2014 the Lessepsian upside-down jellyfish Cassiopea andromeda reached the harbor of Palermo (NW Sicily, Thyrrenian Sea), to date its established westernmost outpost in the Mediterranean Sea. To predict C. andromeda reproductive success in its novel habitat, gonad histology was carried out to record the number and size of mature and immature oocytes. Both male and female simultaneously presented gametes at all stages of development suggesting an asynchronous, yet apparently continuous, reproduction strategy. Indeed, oogenesis was observed throughout the year from pre-vitellogenic, vitellogenetic, and late-vitellogenetic to mature oocytes suggesting multiple reproductive events, as known in other Mediterranean Rhizostomeae. Oocytes were found from May to December, with two seasonal peaks of abundance (late spring = 392 and autumn = 272), suggesting imminent spawning events. Further, jellyfish size varied significantly throughout the year, with maximum diameter (up to 24 cm) in summer, and minimum diameter (6 cm) in winter. Small-sized jellyfish in winter belong to the new cohort, most probably arising from intense summer strobilation of polyps. Late spring fertilization, planula development, and metamorphosis, followed by polyp strobilation in the summer months, may explain the late appearance of a new jellyfish cohort, likely coincident with that recorded throughout winter.

The state of marine systems subject to natural or anthropogenic impacts can be generally summarized by suites of ecological indicators carefully selected to avoid redundancy. Length-based indicators capture the status of fish community structure, fulfilling the Marine Strategy Framework Directive (MSFD) requirement for Descriptor 3 (status of commercial fish species). Although the MSFD recommends the development of regional indicators, a comparison among alternative length-based indicators is so far missing for the Mediterranean Sea. Using principal component analysis and dynamic factor analysis, we identified the most effective subset of length-based indicators, whether or not based on maximum length. Indicator trends and time series of fishing effort and environmental variables are also compared in order to highlight the individual and combined capability of indicators to track system changes across geographical sub-areas. Two indicators, typical length and mean maximum length, constitute the smallest set of non-redundant indicators, capturing together 87.45% of variability. Only in combination can these indicators disentangle changes in the fish community composition from modifications of size structure. Our study supports the inclusion of typical length among the regional MSFD Descriptor 3 indicators for the Mediterranean Sea. Finally, we show dissimilarity between the western and eastern-central Mediterranean, suggesting that there are sub-regional differences in stressors and community responses.

The large-scale distribution pattern of megafauna communities along the Mediterranean middle slope was explored. The study was conducted between 500 and 800 m depth where deep-water fishery occurs. Although community studies carried out deeper than 500 m are partly available for some geographic areas, few large-scale comparative studies have been carried out. Within the framework of the MEDITS survey programme, we compared the megafauna community structure in ten geographical sub-areas (GSAs) along the Mediterranean coasts. Additionally, the spatial distribution of fishing was analysed using vessel monitoring by satellite information. Overall, the community showed a significant difference between sub-areas, with a decreasing eastward pattern in abundance and biomass. Longitude was the main factor explaining variation among sub-areas (by generalized additive models). However, we found a region which did not follow the general pattern. GSA 6 (northern Spain) showed significantly lower abundance and a different composition structure to the adjacent areas. The decrease in community descriptors (i.e. abundance and biomass) in this area is probably a symptom of population changes induced by intense fishery exploitation. Overall, a combination of environmental variables and human-induced impacts appears to influence the bentho-pelagic communities along the slope areas of the Mediterranean.

In this study we investigated the spatio-temporal distribution of gurnards (8 species of Triglidae and one species of Peristediidae) in the northern Mediterranean Sea using 22 years of MEDITS bottom trawl survey data (1994-2015). Gurnards showed significant differences in terms of abundance, dominance and composition among geographical sub-areas and ecoregions, with the highest relative biomass (BIy) being found in Malta, eastern Corsica, the Balearic Islands and the eastern Ionian Sea. The lowest gurnards BIy were observed in the highly exploited areas of the western Mediterranean and the Adriatic Sea, where the largest number of species with a negative linear trend in BIy was also found. The temporal trends in species abundances highlighted a general decrease for the coastal species (C. lucerna, C. lastoviza, C. obscurus) as compared with the species inhabiting the deep continental shelf and slope (T. lyra, P. cataphractum). The results provide for the first time an overview of the spatiotemporal trend in the abundance of gurnards over the wide spatial scale of the northern Mediterranean Sea, also suggesting the possible use of these species as indicators for monitoring the impact of fishing pressure on demersal fish assemblages.

The influence of the lunar cycle on bluefin tuna foraging in the upwelling area of the Strait of Messina was investigated by exploring trophic interaction with mesopelagic fish and cephalopod prey. To focus on how the lunar cycle could affect availability of mesopelagic prey for this predator, we tested potential differences in the diet related to each lunar phase. Moreover, we considered two potential impacts of the lunar cycle: the lunar irradiance and the strength of currents. Overall, 2672 prey items were mesopelagic fish and cephalopods, representing 60.7% of overall diet by number. The main mesopelagic fish prey items were lanternfishes and dragonfishes, while Onychoteuthis banksii was the most important cephalopod prey. In summary, the Strait of Messina has highly specific hydrodynamic and biological features which strongly depend on upwelling currents, which in turn are influenced by the lunar cycle (new and full moon with strong currents, quarters with fewer currents). Upwelling causes water mixing, bringing to the surface a large amount of mesopelagic fauna which become more readily available to tuna. Lunar irradiance contributes to the variation of prey composition, increasing the success of visual predation on mesopelagic resources at high light in the water column.

Mediterranean trawl fisheries are characterized by a critical combination of high fishing effort and low size at first capture for most commercial species. In this study we tested the use of sorting grids installed on bottom trawl nets to minimize the catch of undersized deep-water rose shrimp (Parapenaeus longirostris, DPS) and European hake (Merluccius merluccius, HKE). The catch of a traditional trawl net was compared with that obtained with the same net equipped with ad hoc designed juveniles and trash excluder devices (JTEDs) during an experimental survey. Three different JTEDs were tested: the first (G1-SM40) was built with a net of 40-mm square mesh; the second (G2-ST20) and third (G3-ST25) with vertical steel bars spaced 20 and 25 mm, respectively. The probability of retaining DPS and HKE by length class in trawl nets with and without JTED was analysed using generalized additive mixed models. With G1-SM40, the reduction of undersized individuals in the cod-end was about 60% and 44% for DPS and HKE, respectively. With G2-ST20, a 34% catch decrease of HKE individuals smaller than 20 cm total length was observed. A loss of marketable fractions of DPS was recorded with G1-SM40 (–25%) and G2-ST20 (30%). Finally, JTD G3-ST25 was efficient at reducing the catch of undersized specimens of DPS and HKE, but showed a higher loss of marketable fractions than the other JTEDs. Although further fishing trials would be required to maximize the sorting efficiency of the grids, the results obtained clearly indicated that grids can substantially reduce unwanted catches of undersized DPS and HKE in Mediterranean bottom trawl fisheries.

The recent establishment of the “landing obligation” under the reformed EU Common Fishery Policy has the twofold objective of reducing the excessive practice of discarding unwanted catch at sea and encouraging more selective and sustainable fisheries. Within this context, the awareness of the spatial distribution of potential unwanted catches is important for devising management measures aimed to decrease discards. This study analyzed the distribution of Hot Spot density areas of demersal fish and crustaceans below the Minimum Conservation Reference Size (MCRS) in four different southern European seas: continental Portuguese coast, Catalan Sea, South of Sicily, Liguria and northern Tyrrhenian Seas using both bottom trawl survey data and information on the spatial distribution of commercial fisheries. Critical areas for discarding were identified as zones where the highest densities of individuals below MCRS were consistently recorded throughout a series of years. Results clearly showed a patchy distribution of undersized individuals in each investigated area, highlighting the overlap between high density patches of both discards and fishing effort. The present findings provide a relevant knowledge for supporting the application of spatial-based management actions, such as the designation of Fisheries Restricted Areas (FRAs), in order to minimize the by-catch of undersized specimens and improve the sustainability of demersal fisheries.

Harbors are hotspots for the introduction of alien species, and, usually, investigations on their host populations help fill the knowledge gap in their pathways of invasion and in their impacts on marine biodiversity and ecosystems. In 2014, the upside-down alien jellyfish Cassiopea andromeda invaded a Mediterranean touristic harbor (“Cala”), and its abundance has since increased over time. In the present study, the distribution and trophic behavior of C. andromeda in Cala were investigated for the years 2017–2018 through visual sampling, and GIS-based statistical and stable isotope analyses. Since Cala is a hard-to-reach area (with many anchor cables and boats), Megabenthos Underwater Video was used to count the number and estimate the size of jellyfishes. The variations in size throughout the study period suggest that the population of C. andromeda is quite established in Cala at depths lower than 7.5 m. The ranges of the environmental parameters recorded (temperature, salinity, and transparency) were consistent with the ideal conditions for maintaining a Cassiopea population, but they did not seem to influence aggregation. Additionally, the carbon and nitrogen isotopic signatures studied highlight the mixotrophic behavior of this species. These preliminary results confirm the capacity of C. andromeda to live and reproduce in heavily anthropized areas.

Increasing frequency of native jellyfish proliferations and massive appearance of non-indigenous jellyfish species recently concur to impact Mediterranean coastal ecosystems and human activities at sea. Nonetheless, jellyfish biomass may represent an exploitable novel resource to coastal communities, with reference to its potential use in the pharmaceutical, nutritional, and nutraceutical Blue Growth sectors. The zooxanthellate jellyfish Cassiopea andromeda, Forsskål, 1775 (Cnidaria, Rhizostomeae) entered the Levant Sea through the Suez Canal and spread towards the Western Mediterranean to reach Malta, Tunisia, and recently also the Italian coasts. Here we report on the biochemical characterization and antioxidant activity of C. andromeda specimens with a discussion on their relative biological activities. The biochemical characterization of the aqueous (PBS) and hydroalcoholic (80% ethanol) soluble components of C. andromeda were performed for whole jellyfish, as well as separately for umbrella and oral arms. The insoluble components were hydrolyzed by sequential enzymatic digestion with pepsin and collagenase. The composition and antioxidant activity of the insoluble and enzymatically digestible fractions were not affected by the pre-extraction types, resulting into collagen- and non-collagen-derived peptides with antioxidant activity. Both soluble compounds and hydrolyzed fractions were characterized for the content of proteins, phenolic compounds, and lipids. The presence of compounds coming from the endosymbiont zooxanthellae was also detected. The notable yield and the considerable antioxidant activity detected make this species worthy of further study for its potential biotechnological sustainable exploitation.

Single-species Gadget models were used to assess the effects of using a sorting grid mounted on the traditional trawl net used by Sicilian trawlers to exploit the deep-water rose shrimp in the Strait of Sicily. The main commercial by-catch species of this fleet is the European hake (Merluccius merluccius), often caught at sizes well below the minimum conservation reference size. Selectivity curves based on the results of an experimental survey carried out in the area using a commercial trawler equipped with an ad hoc-designed sorting grid were incorporated into single-species Gadget models to forecast the effects of changing fishery selectivity on the performance of the two stocks in terms of catch and biomass. The models included catch data from the Italian, Tunisian and Maltese fleets as well as MEDITS trawl survey data for the period 2002-2016. Several scenarios were defined to simulate the effect of the Italian trawlers’ adopting the sorting grid under different stock-recruitment assumptions. The results obtained, when compared with status quo simulations of fishing without a sorting grid mounted on the trawl net, indicated a beneficial effect for both stocks in terms of an increase in biomass and for the fleets in terms of the amount and size composition of annual landings.

In recent years, caged finfish mariculture across European seas suffered production losses by severe fish mortality, following episodic outbreaks of invertebrate cnidarian stingers. Due to their stinging cells and injectable venoms, medusozoan jellyfish, or drifting propagules of polyp colonies at high density may impair caged fish health through toxic effects on vulnerable tissues of gills and skin, and related secondary bacterial infections. Gill disorders in European sea bass (Dicentrarchus labrax) fish farms along the Spanish Mediterranean coast are commonly reported, but regular monitoring of the frequency of cnidarian outbreaks and their potential impacts on caged fish is still poorly enforced. In this study, two sea bass mariculture farms in Southern Spain (Málaga; Almería) were monitored biweekly for zooplankton, phytoplankton and fish gills condition, over 13 or 30 months for the Málaga and Almería facilities, respectively, within the period 2012–2014. Significant, direct correlations were found among low water temperature, recorded fish mortalities, and high abundances of planktonic cnidarians, particularly of the hydrozoan siphonophores Muggiaea atlantica and M. kochii, and the larval stage of Ectopleura larynx, a common member of cage biofouling communities. A significant relationship between cnidarian densities and the quantitative scoring of gill pathology was also observed. In addition, high densities of long-bristled planktonic diatoms (Chaetoceros spp.) coincided with a major fish mortality event (April 2012, Almería farm). Standardised monitoring of plankton dynamics and composition may help in promoting response capacities of Mediterranean mariculture managers to fish health challenges (such as stinging plankton blooms) by (a) improving diagnostic tools and preventative countermeasures and (b) supporting the development of science-based spatial planning and sustainable growth of coastal mariculture.

Biological fouling organisms on fish cages represent a major issue and costly factor in marine finfish aquaculture. Cnidarians have been identified as one of the most problematical groups, contributing significantly to the occlusion and structural stress of the cage nets, but also dramatically affecting farmed species health in aquaculture facilities worldwide. Recently, significant relationships were established in different Spanish aquaculture facilities between hydrozoans and juvenile fish affected by gill injuries and mortality episodes. Community composition, growth rate and reproductive potential of biofouling were monitored on fish cages over two seasonal periods of fry cages farming, located in southern Spain (SW Alboran Sea), with a special focus on cnidarians. Biomass and community composition of biofouling changed with time and between studied periods, with a marked seasonality in colonization periods and taxonomic composition, particularly for the colonial hydrozoans. The hydroids Ectopleura larynx and Pennaria disticha were found at the highest densities. P. disticha was responsible for major biomass contribution to total hydroid biomass with the fastest growth rates. In addition, actinulae larvae of E. larynx were identified in zooplankton samples at high densities especially during periods of fry introduction in sea cages (when fish are highly vulnerable). These results corroborate evidence of the detrimental influence of fouling cnidarians in Mediterranean finfish aquaculture due to a direct harmful impact on fish health. Investigations on population dynamics, reproductive biology and envenomation potential of fouling hydrozoans should be regarded as key component of best monitoring practices to ensure good farmed fish welfare, maximization of aquaculture production and overall marine spatial planning.

In recent years, jellyfish blooms have attracted considerable scientific interest for their potential impacts on human activities and ecosystem functioning, with much attention paid to jellyfish as predators and to gelatinous biomass as a carbon sink. Other than qualitative data and observations, few studies have quantified direct predation of fish on jellyfish to clarify whether they may represent a seasonally abundant food source. Here we estimate predation frequency by the commercially valuable Mediterranean bogue, Boops boops on the mauve stinger jellyfish, Pelagia noctiluca, in the Strait of Messina (NE Sicily). A total of 1054 jellyfish were sampled throughout one year to quantify predation by B. boops from bite marks on partially eaten jellyfish and energy density of the jellyfish. Predation by B. boops in summer was almost twice that in winter, and they selectively fed according to medusa gender and body part. Calorimetric analysis and biochemical composition showed that female jellyfish gonads had significantly higher energy content than male gonads due to more lipids and that gonads had six-fold higher energy content than the somatic tissues due to higher lipid and protein concentrations. Energetically, jellyfish gonads represent a highly rewarding food source, largely available to B. boops throughout spring and summer. During the remainder of the year, when gonads were not very evident, fish predation switched towards less-selective foraging on the somatic gelatinous biomass. P. noctiluca, the most abundant jellyfish species in the Mediterranean Sea and a key planktonic predator, may represent not only a nuisance for human leisure activities and a source of mortality for fish eggs and larvae, but also an important resource for fish species of commercial value, such as B. boops.

Genetic drift and non-random mating seldom influence species with large breeding populations and high dispersal potential, characterized by unstructured gene pool and panmixia at a scale lower than the minimum dispersal range of individuals. In the present study, a set of nine microsatellite markers was developed and used to investigate the spatio-temporal genetic patterns of the holoplanktonic jellyfish Pelagia noctiluca (Scyphozoa) in the Southern Tyrrhenian Sea. Homozygote excess was detected at eight loci, and individuals exhibited intra-population relatedness higher than expected by chance in at least three samples. This result was supported by the presence of siblings in at least 5 out 8 samples, 4 of which contained full-sib in addition to half-sib dyads. Having tested and ruled out alternative explanations as null alleles, our results suggest the influence of reproductive and behavioural features in shaping the genetic structure of P. noctiluca, as outcomes of population genetics analyses pointed out. Indeed, the genetic differentiation among populations was globally small but highlighted: a) a spatial genetic patchiness uncorrelated with distance between sampling locations, and b) a significant genetic heterogeneity between samples collected in the same locations in different years. Therefore, despite its extreme dispersal potential, P. noctiluca does not maintain a single homogenous population, but rather these jellyfish appear to have intra-bloom localized recruitment and/or individual cohesiveness, whereby siblings more likely swarm together as a single group and remain close after spawning events. These findings provide the first evidence of family structures and consequent genetic patchiness in a species with highly dispersive potential throughout its whole life cycle, contributing to understanding the patterns of dispersal and connectivity in marine environments.