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The Mediterranean Sea, considered as a true hotspot of biodiversity, is currently experiencing a decline in the number of species and a deterioration of habitats, as a consequence of different anthropogenic pressures, which are predicted to increase in the future. Among these pressures, the increase of human population, habitat modification and loss, pollution, coastal urbanization, overexploitation, the intentional or indirect introduction of Non-Indigenous Species (NIS, i.e. organisms introduced outside of their natural range) and climate changes (i.e. acidification and warming) have been pointed out as the major threats to biodiversity. Therefore, biodiversity monitoring and surveillance plans are strongly required in order to improve information on the distribution and change of biodiversity and/or to find and track NIS and detect early outbreaks of invasive species. In this respect, the creation of early-warning systems could be crucial. Since intensive monitoring programs are very expensive, Citizen Science, actively involving volunteers (e.g. citizen, students, fishermen, divers), could be a useful tool for gathering data, that would otherwise be impossible to collect because of limitations on time and resources. Citizen Science has grown rapidly in recent years, also thanks to mobile technologies, websites and social networks that enable an easy and cheap way to communicate, share and interchange data. Of course, in order to be used for scientific purposes and management decisions, the collected data need appropriate quality assurance measures such as validation and verification by taxonomic experts. We report on the experience of four Citizen Science activities: the Project “Caulerpa cylindracea – Egadi Islands”, the Project “Aliens in the sea”, the Project “Invasive Algae”, included within the “Seawatchers” platform and the Marine Forests platform. These Projects highlight how important Citizen Science is for collecting data on marine biodiversity and marine NIS and to significantly improve the efficacy of monitoring and surveillance plans.

L’introduzione di specie non indigene invasive (IAS, organismi introdotti in aree esterne al loro areale naturale con comportamento invasivo) è considerata una delle maggiori minacce alla biodiversità e al funzionamento degli ecosistemi naturali (Katsanevakis et al. 2014, Vergeś et al. 2016). Una specie non-nativa (NIS) può diventare invasiva e causare perdita di biodiversità e cambiamenti nei servizi ecosistemici (Giakoumi 2014, Vergés et al. 2016). Nel Mediterraneo oggi sono presenti circa 1.000 NIS, delle quali 134 sono macroite (Verlaque et al. 2015, Alós et al. 2016). Per ridurre il rischio di future introduzioni e meglio comprendere il potenziale invasivo e le dinamiche di diffusione delle NIS, sono necessari eficaci piani di monitoraggio e sorveglianza. Altrettanto importanti sono le campagne di sensibilizzazione rivolte ai cittadini. La Citizen science (CS, “scienza dei cittadini” o “scienza partecipata”), coinvolgendo i cittadini (turisti, pescatori, subacquei) nella raccolta di dati, potrebbe essere un utile strumento per ottenere dati sulle NIS, che diversamente sarebbe impossibile raccogliere per limitazioni di tempo e risorse. La Citizen science sta riscuotendo grande successo e il suo valore è ampiamente riconosciuto (Hecker et al. 2018). In questi ultimi anni si è assistito a un rapido aumento di progetti di Citizen science, anche grazie alle nuove tecnologie e all’accesso a internet, che hanno reso semplice e immediata la comunicazione, la condivisione e lo scambio di dati. I dati raccolti devono essere validati e veriicati da esperti prima di essere utilizzati per scopi scientiici e gestionali. La Sicilia e le piccole isole, a seguito della posizione geograica e dell’intenso trafico marittimo (commercio, pesca e diporto), che facilitano l’introduzione di NIS (Katsanevakis et al. 2014), costituiscono una regione particolarmente vulnerabile alle invasioni biologiche (Katsanevakis et al. 2014), che può inoltre avere un ruolo chiave nella circolazione delle NIS all’interno del Mediterraneo. Riportiamo qui due esperienze di Citizen science realizzate lungo le coste siciliane: il Progetto “Caulerpa cylindracea - Egadi Islands” e il Progetto “Aliens in the sea”.

The main purpose of Marine Protected Areas (MPAs) is biodiversity conservation. The effects that invasive species have on MPAs, and vice versa, are still not completely known, even though their assessment is crucial for MPA management and conservation purposes. In this respect, monitoring plans are essential and the involvement of citizen scientists may be fundamental. Our experience of Caulerpa cylindracea Sonder 1845 monitoring within the Egadi Islands MPA highlighted that the alga is widespread within the MPA, mainly at Favignana Island, also threatening valuable habitats such as vermetid reef and coralligenous formations. Moreover, Favignana is the island of the Aegadian archipelago most affected by the introduction of non-indigenous species. Since invasive species are likely to continue to expand, and further arrivals are to be expected, additional management actions (e.g. concerning tourism activities) should be taken in MPAs to effectively control invasive species.

VII International Symposium on Marine Sciences (ISMS 2020), 1-3 July 2020 (Barcelona).-- 3 pages, Observadores del Mar is a marine citizen science platform launched in 2012 devoted to enhancing the understanding ofthe conservation status of marine ecosystems. The platform hosts different projects reporting information on two main topics: i) biodiversity data focusing mainly on species distribution and abundance,and ii) the impacts of anthropogenic activities, including both the occurrence of episodic events (e.g. jellyfish blooms) and associated mid-to long-term changes (e.g. colonization of invasive species). At present Observadores del Mar includes 13 projects covering 8 main taxa: corals, jellyfishes, decapod crustaceans, fishes, seaweeds, seagrasses, seabirdsandmolluscs, in addition to two projects focused on marine litter. The platform provides information on the rationale, methods and materials for each project. A new web interface was designed to facilitate data entry and enhance data validation by scientists. More over, different functionalities were developed to build the Observadores del Mar community. Beyond the web tools, Observadores del Mar has been also very active in promoting citizen science events, training sessions for recreational divers, schools and the general public. Currently the Observadores del Mar platform has more than 2400 volunteers, 240 entities (including more than 40 schools) and 60 scientists from more than 40 research institutions and universities. Almost 12000 observations have been already collected resulting in the publication and presentation of more than 20 scientific papers and communications. The major findings have been new records of introduced and invasive species, tracking the spread of novel pen shell mortality outbreak in the Mediterranean Sea and monitoring microplastic concentrations on beaches. Furthermore, some of the information gathered was transferred to public administrations to inform management and action plansat different levels. In conclusion, Observadores del Mar is providing reliable and relevant scientific information while allowing citizens to collaborate and get involvedin marine sciences, thus facilitating the interaction among different stakeholders aiming to work for a healthy ocean

Habitat modification and loss, climate change and the introduction of Non-Indigenous Species (NIS, i.e. organisms introduced outside of their natural, past or present, range and outside of their natural dispersal potential) are considered to be the main threats to Mediterranean marine biodiversity and natural ecosystem functioning. NIS may become invasive (IAS = Invasive Alien Species) and may have significant environmental, socio-economic and human health impacts. The Mediterranean Sea is one of the major hotspots for NIS introductions, with the total for these species having almost reached the 1,000 figure (equivalent to ca. 6% of the total flora and fauna). NIS are entering the Mediterranean Sea passively or through human-mediated pathways. The Suez Canal is considered to be the main vector for marine introductions into the Mediterranean Sea. The Suez Canal in fact has been responsible to date for 53% of all exotic marine species entering the Mediterranean. The widening of the existing Suez Canal in 2015, so as to cater for increased volumes of shipping, is expected to have a further strong impact on the Mediterranean marine ecosystems. Ship-borne transportation infrastructure is expanding along with volumes of ballast waters, ballast tanks, anchoring and fouling, and collectively they are considered as the second vector of introduction in terms of importance. For instance, Sargassum muticum and Caulerpa taxifolia have been spread in the Mediterranean through shipping and recreational vessels. The jellyfish Rhopilema nomadica has been reported to negatively affect coastal power-generation installations, whilst impacting fisheries, human health and tourism. Lagocephalus sceleratus and Pterois volitans, both Lessepsian migrants, are examples of a toxic and a venomous fish species, respectively. Yet another Lessepsian fish migrant, the bluespotted cornetfish (Fistularia commersonii), is an extremely voracious predator which is aggressive when occurring in schools, whilst the two rabbitfish species Siganus luridus and Siganus rivulatus have largely displaced the native Sarpa salpa in the Levantine swathes of the Mediterranean Basin. The intense maritime traffic within the Strait of Sicily, which witnesses 90% of all the oil traffic traversing the Mediterranean Basin, has made Sicily and its surrounding islands, including MPAs, highly vulnerable and susceptible to biological invasions. Indeed, MPAs seem to be ineffective in protecting native biodiversity from biological invasions. We hereby report on the case study of the Egadi Islands MPA (western Sicily, Tyrrhenian Sea) where 14 NIS and 3 cryptogenic species (Aplysia dactylomela, Asparagopsis taxiformis and Percnon gibbesi, species that cannot be classified with confidence among native nor among introduced ones) have been recorded till now, and where maritime traffic has certainly spearheaded their introduction and spread. Detrimental ecological effects, direct or indirect, on native benthic assemblages have already been exerted by some of the newcomers. Even though the need to control IAS and to mitigate their impacts (on native species, on the structure and function of ecosystems, and on human health) is widely recognized by scientists, policy-makers and environmental managers, comprehensive and effective strategies to manage NIS have not yet been formulated at a pan-European level.

The increasing reliance of human societies on globalised maritime trade has spearheaded the spread of exotic aquatic species worldwide, with the Mediterranean Sea being one of the regional seas mostly affected by the phenomenon of Non-Indigenous Species (NIS) introductions, by virtue of its geographical location. This study attempts to characterise the flow of exotic aquatic biota being imported from non-EU countries to the Maltese Islands by assessing the information contained within a sample of importation licenses., N/A

The introduction of non-indigenous species (NIS) is an ongoing phenomenon which has been pointed out as a major threat to biodiversity at different levels (Wallentinus, Nyberg 2007, Katsanevakis et al. 2014, Vergés et al. 2016). NIS may in time become invasive (Invasive Alien Species “IAS”) and may cause biodiversity loss and ecosystem service changes (Brunel et al. 2013, Giakoumi 2014, Vergés et al. 2016). The Mediterranean Sea is an important hotspot for marine NIS (ca. 1,000 such species recorded to date, Zenetos et al. 2012, Galil et al. 2015, Verlaque et al. 2015). To reduce the risk of future IAS introduction and to better understand their invasive po- tential and spread dynamics, monitoring and surveillance plans are required. The creation of permanent alarm systems and public awareness campaigns are crucial for reducing the risk of IAS introduction. Since intensive monitoring programs could be very expensive, citizen science, involving citizens (e.g. tourists, ishermen, divers) in the collection of data, could be a useful tool for providing data on IAS, that would otherwise be impossible to collect because of limitations on time and resources. Citizen science is having an increasing success worldwide. Citizen science projects has rapidly and enormously increased in recent years (Conrad, Hilchey 2011), also thanks to the wide availability of mobile technologies and internet access that enable an easy and cheap way to communicate, share and interchange data. The value of citizen science has been widely recognized. Of course, in order to be used for scientiic purposes and management decisions, the collected data need appropriate quality assurance measures such as validation and veriication by taxonomic experts. We report on the experi- ence of two citizen science projects: the Project “Caulerpa cylindracea – Egadi Islands” and the Project “Invasive Algae”, included within the “Seawatchers” platform.

The earliest reported alien species that entered the Mediterranean after only nine years from the opening of the Suez Canal was ‘Meleagrina’ sp. This was subsequently identified as the Gulf pearl-oyster, Pinctada radiata (Leach, 1814). Thereafter, an increasing series of records of this species followed. Nowadays it can be considered a well-established species throughout the Mediterranean basin., peer-reviewed

With this study we provide a first baseline assessment of the epifauna associated with the macroalgae of the vermetid reefs present along the coasts of the Island of Favignana (Egadi Islands Marine Protected Area, Italy). A total of 14 taxa were identified. Epifaunal assemblages differed according to structure and composition of algal communities. The amphipod group presented the highest number of individuals. The tubicolous species Ampithoe ramondi Audouin, 1826 (Ampithoidae) was the most abundant species.

The spread dynamics of invasive Caulerpa taxa (i.e. Caulerpa cylindracea, C. taxifolia var. taxi- folia and C. taxifolia var. distichophylla) in Sicily and circum-Sicilian Islands, based on relevant publications, grey literature, unpublished data and in situ observations during the last 23 years, is presented here and discussed. Their known distribution is mapped. New records are also reported. Transport-stowaway is considered the most plausible vector of introduction of invasive Caulerpa in the area. The three invasive taxa showed different spread dynamics. Caulerpa cylindracea and C. taxifolia var. distichophylla, behaved as highly successful and fast-spreading taxa, i.e. as true invasive taxa. On the contrary, C. taxifolia var. taxifolia did not behave like the others, remaining limited to two small areas distant from each other. Due to their geographical position, Sicily and circum-Sicilian Islands are particularly vulnerable to biological invasions and therefore they could play an important role as receiver, transit and donor zone for alien species within the Mediterranean Sea. The creation of permanent observatories and alarm systems in this area might be an effective tool in the management of present and future introductions of alien species in the Mediterranean Sea.

We report on the experience of two citizen science projects: the Project “Caulerpa cylindracea – Egadi Islands” and the Project “Invasive Algae”, included within the “Seawatchers” platform. The first one, sponsored by the STEBICEF Department of the University of Palermo and by the Egadi Islands Marine Protected Area (MPA), aims at creating a database on the spread dynamics of C. cylindracea within the Egadi Islands MPA. The second one, coordinated by the Institute of Marine Sciences of Barcelona (CSIC, Spain), collects data on 10 marine invasive alien species. The results of these projects highlighted the important role that citizen science campaigns can have as early-warning systems. We also present a new citizen science project “Aliens in the Sea”, launched in June 2017, aiming to collect data on marine alien species along the wider Sicilian coast and promoting information and public awareness campaigns.

The Mediterranean sea is an important hotspot for alien species. Following habitat loss, Invasive Alien Species (IAS) are considered to be amongst the most serious threats to biodiversity and natural ecosystem functioning. Among the IAS recorded in the Mediterranean sea, Caulerpa cylindracea Sonder, introduced from Australia and New Caledonia, has raised serious concern due to its negative impact on native communities., peer-reviewed

Intertidal vermetid reefs are highly diverse systems that provide numerous habitats for animal and vegetal species, leading to an increase of intertidal biodiversity. These habitats, particularly vulnerable to environmental changes and human activities, are now experiencing high mortality in several areas of the Mediterranean Sea. Since alien macroalgae are nowadays considered one of the most serious threats to biodiversity and natural ecosystem functioning, we provide a first baseline assessment of the occurrence of alien species in the vermetid reef along the coasts of the Island of Favignana (Egadi Islands Marine Protected Area). Surveyes carried out in 2015 revealed the only presence of Caulerpa cylindracea Sonder (Bryopsidales, Caulerpaceae). The alga, exclusively recorded within the cuvettes, showed low values of abundance (class 1: cover 20%). No significant correlations were highlighted between the abundance values of C. cylindracea and those of the dominant macroalgae inhabiting the cuvettes.

The spread of alien species is an ongoing phenomenon which is widely recognized as a major threat to biodiversity at all levels. The particularly high rate of alien introductions to the Mediterranean Sea has been mainly fuelled by the opening of the Suez Canal, by shipping, aquaculture and by a rising trend in seawater temperature. As far as marine macrophytes are concerned, a total of 134 species have been listed as possible aliens in the Mediterranean Sea. Among the possible pathways of introduction, shipping is considered the dominant vector of unintentional species introduction in coastal marine systems worldwide. Traversing the Strait of Sicily, the chief passageway from south to north and from east to west, is considered crucial for extending the range from west to east or vice versa of alien species introduced into the Mediterranean Sea. Sicily and the circum-Sicilian Islands, as a consequence of their strategic position at the crossroads between the western and eastern Mediterranean and by virtue of the intense maritime traffic volumes skirting the region, are particularly congenial for and vulnerable to biological marine invasions. this area, due to its crucial position within the Mediterranean Sea, could be an important transboundary station for monitoring the entry and spread of marine alien species.

WOS: 000368443200019, Science Citation Index Expanded, The Collective Article "New Mediterranean Biodiversity Records" of the Mediterranean Marine Science journal offers the means to publish biodiversity records in the Mediterranean Sea. The current article has adopted a country-based classification and the countries are listed according to their geographic position, from west to east. New biodiversity data are reported for 7 different countries, although one species reported from Malta is new for the entire Mediterranean basin, and is presumably also present in Israel and Lebanon (see below, under Malta). Italy: the rare native fish Gobius kolombatovici is first reported from the Ionian Sea, whilst the alien jellyfish Rhopilema nomadica and the alien fish Oplegnathus fasciatus are first reported from the entire country. The presence of O. fasciatus from Trieste is concomitantly the first for the entire Adriatic Sea. Finally, the alien bivalve Arcuatula senhousia is reported for the first time from Campania (Tyrrhenian Sea). Tunisia: a bloom of the alien crab Portunus segnis is first reported from the Gulf of Gabes, where it was considered as casual. Malta: the alien flatworm Maritigrella fuscopunctata is recorded in the Mediterranean Sea for the first time, on the basis of 25 specimens. At the same time, web searches include possible unpublished records from Israel and Lebanon. The alien crab P. segnis, already mentioned above, is first formally reported from Malta based on specimens collected in 1972. Concomitantly, the presence of Callinectes sapidus in Maltese waters is excluded since based on misidentifications. Greece: the Atlantic northern brown shrimp Penaeus atzecus, previously known from the Ionian Sea from sporadic records only, is now well established in Greek and international Ionian waters. The alien sea urchin Diadema setosum is reported for the second time from Greece, and its first record from the country is backdated to 2010 in Rhodes Island. The alien lionfish Pterois miles is first reported from Greece and concomitantly from the entire Aegean Sea. Turkey: the alien rhodophyte Antithamnion hubbsii is first reported from Turkey and the entire eastern Mediterranean. New distribution data are also provided for the native fishes Alectis alexandrina and Heptranchias perlo. In particular, the former record consists of a juvenile measuring 21.38 mm total length, whilst the latter by a mature male. Cyprus: the rare native cephalopod Macrotritopus defilippi, and the alien crab Atergatis roseus, sea slug Plocamopherus ocellatus and fish Cheilodipterus novemstriatus are first recorded from the entire country. Lebanon: the alien crabs Actaea savignii and Matuta victor, as well as the alien fish Synanceia verrucosa, are first recorded from the entire country. In addition, the first Mediterranean record of A. savignii is backdated to 2006, whilst the high number of M. victor specimens observed in Lebanon suggest its establishment in the Basin. The Atlantic fishes Paranthias furcifer and Seriola fasciata, and the circumtropical Rachycentron canadum, are also first reported from the country. The P. furcifer record backdates its presence in the Mediterranean to 2007, whilst S. fasciata records backdate its presence in the eastern Mediterranean to 2005. Finally, two of these latter species have been recently ascribed to alien species, but all three species may fit the cryptogenic category, if not a new one, better., TUBITAK, Ankara, Turkey [114Y238]; EEA [Pi-33-51/30.06.2015]; TUBITAK, Ankara, Turkey [114Y238]; EEA [Pi-33-51/30.06.2015], Paolo Balistreri and Maria Ghelia thank Dr. Anna Maria Mannino (University of Palermo). Paul Portelli, Daryl Agius, Constantine Mifsud and Alan Deidun are indebted to Dr. Terrence Gosliner for his taxonomic advice in confirming the identity of Maritigrella fuscopunctata. Julian Evans and Patrick J. Schembri acknowledge John J. Borg (National Museum of Natural History, Mdina, Malta) for allowing them to examine the Portunus segnis specimens collected in 1972. Argyro Zenetos and Maria Giavasi thank Kostas Kapiris (HCMR) for confirmation of the Penaeus atzecus identification, and Petros Giavasis from F/V PETROS/MARIA (N.K.09 Kyllini) for providing the specimens. Maria Corsini-Foka and Gerasimos Kondylatos are grateful to the team of the "Yellow Submarine" Glass Bottom Boat (Mandraki, Rodos) for providing the Diadema setosum specimen, to Josif Makris for immediately alerting the ELNAIS, Hellenic Centre for Marine Research, about the presence of Pterois miles in Rhodes, to Jill Simmons and Antonis Kantaros ("Waterhoppers" Diving School of Rodos) and Adrien E. Flouros for reporting further P. miles sightings. Murat Cakir and Ergun Taskin were supported by TUBITAK, Ankara, Turkey (114Y238) and are grateful to Dr. Athanasios Athanasiadis (University of Gothenburg, Sweden) for critically reviewing the manuscript. Yasar Ozvarol is grateful to Dr. Rainer Froese, Prof. Daniel Golani, Harald Rosental, Ronald Fricke, Bill Smith-Vaniz and Rachel Atanacio for their invaluable help in identifying the juvenile specimen of Alectis alexandrina. Periklis Kleitou, Fabio Crocetta and Dimitrios Poursanidis are grateful to Vangelis Gavallas (Greece), Royce Hatch (United Kingdom), Shelley Patient (United Kingdom, Scuba Tech Diving Centre Cyprus), Philipp Spillmann (Switzerland) and Werner Wolf (Austria), who kindly shared data from Cyprus and gave permission to use their photos, and to Maria Corsini-Foka (Greece), Evgenia Lefkaditou (Greece) and Alp Salman (Turkey), who kindly helped while handling Atergatis roseus and Macrotritopus defilippi. Fabio Crocetta & Michel Bariche acknowledge Messrs Toufic Assal, Marwan Hariri, Abdel Kader Finge, Marwan Khoury, Jean-Paul Massoud, Ahmad Jammal, who provided photographs, videos or specimens of the records from Lebanon, and the website www.yasour.org. Lofti Rabaoui and Radhouan El Zrelli are grateful to fishermen of Gabes Gulf for providing information on the recent bloom of Portunus segnis. Fabio Crocetta also acknowledges the East and South European Network for Invasive Alien Species - a tool to support the management of alien species in Bulgaria (ESENIAS-TOOLS), EEA funded project (Contract No. Pi-33-51/30.06.2015), that supported the study of alien species from central and eastern European countries.

The Non-Indigenous Species (NIS) Caulerpa taxifolia var. distichophylla (Sonder) Verlaque, Huisman & Procaccini has been reported for the first time in the Mediterranean Sea along the coast of South Turkey. This NIS is actively expanding into the Eastern and Western Mediterranean Sea. In this paper, we present an overview of the current distribution of this alga in the Mediterranean Sea, based on relevant scientific publications, grey literature and personal observations. New records from the Sicilian coast (Italy) are also reported. Caulerpa taxifolia var. distichophylla was found over a wide range of environmental conditions (depth, light and substratum), suggesting a broad ecological plasticity of this alga which makes it a potential threat for the Mediterranean benthic communities. In this respect, artificial structures, often linked to harbours and maritime traffic, seem to provide suitable habitats for this NIS. Since maritime traffic is intense in the Mediterranean Sea, further expansion of C. taxifolia var. distichophylla in this region is to be expected. For this reason, it is very important to build up an overview on the current distribution of the species and its possible pattern of colonisation in relation to environmental conditions, as well as in view of future climate change scenarios.

The chief purpose of Marine Protected Areas (MPAs) is biodiversity conservation. The effects that invasive alien species (IAS) have on MPAs are not yet fully known, even though assessing them is fundamental. Effective management plans, indeed, also require knowledge on the dis- tribution, spread dynamics and impact of IAS. We report first observations on the effects of Caulerpa cylindracea Sonder (Chlorophyta Caulerpaceae) on the communities living along the coasts of the Island of Favignana (Egadi Islands MPA, Sicily, Italy). We found that C. cylindracea may have negative effects on the habitat where it settles in two different ways: a) affecting the structure of the native algal community which presents a low diversity, and b) favouring the settlement of other alien species such as Branchiomma bairdi (McIntosh, 1885) (Polychaeta Sabellidae).