Marine exotic isopods from the Iberian Peninsula and nearby waters

Effective management of marine bioinvasions starts with prevention, communication among the scientific community and comprehensive updated data on the distribution ranges of exotic species. Despite being a hotspot for introduction due to numerous shipping routes converging at the Strait of Gibraltar, knowledge of marine exotics in the Iberian Peninsula is scarce, especially of abundant but small-sized and taxonomically challenging taxa such as the Order Isopoda. To fill this gap, we conducted several sampling surveys in 44 marinas and provide the first comprehensive study of marine exotic isopods from the Iberian Peninsula, the southern side of the Strait of Gibraltar (northern Africa) and the Balearic Islands. Exotic species included Ianiropsis serricaudis (first record for the Iberian Peninsula and Lusitanian marine province), Paracerceis sculpta (first record for the Alboran Sea ecoregion), Paradella dianae, Paranthura japonica (earliest record for the Iberian Peninsula) and Sphaeroma walkeri. Photographs with morphological details for identification for non-taxonomic experts are provided, their worldwide distribution is updated and patterns of invasion are discussed. We report an expansion in the distribution range of all species, especially at the Strait of Gibraltar and nearby areas. Ianiropsis serricaudis and Paranthura japonica are polyvectic, with shellfish trade and recreational boating being most probable vectors for their introduction and secondary spread. The subsequent finding of the studied species in additional marinas over the years points at recreational boating as a vector and indicates a future spread. We call for attention to reduce lags in the detection and reporting of small-size exotics, which usually remain overlooked or underestimated until the invasion process is at an advanced stage.


INTRODUCTION
In marine ecosystems, the spread of exotic species is one aspect of global change (Occhipinti-Ambrogi, 2007) and shipping is known to be the main vector for both primary introduction and secondary spread, via ballast water or biofouling (Ruiz et al., 2000). In the Mediterranean Sea, the most invaded sea in Europe, introduction events increased enough to more than double the total number of exotic species between 1970 and 2015, with intensification of commercial shipping being the main reason (Galil, Marchini West Africa, the Caribbean, northern Europe and Australia (Gibraltar Port Authority, 2017;Gibraltar Port marina staff, pers. comm., 2017), thus being a high-risk pathway for exotic species (see Drake & Lodge, 2004).
In marine bioinvasions, once a species has established in a new location, its effects are most often irreversible (Streftaris, Zenetos & Papathanassiou, 2005). Well-known examples are the algae Caulerpa taxifolia and the zebra mussel Dreissena polymorpha. This means that measures need to first focus on prevention and early detection rather than eradication (Simberloff, 2009;Roy et al., 2014). Monitoring surveys are an integral tool in here (see Bishop & Hutchings, 2011), and marinas are suitable spots for this purpose. While being underestimated in the past (Minchin et al., 2006;Clarke-Murray, Pakhomov & Therriault, 2011;Clarke-Murray, Therriault & Pakhomov, 2013), they have proved to be hotspots for introduction and subsequent spreading of non-indigenous species (thereafter NIS) (Cohen et al., 2005;Glasby et al., 2007;Floerl et al., 2009;Lacoursiére-Roussel et al., 2012;Foster et al., 2016;Ferrario et al., 2016a;Ferrario et al., 2017). As such, several sampling surveys along the marinas of the Iberian Peninsula, the Baleares Islands and the northern coast of Africa were carried out from 2011 to 2017, exploring a wide range of fouling substrates, in order to provide the first comprehensive study of marine exotic isopods in the Iberian Peninsula and adjacent waters, and discuss potential pathways and vectors of introduction.

MATERIAL & METHODS
Examined material was collected during several sampling surveys carried out from 2011 to 2017, in order to study the fouling epifauna in 44 marinas around the Iberian Peninsula, the Southern side of the Strait of Gibraltar (northern Africa) and Baleares. Marina choice was based on its vessel traffic and popularity as tourist locality (see Table 1 including number of berths and population density). Data for number of berths was obtained from the FEAPDT (Federación Española de Puertos Deportivos y Turísticos: http://www.feapdt.es) and from the IPTM (Instituto Portuário e dos Transportes Marítimos: http://www.atlanticstrategy.eu/en/partners/iptm-instituto-portu%C3%A1rio-e-dos-transportes-mar%C3%ADtimos-ip). Census data for the locality to which each marina belongs was obtained from the National Statistical Systems of Spain (http://www.ine.es), Portugal (http://www.ine.pt) and Morocco (http://www.hcp.ma) (Ros, Vázquez-Luis & Guerra-García, 2015). In 2011, the abundant bryozoans Bugula neritina and Amathia verticillata, together with its associated epifauna, were collected from marinas around the Peninsula and the Strait of Gibraltar (Ros, Vázquez-Luis & Guerra-García, 2015). Additionally, two monitoring programmes were carried out along the year 2012 in Puerto de Palma marina (Palma de Mallorca, Balearic Islands) and Puerto América marina (Cádiz), in which the substrates Amathia verticillata and Eudendrium sp. were sampled. Finally, a sampling survey was carried out during 2017 along the southern coast of the Iberian Peninsula to cover the main marinas of Andalusian coast. This area was selected as convergence zone between the Mediterranean Sea and the Atlantic Ocean, bearing a big gateway for marine introductions as it is the Strait of Gibraltar. Fouling organisms growing on artificial hard substrate including pontoons, ropes, wheels, buoys and ship hulls were sampled. These included red and green algae, hydroids, bryozoans, ascidians and mollusks plus their associated mobile epifauna. Samples were hand-collected, fixed in 90% ethanol and taken to the laboratory. Isopods were sorted, counted and identified to species level following updated literature on the group. Valid alien status was assigned following the European Environmental Agency criteria EEA, 2012, and valid human-mediated introduction was assessed based on Chapman & Carlton (1991). Photographs of full specimens and morphological parts of interest were taken using the camera Sony DSC-WX50. Worldwide distribution maps were developed using QGIS 1.8.0 Lisboa (QGIS, 2015), and shapefiles of marine ecoregions were obtained from http://maps.tnc.org/gis_data.html (accessed 20/08/2017). Voucher material of each species was deposited in the Museo Nacional de Ciencias Naturales (MNCN,CSIC), Madrid, Spain. The rest of the material was kept in the Laboratorio de Biología Marina, University of Seville, Spain.

DISCUSSION
At present, 12 marine exotic isopod species are known to be present in European waters. Ten of them are free-living species, most of them considered to be established, and two are parasites and considered to be casual (Streftaris, Zenetos & Papathanassiou, 2005;Zenetos et al., 2010;Galil, 2011;Noël, 2011;Lavesque et al., 2013;Chainho et al., 2015;Lorenti et al., 2016;Marchini, Ferrario & Occhipinti-Ambrogi, 2016a;Ulman et al., 2017) (see Table S1). The Iberian Peninsula alone hosts 50% of these ten free-living species, proving to be an important monitoring point for spread as well as future arrivals of exotics. Moreover, 50% of the marinas sampled in 2017 had increased their number of exotic isopods within the timeframe of only six years (Table 1). The case of the marinas in Cádiz Bay (Strait of Gibraltar) is to be noticed. Only Paracerceis sculpta was found in 2011, but they hosted P. sculpta, Paradella dianae, Sphaeroma walkeri and Paranthura japonica in 2017 (see the case of St. 12, 13 and 14.1 in Table 1). It is to be noticed that, despite more habitat-forming species were analyzed in 2017 in comparison with 2011, the increase in NIS was verified for the same species. In fact, a previous study conducted by Ros et al. (2013) demonstrates that about 50% of the dominant sessile species present throughout the year in Puerto América marina (St. 14.1) are introduced. Several factors may be favouring the introduction and establishment of exotic species in this area. Some of these factors may be due to particular environmental conditions of each marina; but others are most likely human-related, like the proximity of these marinas to a major international port in southern Spain (Cádiz Port), together with the high maritime traffic occurring across the Strait of Gibraltar. History of introduction, pathways, vectors and potential spread of each species are discussed below.

Histories of introduction and worldwide distribution
Ianiropsis serricaudis is native to the western Pacific, from the Sea of Okhotsk to the Sea of Japan, including Russia, Japan and Korea (Kussakin, 1962;Jang & Kwon, 1990;Shimomura, Kato & Kajihara, 2001;Yokoyama & Ishihi, 2007) (Fig. 3A). It was reported as NIS in San Francisco Bay, California (Carlton, 1979) in association with the introduced ascidians Ciona intestinalis Linnaeus, 1767 and Styela clava Herdman, 1881, possibly transported in shipping associated with the Vietnam War (Carlton, 1979). In the following years, reports of unknown Ianiropsis or erroneously identified specimens started to appear in the East and West coast of the United States and in 2004 it was already present in Europe, associated with the introduced ascidian Syela clava in Southampton (England) (see Hobbs et al., 2015 and references herein). In the Netherlands it was first observed in 2000 (Faasse, 2007) in an estuary used for shellfish aquaculture, and near the port of Rotterdam, among other locations. In 2010 and 2011, Hobbs and collaborators realized that all the mentioned reports involved the same species, potentially globally distributed by ships. From 2010 to 2013 it was widely reported from Maine to New Jersey (United States, western Atlantic), in association with both native and introduced algae, bryozoans and ascidians from fouling communities on floating dock sites and pilings (Pederson et al., 2005;McIntyre et al., 2013;Janiak & Whitlatch, 2012;Johnson, Winston & Woolacott, 2012;Wells et al., 2014;Hobbs et al., 2015). Also in California and Washington (United States, eastern Pacific), in mudflats near reefs of the introduced Australian serpulid polychaete Ficopomatus enigmaticus (Fauvel, 1923) (Heiman & Micheli, 2010 or in association to the non-native tunicate D. vexillum colonizing mussel aquaculture facilities (Cordell, Levy & Toft, 2013).
The first evidence of its occurrence in the Mediterranean Sea took place in 2012, when it was found to be abundant in the Lagoon of Venice (Adriatic Sea, Italy) (Marchini, Ferrario &  Occhipinti-Ambrogi, 2016a; Marchini, Ferrario & Occhipinti-Ambrogi, 2016b). The Lagoon of Venice is a big center for recreational and commercial harbour as well as flourishing mariculture that hosts a high number of introduced species (Occhipinti-Ambrogi, 2000; Marchini et al., 2015). A couple of years later it was present in Olbia , again a major site for mussel farming which, in fact, imports stocks from Adriatic lagoons (Marchini, Ferrario & Occhipinti-Ambrogi, 2016b); and subsequently in French marinas (Ulman et al., 2017). Our results fill a gap in its distribution, providing the first record for the Iberian Peninsula and the Lusitanian province. We now have evidence that it was already present in 2011 in the North of Spain, in La Graña marina (Ferrol, Galicia). Ferrol city has been a major naval shipbuilding centre for most of its history, and today, aquaculture and fishing stand as its primary industries. Interestingly, the specimens found in Ferrol bear four marginal denticles on pleotelson (Fig. 1D). There are some minor discrepancies regarding this character; Gurjanova (1936) described it as possessing four or five, Kussakin (1962) established a range of four to seven, Jang & Kwon (1990) showed four on the material from Korea, Doti & Wilson (2010) established ''five denticles or more'' but not ''up to four denticles'' and Marchini, Ferrario & Occhipinti-Ambrogi (2016a) ;Marchini, Ferrario & Occhipinti-Ambrogi (2016b) reported three or four from the specimens collected from the Mediterranean Sea. In any case, Hobbs et al. (2015) considered this to be a variable character and they relied on additional characteristics instead. They suggested a founder effect from the narrower range of denticle counts in introduced populations (three to four) versus the reported from native regions (up to seven). Moreover, our specimens were considerably large (males up to 5 mm and ovigerous females up to 3 mm) in comparison to those reported from Russia (2.9 mm for males and 2.7 for females) (Kussakin, 1962, Kussakin, 1988 from the East coast of the United States (largest male being 3.2 mm and female 2.4 mm) (Hobbs et al., 2015) and from the Mediterranean Sea (around 3 mm) (Marchini, Ferrario & Occhipinti-Ambrogi, 2016a;Marchini, Ferrario & Occhipinti-Ambrogi, 2016b). Whether these morphological changes imply changes in the ecological performance of the species in the new range and whether these are the result of changes at the genetic or only phenotypic level are uncertain. The biological, social and economic impact I. serricaudis may have in the introduced areas cannot be estimated until further ecological studies are carried out, since there is a severe lack of information for this species, even in its native range (Hobbs et al., 2015).
In the Iberian Peninsula, the arrival of I. serricaudis is probably linked to accidental introduction with shellfish transfers. This is a likely associated vector (see Marchini, Ferrario & Occhipinti-Ambrogi, 2016a;Marchini, Ferrario & Occhipinti-Ambrogi, 2016b), judging by the occurrence of the species in European mussel aquaculture facilities and hotspots for mariculture and shellfish trade. In fact, Galicia, together with Cataluña, bear the highest oysters, clams and mussel production of Spain, including production of nonnative species such as the Pacific oyster (Crassostrea gigas) and the Japanese clam (Ruditapes philippinarum), and export to other countries of Europe (Instituto Galego de Estatistica, 2017;Ministerio de Agricultura y pesca, 2017). This vector has been attributed to several species with similar routes of introduction (see Gruet, Héral & Robert, 1976), including the isopod Paranthura japonica (see Figs. 3A, 3E) (Lavesque et al., 2013). Nevertheless, shipping transport is an associated vector of this species as well, given its presence in ports and its nature as fouling species of hard substrates such as docks, as well as its adaptability to different substrates (Hobbs et al., 2015). Our finding in a marina adds recreational boating as a vector, at least, for secondary transport. This means I. serricaudis has the potential to spread to further Mediterranean marinas as well as along the Iberian Peninsula coast. This would be not surprising since this species bears broad temperature tolerance and is expected to spread through Europe as was well as temperate waters of the southern hemisphere (see Hobbs et al., 2015). As a small-size organism, it is likely to be overlooked though; therefore, we call for prevention for the detection of this species in the mentioned areas.
There is evidence for attributing shipping, including recreational boating, as vector to Paracerceis sculpta (Hewitt et al., 2004;Katsanevakis et al., 2014;Mead et al., 2011;. It is commonly found in locations of intense vessel traffic; in marinas, bays or coastal lagoons near major harbor facilities (Rezig, 1978;Forniz & Sconfietti, 1983;Rodríguez, Drake & Arias, 1992;Castelló & Carballo, 2001;Espinosa-Pérez & Hendrickx, 2002;. In the 1990s it was already present in the Mediterranean Sea and the Strait of Gibraltar. From there, it has been subsequently found in additional marinas along the southern and eastern sides of the Iberian Peninsula coast from 2011 to 2017 (Table 1); and it currently occurs from southern Portugal to eastern Spain. We report it for the first time for Alboran sea ecoregion, where all the males found belonged to the alpha morph sensu Shuster (1992). This supports the idea that only the alpha morph has made it into the introduced populations, consistent with the lack of beta and gamma male records in other non-native locations (Pires, 1981;Forniz & Maggiore, 1985;Rodríguez, Drake & Arias, 1992;Loyola e Silva, Masunari & Dubiaski-Silva, 1999;Hewitt & Campbell, 2001;Yu & Li, 2001;Ariyama & Otani, 2004;Munguia & Shuster, 2013;. In fact, Shuster & Wade (1991) hypothesized that the shorter lifespan of beta and gamma males is a handicap for surviving long trips and colonizing new regions.
Additionally, we have observed a non-overlapping presence of P. sculpta and the native isopod Dynamene edwardsii in most of the stations. A further study investigating the interspecific interaction of these two species is scheduled, in order to determine the potential biological impact of Paracerceis sculpta.
As well as P. sculpta, it was probably introduced to new locations by hitchhiking on the hulls or other surfaces of ships (Rodríguez, Drake & Arias, 1992;Galil, 2011). Hass & Knott (2000) also point to recreational boating as a likely vector, at least for its introduction to Australia. Our study supports this hypothesis, since it was found again in marinas located in Cádiz Bay (Strait of Gibraltar's vicinity) plus others along the Alboran Sea coast. Marinas of southern Iberian Peninsula coasts are well connected by frequent local traffic; 90% of visiting boats in the sampled marinas are Spanish, plus a percentage of foreign boats usually coming from Europe (UK, France, Holland) and other parts of the world (America, Australia, Arabic countries) (marina staff, personal communication). In fact, our data shows an ongoing expansion of Paradella dianae into additional marinas, potentially colonizing the eastern side of the Iberian Peninsula into the western Mediterranean Sea. Even having the same native range and potentially bearing a similar pattern of introduction than P. sculpta, P. dianae does not seem to be as successful, bearing lower densities than P. sculpta and a smaller introduction range (Figs. 3B, 3C).
Sphaeroma walkeri is the most widespread of these species, reaching numerous ports worldwide (see Carlton & Iverson, 1981). Stebbing (1905) first described it from in Ceylon (now Sri Lanka, Indian Ocean), with the northern Indian Ocean being its native range, including India, Arabian Sea and Bay of Bengal (Carlton & Iverson, 1981). It was known from the Persian Gulf some years later and the introduction status in this locality is doubtful, thus considered cryptogenic (Fofonoff et al., 2017) (Fig. 3D). Carlton & Iverson (1981) propose an episodic dispersal for this species. An initial local transport (pre-1870 period) would have occurred around the Indian Ocean plus South Africa (Stebbing, 1917), where it was found in fouling on pilings, Mozambique (Barnard, 1955) and Australia (Baker, 1928;McNeill, 1932;Iredale, Johnson & McNeill, 1932). A second period would be related to the opening of the Suez Canal in 1869. The record of this species in Port of Suez already in 1904(Stebbing, 1910 is doubtful; therefore, we agree with Fofonoff et al. (2017) and consider S. walkeri cryptogenic from this locality as well (Fig. 3D). From there, it would have travelled through the Suez Canal into the Mediterranean Sea (Omer-Cooper, 1927;Larwood, 1940). A post 1940 period would have been coincident with World War II. Sphaeroma walkeri would have been transported to the American continent associated to the intense shipping traffic since that time. It was found in Brazil (Loyola e Silva, 1960), Puerto Rico (Menzies & Glynn, 1968), Florida (Miller, 1968;Camp, Whitino & Martin, 1977;Nelson & Demetriades, 1992) and Hawaii (Miller, 1968). From those areas, it continued to increase its distribution to different parts of the world. To the western Pacific in Hong Kong in 1972 (Vrijmoed, 1975;Morton, 1987), Hainan (southern China) from pier fouling samples (Kussakin & Malyutina, 1993) and other locations in Australia (National Museum of Natural History (Smithsonian Institution) collections (NMNH), 1967; Montelli & Lewis, 2008). To the eastern Pacific in San Diego Bay (California), it was first detected in 1973 in fouling on pilings, floats and small boats at yacht harbours (Carlton & Iverson, 1981). Along the western Atlantic coast it was found in other locations of the Gulf of Mexico (Clark & Robertson, 1982;Cházaro-Olvera et al., 2002), Cuba in 1994 (USNM 280039, US National Museum of Natural History 2007) and Isla Margarita (Venezuela) in 2004(Gutiérrez, 2012. Along the Northwest coast of Africa, it was also associated with harbours (Jacobs, 1987). On the Indian Ocean it was reported from Malaysia only in the 1990s (Rai-Singh & Sasekumar, 1996) and from Iran in (Khalaji-Pirbalouty & Wägele, 2010. Across the Mediterranean Sea, it continued spreading to further eastern locations until the present year (Glynn, 1972;Kocataş, 1978;Galil, 2008;Ulman et al., 2017). It was recorded in the Italian Peninsula (Lodola, 2013) and found to be completely established with successful populations in Tunisia harbours and lagoons (Ben Souissi et al., 2004;Ben Amor, Ben Slaem & Ben Souissi, 2010). In was also reported in the western Mediterranean (Zibrowius, 1992), being reported from Spain for the first time in 1981 (Jacobs, 1987). In 2017, we report Sphaeroma walkeri from the southern Iberian Peninsula, in Cádiz Bay.
The route of introduction to southern Spain and the Strait of Gibraltar is unknown and several are possible. Initially, specimens may have arrived to the Mediterranean Sea from faraway ports in Indian Ocean or Australia; or from the long-established population in Suez Canal, and subsequently spread towards the western Mediterranean Sea, arriving to France and eastern Spain. It may also have arrived from western Atlantic populations from America or northwestern Africa and entered through the Strait of Gibraltar (Spanier & Galil, 1991;Galil, 2008); or from both Indian and Atlantic populations through multiple introduction events. In any case, its presence in Puerto América marina also indicates a transport via shipping, including recreational boating as vector. This supports the findings of Ulman et al. (2017), who collected individuals of S. walkeri directly from hull fouling of recreational vessels in Mediterranean marinas. Interestingly, S. walkeri was first reported from the Macaronesia biogeographical region only two years ago; at Funchal marina, presumably introduced by means of recreational boating from populations in the Canary Islands (Spain) or the Madeira island system itself (see Ramalhosa et al., 2017). Considering that S. walkeri was already present in Marocco and Mauritania (northwestern Africa) since the early 1980s (Jacobs, 1987), it could have introduced to marinas across Madeira, Canary Islands and the Strait of Gibraltar years ago, even though it was detected only now. An interspecific competition pressure among S. walkeri and its congener S. serratum has been suggested for the Lagoon of Tunis (Ben Amor, Rifi & Ben Soussi, 2015), but further studies are necessary to evaluate its biological impact in the Iberian Peninsula.
It was reported only recently from the Iberian Peninsula, from samples collected from fouling assemblages in marinas of the eastern coast in 2016 (Ulman et al., 2017). Nevertheless, our study proves that P. japonica has been present in Barcelona and Valencia (eastern Iberian Peninsula) at least since 2011. Ulman et al. (2017) suggest this species to be 'polyvectic' (meaning it has been transported by multiple mechanisms, according to Cohen (1977), Carlton & Ruiz (2005)), and points at recreational boating as vector for its secondary spread across the Mediterranean Sea. Our data supports this hypothesis, since P. japonica was found in Barcelona, Benicarló and Mallorca (Balearic Islands), which are popular destinations for vessels cruising the western Mediterranean in between Barcelona to the West and northwestern Italy to the East (Ulman, personal communication). In 2014, two individuals of P. japonica were found within the Strait of Gibraltar's vicinity, in Chipiona rocky shores (Cádiz) (Cabezas, pers.comm); and three years later, it was abundant in marinas located in Cádiz Bay. Cádiz is a great hotspot for both international commercial shipping and pleasure craft, as well as a center for aquaculture production, including the Japanese clam Ruditapes philippinarum (Junta de Andalucía, 2014). Just as in Italy, this clam was intentionally introduced for commercial use in Spain in the 1970s. Despite having conducted several samplings in Cádiz marinas before 2014, this species was never found to be present before that date. On one hand, it is possible that P. japonica has arrived to Cádiz bay due to shellfish transfers since the 1970s, but have remained unnoticed and located only in aquaculture facilities instead of spreading to nearby marinas, thus undetected during sampling campaigns. On the other hand, it seems more likely that it spread via recreational boating from the Italian Peninsula to the eastern Iberian Peninsula (present in 2011), and later on to Cádiz marinas (present in 2017). It is to be noticed that P. japonica was not present in the bryozoan B. neritina in Puerto América marina in 2011; but it was found associated to the same host in 2017. This fact supports this record as a new arrival of NIS into a particular region, and thus represents a Marine Strategy Framework Directive indicator to establish Cádiz Bay as a hotspot for marine introductions, following Olenin et al. (2016).

CONCLUSIONS
We have reported a distribution range extension for all exotic isopod species present in the studied areas, some of them proving to be polyvectic and well established in marinas. The next step is to evaluate their potential biological, social and economical impact, however, there are gaps of knowledge that hamper this task. Baseline studies delving into the ecology of all these species (i.e. role as prey-predator in the trophic chain, habitat selection, role in their ecosystem functioning) are of great need in here (see Table 1 Blackburn et al., 2014). Although none of the NIS found in the present study were found in the extensive survey of natural coastal habitats by Guerra-García et al. (2012), future surveys including natural areas would be necessary to detect a potential secondary spread into these habitats.
There is a critical problem that keeps recurring and needs to be reduced: the lags in detection of a new arrival. In many occasions, much time lapse between the initial introduction and the report of it, with a bias for noticing invaders only after they become an abundant nuisance, due to inadequate monitoring or lack of taxonomic expertise (see Crooks, 2005). This happens often in the case of small-sized and scarcely studied organisms, which often remain overlooked until they reach high densities and the spreading process is advanced. But small does not mean ''unimportant'' (Carlton, 2011) and, since biological invasion processes are ''irritatingly idiosyncratic'' (Richardson et al., 2000), exotics can exist in relatively low numbers before exploding. This means we risk underestimating the potential impact of taxa like the Order Isopoda that, as shown in the present study, can subsequently spread across additional marinas within a short timeframe.
In order to be ready for decision making and implementation of invasion control, as well as assessment of future arrivals, prevention is the key; and all this starts with building comprehensive data on the presence and distribution range of exotic species, especially on new arrivals (see Bishop & Hutchings, 2011;Groom et al., 2015;Olenin et al., 2016). We consider this account serves as documentation and update about the marine exotic isopods dwelling in the Iberian Peninsula, a hotspot for exotics arrival; as well as drawing attention to these overlooked organisms and the risk of recreational boating as vector for introduction and secondary spread.