Biological invasions are a major driver of ecosystem changes (Pyšek et al. 2020) and the dispersal of alien and invasive species in aquatic ecosystems have already determined severe impacts upon ecosystems functions and biodiversity as well as on socio-economic activities (e.g. Katsanevakis et al. (2014), Morri et al. (2019)).

The Mediterranean Sea is considered a hotspot of biological invasions (Bailey et al. 2020, Galil et al. 2018). Throughout time, the Mediterranean has experienced drastic biological changes, occasionally consisting in the replacement of most of its biota. These changes, however, have occurred naturally over thousands of years due, for example, to extreme variations in environmental conditions (Rilov and Galil 2009). In the anthropocene, human-mediated activities are determining comparable biodiversity changes that are taking place at a much faster pace and over shorter timescales (Giangrande et al. 2020, Rilov and Galil 2009). The opening of the Suez Canal in 1869 has facilitated the arrival of new species and climate change is fostering further aided and unaided migrations in the Mediterraneanean which, over the last five decades, has experienced the highest rate of biological introductions (Galil et al. 2018, Mannino et al. 2017, Zenetos et al. 2017).

In the Mediterranean Sea, coastal areas and, particularly, transitional water ecosystems such as estuaries, lagoons and coastal lakes, are largely exploited for their resources as well as for fisheries and acquaculture activities (Pérez-Ruzafa and Marcos 2012). The anthropogenic pressure on such ecosystems has resulted in the degradation and loss of habitats, as well as in the extirpation of local biodiversity, which has been further threatened by the large number of bioinvasions (Lotze et al. 2006). Despite transitional water ecosystems covering only a small fraction of the Mediterranean's coastline, they provide more ecosystem services and societal benefits than other aquatic ecosystems and hold numerous endemisms and unique species assemblages (Chapman 2012, Elliott and Whitfield 2011). Transitional waters are, however, particularly susceptible to biological invasions as they offer natural refugees and favourable conditions for the arrival and settlement of new species (Occhipinti-Ambrogi et al. 2010).

The Italian peninsula, with its 171 transitional water bodies spread along 7,000 km of coastline (Cardone et al. 2013, Servello et al. 2019), lies in a strategic position within the Mediterranean Basin as it is located at the crossroads of three different subregions (Directive 2008/56/EC, European Parliament (2008)) and at the intersection of water masses with different hydrographic conditions (Corriero et al. 2015, Occhipinti-Ambrogi et al. 2010). Italy represents the main passageway of the maritime traffic within the Mediterranean and such pathway is responsible for half of the total alien species introductions along the Italian coast (Servello et al. 2019). Notwithstanding their high invasibility, Italian coastal and transitional waters also harbour a rich native biological diversity (Bianchi and Morri 2000). Native species diversity and community composition are considered key factors in the ecosystem responses to biological invasions; hence, it is crucial to take these ecosystem components into account when studying the impact of biological invasions within a certain geographic area or habitat (Corriero et al. 2015, Colangelo et al. 2017). To date, a number of studies focused on the collection and publication of alien and invasive species checklists along the Italian coast (Occhipinti-Ambrogi et al. 2010, Servello et al. 2019). However, there is a lack of geo-referenced datasets reporting comprehensive biodiversity information including records of native and alien species across a broad range of taxonomic groups and locations in Italian marine and transitional waters.

The access to accurate and comprehensive species distribution data is crucial to evaluate spatio-temporal changes in biodiversity patterns, as well as the impact of alien species. Detailed information of species occurrence can improve our ability to quickly react and mitigate the challenge of biological invasions. Biodiversity data, however, are usually spread over a number of different platforms (e.g. GBIF, EMODnet, OBIS) and it is often difficult for scientists and stakeholders to access such an enormous amount of heterogeneous and diverse information. Furthermore, several international open-access databases, such as the World Register of Marine Species, FishBase and AlgaeBase, gather biodiversity information focusing on a single taxonomic group or ecosystem and it can be difficult to simultaneously extract and combine data from different sources into unique and standardised datasets for different taxa and locations of interest. Here, two datasets with geo-referenced occurrence records in Italian marine and transitional waters are described. The presented datasets include comprehensive biodiversity information belonging to different taxonomic groups (i.e. phytoplankton, algae, invertebrates and fish) and cover several habitats and regions all along the Italian peninsula. In both datasets, each record is associated with the status information, i.e. if the taxon is considered alien or native in the geographic area in which it occurs. Moreover, for each geo-referenced occurrence, the EUNIS habitat type is defined.

The Authors would like to express their sincere gratitude to all the researchers who contributed to data collection and supported this work: Stefano Accoroni, Giorgio Alabiso, Serena Arima, Enrico Barbone, Mauro Bastianini, Giorgio Bavestrello, Anna Maria Bazzoni, Fabrizio Bernardi Aubry, Ferdinando Boero, Maria Cristina Buia, Marina Cabrini, Elisa Camatti, Frine Cardone, Bruno Cataletto, Riccardo Cattaneo Vietti, Francesco Cavraro, Ester Cecere, Tamara Cibic, Paolo Colangelo, Francesco Cozzoli, Alessandra De Olazabal, Gianfranco D'Onghia, Stefania Finotto, Nicola Fiore, Daniela Fornasaro, Piero Franzoi, Simonetta Fraschetti, Maria Cristina Gambi, Lorenzo Gaudiano, Adriana Giangrande, Vojsava Gjoni, Cinzia Gravili, Rosanna Guglielmo, Giovanna Jona-Lasinio, Erica Keppel, Caterina Longo, Maurizio Lorenti, Alessandro Ludovisi, Antonella Lugliè, Porzia Maiorano, Stefano Malavasi, Francesco Mastrototaro, Maria Grazia Mazzocchi, Maria Mercurio, Michele Mistri, Marina Monti, Cristina Munari, Luigi Musco, Carlotta Nonnis Marzano, Bachisio Mario Padedda, Francesco Paolo Patti, Antonella Petrocelli, Maurizio Pinna, Stefano Piraino, Alessio Pollice, Giuseppe Portacci, Alessandra Pugnetti, Silvia Pulina, Tiziana Romagnoli, Leonilde Roselli, Diana Sarno, Cecilia Teodora Satta, Stefano Schiaparelli, Beatrice Scipione, Nicola Sechi, Adriano Sfriso, Marco Sigovini, Letizia Sion, Rocco Sorino, Elena Stanca, Davide Tagliapietra, Antonio Terlizzi, Valentina Tirelli, Cecilia Totti, Angelo Tursi, Nicola Ungaro, Adriana Zingone, Matteo Zucchetta and Valerio Zupo.

CDM and TL wrote the first draft of the manuscript. CDM produced the graphical representations and revised the manuscript and the datasets following the constructive feedback received from the Authors and from the initial technical evaluation of the journal. IR, CP, ABo, GC and ABa contributed to data collection, data aggregation and data quality control and standardisation. All Authors actively contributed to the manuscript editing and quality check and approved the submission of the article.