Invasive species pose a major threat to global diversity, and once they are well established their eradication typically becomes unfeasible. However, certain natural mechanisms can increase the resistance of native communities to invaders and can be used to guide effective management policies. Both competition and herbivory have been identified as potential biotic resistance mechanisms that can limit plant invasiveness, but it is still under debate to what extent they might be effective against well-established invaders. Surprisingly, whereas biotic mechanisms are known to interact strongly, most studies to date have examined single biotic mechanisms separately, which likely influences our understanding of the strength and effectiveness of biotic resistance against invaders. Here we use long-term field data, benthic assemblage sampling, and exclusion experiments to assess the effect of native assemblage complexity and herbivory on the invasion dynamics of a successful invasive species, the alga Caulerpa cylindracea. A higher complexity of the native algal assemblage limited C. cylindracea invasion, probably through competition by canopy-forming and erect algae. Additionally, high herbivory pressure by the fish Sarpa salpa reduced C. cylindracea abundance by more than four times. However, long-term data of the invasion reflects that biotic resistance strength can vary across the invasion process and it is only where high assemblage complexity is concomitant with high herbivory pressure, that the most significant limitation is observed (synergistic effect). Overall, the findings reported in this study highlight that neglecting the interactions between biotic mechanisms during invasive processes and restricting the studied time scales may lead to underestimations of the true capacity of native assemblages to develop resistance to invaders. ; Funding for this project was obtained from the Spanish Ministry Project ANIMA (CGL2016-76341-R, MINECO/FEDER, UE), the European Union's EMFS Program, AFRIMED (EASME/EMFF/2017/1.2.1.12/S4/01/SI2.789059), the Spanish Autonomous Organism of National Parks through the project BIGPARK (project 2017-2462), and the Padi Foundation to FT (CGA App: 5134). JS received the support of a fellowship from "La Caixa" Foundation (ID 100010434) with code (LCF/BQ/DE17/11600001).
Este artículo contiene 18 páginas, 4 figuras. ; Good datasets of geo-referenced records of alien species are a prerequisite for assessing the spatio-temporal dynamics of biological invasions, their invasive potential, and the magnitude of their impacts. However, with the exception of first records on a country level or wider regions, observations of species presence tend to remain unpublished, buried in scattered repositories or in the personal databases of experts. Through an initiative to collect, harmonize and make such unpublished data for marine alien and cryptogenic species in the Mediterranean Sea available, a large dataset comprising 5376 records was created. It includes records of 239 alien or cryptogenic taxa (192 Animalia, 24 Plantae, 23 Chromista) from 19 countries surrounding the Mediterranean Sea. In terms of records, the most reported Phyla in descending order were Chordata, Mollusca, Chlorophyta, Arthropoda, and Rhodophyta. The most recorded species was Caulerpa cylindracea, followed by Siganus luridus, Magallana sp. (cf. gigas or angulata) and Pterois miles. The dataset includes records from 1972 to 2020, with the highest number of records observed in 2018. Among the records of the dataset, Dictyota acutiloba is a first record for the Mediterranean Sea. Nine first country records are also included: the alga Caulerpa taxifolia var. distichophylla, the cube boxfish Ostracion cubicus, and the cleaner shrimp Urocaridella pulchella from Israel; the sponge Paraleucilla magna from Libya and Slovenia; the lumpfish Cyclopterus lumpus from Cyprus; the bryozoan Celleporaria vermiformis and the polychaetes Prionospio depauperata and Notomastus aberans from Malta. ; The publication of this article is supported by the Open Access Publishing Fund of the International Association for Open Knowledge on Invasive Alien Species (INVASIVESNET; www.invasivesnet.org). Stelios Katsanevakis, Maria Sini and Konstantinos Tsirintanis were supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the "First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant" (Project Number: HFRI-FM17-1597). Enalia Physis acknowledges Pantelis Patsalou for his support with field-logistics and links with fishers. Fiona Tomas would like to acknowledge funding from FECYT FCT- 14-9319 (¡OJO A LAS INVASORAS! BIODIVERSIDAD Y ESPECIES INVASORAS DEL MEDITERRÁNEO BALEAR). Vasilis Gerovasileiou, Thanos Dailianis and Maria Sini acknowledge the support by the MARISCA project (www.marisca.eu), co-funded (85%) by EEA GRANTS, 2009–2014, and the Public Investments Program (PIP) of the Hellenic Republic (15%). Razy Hoffman acknowledges funding by Yad-Hanadiv foundation, through the Israel Society of Ecology and Environmental Sciences and Israel Nature and Parks Authority (An integrated program for establishing biological baselines and monitoring protocols for marine reserves in the Israeli Mediterranean Sea). Argyro Zenetos and Paraskevi K. Karachle would like to thank the citizenscientists collaborating with the Ellenic Network on Aquatic Invasive Species (ELNAIS – elnais.hcmr.gr). Nikolaos Doumpas, Ioannis Giovos, Periklis Kleirou and Francesco Tiralongo would like to thank all the citizen-scientists that contributed with their shared records and data in the citizen-science project "Is it alien to you? Share it!!!" (https://www.facebook.com/ groups/104915386661854/). Data from Gyaros Island marine reserve were collected under the "GyarosMPA" project, funded by "MAVA Fondation pour la Nature". Data from Corsica coastline were mainly collected in the framework of the "Corsica Alien Network" initiated by "Office de l'Environnement de la Corse". Carla Morri and Carlo Nike Bianchi received financial support from FFARB (funds for basic research activities) by the Italian Ministry of Education, University and Research. Ergün Taşkın has been supported by TÜBİTAK, Ankara, Turkey (Project Number: 114Y238). The Slovenian authors would like to acknowledge their financial support from the Slovenian Research Agency (research core funding No. P1-0237) and the Ministry of Agriculture, Forestry and Food of the Republic of Slovenia. Mehmet Fatih Huseyinoglu thanks University of Kyrenia's Scientific Research Project numbered GRN-20191-004. Fabio Crocetta was funded by the COST (European Cooperation in Science and Technology) Action TD1209 Alien Challenge project. The FRI (HAO DEMETER) team is very grateful to the Marine Strategy Project for financial support. Records of NIS in Jbel Moussa, the National Park of Al Hoceima and Cap des Trois Fourches sites from Morocco were obtained during surveys conducted within the framework of the MedKeyHabitats and the MedMPAnet Projects implemented by UNEP/MAP-RAC/SPA in close collaboration with the Haut Commissariat aux Eaux et Forêts et à la Lutte Contre la Désertification (HCEFLCD) and financially supported by RAC/SPA, Tunisia and the MAVA Foundation, Switzerland (MedKeyHabitats Project) and the European Commission (EC), the Spanish Agency for International Cooperation to Development (AECID), and the French Global Environment Facility (MedMPAnet Project). Jamila Ben Souissi was partially funded by BiodivMex /Chantier MISTRALS. Konstantinos Tsiamis sampling records were retrieved during his post in the Hellenic Centre for Marine Research, which he would like to thank for. Periklis Kleitou and Demetris Kletou were supported by the LIFE financial instrument of the European Union – RELIONMED project [Grant Agreement LIFE16 NAT/ CY/000832]. Some of the data included in the dataset were obtained through the marine citizen science platform Observadores del Mar www.observadoresdelmar.es with the support of FECYT FCT-17-12469, LIFE IP Intemares and Fundació Marilles, and through the citizen science site of the Italian Marine Protected Area of "Regno di Nettuno" (islands of Ischia, Procida and Vivara): www.citizensciencerdn.org. Most data from Lebanon were retrieved from social media dedicated to citizen science (Facebook group: Sea Lebanon https://www.facebook.com/ groups/109615625861815/) or fishers and scuba divers WhatsApp groups). Jamila Rizgalla wishes to thank the administration of Regatta for granting a free pass to conduct field surveys and the security personnel for providing a safe environment. Anna Occhipinti-Ambrogi was supported by European Community's Seventh Framework Program VECTORS (Vectors of Change in Oceans and Seas Marine Life, Impact on Economic Sectors). The long lasting collaboration with the ICES Working Group on Introductions and Transfer of Marine Organisms (WGITMO) has been a good forum where many information and ideas could be exchanged within some of the authors (Anna Occhipinti-Ambrogi, Argyro Zenetos, Agnese Marchini, and a wider community of scientists working on biological invasions). A. Rosso and R. Sanfilippo received grants from the Catania University Research Plan 2016/2018. Data from Kuriat island were collected under the "Kuriat project", funded by "MAVA Fondation pour la Nature" executed by SPA/RAC in partnership with the Coastal Protection and Management Agency (APAL) and Notre Grand Bleu (NGB) NGO. The AIS/ERA (Environment and Resources Authority) Maltese data were obtained from the EU funded project EMFF 8.3.1 under the European Maritime and Fisheries Fund 2014–2020 with a total cost of €1.6 million in public eligible EMFF funds (75% EU 25% MT), managed by AIS/ERA (Environment and Resources Authority). The ultimate goals of this European Maritime and Fisheries Fund (EMFF 2014–2020) project are to devise a holistic approach towards marine monitoring and develop a comprehensive database of data collected about the Maltese waters. ; Peer reviewed
