Status and Trends in the Rate of Introduction of Marine Non-Indigenous Species in European Seas

Slavica Petovic; Romeu Ribeiro

Invasive alien species are a major worldwide driver of biodiversity change. The current study lists verified records of non-indigenous species (NIS) in European marine waters until 2020, with the purpose of establishing a baseline, assessing trends, and discussing appropriate threshold values for good environmental status (GES) according to the relevant European legislation. All NIS records were verified by national experts and trends are presented in six-year assessment periods from 1970 to 2020 according to the European Union Marine Strategy Framework Directive. Altogether, 874 NIS have been introduced to European marine waters until 2020 with the Mediterranean Sea and North-East Atlantic Ocean hosting most of the introductions. Overall, the number of new introductions has steadily increased since 2000. The annual rate of new introductions reached 21 new NIS in European seas within the last six-year assessment period (2012–2017). This increase is likely due to increased human acti...

diversity Article Status and Trends in the Rate of Introduction of Marine Non-Indigenous Species in European Seas Argyro ZENETOS 1, * , Konstantinos TSIAMIS 2 , Marika GALANIDI 3 , Natacha CARVALHO 4 , Cátia BARTILOTTI 5,6 , João CANNING-CLODE 7,8 , Luca CASTRIOTA 9 , Paula CHAINHO 10,11 , Robert COMAS-GONZÁLEZ 12 , Ana C. COSTA 13 , Branko DRAGIČEVIĆ 14 , Jakov DULČIĆ 14 , Marco FAASSE 15,16 , Ann-Britt FLORIN 17 , Arjan GITTENBERGER 16,18 , Hans JAKOBSEN 19 , Anders JELMERT 20 , Francis KERCKHOF 21 , Maiju LEHTINIEMI 22 , Silvia LIVI 23 , Kim LUNDGREEN 24 , Vesna MACIC 25 , Cécile MASSÉ 26 , Borut MAVRIČ 27 , Rahmat NADDAFI 17 , Martina ORLANDO-BONACA 27 , Slavica PETOVIC 25 , Lydia PNG-GONZALEZ 12 , Aina CARBONELL QUETGLAS 12 , Romeu S. RIBEIRO 10,11 , Tiago CIDADE 10 , Sander SMOLDERS 28 , Peter A. U. STÆHR 19 , Frederique VIARD 29 and Okko OUTINEN 22 1 2 3 4 5 6 7 Citation: ZENETOS, A.; TSIAMIS, K.; GALANIDI, M.; CARVALHO, N.; BARTILOTTI, C.; CANNING- 8 9 CLODE, J.; CASTRIOTA, L.; CHAINHO, P.; COMAS-GONZÁLEZ, 10 R.; COSTA, A.C.; et al. Status and Trends in the Rate of Introduction of 11 Marine Non-Indigenous Species in European Seas. Diversity 2022, 14, 1077. https://doi.org/10.3390/ d14121077 12 13 Academic Editor: Bert W. Hoeksema 14 Received: 1 November 2022 15 Accepted: 28 November 2022 16 Published: 6 December 2022 17 18 Publisher’s Note: MDPI stays neutral 19 with regard to jurisdictional claims in 20 published maps and institutional affil- 21 iations. 22 23 24 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and 25 26 27 28 conditions of the Creative Commons Attribution (CC BY) license (https:// 29 creativecommons.org/licenses/by/ 4.0/). * Hellenic Centre for Marine Research (HCMR), 16604 Anavyssos, Greece Karaiskaki 16 Voula, 16673 Athens, Greece ÜEE LLC, Marine Ecology Division, Teknopark Izmir A1/49, 35437 Urla, Turkey EEA-European Environment Agency, Kongens Nytorv 6, 1050 Copenhagen, Denmark IPMA, I.P.-Portuguese Institute for the Sea and Atmosphere, Rua Alfredo Magalhães Ramalho nº 6, 1495-006 Algés, Portugal MARE-Marine and Environmental Sciences Centre, Departamento de Ciências e Engenharia do Ambiente, Universidade NOVA de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal MARE-Marine and Environmental Sciences Centre/ARNET—Aquatic Research Network, Regional Agency for the Development of Research, Technology and Innovation (ARDITI), Madeira Island, 9020-105 Funchal, Portugal Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037, USA Italian Institute for Environmental Protection and Research (ISPRA), Department for the Monitoring and Protection of the Environment and for the Conservation of Biodiversity, Lungomare C. Colombo 4521–Addaura, 90149 Palermo, Italy MARE, Marine and Environmental Sciences Center, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal CINEA and ESTS, IPS–Energy and Environment Research Center, Instituto Politécnico de Setúbal, Estefanilha, 2910-761 Setúbal, Portugal Instituto Español de Oceanografía (IEO, CSIC), Centro Oceanográfico de Baleares, Muelle de Poniente s/n, 07015 Palma de Mallorca, Spain Faculdade de Ciências e Tecnologias and BIOPOLIS Program in Genomics, InBIO/CIBIO-Research Center in Biodiversity and Genetic Resources, Universidade dos Açores, R. Mãe de Deus 13A, 9500-321 Ponta Delgada, Portugal Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21000 Split, Croatia Eurofins AquaSense, Korringaweg 7, 4401NT Yerseke, The Netherlands Naturalis Biodiversity Center, Darwiweg 2, 2333CR Leiden, The Netherlands Department of Aquatic Resources, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden GiMaRIS, Rijksstraatweg 75, 2171AK Sassenheim, The Netherlands Department of Ecoscience, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark Institute of Marine Research, Nye Flødevigveien 20, 4817 His, Norway Royal Belgian Institute of Natural Sciences (RBINS), 8400 Oostende, Belgium Marine Research Centre, Finnish Environment Institute, Latokartanonkaari 11, 00790 Helsinki, Finland Italian Institute for Environmental Protection and Research (ISPRA), Department for the Monitoring and Protection of the Environment and for the Conservation of Biodiversity, Via Brancati 60, 00144 Rome, Italy Marine & Aquatic Environment, Ministry of Environment, Environmental Protection Agency, Tolderlundsvej 5, 5000 Odense, Denmark Institute of Marine Biology, University of Montenegro, Put I Bokeljske Brigade 68, 85330 Kotor, Montenegro Centre D’expertise et de Données Patrimoine Naturel, OFB, CNRS, MNHN, 75005 Paris, France Marine Biology Station Piran, National Institute of Biology, Fornače 41, SI–6330 Piran, Slovenia Office for Risk Assessment and Research, Netherlands Food and Customer Product Safety Authority, Ministry of Economical Affairs, 3540AA Utrecht, The Netherlands Institute of Evolutionary Sciences of Montpellier (ISE-M, UMR 5554), University of Montpellier, CNRS, Bâtiment 24, 34095 Montpellier, France Correspondence: zenetos@hcmr.gr Diversity 2022, 14, 1077. https://doi.org/10.3390/d14121077 https://www.mdpi.com/journal/diversity Diversity 2022, 14, 1077 2 of 50 Abstract: Invasive alien species are a major worldwide driver of biodiversity change. The current study lists verified records of non-indigenous species (NIS) in European marine waters until 2020, with the purpose of establishing a baseline, assessing trends, and discussing appropriate threshold values for good environmental status (GES) according to the relevant European legislation. All NIS records were verified by national experts and trends are presented in six-year assessment periods from 1970 to 2020 according to the European Union Marine Strategy Framework Directive. Altogether, 874 NIS have been introduced to European marine waters until 2020 with the Mediterranean Sea and North-East Atlantic Ocean hosting most of the introductions. Overall, the number of new introductions has steadily increased since 2000. The annual rate of new introductions reached 21 new NIS in European seas within the last six-year assessment period (2012–2017). This increase is likely due to increased human activities and research efforts that have intensified during the early 21st century within European Seas. As Europe seas are not environmentally, nor geographically homogenous, the setting of threshold values for assessing GES requires regional expertise. Further, once management measures are operational, pathway-specific threshold values would enable assessing the effectiveness of such measures. Keywords: non-indigenous species; European seas; regional seas; MSFD; good environmental status; validation; uncertainties 1. Introduction The introduction of marine Non-Indigenous Species (NIS) is widely perceived as one of the main threats to biological diversity next to habitat destruction at a global scale [1,2]. Invasive Alien Species (IAS) are a subset of NIS, which are of particular concern due to their ability to naturally reproduce in the recipient areas, spread rapidly, and threaten biological diversity in various ways, from reducing genetic variation and modifying gene pools, displacing, hybridizing or competing with local endemic or native species to altering habitat and ecosystem functioning [3–7]. It is essential to note that the term “invasive” may have various implications depending on the context. From a scientific perspective, “invasive” refers to the ability of the species to survive, reproduce and spread in the invaded region [8], whereas political frameworks, such as the EU Regulation (No 1143/2014) on the prevention and management of the introduction and spread of invasive alien species (IAS Regulation) often connect invasiveness to impact. Marine NIS, and IAS in particular, are addressed by European Union (EU) policies, such as the EU Biodiversity Strategy 2020 (COM (2011) 244) target 5; the European Water Framework Directive (WFD) (2000/60/EC); the EU Marine Strategy Framework Directive (MSFD) (2008/56/EC) with a dedicated descriptor (D2 “Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystems”) and the IAS Regulation (No 1143/2014). Non-indigenous species is one of the 11 descriptors in the MSFD that refer to anthropogenic pressures on the marine environment of the EU [9]. In the latest MSFD update [9] among the criteria for assessing descriptor D2 on marine NIS, primary criterion D2C1 concerning new NIS introductions states that: “The number of non-indigenous species which are newly introduced via human activity into the wild, per assessment period (6 years), measured from the reference year (2011) as reported for initial assessment under Article 8(1) of Directive 2008/56/EC, is minimised and where possible reduced to zero”. Efforts to make this target more quantitative are ongoing [10–12], further encouraged by Target 6 of the first draft of the Convention on Biological Diversity (CBD) Post-2020 Global Biodiversity Framework, which stipulates at least a 50% reduction in the rate of new introductions [13]. However, to date, only the Baltic Marine Environment Protection Commission (Helsinki Convention, HELCOM) has set a numerical threshold of zero new NIS introductions through anthropogenic activities in the Baltic Sea [10]. At the EU level, Tsiamis et al. [14] suggested that the most suitable approach for setting the Good Environmental Status (GES) thresholds for criterion D2C1 would be a percentage reduction of new NIS introductions Diversity 2022, 14, 1077 3 of 50 for an assessment period compared to the previous six-year assessment period (baseline). Preferably, the more previous six-year cycles that are included in the assessment, the better (e.g., starting from the 1970s) since the inclusion of earlier assessment periods enables tracking down how management measures have changed the result of the assessment over time. Thus, as qualitative GES descriptions turn into quantitative targets, it is now more imperative than ever that information on NIS in European seas is as accurate and complete as possible to provide a sound baseline for future management. The first compilation of marine NIS inventory in Europe was conducted by Streftaris et al. [15] and followed by an update in 2009 toward the SEBI2010 report [16]. In the same period, comprehensive data collection from a wide range of taxonomic groups through the EU-funded project Delivering Alien Species Inventories for Europe resulted in a European database [17]. The DAISIE database, which included recorded information on the impacts, pathways of introduction, and associated references, was integrated into the information system on Aquatic Non-Indigenous and Cryptogenic Species (AquaNIS) [18]. In parallel, the European Alien Species Information Network (EASIN) [19] has been developed by the European Commission’s Joint Research Centre (JRC) aiming to facilitate the exploration of existing alien species information from a variety of distributed information sources through freely available tools and interoperable web services, compliant with internationally recognized standards. Updated information on NIS is provided by data partners and the editorial board of EASIN [20]. AquaNIS stores and disseminates information on NIS introduction histories, recipient regions, taxonomy, biological traits, impacts, and other relevant documented data. The system is continuously updated with new NIS records provided by registered data providers. With the digital infrastructure in place and prompted by the increased demands placed by legislation, there is an increasing availability of national (e.g., Portugal) [21] and regional inventories of NIS (e.g., Baltic [22], Mediterranean [23], Black Sea [24]), which have been instrumental for analyzing trends and pathways of NIS introductions at national (e.g., Italy [25], Greece [26], Denmark [27], Belgium [28]), subregional (Macaronesia [29]), regional (Mediterranean [30], Baltic [22]), and global scales [31]. All these assessments have the shared ambition to assess the most updated status of NIS and provide a robust baseline for understanding trends in new NIS arrivals and pathways. Such knowledge is essential for the optimal implementation of existing policies and for evaluating policy effectiveness. Furthermore, knowledge is important to evaluate the need for new policies and management strategies. Updated and validated NIS inventories constitute a milestone for the implementation of the MSFD D2. Based on refined baseline inventories of NIS set by each EU Member State (MS), in the context of the MSFD and the updated data of EASIN, Tsiamis et al. [32] estimated that 787 non-indigenous taxa were found in EU marine and partially transitional waters (including Macaronesia) by the end of 2011. Further, Tsiamis et al. [14] updated the EASIN marine data at the national and MSFD subregional levels up to 31 December 2017. In the period of 2018–2020, not only have new NIS been identified in the European seas, but also new information has emerged on the taxonomic identity (e.g., as a consequence of recent taxonomic revision efforts), biogeographic origin, and distribution of NIS records, resulting in significant changes in both the status and distribution of several species. Now more than ever, it is crucial to reassess, revise and update the NIS inventories at all spatial assessment levels. In this context, the present work presents the most updated list of marine NIS introduced in the EU and surrounding waters validated by national experts and examines trends in these NIS introductions at European, regional, and subregional levels paving the way for the setting of threshold values for new NIS introductions in the context of the MSFD, and particularly of the primary criterion D2C1. 2. Methodology The national inventories of EU countries submitted to JRC for the purposes of the 2012–2017 assessment cycle [33] formed the starting point for the revision process. They Diversity 2022, 14, 1077 4 of 50 were updated with published data from biodiversity and hot-spot campaigns, academic surveys, and citizen science project observations until December 2020 (reported until June 2022). For Norway, Albania, and Montenegro, local experts were invited. The subsequent validation of the revised lists with the contribution of national experts included several rounds of communication whereby many discrepancies were resolved, and several controversial species were agreed upon. Subsequently, the national data were aggregated at subregional, regional, and Pan-European levels. The species list includes every first novel report of species introduction, irrespective of the establishment status. In our analysis, we only considered the first new record of a NIS within a region/subregion. Duplicate records for any given species were removed to avoid overestimating new NIS records at all spatial levels. The number of species detected/observed per six-year cycles since 1970 was analyzed from these datasets. 2.1. Geographic Coverage The study area included European marine waters surrounding EU countries, EU candidate countries (Albania, Montenegro), and Norway a country of the European Economic Area (EEA) all divided into regions and subregions (Figure 1, Table 1) as per the MSFD delineation [33]. Marine waters of the United Kingdom (UK), Turkey, and Russian Federation were not considered in this work, meaning that NIS records from these countries are not included. Figure 1. European subregions (modified from Jensen et al. [34]). BAL = Baltic Sea, ANS = Greater North Sea, ACS = Celtic Seas, ABI = Bay of Biscay-Iberian Shelf, AMA = Macaronesia, MWE = Western Mediterranean, MIC = Central Mediterranean, MAD = Adriatic Sea, MAL = Eastern Mediterranean, BLK = Black Sea. Diversity 2022, 14, 1077 5 of 50 Table 1. Geographic coverage of new NIS introductions in the present study at regional and subregional levels. Abbreviation: ABI = Bay of Biscay and the Iberian Coast, ACS = Celtic Seas, ANS = Greater North Sea, AMA = Macaronesia, MWE = Western Mediterranean Sea, MIC = Ionian Sea and the Central Mediterranean Sea, MAD = Adriatic Sea, MAL = Aegean-Levantine Sea (Eastern Mediterranean Sea). Regional Level Subregional Level Baltic Sea (BAL) BAL Denmark (In the Sound area of the Kattegat, the border follows the Øresund/Öresund bridge between Denmark and Sweden and in Copenhagen harbor, the border is defined by a lock just north of the bridge. On the west side of Sjælland, the border follows the OSPAR Convention boundary connecting Gniben Point on Sjællands Odde with Hasenore Head on the coast of Jutland), Estonia, Finland, Germany (Baltic Sea-side), Latvia, Lithuania, Poland, Sweden (Baltic Sea-side) North-East Atlantic Ocean (NEA) ANS France (including Eastern English Channel, and a small area of the Western English Channel), Belgium, Netherlands, Germany, Denmark, Sweden, Norway up to 62◦ N (EEA country). ACS Ireland and France (Western English Channel) ABI Spain (mainland), Portugal (mainland), and France. AMA Portugal (Azores, and Madeira) Spain (Canary Islands) Mediterranean Sea (MED) WME Spain, France, and Western Italy MIC Western Greece (Ionian Sea), Ionian coasts of Italy, and Malta MAD Adriatic coasts of Italy, Slovenia, Croatia, and Albania and Montenegro (EU candidates) MAL Cyprus and Eastern Greece Black Sea (BLK) BLK Bulgaria and Romania The Baltic Sea (BAL) is here regarded as both a region and a subregion according to the MSFD delineation, and the same applies to the Black Sea (BLK). The North-East Atlantic (NEA) comprises four MSFD subregions, namely: (a) Greater North Sea (ANS) (b) Celtic Seas (ACS), (c) the Bay of Biscay and the Iberian Coast (ABI), and (d) Macaronesia (AMA). The ANS spans the Kattegat, the eastern English Channel, and a small part of the Western English Channel. It covers NIS in coastal and estuarine waters from seven countries including Norway (an EEA country). The Celtic Seas (ACS) are represented only by Ireland and the western English Channel waters of France. Macaronesia (AMA) is a complex of oceanic islands located in the NEA. The region comprises the archipelagos of the Azores (Portugal), Madeira (Portugal), Canary Islands (Spain), and Cabo Verde. For the present paper exclusively European Macaronesia (i.e., the Azores, Madeira, and Canary Islands), which.h is the European marine ecoregion within the Lusitanian province following the proposed classification in [35], was considered. The Mediterranean Sea (MED) includes four MSFD subregions: (a) the Western Mediterranean Sea (MWE); (b) the Ionian Sea and the Central Mediterranean Sea (MIC); (c) the Adriatic Sea (MAD); and (d) the Eastern Mediterranean Sea (MAL), encompassing the Aegean and Levantine basins. 2.2. Data Included The most recent MSFD D2 evaluation recommendations [13] were largely followed for the inclusion of marine NIS in the present analyses. Accordingly, cryptogenic, and crypto-expanding species for the regions considered were removed from NIS lists and subsequent analyses. The terms cryptogenic and crypto expanding refer to uncertainties in the status of a species in relation to either their true native range [36] or true dispersion pathway (i.e., natural range expansion vs. human-mediated expansion) [14]. Species with insufficient information or new records unverified by experts or NIS with unresolved taxonomic status [32] were included in this study only after detailed scrutiny Diversity 2022, 14, 1077 6 of 50 by different experts and a general agreement that there is a strong indication that their presence and distribution pattern implies an introduction event. It is worth mentioning the case of the annelid Laonome xeprovala, by Bick and Bastrop in Bick et al., 2018, a species described from the Netherlands and subsequently found in other Dutch rivers, canals, and estuaries [37], as well as in the eastern part of the Baltic Sea, and identified originally as Laonome calida Capa, 2007 [38]. Previous literature suggests that North America’s eastern coast is a potential native origin for Laonome xeprovala, although further clarification is still required [39]. It has been heavily debated in recent years whether parasitic NIS and pathogens (including disease agents) should be omitted from MSFD D2 since they are managed under the Aquatic Animal Health Directive (2006/88/EC) [32]. Overall, the JRC group agreed that these NIS should be reported in D2 criteria, but not considered when assessing against a GES threshold [14]. Aiming to produce results that are as representative and comparable as possible with future GES assessments, parasites and pathogens are listed in Table 2 but were not considered in the D2 trend and status analyses. There are contrasting opinions among national NIS experts with regard to microscopic algae (phytoplankton) and to their native, cryptogenic, or NIS status, which is reflected in the literature [40] but also in the information systems of EASIN and AquaNIS. However, due to the high reproductive potential of phytoplankton and thus the high potential of spreading, it is important to have a gauge on phytoplankton expansion. The JRC invited the D2 NIS experts’ network to contact phytoplankton experts across Europe, to set up a working group that could deliver a consolidated revision of phytoplankton NIS in European seas [14]. Given that further clarification is yet to be provided regarding the status of microalgae in Europe, they are listed in Table 2 but were not considered in the D2 trend and status analyses. Oligohaline species are included if such species were found in estuarine or coastal systems of the marine region. NIS spreading from one region/subregion to another through natural dispersal mechanisms (secondary introduction) is included in our analyses. Their introduction pathway was classified as UNAIDED. Such is the case of many Red Sea species that have invaded the eastern Mediterranean (known as Lessepsian immigrants) and are progressively moving to the central and western Mediterranean as well as to the Adriatic Sea. However, species that have undergone tropicalization processes (i.e., shifts in range distribution induced by climate change) [41] were not included as NIS, and thus not considered in these analyses. With regards to partly native and partly cryptogenic species, here defined as species that are native or cryptogenic in one EU region while they are non-indigenous (i.e., introduced by humans), in another EU region, they were included in the analyses at regional and/or subregional level but not at the pan-European level. Such NIS notably include Mediterranean molluscan transported with shellfish movements to the North-East Atlantic and vice versa, as well as also sessile biota, such as tunicates. Species native within a subregion (e.g., North Sea) that have been anthropogenically transferred to another country within the same subregion, were not included in the subregional analysis, although they are regarded as NIS in the countries they have invaded. This also applies to countries with coastal areas in more than one regional sea (Denmark, France, Germany, Spain, and Sweden). 2.3. Detection Year The year of introduction was based on the reported date of the first collection/detection. However, it is important to point out that this date does not necessarily reflect the actual year of introduction which may have occurred years or even decades earlier since most species are often overlooked in the early stages of the invasion process, e.g., the green alga Codium fragile that has spread rapidly throughout the globe from its native range in Japan and the North Pacific was first detected in Europe c. 1900 in the Netherlands but reported in 1955 [42]. In addition, the date of first detection/collection is not always documented. In such cases, the publication date was accepted as the first record date. Moreover, in cases Diversity 2022, 14, 1077 7 of 50 where only a time range has been supplied (e.g., 1986–1994), or the first record refers to a decade (e.g., the 1970s), the introduction date was set approximately as the average year for that given period (1990 and 1975, respectively). 3. Results In total, 874 NIS were identified across European seas by December 2020 including 22 species of parasites and pathogens, and 50 species of microalgae (Table 2, Figure 2a). Of these 80% (701 taxa) were first reported in 1970. The vast majority of NIS are invertebrates (59%), followed by primary producers (algae and plants) (25%) and vertebrates (16%). Dissimilar proportions of all mentioned groups were evidenced across regions and subregions (Figure 3). While invertebrates dominate at all regional seas, the contribution of vertebrates (fishes) at the pan-European level is largely driven by the high contribution of Red Sea fish species in the Mediterranean Sea (Lessepsian immigrants) as opposed to their low presence in the NEA and Black Sea. Primary producers have a higher share in the NEA (29%) than the other regional seas (14–22%). Table 2. List of NIS and their first year of detection at pan-European and regional levels. Group: VER = vertebrate, INV = invertebrate, PP = primary producer, INV/par = parasite, PP/micro = microalgae. BAL = Baltic Sea, NEA = North-East Atlantic Sea, MED = Mediterranean Sea, BLK = Black Sea. In bold, species detected since 1970. Asterisk denotes freshwater species detected in marine/ estuarine environments. Group Species Pan-European VER Ablennes hians (Valenciennes, 1846) 2018 BAL NEA MED 2018 VER Abudefduf sexfasciatus (Lacepède, 1801) 2017 2017 VER Abudefduf vaigiensis (Quoy & Gaimard, 1825) 2005 2005 VER Abudefduf hoefleri (Steindachner, 1881) 2014 2014 INV Acanthaster planci (Linnaeus, 1758) 2006 2006 VER Acanthopagrus bifasciatus (Forsskål, 1775) 2019 2019 PP Acanthosiphonia echinata (Harvey) A.M.Savoie & G.W.Saunders 2018 2018 VER Acanthurus bahianus Castelnau, 1855 2013 VER Acanthurus cfr gahhm (Forsskål, 1775) 2019 VER Acanthurus coeruleus Bloch & Schneider, 1801 2011 VER Acanthurus sohal (Forsskål, 1775) 2017 VER Acanthurus chirurgus (Bloch, 1787) 2012 INV Acartia (Acanthacartia) tonsa Dana, 1849 1921 INV Acartia (Acartiura) omorii Bradford, 1976 2004 INV Achelia sawayai Marcus, 1940 2016 VER Acipenser baerii Brandt, 1869 1960 1960 1985 VER Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833* 1962 1962 2010 VER Acipenser ruthenus Linnaeus, 1758* 1887 1887 VER Acipenser stellatus Pallas, 1771 1999 1999 VER Acipenser transmontanus Richardson, 1836 1999 1999 PP Acrochaetium catenulatum M.A.Howe 1967 1967 BLK 2013 2019 2013 2011 2017 1921 2013 2012 1921 1986 2004 2016 1976 Diversity 2022, 14, 1077 8 of 50 Table 2. Cont. Group Species Pan-European PP Acrothamnion preissii (Sonder) E.M.Wollaston 1968 BAL INV Actaeodes tomentosus (H. Milne Edwards, 1834) 2013 2013 INV Acteocina mucronata (Philippi, 1849) 1991 1991 INV Actumnus globulus Heller, 1861 1978 1978 PP Adelosina carinatastriata (Wiesner) 2004 2004 Pathogen Aerococcus viridans Williams, Hirch & Cowan 1961 1961 PP Agardhiella subulata (C.Agardh) Kraft & M.J.Wynne 1984 1989 1984 PP Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N.Norris & Fredericq 1989 1989 2008 PP Aglaothamnion halliae (Collins) Aponte, D.L.Ballantine & J.N.Norris 1960 1960 2016 VER Agonus cataphractus (Linnaeus, 1758) 2005 2005 PP Ahnfeltiopsis flabelliformis (Harvey) Masuda, 1993 1994 1994 PP/micro Akashiwo sanguinea (K.Hirasaka) G.Hansen & Ø.Moestrup 1982 VER Alepes djedaba (Forsskål, 1775) 1960 PP/micro Alexandrium ostenfeldii (Paulsen) Balech & Tangen 1986 1986 PP/micro Alexandrium affine (H.Inoue & Y.Fukuyo) Balech 1987 1987 PP/micro Alexandrium leei Balech 1991 1991 PP/micro Alexandrium margalefii Balech 2006 2006 PP/micro Alexandrium taylori Balech 1994 1994 INV Aliculastrum cylindricum (Helbling, 1779) 2020 2020 INV/par Allolepidapedon fistulariae Yamaguti, 1940 2005 2005 INV Alpheus rapacida de Man, 1908 1998 1998 INV Amathina tricarinata (Linnaeus, 1767) 2012 2012 INV Ammothea hilgendorfi (Böhm, 1879) 1979 2013 INV Ampelisca cavicoxa Reid, 1951 2005 2005 INV Ampelisca heterodactyla Schellenberg, 1925 1986 1986 INV Amphibalanus eburneus (Gould, 1841) 1818 1872 1818 INV Amphibalanus reticulatus (Utinomi, 1967) 1977 1997 1977 INV Amphibalanus variegatus (Darwin, 1854) 1997 1997 INV Amphinome rostrata (Pallas, 1766) 1900 1900 PP Amphistegina cf. papillosa Said, 1949 2005 2005 PP Amphistegina lessonii d’Orbigny in Guérin-Méneville, 1832 2001 2001 PP Amphistegina lobifera Larsen, 1976 1959 1959 INV Ampithoe valida Smith, 1873 1985 1985 2000 INV Anadara kagoshimensis (Tokunaga, 1906) 1966 1993 1966 2003 NEA MED 2009 1968 BLK 1982 1960 1979 1933 1981 Diversity 2022, 14, 1077 9 of 50 Table 2. Cont. Group Species Pan-European INV Anadara transversa (Say, 1822) 1975 BAL INV/par Anguillicola crassus (Kuwahara, Niimi & Itagaki, 1974) 1980 INV Anomia chinensis Philippi, 1849 1974 INV Anoplodactylus californicus Hall, 1912 1965 PP Anotrichium furcellatum (J.Agardh) Baldock 1950 1950 PP Antithamnion densum (Suhr) M.Howe 1964 1964 PP Antithamnion diminuatum Wollaston 1989 1989 PP Antithamnion hubbsii E.Y.Dawson 1987 1989 1987 PP Antithamnion amphigeneum A.J.K.Millar 1992 1995 1992 PP Antithamnionella ternifolia (Hooker fil. & Harvey) Lyle 1910 1910 1981 INV Aoroides curvipes Ariyama, 2004 2009 2009 INV Aoroides semicurvatus Ariyama, 2004 2009 2009 INV Aoroides longimerus Ren & Zheng, 1996 2013 2013 INV Apanthura addui Wägele, 1981 1998 INV Aplidium antillense (Gravier, 1955) 2004 INV Aplidium accarense (Millar, 1953) 2012 2012 VER Apogonichthyoides pharaonis (Bellotti, 1874) 1964 1964 INV Aquilonastra burtoni (Gray, 1840) 2003 2003 INV Arachnidium lacourti d’Hondt & Faasse, 2006 1999 INV Arachnoidella protecta Harmer, 1915 1992 1992 INV Arbopercula tenella (Hincks, 1880) 1990 1990 INV Arctapodema australis (Vanhöffen, 1912) 1967 1967 INV Arcuatula senhousia (Benson, 1842) 1982 2002 INV Argopecten gibbus (Linnaeus, 1758) 2016 2016 INV Arhynchite arhynchite (Ikeda, 1924) 2001 2001 INV Arietellus pavoninus Sars G.O., 1905 1967 1967 VER Arothron hispidus (Linnaeus, 1758) 2018 2018 INV Artemia monica Verrill, 1869 1972 1987 INV Ascidia curvata (Traustedt, 1882) 2014 2014 INV Ascidia interrupta Heller, 1878 1990 1990 INV Asclerocheilus ashworthi Blake, 1981 2005 2005 PP Ascophyllum nodosum (Linnaeus) Le Jolis 2009 PP Asparagopsis taxiformis (Delile) Trevisan de Saint-Léon (lineage 2) 1928 1928 1992 PP Asparagopsis armata Harvey 1880 1922 1880 INV Asterocarpa humilis (Heller, 1878) 2005 2005 PP/micro Asteromphalus sarcophagus Wallich, 1860 1993 1993 INV Atactodea striata (Gmelin, 1791) 1977 1988 NEA MED 2016 1975 1982 1980 BLK 1974 1965 2014 2015 1998 2004 2015 1999 1982 1972 2009 1977 2002 Diversity 2022, 14, 1077 10 of 50 Table 2. Cont. Group Species Pan-European INV Atergatis roseus (Rüppell, 1830) 2009 BAL NEA 2009 VER Atherinomorus forskalii (Rüppell, 1838) 1929 1929 INV Atys angustatus E. A. Smith, 1872 2017 2017 INV Atys ehrenbergi (Issel, 1869) 2016 2016 INV Aurelia coerulea von Lendenfeld, 1884 2002 2002 INV Aurelia solida Browne, 1905 2000 2000 INV Austrominius modestus (Darwin, 1854) 1944 INV Axionice medusa (Savigny in Lamarck, 1818) 1976 1976 INV Baeolidia moebii Bergh, 1888 2017 2017 INV Balanus glandula Darwin, 1854 2015 2015 INV Balanus trigonus Darwin, 1854 1887 1887 VER Balistoides conspicillum (Bloch & Schneider, 1801) 2012 INV Bankia fimbriatula Moll & Roch, 1931 1847 1847 INV Barentsia ramosa (Robertson, 1900) 1962 1962 PP Batophora occidentalis var. largoensis (Harvey) S.Berger & Kaever ex M.J.Wynne 2020 INV Beania maxilladentata Ramalho, Muricy & Taylor, 2010 2013 INV Bemlos leptocheirus (Walker, 1909) 2015 INV Beroe ovata Bruguière, 1789 1997 INV Berthellina citrina (Rüppell & Leuckart, 1828) 2019 PP/micro Biddulphia rhombus (Ehrenberg) W.Smith 1983 PP/micro Biddulphia sinensis Greville 1903 INV Biflustra grandicella (Canu & Bassler, 1929) 2016 2016 INV Bispira polyomma Giangrande & Faasse, 2012 2010 2010 INV Biuve fulvipunctata (Baba, 1938) 1993 INV Boccardia proboscidea Hartman, 1940 1996 1996 INV Boccardia semibranchiata Guérin, 1990 1999 1999 INV Boccardiella hamata (Webster, 1879) 2001 2001 Pathogen Bonamia exitiosa Hine, Cochennac & Berthe 2006 2006 2007 Pathogen Bonamia ostreae Pichot, Comps, Tigé, Grizel & Rabouin 1978 1978 1990 PP Bonnemaisonia hamifera Hariot 1898 1898 1932 INV Bostrycapulus odites Collin, 2005 1973 INV Botrylloides diegensis Ritter & Forsyth, 1917 1999 INV Botrylloides giganteum (Pérès, 1949) 2003 INV Botrylloides niger Herdman, 1886 2013 2013 2014 INV Botrylloides violaceus Oka, 1927 1991 1999 1991 1944 MED BLK 1990 1927 2012 2020 2013 2015 2011 2013 2004 2019 1983 1904 1903 2014 1993 1900 2014 1973 1999 2004 2003 1997 Diversity 2022, 14, 1077 11 of 50 Table 2. Cont. Group Species Pan-European PP Botryocladia wrightii (Harvey) W.E.Schmidt, D.L.Ballantine & Fredericq BAL NEA MED 1978 2005 1978 PP Botryocladia madagascariensis G.Feldmann 1978 1978 PP Botrytella parva (Takamatsu) H.S.Kim 1996 1996 INV Bougainvillia macloviana Lesson, 1830 1895 1895 INV Brachidontes exustus (Linnaeus, 1758) 1977 1977 INV Brachidontes pharaonis (P. Fischer, 1870) 1960 INV Branchiomma bairdi (McIntsosh, 1885) 1998 INV Branchiomma boholense (Grube, 1878) 2004 INV Branchiomma luctuosum (Grube, 1870) 1978 VER Bregmaceros nectabanus Whitley, 1941 2014 INV Bugulina simplex (Hincks, 1886) 1982 1982 INV Bugulina stolonifera (Ryland, 1960) 1976 1976 INV Bulla arabica Malaquias & Reid, 2008 1998 1998 INV Bursatella leachii Blainville, 1817 1969 1969 INV Calanopia elliptica (Dana, 1849) 1891 1891 INV Callinectes danae Smith, 1869 1981 1981 INV Callinectes pallidus (de Rochebrune, 1883) 2013 INV Callinectes sapidus Rathbun, 1896 1901 VER Callionymus filamentosus Valenciennes, 1837 2003 BLK 1960 2012 1998 2004 2015 1978 2014 2013 1951 1901 1947 1967 2003 INV Calyptospadix cerulea Clarke, 1882 1940 VER Cantherhines pullus (Ranzani, 1842) 2015 2014 1978 INV Caprella mutica Schurin, 1935 1985 INV Caprella scaura Templeton, 1836 1985 1985 VER Carassius auratus (Linnaeus, 1758) 2012 2012 VER Carassius gibelio (Bloch, 1782)* 1800 INV Carijoa riisei (Duchassaing & Michelotti, 1860) 2016 INV Carupa tenuipes Dana, 1852 2009 2009 INV Cassiopea andromeda (Forsskål, 1775) 1903 1903 PP Caulacanthus okamurae Yamada 1999 1999 2002 PP Caulerpa cylindracea Sonder 1991 1997 1991 PP Caulerpa lamourouxii (Turner) C.Agardh 1956 1956 PP Caulerpa taxifolia (M.Vahl) C.Agardh 1984 1984 PP Caulerpa taxifolia var. distichophylla (Sonder) Verlaque, Huisman & Procaccini 2007 2007 PP Caulerpa webbiana Montagne 2002 2002 INV Caulibugula zanzibariensis (Waters, 1913) 2003 2003 INV Cellana rota (Gmelin, 1791) 2007 INV Celleporaria inaudita Tilbrook, Hayward & Gordon, 2001 2007 2015 2017 1985 1994 1800 2016 2007 2007 1940 Diversity 2022, 14, 1077 12 of 50 Table 2. Cont. Group Species Pan-European INV Celleporaria aperta (Hincks, 1882) 1975 BAL NEA MED INV Celleporaria brunnea (Hincks, 1884) 2007 INV Celleporaria vermiformis (Waters, 1909) 2015 2015 INV Celleporella carolinensis Ryland, 1979 1993 1993 INV Celtodoryx ciocalyptoides (Burton, 1935) 1996 INV Centropages furcatus (Dana, 1849) 1988 1988 VER Cephalopholis hemistiktos (Rüppell, 1830) 2009 2009 VER Cephalopholis taeniops (Valenciennes, 1828) 2009 VER Cephalopholis nigri (Günther, 1859) 2016 INV Cephalothrix simula Iwata, 1952 2012 2012 PP Ceramium atrorubescens Kylin 1988 1988 PP Ceramium sungminbooi Hughey & Boo 2018 2018 PP Ceramium tenuicorne (Kützing) Waern 2011 2011 PP Ceramium bisporum D.L.Ballantine 1980 1980 PP Ceramium strobiliforme G.W.Lawson & D.M.John 1991 1991 INV Ceratonereis mirabilis Kinberg, 1865 1997 1997 INV INV Cerithidium perparvulum (Watson, 1886) Cerithiopsis pulvis (Issel, 1869) 1995 1985 1995 1985 INV Cerithiopsis tenthrenois (Melvill, 1896) 1985 1985 INV Cerithium scabridum Philippi, 1848 1972 1972 PP/micro Chaetoceros peruvianus Brightwell 1981 1981 PP/micro Chaetoceros rostratus Ralfs 2003 2003 PP/micro Chaetoceros bacteriastroides G.H.H.Karsten 1996 PP/micro Chaetoceros concavicornis Mangin 2011 PP/micro Chaetoceros pseudosymmetricus Nielsen 2015 2015 VER Chaetodipterus faber (Broussonet, 1782) 2019 2019 VER Chaetodon sanctaehelenae Günther, 1868 1993 VER Chaetodon auriga Forsskål, 1775 2015 VER Chaetodontoplus septentrionalis (Temminck & Schlegel, 1844) 2015 2015 INV Chaetopleura angulata (Spengler, 1797) 1850 1850 INV Chaetozone corona Berkeley & Berkeley, 1941 1982 1996 INV Chama asperella Lamarck, 1819 2007 2007 INV VER Chama pacifica Broderip, 1835 Champsodon nudivittis (Ogilby, 1895) 1998 2012 1998 2012 INV Charybdis (Charybdis) japonica (A. Milne-Edwards, 1861) 2006 2006 INV Charybdis (Charybdis) feriata (Linnaeus, 1758) 2004 2004 INV Charybdis (Charybdis) hellerii (A. Milne-Edwards, 1867) 1998 1998 1975 2007 2010 1996 2009 2016 1996 2011 1993 2015 1982 BLK Diversity 2022, 14, 1077 13 of 50 Table 2. Cont. Group Species Pan-European INV Charybdis (Charybdis) lucifera (Fabricius, 1798) BAL NEA MED 2006 2006 INV Charybdis (Goniohellenus) longicollis Leene, 1938 1969 1969 PP/micro Chattonella marina (Subrahmanyan) Hara & Chihara 1974 VER Cheilodipterus novemstriatus (Rüppell, 1838) 2015 INV Chelicorophium robustum (G.O. Sars, 1895) 2018 2018 INV Chelicorophium curvispinum (G.O. Sars, 1895) 1912 1921 VER Chlorurus rhakoura Randall & Anderson, 1997 2017 2017 PP Chondria pygmaea Garbary & Vandermeulen 1974 1974 PP Chondria curvilineata F.S.Collins & Hervey 1981 1981 PP Chondrus giganteus f. flabellatus Mikami 1994 1994 VER Chromis multilineata (Guichenot, 1853) 2015 INV Chromodoris quadricolor (Rüppell & Leuckart, 1830) 1982 1982 INV Chrysaora achlyos Martin, Gershwin, Burnett, Cargo & Bloom, 1997 2018 2018 VER Chrysiptera cyanea (Quoy & Gaimard, 1825) 2013 2013 VER Chrysiptera hemicyanea (Weber, 1913) 2017 2017 PP Chrysonephos lewisii (W.R.Taylor) W.R.Taylor 1988 1988 INV Cingulina isseli (Tryon, 1886) 1998 1998 INV Ciona robusta Hoshino & Tokioka, 1967 1901 2007 VER Cirrhitus atlanticus Osório, 1893 2018 2018 PP Cladophora patentiramea (Montagne) Kützing 1991 INV Clavelina oblonga Herdman, 1880 1929 1971 Pathogen Claviceps purpurea (Fr.:Fr.)Tul. 1960 1960 1974 2015 1912 2015 1901 1991 1929 PP Clavulina cf. multicamerata Chapman, 1907 2012 2012 INV Clementia papyracea (Gmelin, 1791) 1985 1985 INV Clymenella torquata (Leidy, 1855) 1977 1977 INV Clytia gregaria (Agassiz, 1862) 2017 2017 INV Clytia hummelincki (Leloup, 1935) 1996 INV Clytia linearis (Thorneley, 1900) 1951 1983 PP Codium arabicum Kützing 2006 2006 PP Codium fragile subsp. fragile (Suringar) Hariot 1895 PP Colaconema codicola (Børgesen) H.Stegenga, J.J. Bolton & R.J.Anderson PP Colaconema dasyae (F.S.Collins) Stegenga, I.Mol, Prud’homme van Reine & Lokhorst 1996 1919 1951 1895 1946 1926 1926 1952 1951 1951 BLK Diversity 2022, 14, 1077 14 of 50 Table 2. Cont. Group Species Pan-European INV Coleusia signata (Paul’son, 1875) 2005 BAL NEA MED PP Colpomenia peregrina Sauvageau 1905 INV Conomurex persicus (Swainson, 1821) 1983 INV Corambe obscura (A.E. Verrill, 1870) 1879 1879 INV Corbicula fluminea (O. F. Müller, 1774) 1978 1978 INV Corella eumyota Traustedt, 1882 2002 2002 PP/micro Corymbellus aureus J.C.Green 1992 1992 PP Corynomorpha prismatica (J.Agardh) J.Agardh 1990 1990 PP Corynophlaea verruculiformis (Y.-P.Lee & I.K.Lee) Y.-P.Lee 1994 1994 INV Coryphellina rubrolineata O’Donoghue, 1929 2008 INV Crassostrea rhizophorae (Guilding, 1828) 1976 1976 INV Crassostrea virginica (Gmelin, 1791) 1861 1861 INV Crepidacantha poissonii (Audouin, 1826) 1982 INV Crepidula fornicata (Linnaeus, 1758) 1902 1902 1957 INV Crepipatella dilatata (Lamarck, 1822) 2005 2005 2014 INV Crisularia plumosa (Pallas, 1766) 1937 1937 INV Crisularia serrata (Lamarck, 1816) 1902 PP Cryptonemia hibernica Guiry & L.M.Irvine 1911 PP Cushmanina striatopunctata (Parker & Jones, 1865) 1913 1913 INV Cuthona perca (Er. Marcus, 1958) 1976 1976 INV Cycloscala hyalina (G. B. Sowerby II, 1844) 1992 1992 INV Cymodoce fuscina Schotte & Kensley, 2005 2015 2015 VER Cynoscion regalis (Bloch & Schneider, 1801) 2009 VER Cyprinus carpio (Linnaeus, 1758)* 1200 PP Dasya sessilis Yamada 1984 1989 1984 PP Dasysiphonia japonica (Yendo) H.-S.Kim 1984 1984 1998 INV Dendostrea frons (Linnaeus, 1758) 1983 1983 INV Dendostrea folium (Linnaeus, 1758) 2005 2005 PP Derbesia rhizophora Yamada 1984 1984 INV Desdemona ornata Banse, 1957 1983 INV Diadema setosum (Leske, 1778) 2010 INV Diadumene lineata (Verrill, 1869) 1925 PP/micro Dicroerisma psilonereiella F.J.R.Taylor & S.A. Cattell 1998 1998 PP Dictyota cyanoloma Tronholm, De Clerck, A.Gómez-Garreta & Rull Lluch in Tronholm et al. 1935 2006 INV Didemnum perlucidum Monniot F., 1983 2006 2006 BLK 2005 1905 1918 1983 1986 2008 1974 1982 1902 1911 2009 1200 1879 1993 1983 2010 2011 1963 1925 1935 1945 Diversity 2022, 14, 1077 15 of 50 Table 2. Cont. Group Species Pan-European INV Didemnum vexillum Kott, 2002 1968 BAL NEA MED 1968 2007 INV Dikerogammarus villosus (Sowinsky, 1894) 2015 INV Dikoleps micalii Agamennone, Sbrana, Nardi, Siragusa & Germanà, 2020 2016 PP/micro Dinophysis sacculus Stein 2004 INV Diodora funiculata (Reeve, 1850) 2013 2013 INV Diplosoma listerianum (Milne Edwards, 1841) 1877 1877 INV Dipolydora quadrilobata (Jacobi, 1883) 2003 INV Dipolydora socialis (Schmarda, 1861) 2006 2006 INV Dipolydora tentaculata (Blake & Kudenov, 1978) 2005 2005 PP Dipterosiphonia dendritica (C.Agardh) F.Schmitz 1961 1961 INV Dispio magna (Day, 1955) 1982 PP/micro Dissodinium pseudocalani (Gonnert) Drebes ex Elbrachter & Drebes 2003 2003 INV Distaplia magnilarva (Della Valle, 1881) 1929 1929 INV Distaplia bermudensis Van Name, 1902 1953 2006 INV Distaplia corolla Monniot F., 1974 1971 1971 INV Dodecaceria capensis Day, 1961 1976 1976 INV Dorvillea similis (Crossland, 1924) 2014 2014 INV Dreissena rostriformis bugensis (Andrusov, 1897) 2014 VER Dussumieria elopsoides Bleeker, 1849 2005 INV Dyspanopeus texanus (Stimpson, 1859) 2015 2015 INV Dyspanopeus sayi (Smith, 1869) 1992 2007 INV Echinogammarus trichiatus (Martynov, 1932) 2014 INV Ecteinascidia styeloides (Traustedt, 1882) 1983 INV Ectopleura crocea (Agassiz, 1862) 1895 1989 INV Edwardsiella lineata (Verrill in Baird, 1873) 2010 2010 PP Elachista spp mentioned as E. flaccida 1993 1993 VER Elates ransonnettii (Steindachner, 1876) 2005 BLK 2015 2016 2004 2003 1982 1953 2014 2005 1992 2014 1983 1895 2005 PP Elodea canadensis Michx.* 1873 1873 PP Elodea nuttallii (Planch.) H.St.John 1991 1991 PP Elphidium striatopunctatum (Fichtel & Moll, 1798) 1911 1911 INV Elysia nealae (Ostergaard, 1955) 2018 2018 PP/micro Emiliania huxleyi (Lohmann) W.W.Hay & H.P.Mohler 1989 INV Endeis biseriata Stock, 1968 1979 INV Ensis leei M. Huber, 2015 1978 INV Eocuma dimorphum Fage, 1928 1992 INV Eocuma sarsii (Kossmann), 1880 1901 2006 1989 1979 1991 1978 1992 1901 Diversity 2022, 14, 1077 16 of 50 Table 2. Cont. Group Species Pan-European VER Epinephelus fasciatus (Forsskål, 1775) 2018 BAL NEA MED VER Epinephelus coioides (Hamilton, 1822) 1998 1998 VER Epinephelus malabaricus (Bloch & Schneider, 1801) 2011 2011 VER Epinephelus merra Bloch, 1793 2004 2004 VER Equulites klunzingeri (Steindachner, 1898) 1955 1955 INV Ergalatax junionae Houart, 2008 1993 1993 BLK 2018 INV Eriocheir sinensis H. Milne Edwards, 1853* 1912 INV Erugosquilla massavensis (Kossmann, 1880) 1956 1921 1912 1959 PP/micro Ethmodiscus punctiger Castracane 1800 VER Etrumeus golanii DiBattista, Randall & Bowen, 2012 1999 1999 INV Euchaeta concinna Dana, 1849 1987 1987 INV Eucheilota paradoxica Mayer, 1900 1967 1967 INV Euchone limnicola Reish, 1959 2015 INV Eucidaris tribuloides (Lamarck, 1816) 1998 1998 INV Eudendrium carneum Clarke, 1882 1950 1950 INV Eudendrium merulum Watson, 1985 1969 1969 INV Eunaticina papilla (Gmelin, 1791) 2020 2020 INV Euplana gracilis Girard, 1853 2002 2002 INV Euplokamis dunlapae Mills, 1987 2011 2011 PP/micro Eupyxidicula turris (Greville) S.Blanco & C.E. Wetzel 1983 1983 INV Eurypanopeus depressus (Smith, 1869) 2009 INV Eurytemora americana Williams, 1906 1938 INV Eurytemora carolleeae Alekseev & Souissi, 2011 2011 INV Eurytemora pacifica Sato, 1913 2014 INV Eurythoe laevisetis Fauvel, 1914 2011 INV Eusarsiella zostericola (Cushman, 1906) 2012 INV Eusyllis kupfferi Langerhans, 1879 1998 1998 2017 1997 1956 1979 1800 2015 2009 1938 2012 2011 2014 2011 2012 INV Euthymella colzumensis (Jousseaume, 1898) 2017 PP/micro Eutintinnus lusus-undae (Entz) 2001 INV Fauveliopsis glabra (Hartman, 1960) 2007 2007 INV Favorinus ghanensis Edmunds, 1968 2020 2020 INV Faxonius limosus (Rafinesque, 1817) 2015 INV Fenestrulina malusii (Audouin, 1826) 2011 2011 INV Fenestrulina delicia Winston, Hayward & Craig, 2000 2002 2002 INV Ferosagitta galerita (Dallot, 1971) 2011 PP/micro Fibrocapsa japonica S.Toriumi & H.Takano 1924 INV Ficopomatus enigmaticus (Fauvel, 1923) 1919 2001 2015 2011 1924 1939 1921 1919 1935 Diversity 2022, 14, 1077 17 of 50 Table 2. Cont. Group Species Pan-European INV Finella pupoides A. Adams, 1860 1996 BAL NEA MED 1996 VER Fistularia petimba Lacepède, 1803 2018 2018 VER Fistularia commersonii Rüppell, 1838 1999 1999 INV Fistulobalanus albicostatus (Pilsbry, 1916) 1973 INV Fulvia fragilis (Forsskål in Niebuhr, 1775) 1983 VER Fundulus heteroclitus heteroclitus (Linnaeus, 1766) 1970 INV Gafrarium savignyi (Jonas, 1846) 2005 INV Gammarus tigrinus Sexton, 1939 1931 PP Gelidium microdonticum W.R.Taylor 2017 2017 PP Gelidium vagum Okamura 2010 2010 VER Genyatremus cavifrons (Cuvier, 1830) 2015 2015 INV Glabropilumnus laevis (Dana, 1852) 1956 1956 INV Glycinde bonhourei Gravier, 1904 2007 2007 VER Gobiosoma bosc (Lacepède, 1800) 2009 INV Godiva quadricolor (Barnard, 1927) 1985 INV Goniadella gracilis (Verrill, 1873) 1968 INV Goniobranchus annulatus (Eliot, 1904) 2004 2004 INV Goniobranchus obsoletus (Rüppell & Leuckart, 1830) 2018 2018 INV Gonioinfradens giardi (Nobili, 1905) 2010 2010 INV Gonionemus vertens A. Agassiz, 1862 1700 1700 1918 PP Goniotrichopsis sublittoralis G.M.Smith 1975 1975 1989 PP Gracilariopsis chorda (Holmes) Ohmi 2010 2010 INV Grandidierella japonica Stephensen, 1938 2010 PP Grateloupia imbricata Holmes 2005 PP Grateloupia asiatica S.Kawaguchi & H.W.Wang 1984 1984 PP Grateloupia patens (Okamura) S.Kawaguchi & H.W.Wang 1994 1994 PP Grateloupia subpectinata Holmes 1978 1978 1990 PP Grateloupia turuturu Yamada 1982 1989 1982 PP Grateloupia yinggehaiensis H.W.Wang & R.X.Luan 2008 INV Guinearma alberti (Rathbun, 1921) 2016 2016 VER Gymnomuraena zebra (Shaw, 1797) 2002 2002 PP Gymnophycus hapsiphorus Huisman & Kraft 2011 2011 INV/par Gyrodactylus salaris Malmberg, 1957 1975 1975 PP/micro Gyrodinium corallinum Kofoid & Swezy 2001 2001 INV Halgerda willeyi Eliot, 1904 1988 1973 1983 1970 2005 2005 1975 1931 2009 1985 1968 2010 2010 2013 2005 2008 1988 BLK Diversity 2022, 14, 1077 18 of 50 Table 2. Cont. Group Species Pan-European INV Haliclona (Halichoclona) vansoesti de Weerdt, de Kluijver & Gómez, 1999 BAL NEA 2019 INV Haliclystus tenuis Kishinouye, 1910 2010 PP Halimeda incrassata (J.Ellis) J.V.Lamouroux 2011 INV Haliotis discus hannai Ino, 1953 1985 1985 INV Haloa japonica (Pilsbry, 1895) 1992 1992 PP Halophila stipulacea (Forsskål) Ascherson 1894 INV Haminella solitaria (Say, 1822) 2016 Pathogen Haplosporidium nelsoni Haskin, Stauber & Mackin 1975 1975 INV Heleobia charruana (d’Orbigny, 1841) 2014 2014 INV Heliacus implexus (Mighels, 1845) 2019 INV Hemigrapsus sanguineus (De Haan, 1835) 1999 INV Hemigrapsus takanoi Asakura & Watanabe, 2005 1993 2014 1993 INV Hemimysis anomala G.O. Sars, 1907* 1962 1962 1999 VER Hemiramphus far (Forsskål, 1775) 1943 MED BLK 2019 2010 2011 1992 1894 2016 2020 2019 1999 1999 2007 1943 VER Heniochus acuminatus (Linnaeus, 1758) 2014 2014 VER Heniochus intermedius Steindachner, 1893 2013 2013 INV Herbstia nitida Manning & Holthuis, 1981 2002 2002 INV Herdmania momus (Savigny, 1816) 1998 1998 PP Herposiphonia parca Setchell 1997 2006 1997 INV Hesperibalanus fallax (Broch, 1927) 1976 1976 1976 PP Heterostegina depressa d’Orbigny, 1826 1988 1988 INV Heterotentacula mirabilis (Kramp, 1957) 1997 1997 PP Hildenbrandia occidentalis Setch. 2011 VER Hippocampus kuda Bleeker, 1852 2014 2014 INV Hippopodina feegeensis (Busk, 1884) 1996 1996 VER Holacanthus africanus Cadenat, 1951 2017 VER Holacanthus ciliaris (Linnaeus, 1758) 2011 2011 VER Holocentrus adscensionis (Osbeck, 1765) 2016 2016 INV Homarus americanus H. Milne Edwards, 1837 1961 2007 VER Huso huso (Linnaeus, 1758)* 1962 1962 PP Hydroclathrus tilesii (Endlicher) Santiañez & M.J.Wynne 2006 INV Hydroides brachyacantha Rioja, 1941 2015 INV Hydroides dirampha Mörch, 1863 1981 1982 1981 INV Hydroides elegans (Haswell, 1883) 1868 1973 1868 INV Hydroides ezoensis Okuda, 1934 1968 1968 INV Hydroides heterocera (Grube, 1868) 1998 INV Hymeniacidon gracilis (Hentschel, 1912) 2017 2017 INV Hypania invalida (Grube, 1860) 1995 1995 2014 2011 2018 1961 2017 2018 2006 2015 1998 2008 Diversity 2022, 14, 1077 19 of 50 Table 2. Cont. Group Species Pan-European INV Hypereteone heteropoda (Hartman, 1951) 2017 BAL NEA 2017 PP Hypnea musciformis (Wulfen) J.V.Lamouroux 2005 2005 PP Hypnea anastomosans Papenfuss, Lipkin & P.C.Silva 2008 2008 PP Hypnea cervicornis J.Agardh 2009 2009 PP Hypnea cornuta (Kützing) J.Agardh 1894 1894 PP Hypnea spinella (C.Agardh) Kützing 1977 1977 PP Hypnea valentiae (Turner) Montagne 1996 INV Hypselodoris infucata (Rüppell & Leuckart, 1830) 2002 INV Ianiropsis serricaudis Gurjanova, 1936 2000 2000 INV Incisocalliope aestuarius (Watling & Maurer, 1973) 1975 1975 INV Indothais lacera (Born, 1778) 1983 1983 INV Isognomon aff. australicus (Reeve, 1858) 2016 2016 INV Isognomon legumen (Gmelin, 1791) 2016 2016 INV Isognomon radiatus (Anton, 1838) 1996 1996 INV Isolda pulchella Müller in Grube, 1858 1994 1994 INV Ixa monodi Holthuis & Gottlieb, 1956 1999 INV Jasus lalandii (H. Milne Edwards, 1837) 1980 1980 PP Kapraunia schneideri (Stuercke & Freshwater) A.M.Savoie & G.W.Saunders 2010 2010 PP/micro Karenia longicanalis Z.B.Yang, I.J.Hodgkiss & Gerd Hansen 2008 2008 PP/micro Karenia mikimotoi (Miyake & Kominami ex Oda) Gert Hansen & Ø.Moestrup 1968 PP/micro Karenia papilionacea A.J.Haywood & K.A.Steidinger 1994 1994 INV Koinostylochus ostreophagus (Hyman, 1955) 1970 1970 Pathogen Labyrinthula zosterae D. Porter & Muehlst. in Muehlstein & Short 1930 1930 VER Lactophrys triqueter (Linnaeus, 1758) 1909 1909 VER Lagocephalus guentheri Miranda Ribeiro, 1915 1952 1952 VER Lagocephalus sceleratus (Gmelin, 1789) 2004 2004 VER Lagocephalus suezensis Clark & Gohar, 1953 2003 2003 INV Lamprohaminoea ovalis (Pease, 1868) 2001 2001 INV Laonome xeprovala Bick & Bastrop, in Bick et al., 2018 2012 INV Latopilumnus malardi (De Man, 1914) 1910 PP/micro Lauderia pumila Castracane 1995 PP Laurencia brongniartii J.Agardh 1989 PP Laurencia caduciramulosa Masuda & Kawaguchi 1991 2006 MED BLK 1996 2002 2012 1999 1980 2012 2016 1968 2016 2018 1910 1995 1989 1991 Diversity 2022, 14, 1077 20 of 50 Table 2. Cont. Group Species Pan-European PP Laurencia okamurae Yamada 1984 BAL NEA MED 1984 PP Leathesia marina (Lyngbye) Decaisne 1905 1905 INV Leiocapitellides analis Hartmann-Schröder, 1960 2000 2000 INV Leiochrides australis Augener, 1914 2002 2002 PP/micro Lennoxia faveolata H.A.Thomsen & K.R.Buck 2007 INV Leonnates persicus Wesenberg-Lund, 1949 2013 2013 INV Lepidonotus tenuisetosus (Gravier, 1902) 2007 2007 INV Lepidonotus carinulatus (Grube, 1870) 1984 1984 INV Leucotina natalensis E. A. Smith, 1910 1996 1996 INV Limnodrilus profundicola (Verrill, 1871) 2014 INV Limulus polyphemus (Linnaeus, 1758) 1866 INV Linguimaera caesaris Krapp-Schickel, 2003 1997 1997 INV Linopherus canariensis Langerhans, 1881 1997 1997 INV Lioberus ligneus (Reeve, 1858) 2019 2019 PP Lithophyllum yessoense Foslie 1994 1994 PP Lomentaria flaccida Tanaka 2002 2002 PP Lomentaria hakodatensis Yendo 1978 PP Lophocladia lallemandii (Montagne) F.Schmitz 1908 1908 INV Lottia sp. 2015 2015 INV Lovenella assimilis (Browne, 1905) 2007 2007 INV Lumbrinerides crassicephala (Hartman, 1965) 1994 1994 INV Lumbrinerides neogesae Miura, 1981 2002 2002 INV Lumbrineris perkinsi Carrera-Parra, 2001 1973 1973 VER Lutjanus argentimaculatus (Forsskål, 1775) 2019 2019 VER Lutjanus griseus (Linnaeus, 1758) 2018 VER Lutjanus jocu (Bloch & Schneider, 1801) 2005 2005 VER Lutjanus sebae (Cuvier, 1816) 2010 2010 VER Lutjanus fulviflamma (Forsskål, 1775) 2013 2013 INV Lysidice collaris Grube, 1870 1961 1961 PP Macrocystis pyrifera (Linnaeus) C.Agardh 1972 1972 INV Macromedaeus voeltzkowi (Lenz, 1905) 1910 1910 INV Macrophthalmus (Macrophthalmus) indicus Davie, 2012 2009 INV Macrorhynchia philippina Kirchenpauer, 1872 1982 1982 INV Magallana angulata (Lamarck, 1819) 1700 1700 INV Magallana gigas (Thunberg, 1793) 1700 INV Magallana rivularis (Gould, 1861) 1994 1994 INV Magallana sikamea (Amemiya, 1928) 1994 1994 INV Malleus regula (Forsskål in Niebuhr, 1775) 1970 BLK 2007 2014 1866 1984 1978 2018 2009 2019 1700 1850 1970 2010 Diversity 2022, 14, 1077 21 of 50 Table 2. Cont. Group Species Pan-European BAL INV Marenzelleria arctia (Chamberlin, 1920) 2004 2004 NEA MED INV Marenzelleria neglecta Sikorski & Bick, 2004 1983 1983 1985 INV Marenzelleria viridis (Verrill, 1873) 1983 1985 1983 INV Marginella glabella (Linnaeus, 1758) 2009 2009 INV Maritigrella fuscopunctata (Prudhoe, 1978) 2014 2014 INV Marivagia stellata Galil & Gershwin, 2010 2019 2019 INV Marphysa victori Lavesque, Daffe, Bonifácio & Hutchings, 2017 1975 1975 Pathogen Marteilia refringens Grizel, Comps, Bonami, Cousserans, Duthoit & Le Pennec 1975 1975 INV Matuta victor (J.C. Fabricius, 1781) 2018 PP/micro Mediopyxis helysia Kühn, Hargreaves & Halliger 2003 2003 INV Megabalanus tintinnabulum (Linnaeus, 1758) 1764 1764 INV Megabalanus coccopoma (Darwin, 1854) 1851 1851 INV Melanella orientalis Agamennone, Micali & Siragusa, 2020 2016 PP Melanothamnus flavimarinus (M.-S.Kim & I.K.Lee) Díaz-Tapia & Maggs 2010 PP Melanothamnus harveyi (Bailey) Díaz-Tapia & Maggs 1958 PP Melanothamnus japonicus (Harvey) Díaz-Tapia & Maggs 2016 2016 INV Melibe viridis (Kelaart, 1858) 1970 1970 INV Melita nitida S.I. Smith in Verrill, 1873 1996 INV Menaethius monoceros (Latreille, 1825) 1978 INV Mercenaria mercenaria (Linnaeus, 1758) 1861 INV Mesanthura cfr. romulea Poore & Lew Ton, 1986 2000 2000 INV Metacalanus acutioperculum Ohtsuka, 1984 1995 1995 INV Metacirolana rotunda (Bruce & Jones, 1978) 1998 1998 INV Metapenaeopsis aegyptia Galil & Golani, 1990 1996 1996 INV Metapenaeopsis mogiensis consobrina (Nobili, 1904) 1995 1995 INV Metapenaeus monoceros (Fabricius, 1798) 1961 1961 INV Metaxia bacillum (Issel, 1869) 1995 1995 INV Microcosmus anchylodeirus Traustedt, 1883 1980 1980 INV Microcosmus squamiger Michaelsen, 1927 1971 1992 1971 INV Microcosmus exasperatus Heller, 1878 2005 2005 2014 VER Micropogonias undulatus (Linnaeus, 1766) 1998 1998 PP Miliolinella fichteliana (d’Orbigny, 1839) 1911 INV Millepora alcicornis Linnaeus, 1758 2004 1992 2018 1971 2016 2010 1982 2010 2015 1958 1996 1978 1861 1964 1911 2004 BLK Diversity 2022, 14, 1077 22 of 50 Table 2. Cont. Group Species Pan-European PP Mimosina affinis Millett, 1900 2012 BAL NEA MED 2012 INV Mitrella psilla (Duclos, 1846) 2016 2016 INV Mizuhopecten yessoensis (Jay, 1857) 1979 INV Mnemiopsis leidyi A. Agassiz, 1865 1986 INV Mnestia girardi (Audouin, 1826) 1990 INV Moerisia inkermanica Paltschikowa-Ostroumowa 1959 INV Molgula occidentalis Traustedt, 1883 2010 2010 INV Monocorophium uenoi (Stephensen, 1932) 2007 2007 VER Morone saxatilis x Morone chrysops 2019 INV Mulinia lateralis (Say, 1822) 2017 INV Murchisonellidae T. L. Casey, 1904 2013 BLK 1979 2006 2001 1990 1990 2018 1959 2019 2017 2013 INV Mycale (Carmia) senegalensis Lévi, 1952 2002 2002 VER Mycteroperca tigris (Valenciennes, 1833) 2018 2018 INV/par Myicola ostreae Hoshina & Sugiura, 1953 1972 1972 INV Myra subgranulata Kossmann, 1877 2004 INV/par Mytilicola orientalis Mori, 1935 1977 2018 1977 INV Mytilopsis leucophaeata (Conrad, 1831) 1835 1928 1835 INV Naineris setosa (Verrill, 1900) 2010 INV Namanereis littoralis (Grube, 1872) 1991 INV Neanthes agulhana (Day, 1963) 2007 2007 PP Nemalion vermiculare Suringar 2005 2005 VER Nemipterus randalli Russell, 1986 2014 2014 INV Nemopsis bachei L. Agassiz, 1849 1905 1905 INV Neodexiospira brasiliensis (Grube, 1872) 1982 1982 PP Neogastroclonium subarticulatum (Turner) L.Le Gall, Dalen & G.W.Saunders 2017 2017 VER Neogobius melanostomus (Pallas, 1814) 1990 PP Neoizziella divaricata (C.K.Tseng) S.-M.Lin, S.-Y.Yang & Huisman 1989 1989 INV Neomysis americana (S.I. Smith, 1873) 2010 2010 INV Nereis jacksoni Kinberg, 1865 1964 1964 INV Nerita sanguinolenta Menke, 1829 1969 1969 INV Nippoleucon hinumensis (Gamô, 1967) 2019 PP Nitophyllum stellato-corticatum Okamura 1984 PP Nonionella sp. T1/Nonionella stella 2012 INV Notocochlis gualtieriana (Récluz, 1844) 1978 1978 INV Notomastus aberans Day, 1957 1964 1964 INV Notomastus mossambicus (Thomassin, 1970) 1997 INV Novafabricia infratorquata (Fitzhugh, 1973) 1985 INV/par Nybelinia africana Dollfus, 1960 2005 1972 2004 1977 2010 1991 1990 2004 2019 1984 2012 1997 2013 1985 2005 1986 Diversity 2022, 14, 1077 23 of 50 Table 2. Cont. Group Species Pan-European BAL NEA INV Obesogammarus crassus (Sars G.O., 1894)* 1962 1962 2016 MED BLK INV Ocinebrellus inornatus (Récluz, 1851) 1993 1993 INV Odontodactylus scyllarus (Linnaeus, 1758) 2009 2009 INV Oithona davisae Ferrari F.D. & Orsi, 1984 2000 2002 2000 2009 VER Oncorhynchus gorbuscha (Walbaum, 1792) 1958 1958 1958 VER Oncorhynchus kisutch (Walbaum, 1792)* 1905 1984 1905 VER Oncorhynchus mykiss (Walbaum, 1792)* 1882 1882 1899 PP Operculina ammonoides (Gronovius, 1781) 1911 1911 INV Ophiactis macrolepidota Marktanner-Turneretscher, 1887 1998 1998 INV Ophiactis savignyi (Müller & Troschel, 1842) 1968 1968 VER Ophioblennius atlanticus (Valenciennes, 1836) 2017 2017 INV Ophryotrocha japonica Paxton & Åkesson, 2010 1999 1999 INV Ophryotrocha diadema Åkesson, 1976 2006 2006 VER Oplegnathus fasciatus (Temminck & Schlegel, 1844) 2009 2009 VER Orthopristis chrysoptera (Linnaeus, 1766) 2020 2020 INV Oscilla galilae Bogi, Karhan & Yokeş, 2012 2016 2016 VER Ostorhinchus fasciatus (White, 1790) 2014 2014 Pathogen Ostracoblabe implexa Born & Flahault 1951 1951 INV Ostraea angasi G. B. Sowerby II, 1871 1985 1985 INV Ostrea equestris Say, 1834 1995 1995 INV Ostrea denselamellosa Lischke, 1869 1982 1982 INV Ostrea puelchana d’Orbigny, 1842 1989 1989 INV Oulastrea crispata (Lamarck, 1816) 2012 INV Oxydromus humesi (Pettibone, 1961) 2009 2009 PP/micro Oxytoxum criophilum Balech 2003 2003 VER Oxyurichthys papuensis (Valenciennes, 1837) 2010 INV Pachygrapsus gracilis (de Saussure, 1857) 2013 2013 PP Pachymeniopsis gargiuli S.Y.Kim, Manghisi, Morabito & S.M.Boo 1968 2001 1968 PP Pachymeniopsis lanceolata (K.Okamura) Y.Yamada ex S.Kawabata 1982 2006 1982 INV Pacifastacus leniusculus (Dana, 1852) 2014 INV Pacificincola perforata (Okada & Mawatari, 1937) 2001 PP Padina boergesenii Allender & Kraft 1965 1965 VER Pagrus major (Temminck & Schlegel, 1843) 2004 2004 INV Pagurus longicarpus (Say, 1817) 2020 INV Palaemon macrodactylus Rathbun, 1902 1998 2012 2010 2014 2001 2020 2014 1998 2005 2002 Diversity 2022, 14, 1077 24 of 50 Table 2. Cont. Group Species Pan-European INV Palola valida (Gravier, 1900) 2014 BAL NEA MED 2014 VER Pampus argenteus (Euphrasen, 1788) 1896 1896 INV Panopeus occidentalis Saussure, 1857 2015 2015 PP Papenfussiella kuromo (Yendo) Inagaki 1990 1990 INV Paracalanus quasimodo Bowman, 1971 2017 2017 INV Paracaprella pusilla Mayer, 1890 2010 2010 2011 INV Paracerceis sculpta (Holmes, 1904) 1981 1988 1981 INV Paradella dianae (Menzies, 1962) 1985 1988 1985 INV Paradyte cf. crinoidicola (Potts, 1910) 1968 INV Paraleucilla magna Klautau, Monteiro & Borojevic, 2004 2000 INV Paralithodes camtschaticus (Tilesius, 1815) 2008 2008 INV Parametopella cypris Holmes, 1905 2014 2014 INV Paramysis (Mesomysis) intermedia (Czerniavsky, 1882) 2008 2008 INV Paramysis (Serrapalpisis) lacustris (Czerniavsky, 1882) 1962 1962 1970 1968 2006 2000 INV Paranais frici Hrabĕ, 1941 1970 VER Paranthias furcifer (Valenciennes, 1828) 2011 2014 2011 INV Paranthura japonica Richardson, 1909 2005 2007 2005 INV Parasmittina alba Ramalho, Muricy & Taylor, 2011 2014 2014 INV Parasmittina multiaviculata Souto, Ramalhosa & Canning-Clode, 2016 2016 2016 INV Parasmittina egyptiaca (Waters, 1909) 2016 2016 PP Parasorites orbitolitoides Hofker, 1930 2016 2016 INV Paratapes textilis (Gmelin, 1791) 2004 2004 INV/par Paratenuisentis ambiguus (Van Cleave, 1921) 2001 VER Parexocoetus mento (Valenciennes, 1847) 1955 1955 VER Parupeneus forsskali (Fourmanoir & Guézé, 1976) 2014 2014 INV Parvocalanus crassirostris (Dahl F., 1894) 2009 2009 PP Pegidia lacunata McCulloch, 1977 2010 2010 VER Pempheris rhomboidea Kossmann & Räuber, 1877 1983 1983 INV Penaeus aztecus Ives, 1891 2012 INV Penaeus hathor (Burkenroad, 1959) 2012 2001 2018 2012 2012 INV Penaeus monodon Fabricius, 1798 2011 2011 INV Penaeus japonicus Spence Bate, 1888 1972 1980 1972 INV Penaeus pulchricaudatus Stebbing, 1914 1961 1982 1961 INV Penaeus semisulcatus De Haan, 1844 [in De Haan, 1833–1850] 2016 2016 PP/micro Peridiniella catenata (Levander) Balech 1987 1987 BLK Diversity 2022, 14, 1077 25 of 50 Table 2. Cont. Group Species Pan-European PP/micro Peridiniella danica (Paulsen) Y.B.Okolodkov & J.D.Dodge BAL NEA MED 1901 PP/micro Peridinium quadridentatum (F.Stein) Gert Hansen 2005 INV Perinereis linea (Treadwell, 1936) 2012 Pathogen Perkinsus chesapeaki McLaughlin, Tall, Shaheen, El Sayed & Faisal 1992 1992 Pathogen Perkinsus olsenii R.J.G.Lester & G.H.G.Davis 1983 1983 INV Perophora multiclathrata (Sluiter, 1904) 1983 INV Perophora viridis Verrill, 1871 1971 1971 INV Perophora japonica Oka, 1927 1982 1982 PP Petalonia binghamiseae (J.Agardh) K.L.Vinogradova 1985 1985 INV Petricolaria pholadiformis (Lamarck, 1818) 1896 VER Petroscirtes ancylodon Rüppell, 1835 2004 2004 INV Phallusia nigra Savigny, 1816 2008 2008 INV Phascolion convestitum Sluiter, 1902 1977 1977 INV Phascolosoma (Phascolosoma) scolops (Selenka & de Man, 1883) 1975 1975 INV Photis lamellifera Schellenberg, 1928 1990 1990 Pathogen Photobacterium damsela Love, Teebken-Fisher, Hose, Farmer III, Hickman & Fanning 1992 1992 PP Phrix spatulata (E.Y.Dawson) M.J.Wynne, M.Kamiya & J.A.West 1992 1992 INV Phyllorhiza punctata Lendenfeld, 1884 2005 2018 VER Piaractus brachypomus (Cuvier, 1818) 2013 2013 PP Pikea californica Harvey 1991 1991 INV Pileolaria berkeleyana (Rioja, 1942) 1977 2007 INV Pilumnopeus africanus (de Man, 1902) 2013 2013 INV Pilumnopeus vauquelini (Audouin, 1826) 1963 1963 INV Pilumnus minutus De Haan, 1835 [in De Haan, 1833–1850] 2017 2017 INV Pinctada fucata (A. Gould, 1850) 2018 2018 INV Pinctada radiata (Leach, 1814) 1899 VER Pinguipes brasilianus Cuvier, 1829 1990 INV/par Piscicola pojmanskae Bielecki, 1994 2008 INV Pista unibranchia Day, 1963 1997 INV Plagusia squamosa (Herbst, 1790) 1906 1906 VER Planiliza haematocheila (Temminck & Schlegel, 1845) 1972 1995 PP Planispirinella exigua (Brady, 1879) 1910 1910 PP Planogypsina acervalis (Brady, 1884) 1909 1909 BLK 1901 2008 2005 2012 1992 1983 1927 1896 1998 1985 2005 1977 1899 1990 2008 2005 1997 1972 Diversity 2022, 14, 1077 26 of 50 Table 2. Cont. Group Species Pan-European VER Platycephalus indicus (Linnaeus, 1758) 1978 BAL NEA MED 1978 PP Plocamium secundatum (Kützing) Kützing 1991 1991 INV Plocamopherus ocellatus Rüppell & Leuckart, 1828 2015 2015 VER Poecilopsetta beanii (Goode, 1881) 1995 INV Polyandrocarpa zorritensis (Van Name, 1931) 1974 INV Polycera hedgpethi Er. Marcus, 1964 1986 2001 1986 INV Polycerella emertoni A. E. Verrill, 1880 1964 1981 1964 INV Polycirrus twisti Potts, 1928 1983 1983 INV Polyclinum constellatum Savigny, 1816 2014 2014 INV Polydora colonia Moore, 1907 1983 2018 INV Polydora triglanda Radashevsky & Hsieh, 2000 2014 2014 INV Polydora websteri Hartman in Loosanoff & Engle, 1943 2014 2014 PP Polyopes lancifolius (Harvey) Kawaguchi & Wang 2008 2008 PP Polysiphonia paniculata Montagne 1967 PP Polysiphonia forfex Harvey 2011 2011 PP Polysiphonia morrowii Harvey 1975 1975 PP Polysiphonia senticulosa Harvey 1993 1993 VER Pomacanthus imperator (Bloch, 1787) 2016 VER Pomacanthus paru (Bloch, 1787) 2015 2015 VER Pomacanthus maculosus (Forsskål, 1775) 1994 1994 VER Pomadasys stridens (Forsskål, 1775) 1968 INV Pontogammarus robustoides (Sars, 1894)* 1962 1962 PP Porphyra umbilicalis Kützing 1989 1989 INV Portunus segnis (Forskål, 1775) 1958 INV Potamocorbula amurensis (Schrenck, 1862) 2018 INV Potamopyrgus antipodarum (Gray, 1843)* 1801 1801 INV Potamothrix moldaviensis Vejdovský & Mrázek, 1903 2008 2008 INV Potamothrix bavaricus (Oschmann, 1913) 2015 2015 INV Potamothrix bedoti (Piguet, 1913) 1915 1915 INV Potamothrix heuscheri (Bretscher, 1900)* 1960 1960 INV Potamothrix vejdovskyi (Hrabĕ, 1941)* 1967 1967 inv Prionospio aluta Maciolek, 1985 1994 INV Prionospio depauperata Imajima, 1990 2018 INV Prionospio pulchra Imajima, 1990 1989 INV Proasellus coxalis (Dollfus, 1892) 2011 INV Procambarus clarkii (Girard, 1852)* 2000 1995 1974 1983 1967 1997 2016 2012 1968 1958 2018 1887 1994 2018 1989 1991 2011 2000 BLK Diversity 2022, 14, 1077 27 of 50 Table 2. Cont. Group Species Pan-European INV Prokelisia marginata (Van Duzee, 1897) 2011 BAL NEA 2011 MED PP/micro Prorocentrum gracile Schütt 1989 1989 INV Prosphaerosyllis longipapillata (Hartmann-Schröder, 1979) 1997 VER Proterorhinus nasalis (De Filippi, 1863) 2020 INV Protodorvillea biarticulata Day, 1963 1975 1975 INV Protoreaster nodosus (Linnaeus, 1758) 1981 1981 BLK 1997 2020 INV Psammacoma gubernaculum (Hanley, 1844) 2009 PP/micro Pseudochattonella farcimen (Riisberg I.) 1998 2001 1998 PP/micro Pseudochattonella verruculosa (Y.Hara & M.Chihara) S.Tanabe-Hosoi, D.Honda, S.Fukaya, Y.Inagaki & Y.Sako 1998 2015 1998 INV/par Pseudodactylogyrus anguillae (Yin & Sproston, 1948) 1982 1985 1982 INV/par Pseudodactylogyrus bini (Kikuchi, 1929) 1985 1985 1997 INV Pseudodiaptomus marinus Sato, 1913 2007 INV Pseudonereis anomala Gravier, 1899 1969 PP/micro Pseudo-nitzschia australis Frenguelli 1995 1995 PP/micro Pseudo-nitzschia multistriata (Takano) Takano 1985 1985 INV Pseudopolydora paucibranchiata (Okuda, 1937) 1977 1982 VER Pteragogus trispilus Randall, 2013 1992 1992 VER Pterois miles (Bennett, 1828) 2009 2009 2009 2010 2007 1969 2000 1977 INV Ptilohyale littoralis (Stimpson, 1853) 2009 INV Purpuradusta gracilis notata (Gill, 1858) 1988 1988 INV Pyrgulina pupaeformis (Souverbie, 1865) 1995 1995 INV Pyromaia tuberculata (Lockington, 1877) 2016 2016 PP Pyropia yezoensis (Ueda) M.S.Hwang & H.G.Choi 1975 1984 1975 PP Pyropia suborbiculata (Kjellman) J.E.Sutherland, H.G.Choi, M.S.Hwang & W.A.Nelson 2010 2010 2014 INV Pyrunculus fourierii (Audouin, 1826) 1995 INV Rangia cuneata (G. B. Sowerby I, 1832) 1997 INV Rapana venosa (Valenciennes, 1846) 1956 VER Rastrelliger kanagurta (Cuvier, 1816) 2018 2018 INV Rhinoclavis kochi (Philippi, 1848) 1976 1976 INV Rhithropanopeus harrisii (Gould, 1841) 1936 PP/micro Rhizosolenia calcar-avis Schultze 2009 INV Rhopilema nomadica Galil, 1990 1995 1995 INV Ringicula minuta H. Adams, 1872 2019 2019 INV Rissoina bertholleti Issel, 1869 1985 1985 2009 1995 2011 1997 1997 1936 1950 1973 1994 2009 1956 1948 Diversity 2022, 14, 1077 28 of 50 Table 2. Cont. Group Species Pan-European INV Ruditapes philippinarum (Adams & Reeve, 1850) PP BAL NEA MED 1973 1973 1980 Rugulopteryx okamurae (E.Y.Dawson) I.K.Hwang, W.J.Lee & H.S.Kim 2002 2015 2002 PP Saccharina japonica (J.E. Areschoug) C.E.Lane, C.Mayes, Druehl & G.W.Saunders 1976 1980 1976 INV Saccostrea cuccullata (Born, 1778) 2007 2007 INV Saccostrea glomerata (Gould, 1850) 1984 VER Salvelinus fontinalis (Mitchill, 1814)* 1916 PP Sarconema filiforme (Sonder) Kylin 1990 1990 PP Sarconema scinaioides Børgesen 1980 1980 PP Sargassum muticum (Yendo) Fensholt 1972 VER Sargocentron rubrum (Forsskål, 1775) 1943 1943 VER Saurida lessepsianus Russell, Golani & Tikochinski, 2015 1960 1960 PP Scageliopsis patens Wollaston 1989 VER Scarus ghobban Forsskål, 1775 2010 2010 VER Scatophagus argus (Linnaeus, 1766) 2007 2007 INV Schizoporella japonica Ortmann, 1890 1976 1976 INV Schizoporella pungens Canu & Bassler, 1928 2010 2010 VER Sciaenops ocellatus (Linnaeus, 1766) 2016 2016 INV Scolelepis (Parascolelepis) gilchristi (Day, 1961) 1977 1977 INV Scolelepis korsuni Sikorski, 1994 1994 INV Scolionema suvaense (Agassiz & Mayer, 1899) 1950 1950 VER Scomberomorus commerson (Lacepède, 1800) 2008 2008 INV Scyllarus caparti Holthuis, 1952 1977 1977 1984 1916 1972 1980 1989 1994 PP Scytosiphon dotyi M.J.Wynne 1968 1991 VER Sebastes schlegelii Hilgendorf, 1880 2008 2008 INV Sebastiscus marmoratus (Cuvier, 1829) 2016 2016 INV Sepioteuthis lessoniana Férussac [in Lesson], 1831 2009 2009 INV Septifer cumingii Récluz, 1848 2005 2005 VER Siganus fuscescens (Houttuyn, 1782) 2020 2020 VER Siganus virgatus (Valenciennes, 1835) 1975 1975 VER Siganus luridus (Rüppell, 1829) 1964 1964 VER Siganus rivulatus Forsskål & Niebuhr, 1775 1925 1925 PP Sigmamiliolinella australis (Parr, 1932) 2001 2001 VER Sillago suezensis Golani, Fricke & Tikochinski, 2013 2009 2009 INV Sinelobus vanhaareni Bamber, 2014 2006 INV Sinezona plicata (Hedley, 1899) 2019 2010 1968 2006 2019 BLK Diversity 2022, 14, 1077 29 of 50 Table 2. Cont. Group Species Pan-European INV Smaragdia souverbiana (Montrouzier in Souverbie & Montrouzier, 1863) BAL NEA MED 1993 1993 INV Smittina nitidissima (Hincks, 1880) 2014 2014 INV Smittoidea prolifica Osburn, 1952 1995 PP Solieria filiformis (Kützing) P.W.Gabrielson 1922 1922 PP Sorites variabilis Lacroix, 1941 1996 1996 PP Spartina anglica C.E. Hubbard 1924 1924 PP Spartina densiflora Brongn. 1986 1986 PP Spartina patens (Aiton) Muhl. 1986 1986 PP Spartina alterniflora Loisel 1806 1806 PP Spermothamnion cymosum (Harvey) De Toni 2010 INV Sphaeroma walkeri Stebbing, 1905 1977 PP Sphaerotrichia firma (E.S.Gepp) A.D.Zinova 1981 1981 INV Sphaerozius nitidus Stimpson, 1858 2013 2013 VER Sphyraena chrysotaenia Klunzinger, 1884 1964 1964 VER Sphyraena flavicauda Rüppell, 1838 2003 2003 INV Spirobranchus tetraceros (Schmarda, 1861) 1970 1970 PP Spiroloculina angulata Cushman, 1917 1996 1996 PP Spiroloculina antillarum d’Orbigny, 1839 1911 1911 INV Spirorbis (Spirorbis) marioni Caullery & Mesnil, 1897 1974 INV Spondylus spinosus Schreibers, 1793 2001 PP Spongoclonium caribaeum (Børgesen) M.J.Wynne 1967 VER Spratelloides delicatulus (Bennett, 1832) 2014 2014 VER Stegastes variabilis (Castelnau, 1855) 2014 2014 INV Stenothoe georgiana Bynum & Fox, 1977 2010 VER Stephanolepis diaspros Fraser-Brunner, 1940 1935 1935 INV Sternodromia spinirostris (Miers, 1881) 1969 1969 INV Sticteulima lentiginosa (A. Adams, 1861) 1995 1995 INV Stomatella sp. 2011 2011 INV Streblospio gynobranchiata Rice & Levin, 1998 2011 INV Streblospio benedicti Webster, 1879 1982 1982 INV Styela plicata (Lesueur, 1823) 1877 1989 INV Styela canopus (Savigny, 1816) 2006 2006 INV Styela clava Herdman, 1881 1968 PP Stypopodium schimperi (Kützing) M.Verlaque & Boudouresque 1990 1990 INV Syllis hyllebergi (Licher, 1999) 1972 1972 INV Syllis pectinans Haswell, 1920 1982 BLK 1995 2010 2015 1974 1977 2004 1977 2001 1967 2011 1974 2010 2011 2017 1968 1982 1877 2005 2013 2002 Diversity 2022, 14, 1077 30 of 50 Table 2. Cont. Group Species Pan-European PP Symphyocladia marchantioides (Harvey) Falkenberg PP BAL NEA MED 1971 1971 1984 Symphyocladiella dendroidea (Montagne) D.Bustamante, B.Y.Won, S.C.Lindstrom & T.O.Cho 1993 2005 1993 INV Symplegma rubra Monniot C., 1972 2014 2014 INV Symplegma brakenhielmi (Michaelsen, 1904) 2003 2003 VER Synagrops japonicus (Döderlein, 1883) 1987 1987 INV Synaptula reciprocans (Forsskål, 1775) 1967 1967 VER Synchiropus sechellensis Regan, 1908 2014 2014 INV Synidotea laticauda Benedict, 1897 1975 INV Syphonota geographica (A. Adams & Reeve, 1850) 1999 1999 INV Syrnola fasciata Jickeli, 1882 1995 1995 INV/par Taeniastrotos sp. 1993 1993 PP/micro Takayama tasmanica de Salas, Bolch & Hallegraeff 2008 2008 INV Telmatogeton japonicus Tokunaga, 1933 1962 INV Tenellia adspersa (Nordmann, 1845) 2001 VER Terapon theraps (Cuvier, 1829) 2007 2007 INV Terebella ehrenbergi Gravier, 1906 1952 1952 INV Teredo bartschi Clapp, 1923 2003 INV Thalamita gloriensis Crosnier, 1962 1977 1977 INV Thalamita poissonii (Audouin, 1826) 1969 1969 PP/micro Thalassiosira nordenskioeldii Cleve 1967 PP/micro Thalassiosira hendeyi Hasle & G.Fryxell 1978 1978 PP/micro Thalassiosira tealata Takano 1968 1968 PP/micro Thecadinium yashimaense S.Yoshimatsu, S.Toriumi & J.D.Dodge 2002 2002 INV Thelepus japonicus Marenzeller, 1884 2017 2017 INV Theora lubrica Gould, 1861 2001 2010 INV Timarete punctata (Grube, 1859) 2006 INV Tonicia atrata (G.B. Sowerby II, 1840) 1978 VER Torquigener flavimaculosus Hardy & Randall, 1983 2006 2006 INV Trachysalambria palaestinensis (Steinitz, 1932) 1995 1995 INV Tremoctopus gracilis (Souleyet, 1852) 1937 1937 INV Tricellaria inopinata d’Hondt & Occhipinti Ambrogi, 1985 1982 INV Triconia rufa (Boxshall & Böttger, 1987) 2004 2004 INV Triconia umerus (Böttger-Schnack & Boxshall, 1990) 2004 2004 BLK 1975 1962 1979 2001 2003 2007 1967 2001 2006 1978 1996 1982 Diversity 2022, 14, 1077 31 of 50 Table 2. Cont. Group Species Pan-European NEA MED INV Tridentata marginata (Kirchenpauer, 1864) 1980 BAL 1980 1990 VER Tridentiger barbatus (Günther, 1861) 2016 2016 PP/micro Trieres mobiliensis (J.W.Bailey) Ashworth & Theriot 1983 1983 PP/micro Trieres regia (M.Schultze) M.P.Ashworth & E.C.Theriot 1989 1989 VER Trinectes maculatus (Bloch & Schneider, 1801) 1984 1984 PP/micro Tripos arietinus (Cleve) F.Gómez 1992 1992 PP/micro Tripos macroceros (Ehrenberg) F.Gómez 1983 1983 INV Trochus erithreus Brocchi, 1821 1985 INV Tubastraea tagusensis Wells, 1982 2017 INV Turbonilla edgarii (Melvill, 1896) 1996 1996 VER Tylerius spinosissimus (Regan, 1908) 2004 2004 VER Tylosurus crocodilus crocodilus (Péron & Lesueur, 1821) 2003 2003 PP Ulva australis Areschoug 1984 1990 1984 PP Ulva californica Wille 2006 2006 2011 PP Ulva gigantea (Kützing) Bliding 2015 2015 PP Ulva ohnoi M.Hiraoka & S.Shimada 2011 2015 PP Ulvaria obscura (Kützing) P.Gayral ex C.Bliding 1985 PP Umbraulva dangeardii M.J.Wynne & G.Furnari 2014 2014 PP Undaria pinnatifida (Harvey) Suringar 1971 1975 PP Undella hadai Balech 2004 2004 VER Upeneus moluccensis (Bleeker, 1855) 1947 1947 VER Upeneus pori Ben-Tuvia & Golani, 1989 2003 2003 INV Urocaridella pulchella Yokes & Galil, 2006 2018 2018 PP Uronema marinum Womersley 1989 1989 INV Urosalpinx cinerea (Say, 1822) 1960 1960 INV Vallicula multiformis Rankin, 1956 1998 1998 VER Vanderhorstia mertensi Klausewitz, 1974 2019 2019 VER Variola louti (Forsskål, 1775) 2018 2018 PP Vaucheria longicaulis Hoppaugh 2020 INV Viriola sp.[cf. bayani] Jousseaume, 1884 2016 INV Watersipora aterrima (Ortmann, 1890) 1983 1983 INV Watersipora subatra (Ortmann, 1890) 1987 1987 INV Watersipora arcuata Banta, 1969 1990 1990 PP Womersleyella setacea (Hollenberg) R.E.Norris 1986 1986 INV Xanthias lamarckii (H. Milne Edwards, 1834) 2013 2013 1985 2017 2011 1985 1971 2020 2016 2013 BLK Diversity 2022, 14, 1077 32 of 50 Table 2. Cont. Group INV Species Xenostrobus securis (Lamarck, 1819) INV – Pan-European NEA MED 1991 BAL 2005 1991 Yoldia limatula (Say, 1831) 2019 2019 INV Zafra savignyi (Moazzo, 1939) 1995 1995 INV Zafra selasphora (Melvill & Standen, 1901) 1995 1995 VER Zebrasoma flavescens (Bennett, 1828) 2008 2008 VER Zebrasoma xanthurum (Blyth, 1852) 2015 2015 BLK Figure 2. Number of NIS detected by December 2020. (a) European waters and regional Seas, (b) North-East Atlantic subregions: ANS = Greater North Sea, ABI = Bay of Biscay-Iberian Shelf, AMA = Macaronesia, ACS = Celtic Seas; (c) Mediterranean subregions: MWE = Western Mediterranean, MAL = Eastern Mediterranean, MIC = Central Mediterranean, MAD = Adriatic Sea. The Baltic Sea dataset encompasses 100 NIS introductions (including 6 parasites and 9 microalgae), 34 of which were introduced before 1970. The major proportion of the introductions since 1970 have been invertebrates (42 species, ~83%), followed by primary producers (5 species, ~10%), and vertebrates (4 species, ~8%). Invertebrates consist of a wide range of benthic crustaceans, as well as pelagic zooplanktonic taxa, whereas primary producers include both, phytoplankton, and phytobenthic species. Vertebrate species include Ponto-Caspian sturgeons and gobies, as well as cultured salmonids. 456 NIS are known from the North-East Atlantic (NEA), 372 of which have been detected since 1970 (81%). The Greater North Sea (ANS) hosts 260 NIS including parasites and pathogens (Figure 4b), 193 of which (74%) have been observed since 1970. The NIS biota is dominated by invertebrates (154 taxa = 59%) and primary producers (macroalgae, microalgae, pathogens) 88 taxa (34%). The proportion of vertebrates (fish) is low (18 taxa = 7%), and mostly related to freshwater NIS expanding their distribution into estuarine coastal waters. The Celtic Seas (ACS) host 107 NIS including parasites and pathogens (Figure 4b), 72 of which (67%) have been detected since 1970. The vast majority (69 taxa = 64%) are invertebrates, followed by primary producers (35 taxa = 33%) while vertebrates are represented only by three freshwater fishes that have been observed in Irish estuarine waters. The Bay of Biscay and Iberian Shelf (ABI) subregion hosts 250 NIS, 215 of which (86%) have been introduced since 1970. Most of them are invertebrates (180 taxa = 72%), followed by primary producers (68 taxa = 27%) and vertebrates (2 taxa = 1%). Diversity 2022, 14, 1077 – 33 of 50 Figure 3. Status and trends in introduction of NIS in European seas. Bars depict the cumulative number of NIS, from historical times to 2020. Details for the status in 2020 (black bar) as in Figure 2. Lines show the trends in new NIS introductions per 6-year intervals from 1970 to 2017. Note: parasites/pathogens and microalgae were excluded from the trend analyses. The Macaronesia (AMA) hosts 121 species, 109 (90%) introduced since 1970. Invertebrates dominate (72 taxa = 59%), followed by primary producers (29 taxa = 24%) and 0′ – vertebrates (20 taxa = 17%). The Mediterranean NIS list includes 578 species (473 = 83% since 1970) dominated by invertebrates (59%) (Figure 4a). Primary producers follow with approximately 23% of – which macroalgae and Rhodophyta prevail. Vertebrates (103 taxa = 18%) are species among dominated by Red Sea (Lessepsian) fishes. The contribution of NIS groups varies among the Mediterranean subregions (Figure 2c). Primary producers have their largest representation in MWE and MAD (31–32%), introduced as contaminants in shellfish consignments in the major shellfish culture areas of the northern Adriatic and the French coast. On the other hand, the percentage of vertebrates is higher in MAL where they mostly arrived through – fish from MAL than all the Suez Canal, and in MIC which receives naturally dispersing other subregions. The EU part of the Black Sea (Bulgaria and Romania) hosts only 38 validated NIS out of a total of more than 110 NIS reported for the whole Black Sea. These are mostly invertebrates (33 species) with crustacean and molluscan species dominating. Only 24 NIS have been reported since 1970 including two microalgae. In addition to the 874 NIS in European waters, 57 NIS detected in one regional sea are native or cryptogenic in at least one other regional Sea (Supplementary Table S1). These include macroalgae (18 taxa), mollusks (13 taxa), crustaceans (11 taxa), cnidarian (5 taxa), polychaetes (5 taxa), tunicates (2 taxa), bryozoan (1 taxon), Fish (1 taxon), and microalgae Diversity 2022, 14, 1077 34 of 50 (1 taxon). They have been transferred from the NEA to the MED and BLK Seas (more than 27 taxa), but also from the MED to the NEA (more than 22 taxa). Finally, six species have been transferred from the EU BLK waters to the BAL. Figure 4. Annual rate of NIS introductions (6-year average) at different geographic levels: (a) European waters; (b) regional seas, (c) North-East Atlantic subregions: ABI = Bay of BiscayIberian Shelf, ACS = Celtic Seas, ANS = Greater North Sea, AMA = Macaronesia (d) Mediterranean subregions. MWE = Western Mediterranean, MIC = Central Mediterranean, MAD = Adriatic Sea, MAL = Eastern Mediterranean. Dotted line for the EU trend (Figure 4a) is a linear regression line. Note that the annual average for the final interval has been calculated for three years only. Species classified as NIS in a country but partly native or cryptogenic within the subregion/region of the country were not included in the analyses, with some examples provided in Table 3. In contrast, species native in one subregion, but NIS in another subregion within the same MSFD region were not listed in Table 2 but are considered as NIS at the subregional level (Supplementary Table S2). They are mostly widespread native or cryptogenic species in the MED and NEA that have been classified as NIS in Macaronesia. Table 3. Examples of partly native/cryptogenic species within the same region/subregion excluded from the analyses. For regions/subregions’ abbreviations see Table 1. Group Species Region/Subregion Native Country/Region Introduced Dinoflagellates Prorocentrum lima (Ehrenberg) F.Stein, 1878 NEA Denmark/NEA Macroalgae Asperococcus scaber Kuckuck, 1899 NEA/ANS Netherlands Macroalgae Fucus distichus subsp. evanescens (C.Agardh) H.T.Powell NEA/ANS CRY in Norway Sweden/NEA Crustacea Necora puber (Linnaeus, 1767) NEA, MED Sweden/NEA Crustacea Pseudomyicola spinosus spinosus (Raffaele & Monticelli, 1885) NEA, MED France/NEA Diversity 2022, 14, 1077 35 of 50 Table 3. Cont. Group Species Region/Subregion Native Country/Region Introduced Crustacea Pilumnus spinifer H. Milne Edwards, 1834 NEA, MED Sweden/NEA Mollusca Calliostoma zizyphinum (Linnaeus, 1758) NEA, MED Netherlands Mollusca Cymbium olla (Linnaeus, 1758) NEA/ABI Spain/MED Mollusca Tritia corniculum (Olivi, 1792) NEA, MED Spain/NEA Mollusca Tritia neritea (Linnaeus, 1758) MED, partly in ABI France/NEA Cnidaria Cereus pedunculatus (Pennant, 1777) NEA/ANS Denmark/NEA Porifera Suberites massa Nardo, 1847 NEA/ANS Netherlands Porifera Haliclona (Haliclona) urceolus (Rathke & Vahl, 1806) NEA/ANS Netherlands Porifera Haliclona (Reniera) cinerea (Grant, 1826) NEA/ANS Netherlands Bryozoa Reptadeonella violacea (Johnston, 1847) NEA Portugal The trend in new NIS introductions per 6 year assessment periods varies among groups and regional seas (Figure 3). The upward trend observed for invertebrates at the pan-European level is evident in the BAL, NEA, and MED Seas but not in the BLK Sea. Overall, the rate of new NIS introductions (excluding parasites, pathogens, and microalgae) at the Pan-European level has increased at what appears to be a linear trend since 1970 from six to 21 NIS per year (Figure 4a). While evident in most regional seas, the increase also obscures large regional differences such as the steep increase from the early 2000s to 2017 in the Baltic Sea (Figure 4b) and a decreasing trend in the Black Sea (Figure 4b) and the Celtic Seas (Figure 4c). Comparison with the latest assessment period (2018–2020) shows a decline in the annual average rate of new NIS introductions compared to the preceding trends in many regional seas. Thus, while the annual rate of NIS in the North-East Atlantic steadily increased since 1970, although with subregional differences, reaching 11 new NIS per year in the 2012–2017 period, the latest assessment period (2018–2020) indicated a decline to an average of five NIS per year (Figure 4b). The annual rate of new NIS in the Greater North Sea (ANS) increased rapidly in the 1994–1999 period and maintained the upward trend in the last assessment period reaching six new NIS per year (Figure 4c). In the Bay of Biscay and Iberian Shelf (ABI), a steady upward trend was observed until 2005, followed by a sharp increase in the following periods, reaching seven new NIS per year in the 2012–2017 period. A similar pattern to that of ABI was observed in Macaronesia where the annual rate reached five NIS/per year in the 2012–2017 period. The highest number of new NIS introductions in the Celtic Seas occurred in the assessment period 1994–2005 with two new NIS per year. A declining trend was observed in the last assessment periods. Only five invertebrates were detected in the 2012–2017 period, and none since 2017. All analyses in the Mediterranean Sea are based on 460 NIS taxa observed for the first time since 1970. On an annual basis, the number of newly introduced NIS has increased in the Mediterranean since the late 1990′ s reaching 14 species per year in the period 2012–2017 (Figure 4b). This increasing trend is also observed at a subregional level for all regions but the MWE. Specifically, the annual new NIS rate calculated in the assessment period (2012–2017) reached 11 new NIS per year in the MIC, followed by nine in the MAL, seven in the MWE and six in the MAD (Figure 4d). In the MWE, the annual rate of NIS introductions fluctuates between two and seven species per year without any pronounced peaks or temporal trends. In contrast, a slight leveling off in the introductions rate appears in the MAD, while the rate of new NIS introductions presents a steeper increase in the MAL and MIC after the mid-2000s. The rate of introductions in the BLK peaked in the 1994–2006 period reaching one new NIS per year but dropped in the following periods (Figure 4b). As many as six Diversity 2022, 14, 1077 36 of 50 species (18%) have expanded the geographic range from neighboring areas surrounding the Black Sea where they first invaded, while the presence of two NIS namely the oysters Crassostrea virginica and Magallana gigas is attributed to escape from confinement (oyster culture facilities). 4. Discussion With the current work, we aimed at establishing an updated status of NIS in European waters to provide a robust baseline for understanding trends in new NIS arrivals. The presented analyses documented an increasing trend in the annual rate of new NIS at all spatial levels until 2017 while highlighting some major regional differences both in the composition of xenodiversity and the temporal evolution of new NIS introductions at the subregional level, that can prove useful in further steps of setting thresholds for NIS trends indicators. Our findings are discussed in the context of spatial, temporal, species-specific and effort-related sources of uncertainty (Figure 5), which are primarily epistemic in nature (sensu [43,44]) i.e., they relate to measurement or systematic error, be it in species taxonomy, identification, and origin, in the spatial aspects of inventories or the temporal uncertainties associated with trends estimation. Subjective judgment may introduce additional uncertainty in determining species to include/exclude from management actions, such as cryptogenic species or functional groups addressed with different policy instruments. Finally, we provided an explicit account of partly native species in different management units, helping to resolve linguistic uncertainties stemming from a context-dependent definition of the terms alien/native. Figure 5. Schematic diagram of the process of NIS trends calculation identifying sources of uncertainty (outlined in rectangles) as they propagate from species to inventories to trends. Additional considerations for threshold setting are indicated by oval outlines. Sp. complexes = species complexes, Tax. Revisions = taxonomic revisions. Sp.nov. = species novae. 4.1. Validation of European NIS: A Challenging and Dynamic Task One of the main challenges in establishing a robust and accurate baseline is addressing taxonomic or biogeographic uncertainties and incorporating new taxonomic information. To maintain a conservative viewpoint and avoid potential false positives, the authors agreed to exclude species that have raised uncertainties regarding (i) the known existence of cryptic species, (ii) recent taxonomic revisions, (iii) suspicions of possible errors for taxa belonging to species complex, and/or (iv) species that are possibly non-native but Diversity 2022, 14, 1077 37 of 50 only recently described and thus requiring further clarification about their status. Issues arising from cryptic species, taxonomic revision, and occurrence of species complexes were noticed in the NEA for the ascidians Botrylloides schlosseri, Ciona intestinalis, and the mussels Mytilus galloprovincialis and Mytilus trossulus. Botrylloides schlosseri is an example of the problems associated with the identification of cryptic species complexes, which are common among widely distributed marine taxa [45]. An extensive study by Bock et al. [46] showed that several cryptic species of B. schlosseri coexist at a regional scale in northwestern Europe. Some are probably native (e.g., clade E in Brittany, France) while others are likely to be introduced, considering their near-global distribution (e.g., clade A in Brittany, France). The specimens of B. schlosseri, reported in the North-East Atlantic, could thus be either NIS or native species. Thus, overall, it seems more reasonable to assign B. schlosseri a cryptogenic status. In the case of Ciona intestinalis, uncertainties stem from a recent extensive taxonomic revision [47]. Based on a series of morphological and molecular investigations (references in 47), this species name was shown to bring together two distinct species, namely Ciona intestinalis and Ciona robusta, which had previously been described as two distinct species but unfortunately synonymized in 1985. Until a recent taxonomic revision, C. robusta was known as C. intestinalis type A and C. intestinalis as C. intestinalis type B although the type was not always reported. Furthermore, since the taxonomic revision was announced in 2017, the use of the correct species name is questionable for our dataset ending in 2020. C. robusta, native to Asia, is the only Ciona species introduced, so far, to the North-East Atlantic (in the early 2000s) [48,49]. We, therefore, excluded records of C. intestinalis and retained only records of C. robusta or C. intestinalis type A, as the use of these names refers to the Pacific-origin species. The situation is even more complicated with the Mytilus edulis species complex, which obscures three European accepted species M. edulis, M. galloprovincialis and M. trossulus that still hybridize and exchange genes at contact zones. In our list, we have two species reported as introduced in the North-East Atlantic, for which reports are questionable: M.e galloprovincialis and M. trossulus. The use of the species name M. galloprovincialis is insufficient to determine native vs. introduced status, as it covers two distinct lineages, one present in the Mediterranean Sea, and the other in the Atlantic [50]. As with C. intestinalis prior to its taxonomic revision, the name M. galloprovincialis does not allow us to determine the native or introduced status of specimens reported from the North-East Atlantic. In addition, the natural presence of the Atlantic lineage as enclosed population patches in Brittany, Wales, Scotland, and Northern Ireland is not always recognized by some specialists and is debated. In the case of M. trossulus, identification has most often been established using barcoding or metabarcoding based on the COI mitochondrial marker. However, in the absence of details regarding the reference sequence that was used for the taxonomic assignment, we face another problem here. Some of the reference data available in public databases are indeed from specimens collected in the Baltic Sea, where the mitochondrial genome of M. trossulus has been extensively introgressed (i.e., replaced) by that of M. edulis, which may lead to a false taxonomic assignment of a M. edulis specimen to M. trossulus [51]. In addition, recent work has shown that M. edulis carries a transmissible cancer of M. trossulus origin. Thus, molecular-based identification may lead to the assignment of M. trossulus or edulis-trossulus hybrids for M. edulis specimens with this cancer [52,53]. The so-called “Baltic Mytilus trossulus” actually differs distinctly in morphology, ecology and genetic characters from M. trossulus, i.e., a species described from the NE Pacific [54]. To resolve this, Mytilus edulis balthicus by Gittenberger and Gittenberger, 2021, has recently been described. In addition, to further the nomenclatorial stability within the M. edulis complex, the locus typicus restrictus of the nominal taxon M. edulis has been restricted to the North Sea off the Dutch coast [54]. The improvement of molecular methods in ecological studies has helped to shed some light on species’ origins and their actual distribution, (see for instance the case of Tritia neritea detailed in the next Section). However, at the same time, this may give rise Diversity 2022, 14, 1077 38 of 50 to some controversies until further studies finally provide unequivocal confirmation of status with more data. This is the case, for example, of the oyster Ostrea stentina, which was recently found to encompass two different genotypes, one of them belonging to the newly described Ostrea neostentina with type locality in Hong Kong [55]. A new distribution map of this genus has thus been constructed, with O. stentina present in both the MED and NEA regions, and O. neostentina only in the MED. New studies are taking place to confirm the native range, but, so far, regarding the present knowledge of historical records and taxonomical studies, the population of O. stentina present in the ABI subregion is considered introduced. In addition, systematics is a dynamic field of research, as novel species are continuously being described; some of them possibly being novel introduced species. However, in the absence of further verification regarding their status, we did not include some of these species in our list. A case in point is that of the spaghetti worm Terebella banksyi nov. sp [56] newly described following its collection in 2017 in Arcachon Bay and found in farms or reefs of the Pacific oyster Magallana gigas. Similar uncertainty is occurring for the newly described colonial tunicate Didemnum pseudovexillum nov. sp [57], distinctive from the well-known invader D. vexillum by morphological traits and genetic characteristics and found only in marinas in the Celtic Seas (Brittany, France) and NW Mediterranean Sea (Spain). Considering the habitats (farms, marinas) and extensive range of D. pseudovexillum nov., it is likely that it had been introduced. However, further clarification would be needed to ascertain its introduced or cryptogenic status. We included in the list of accepted species that arose following hybridization between a NIS and a native species. Hybridization between native and introduced species is very common in plants [58,59]. It has also been documented in marine species although being still poorly examined, and yet an important issue to consider for marine NIS management [6]. In coastal systems, this process is well-illustrated by cordgrass species from the Spartina genus [60,61]. For instance, S. alterniflora hybridized with the native species S. maritima after its introduction in the United Kingdom. This hybridization gave rise to S. townsendii, a sterile species, which then gave rise through polyploidization to S. anglica. The latter species is highly successful, displacing the native S. maritima, and is present in most of the ANS and locally in the western BAL. Thus, S. anglica is not per se introduced but is included in our list, because it would have never existed without the introduction of S. alterniflora in Europe. Another cordgrass species, Spartina versicolor Fabre, has also a controversial taxonomic status. Although it was recorded as NIS in several European countries in the 19th and 20th centuries, it was considered synonymous with Spartina patens, due to morphological similarities [62,63] sampled several populations of S. versicolor in the Mediterranean, Atlantic, and North Africa saltmarshes and conducted cytogenetic and molecular analysis (microsatellite, nuclear and chloroplast DNA sequences) and compared it to North American Spartina species. Their results supported the hypothesis that all European and African populations of S. versicolor are, in fact, North American S. patens, introduced before or at the beginning of the nineteenth century. Due to potential hybridization within Spartina species, further investigations are needed to clarify any potential hybridizations between introduced species with the native ones (e.g., S. maritima). 4.2. Issues with Assessing the Spatial Distribution of NIS in Europe’s Seas The NIS data-gathering process is not standardized (there is no consistent methodology) among EU Member States, which is a drawback and likely to generate bias and uncertainty in the assessment itself. In addition, biases may arise from the lack of dedicated surveillance programs. Not only studies focused on NIS introduction hot spots, such as ports and marinas or aquaculture facilities, but also the increment of monitoring programs to give responses to other MSFD descriptors increased the probability of finding newly introduced NIS during the surveys. However, it must be highlighted that several new records are introductions that most probably either went unnoticed in previous surveys Diversity 2022, 14, 1077 39 of 50 or from areas that were never previously investigated. Monitoring programs are also not equally implemented in all subregions, and only a few have specifically focused on NIS and cryptogenic species detection [14]. Therefore, data need to be updated continuously from other monitoring programs or scientific literature reporting NIS. For example, in the NEA region, subregions such as ANS or ACS have historically received more attention than ABI [64]. In several countries such as Spain, Portugal, and Denmark, there were no baseline studies for NIS until very recently and the list included in the last assessment period (2012–2017), can therefore be considered as a baseline for some countries. Boundaries between sub-regions established for MSFD reports are also challenging. In particular, the ABI subregion boundaries, as the boundaries between ANS and ACS, very often raise questions when establishing the status of some species because the natural borders between water masses are not static at these human-established borders (Figure 1). The same holds for the MWE subregion. Its western limit finishes a few kilometers after the strait of Gibraltar making it difficult to establish proper frontiers between Mediterranean and Atlantic waters since the Mediterranean shows a high influence even until central Atlantic waters [65]. In this sense in the southern extension of the ABI subregion, being highly influenced by Mediterranean waters, some species whose native range extends in both NEA and MED regions can be found, giving them the category of partly native species in a subregion, but being NIS in a country of this same subregion (Table 3) or in another subregion of the same region. This is the case, for example, of the gastropod Cymbium olla, whose native range includes Algarve (southern Portugal) and the Gulf of Cadiz (southern Spain—Atlantic coast), which are part of the ABI subregion, but also Cadiz in the Alboran Sea site, which is in the MWE subregion. Therefore, Cymbium olla, which is partly native in the MWE subregion even in some other localities in the MWE, might be locally classified as NIS [66]. Species distribution and their possible expansion, are never contained within any human delineation of marine borders, making it difficult to categorize their status when it comes to classification at any bordering level (subregion, region, or Pan-European). This issue is particularly important for species spreading gradually, which might be considered either as a natural expansion or introduced by human activities. For example, the nassariid gastropod Tritia neritea’s native range includes the Mediterranean and the Black Sea, as well as all around the Iberian Peninsula (Hidalgo [67] as Cyclops neriteum), but since the 1970s, this gastropod has been extending its range along the coast of Frances since its first record in 1976 in Arcachon Bay [68]. Its presence almost exclusively in oyster farming areas and the genetic characteristics of the French populations (e.g., admixture of lineages found in different locations of the Mediterranean Sea that indicated multiple introductions [69]) finally concur to report this nassariid gastropod as a NIS, probably introduced by oyster cultures in France [70]. Therefore, it is considered partly native to the ABI subregion because of its native range in Portugal and Spain, and its later introduction in France (Table 3). Some cases such as Tritia neritea, exemplify the difficulty of sometimes categorizing species as either NIS, cryptogenic or native because of their life history, migratory and demographic history, influenced by paleoclimatic events in a longer time scale and more recently by human activities [69,71]. These processes determine the species’ contemporary distribution, showing a patched map of native and introduced localities, even at local small scales [72]. Another example of a partly native species is that of the amphipod Ericthonius didymus (Krapp-Schickel, 2013), which was described in the Adriatic Sea from the Venice Lagoon (Italy). This recent description was rapidly followed by new records in Europe both in the Mediterranean and the Atlantic between 2013 and 2017 [73]. These observations, some of which date back to the year of description of the species, do not allow an unequivocal designation of the species as non-indigenous in the Bay of Biscay. However, the species is considered NIS in the ANS and the AMA, due to its presence in anthropogenically stressed sites, such as harbors/marinas and shellfish grounds [73]. Diversity 2022, 14, 1077 40 of 50 4.3. Trends Indicator Across all taxonomic groups, the rate of new NIS introductions in EU waters has increased gradually since 1970 and reached an average of 21 NIS per year in the period 2012–2017. The same upward trend was noticed for the Baltic, North-East Atlantic, and the Mediterranean Sea, but was more evident in the Mediterranean and Baltic Seas. In contrast, a decreasing trend was seen in the Black Sea with only one new species detected in the last assessment periods (0.2–0.3 NIS per year). Low figures noticed in the periods of 1988–1993 and 2000–2005 are likely an artifact of varying monitoring and reporting efforts between the regions over these periods. The high rate of annual Introductions from 2000–2005 was very likely associated with a growing research interest in NIS, rather than discrete episodic events leading to high levels of new introductions during these years. Indeed, the development of several dedicated projects (AquaNIS, DAISIE, EASIN) produced outputs with updates on the list of NIS. The decreased annual rate of new NIS introductions in the period 2018–2020 at almost all geographic levels examined has recently been attributed to time lags in reporting [74] rather than a result of NIS intervention programs. Also, there are fewer sampling years in this last interval analyzed, which might entail larger variability in the annual rate. This provisional reduction of new NIS registered is furthermore not likely to be associated with the implementation of measures since no new programs of measures have been implemented yet (e.g., only three marine NIS, the fish Plotosus lineatus, the seaweed Rugulopteryx okamurae, and the crab Eriocheir sinensis (only partly marine), are in the EU list of Invasive Alien Species of Union concern) and the implementation of the Ballast Water Management Convention at the European level is still in progress [75]. The only exception is the Council Regulation (EC) No 708/2007 of 11 June 2007 concerning the use of alien and locally absent species in aquaculture that may have decreased the risk of novel species introduced for cultivation purposes, although not preventing transfer within each EU country’s borders. A decrease in new NIS records in the last assessment period (2018–2020) for most regions might furthermore be explained by the homogeneity of marine NIS fauna since more and more species previously found exclusively in one of the countries are now found in more countries. Probably many species are expanding naturally from previously invaded countries. The present upward trend in new NIS introductions to the Baltic Sea contradicts the previous D2C1 assessment, which indicated that the trend was decreasing since 2011 [76]. The discrepancy is very likely due to updated NIS records from several countries around the Baltic Sea. The latest assessment period in the present study covered only three years (2018–2020), but already five new NIS were recorded from the EU marine waters of the Baltic Sea during this time, suggesting that the ultimate HELCOM goal of zero new NIS introductions will not be reached, even though the rate of new NIS introductions has dropped to less than two new NIS per year. Overall, the current Baltic Sea analysis indicated that the number of new introductions has had a steep increase from the early 2000s to 2017. The increase may be due to growing scientific interest and promotion of citizen science projects [77], but it is evident that anthropogenic pressure through intensified shipping has steadily increased toward the marine environment of the Baltic Sea [78]. The NEA region encompasses several ecoregions, 4 sub-regions, and 10 different countries, making this region a very complex one for analyzing trends because of the heterogeneity in surveys and ecosystems. It is thus not surprising that quite a large number of species are reported as NIS within the region, and subregions (Figure 4b,c). Altogether the number of novel NIS has always been increasing, at least for invertebrates that are the most numerous NIS in this region (Figure 3). This is likely attributed to the continued increased maritime traffic in the region. Indeed, overall shipping density increased across the North-East Atlantic by 33.6% between 2013 and 2017 [79]. In comparison to the previous assessment [3,15,32], this work does not consider data from the UK waters. This leads to differences not only in the total number of NIS but Diversity 2022, 14, 1077 41 of 50 also in the trends indicator as first detection dates may be years earlier in neighboring non-EU countries. An earlier assessment (over the period of 2003–2014) of NIS in the ANS, ACS, and the ABI subregions showed that the number of newly recorded NIS varied by year and region showing a relatively constant linear increase in the ANS only, but not so in the ACS and ABI [80]. In this study, an increasing trend was observed in all subregions but the ACS. The high number of NIS in the ABI in the 2012–2017 period (7 NIS/year) is partly attributed to intensive studies in port areas and marinas [81–83] in the framework of the implementation of the MSFD descriptor 2 or research projects dedicated to NIS surveys. Furthermore, the increase of studies based on genetic analyses within this last decade has helped to rapidly and accurately detect newly introduced species reassess some species that have been misidentified, and elaborate an updated checklist of NIS [84–86]. In addition to traditional genetic approaches, in recent years metabarcoding of environmental DNA had been proposed and is increasingly used as a new tool to improve NIS detection [87]. The approach is promising and effective although it needs to be used cautiously to avoid both false negatives (i.e., present, but undetected NIS) and false positives (i.e., NIS erroneously detected) [51]. NIS detection by these methods requires fit-to-purpose protocols and should not be based on molecular data obtained for general biodiversity assessments [88]. Either way, the data show that the increase seems to be stabilizing, indicating that it is a good time to set the baseline. The increasing trend in introductions in ANS, which culminated in the 2012–2017 period with six NIS per year, appears to be slowing down in the last assessment period (2018–2020) with four new NIS per year, although future publications are expected to bring to light more NIS. During the period 2018–2020, in France, the number of records increased. However, this is the only French subregion with such an increase, thanks to dedicated surveys programs carried out in the Normandy region [86]; these reports are not new either for France or for ANS [89] (and references therein), suggesting a decrease of new species but an important dispersal between subregions. In the ACS, the decrease is even more pronounced than in the ANS, with no novel NIS reported after 2017. As for the ANS, the difference from the previous assessment can be partly attributed to the geographic areas involved. In the previous assessment [76] the NIS of the United Kingdom in ACS were included in the analysis. Moreover, pathogens were also included. Additionally, in the Western English Channel (French and UK coastline), a research project (Interreg Marinexus project) dedicated to rapid assessment surveys of NIS in marinas, well-known introduction hotspots, was carried out over 2010–2017 [78], and provided novel reports for European waters (e.g., the ascidian Asterocarpa humilis [90]). The AMA NIS list presented here represents an updated version of the list reported by Castro et al. [29] following similar criteria. As opposed to the current study, species that underwent tropicalization processes (see 29, 41) were considered one of the criteria for NIS attributes in Castro et al. [29] inventory. Most changes were made on macroalgae records for the Azores as more information on records, taxonomy, and distributional updates have been gathered and led to some changes. In addition, a few new records have been added as [29] included records only until 2020 whereas the present account includes records reported until summer 2022. Comparisons with the full NIS inventory of the MED are somewhat hampered by the geographic coverage of the current study, which is limited to the EU waters of the Mediterranean (plus Albania and Montenegro). As a result, total numbers of new NIS, as well as annual introduction rates, appear to be reduced in comparison to, e.g., [30], especially for the eastern Mediterranean, as primary Lessepsian introductions restricted to the Levantine were outside the spatial scope of this study. Indicatively, the whole Mediterranean Sea hosts upward of 1000 validated NIS, 786 of which are in the MAL [12,23,91], compared with the 579 NIS present in the EU parts of these waters. As such, it is not surprising that the annual introduction rate in the central Mediterranean in the 2012–2017 period exceeds that of the eastern Mediterranean, as the accelerated sea warming rates Diversity 2022, 14, 1077 42 of 50 favor the spread of Indo-Pacific species already present in the Levantine [92]. On the other hand, the reduction in Transport-Contaminant species [76], which are more prevalent in the Adriatic and the western Mediterranean, may have contributed to the observed leveling off or decreasing NIS trends in these two subregions. For the Mediterranean Sea as a whole, there appear to be two “stepwise” increases in new NIS introductions, the first one in the late 1990′ s, mostly driven by introductions in the MAL and likely related to sea surface warming [30,93], and the second in the 2012–2017 period. This last peak could partly reflect intensified research efforts, which the whole basin has undoubtedly experienced in the last decade [94] as already suggested for other regions and subregions of the NEA, and in line with comments by Bailey et al. [31]. In Slovenia, for example, the number of detected NIS has increased from 17 in 2012 to 57 in 2021, which is due to increased targeted research, mainly founded by the Ministry of Agriculture, Forestry and Food for the implementation of D2 in the country [95]. It also coincides with a sharp increase in the introduction rate of fouling species, notably in marinas and on leisure boats, at least in their detection and reporting [96,97]. Hence it is difficult to really evaluate the significance of these trends without considering a measure of “effort”, which again starkly exemplifies the need for standardized monitoring for any assessments to be meaningful. Some of the earlier invading NIS in the BLK such as the blue crab Callinectes sapidus (Rathbun, 1896) appear to be established and spreading in the area over the years. Callinectes sapidus was first found on the Bulgarian coast of the Black Sea in 1967 [98], most likely transferred in ballast water but could have been spreading via the Marmara Sea from an invasive population in the northern Aegean. Six new records of the blue crab have been documented near the Bulgarian Black Sea coast since 2010. This is evidence of a recent expansion of the species in this part of the Black Sea. This expansion could be explained by the existence of an established population in the area and is confirmed by the capturing of an egg-bearing female in Varna Bay in 2005 [99]. It is anticipated that in the face of climate change the number of NIS in the EU areas of the BLK will increase in the near future due to the spreading (Unaided pathway) of NIS from the North Aegean Sea that has already invaded the BLK via the Sea of Marmara such as the marbled pine foot Siganus rivulatus [100,101]. Moreover, NIS recently introduced via vessels in the northeastern and southern Black Sea could spread unaided in the study area [102,103]. Such is the case of the polychaetes Laonome xeprovala that spread in the Danube Delta–Black Sea Ecosystem and Marenzelleria neglecta that was detected in 2021 in the same area [103]. 4.4. Uncertainties in Trends Uncertainties in trends first rely on the uncertainty of the first date of the report (if not consistent across periods). The true introduction year of NIS may be different from the detection year. As an example, the Terebellid polychaete Marphysa victori was detected in 2016 and described in 2017 from French waters in the Arcachon Bay, with doubts already surrounding its true origin due to its presence in and close to oyster farms where Magallana gigas is cultivated [104]. This possibility was verified several years later. Marphysa victori is native to the Northwest Pacific [105], and it has undoubtedly been introduced as a contaminant with oyster transfers. However, it remains unproven if its introduction is a consequence of oyster importation from Japan. Between 1971 and 1975, about 1200 t of Magallana gigas spat collected from Sendai Bay (Japan) were introduced into Arcachon Bay. Marphysa victori has a substantial economic value as bait and is widely collected by recreational and professional fishermen. The number of worms collected in the lagoon (13 companies) could reach 1 million per year [104]. Reaching such densities within a year would be impossible. Thus 1975 was set as the most plausible year of its introduction. Other examples include Mollusca species observations in EU waters around 80 years after their first detection in neighboring non-EU waters. Such are the cases of the gastropod Berthellina citrina (Rüppell & Leuckart, 1828), which was first reported in the MED from the Gaza Strip in 1940 [106], but only in 2019 in EU Mediterranean waters: Cyprus [107] or of Diversity 2022, 14, 1077 43 of 50 the bivalve Gafrarium savignyi (Jonas, 1846) with a first Mediterranean record in 1905 from Egypt [108] but an EU record in 2005 from Cyprus [109]. Various policy measures relevant to the Baltic Sea countries can result in uncertainties regarding the emergent reports of new NIS introductions. Trend analyses on new NIS introductions to the Baltic Sea, such as [22,27,110] may differ mainly due to the applied assessment principles, e.g., area of interest, and species included in the analyses. Baltic Sea delineation determined according to the EU MSFD differs from HELCOM delineation, and this often leads to NIS being reported, for example, from the Kattegat area, which is BAL according to the HELCOM delineation, but at the same time a part of the ANS according to the EU MSFD delineation. In addition, Russian coastal waters outside of St. Petersburg and Kaliningrad are obviously part of the Baltic Sea but are not included in assessments that refer to the marine waters of the EU. Even more, pronounced discrepancies may be observed with pan-Mediterranean assessments due to the exclusion of non-EU Mediterranean countries in this study (see above). Regardless of administrative boundaries for EU policies, it is crucial that the marine environment is managed with sufficient harmonization between regional policies. Toward that end, the Contracting Parties to the Barcelona Convention—21 Mediterranean countries and the European Union—have recently developed and adopted the Integrated Monitoring and Assessment Programme for the Mediterranean region (IMAP) [111]. Within its framework and in accordance with the MSFD [9], GES for NIS in the Mediterranean was defined as the minimization of the introduction and spread of NIS linked to human activities, in particular for potential IAS, with the reduction in human-mediated introductions as the proposed State Target [112], a target that clearly needs to be further refined but seems far from achieved based on our latest data. 4.5. Threshold Values Qualitative GES assessments to date have been based on directional trends and, despite ongoing efforts [110], threshold values for the NIS trend indicator have not been set yet and neither have more specific recommendations been made for the magnitude of this reduction or the number of reporting cycles that will define the reference conditions [113]. Waiting for a value of the percentage reduction to be established at a European level, as suggested by [14], the French decree relating to the definition of GES states that GES is achieved if there is a significant decrease in the number of new NIS over two cycles at minimum. As visible in this work, the number of new NIS increased in all French marine subregions during the previous cycle (2012–2017), and the goal has therefore not been reached to date. The identification and comprehension of impact thresholds on ABI marine native communities is required. ABI countries must collaborate more closely to implement common methodologies for MSFD implementation, particularly regarding non-indigenous species (D2) [114]. Furthermore, good coordination is required for the creation of an effective alert system. It is worth mentioning the risk-based approaches to good environmental status (RAGES) project, which attempted to establish reproducible, transparent, and standardized risk management decision procedures based on international best practices. The increase in the number of new NIS introductions in the period 2006–2017 seems to be stabilizing, indicating that it is a good time to set the baseline. This decrease in new NIS records might be explained by a biotic homogenization of the ABI marine NIS fauna since more and more species previously found exclusively in one of the countries are now found in all three ABI countries. Probably many species are expanding naturally from previously invaded countries. In the Mediterranean Sea, preliminary analyses [12] indicated that threshold values should be established separately for each subregion and should be sought by examining the data of the last two decades, if not an even more recent period. Further work by Galanidi and Zenetos [30], based on breakpoint analysis of 1970–2017 NIS data, corroborated the validity of a subregional approach, demonstrating different temporal breakpoints in the Diversity 2022, 14, 1077 44 of 50 rate of NIS introductions per subregion, ranging from 1997 in the MAL, to 2000 in the MAD, 2003 in the MWE and 2012 in the MIC. They suggest that the mean introduction rate of these periods can be used to define threshold values but stress that GES target refinement and percentage reduction cannot proceed without careful consideration of management objectives and pathway pressure, as also pointed out in Tsiamis et al. [14]. Trends in the arrival of new NIS is a core indicator of the Baltic Marine Environment Protection Commission (Helsinki Convention, HELCOM), and the primary criterion D2C1 was assessed for the first time for a six-year assessment period (2011–2016) in 2018 [10]. The report listed new NIS and cryptogenic species for BAL over the assessment period. Contracting Parties of HELCOM have set a precautionary threshold to assess GES in relation to NIS. Zero new NIS introductions through anthropogenic activities to the Baltic Sea per six-year assessment period has been defined as the GES for NIS [10], and therefore one or more introductions to BAL would result in GES not being reached. Furthermore, it has been argued whether a reduction in new NIS introductions could be set as an intermediate objective if the goal of no new introductions cannot be reached. Even though a proportional reduction of new NIS introductions between the assessment periods would indicate temporary improvement of GES, the “zero tolerance policy” was chosen as the GES threshold to the BAL, because it is pragmatic, independent of earlier assessment periods, applicable even with uncertainties in relation to taxonomy and introduction pathways, and efficiently reflecting management measures [10,110]. 4.6. Concluding Remarks—The Way forward Considering how dynamic biological invasions are, NIS inventories should be curated regularly, especially when used to inform policy, in order to minimize errors and avoid over- or under-estimating the state of invasions in a region [44]. While the validation process in this work explicitly addressed many of the taxonomic and spatial components of uncertainty in the EU NIS baseline, other issues remain unresolved, among which the lack of standardized monitoring needs to be urgently rectified both for the meaningful interpretation of results and for the refinement of the relevant indicators. Regional and sub-regional analyses revealed that there are relatively strong variations in the number of new NIS introductions between the European seas, as well as among the subregions within the same region. Hence, it is natural that GES threshold values for the primary criterion D2C1 are discussed and decided under regional cooperation, as some regions have preferable conditions for a wider variety of species and thus tend to suffer from a higher number of introductions. In addition, NIS pathways are regionspecific (e.g., the Suez Canal in the MED, shipping in the NEA). Shipping was found to be a likely vector for over half of NIS in European waters both through biofouling and ballast discharges [2], while biofouling, particularly of recreational vessels, appears to be an important driver for the homogenization of the alien biota in the Mediterranean. As such, a more detailed focus on quantitative measures of pathway pressure would help better elucidate the observed NIS patterns, inform target setting and evaluate GES achievement in relation to management. Considering that currently only aquaculture-related introductions are addressed with EU-wide legislation and that the BWMC is not expected to be fully implemented until 2024 at the earliest, expectations for percentage reduction should have a realistic temporal horizon and, if possible, promote management implementation for the remaining major introduction pathways. More specific national or local measures may be put in place to protect sectors or sensitive habitats, e.g., see [115] for additional measures related to shellfish culture in the Wadden Sea), pathways of species introductions however operate globally and should be managed at appropriate scales. Supplementary Materials: The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/d14121077/s1, Table S1: Partly native or cryptogenic (CRY) species in European seas; Table S2: Species native/cryptogenic in one subregion, but NIS in another subregion. Diversity 2022, 14, 1077 45 of 50 Author Contributions: A.Z. and O.O.: conceptualization, review, and data collection. All authors: providing and validating national data, contribution with taxonomic expertise, interpretation of data. A.Z., O.O., M.G.: data analysis, writing the first draft of the manuscript. F.V. made significant contributions to early drafts of the manuscript. All authors wrote, revised, and contributed to the editing of the final manuscript. All authors have read and agreed to the published version of the manuscript. Funding: A.Z. and O.O. were partially funded by the European Environment Agency, through ETC/ICM 2021. The authors from the National Institute of Biology (Slovenia) acknowledge the financial support of the Slovenian Research Agency (Research Core Funding No. P1-0237) and of the Ministry of Agriculture, Forestry and Food. F.V. is supported by the CNRS Institute for Ecology and Environment. This work benefited from results obtained during surveys carried out in the Interreg IVa Marinexus programme and the Aquanis2.0 (TOTAL Foundation) and MarEEE (i-site MUSE; French National Research Agency under the “Investissements d’Avenir” programme ANR-16-IDEX-0006) projects allocated to FV. This is publication ISEM 2022-296. A.C.C.’s work was partially funded by FEDER funds through the Operational Programme for Competitiveness Factors—COMPETE and by Portuguese National Funds through FCT (Foundation for Science and Technology) under the UID/BIA/50027/2020 and POCI-01-0145-FEDER-006821. P.C. is supported by 2020.01797.CEECIND and (UIDB/04292/2020), granted by Fundação para a Ciência (FCT) e Tecnologia. RR’s work id funded by GI4Sado—IPS RD project. C.B.’s work is partially supported by programme MarBIS—Marine Biodiversity Information System financed through the Portuguese Government. Other support was provided by the Marine and Environmental Sciences Centre (MARE) financed by Portuguese National Funds through FCT/MCTES (UIDB/04292/2020), and by the project LA/P/0069/2020 granted to the Associate Laboratory ARNET. The Portuguese assessment benefited from the contribution of all the Portuguese experts working group on marine NIS. Authors from SLU acknowledge funding from The Swedish Agency for Sea and Water Management. Institutional Review Board Statement: Not Applicable. Data Availability Statement: The data availability statement for this manuscript is already described in the results section and the Supplementary Materials. Acknowledgments: The outcome of the present study was improved through cooperation within the Joint Working Group on Ballast and Other Ship Vectors under the International Council for the Exploration of the Seas (ICES), Intergovernmental Oceanographic Commission of Unesco and International Maritime Organization, as well as the ICES Working Group on Introductions and Transfers of Marine Organisms. The authors thank Nicholas Jason Xentidis for preparing the figures. Conflicts of Interest: The authors declare no conflict of interest. References 1. 2. 3. 4. 5. 6. 7. 8. Díaz, S.; Settele, J.; Brondízio, E.S.; Ngo, H.T.; Agard, J.; Arneth, A.; Zayas, C.N. 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