Crustacean Biology

Journal of Crustacean Biology

Journal of The Crustacean Society

Crustacean Biology Journal of Crustacean Biology (2018) 1–6. doi:10.1093/jcbiol/ruy076

Alan Deidun1, , Arnold Sciberras2, Justin Formosa3, Bruno Zava4, Gianni Insacco5, Maria Corsini-Foka6 and Keith A. Crandall7, 1Department

of Geosciences, University of Malta, Msida, MSD 2080 Malta; Kingdom Ltd. 136, Ditch St., Paola, PLA 1234 Malta; 3270 Liedna St., Fgura, FGR 1030 Malta; 4Wilderness Studi Ambientali, Via Cruillas, 27, 90146 Palermo, Italy; 5Museo Civico di Storia Naturale, via degli Studi 9, 97013 Comiso (Ragusa), Italy; 6Hellenic Centre for Marine Research, Institute of Oceanography, Hydrobiological Station of Rhodes, Cos Street, 85100 Rhodes, Greece; and 7Computational Biology Institute, The George Washington University, 45085 University Drive, Ashburn, VA 20147, USA & Department of Invertebrate Zoology, Smithsonian Institution, Washington, DC 20013, USA 2Animal

Correspondence: A. Deidun; e-mail: [email protected] (Received 22 May 2018; accepted 13 August 2018)

ABSTRACT Invasive species can cause significant changes in local and regional ecologies, especially in freshwater ecosystems. It is thus important to monitor and document the spread of non-indigenous species to such habitats as such information can be critical to preserving habitats and species. We document the spread of the red swamp crayfish Procambarus clarkii (Girard, 1852) (Cambaridae), a highly invasive non-indigenous species, in Malta and south Sicily. We also document the first records of other non-indigenous decapods important in the pet trade or in aquaculture, Procambarus virginalis Lyko, 2017 (Cambaridae), Pontastacus leptodactylus (Eschscholtz, 1823) (Astacidae), Cherax quadricarinatus von Martens, 1868 (Parastacidae), Pacifastacus leniusculus (Dana, 1852) (Astacidae), and Atyopsis moluccensis (De Haan, 1849 (Atyidae) from freshwater localities in the Maltese Archipelago and Cherax destructor Clark, 1936 (Parastacidae) from southeastern Sicily. The study provides recommendations on the adoption of control measures by the competent national authorities with respect to these non-indigenous species. Key Words: aquaculture, freshwater habitats, intentional release, introduced species, pet trade

INTROD U CTION By virtue of their large adult size, high abundance and population biomass, and omnivory, freshwater crayfishes represent an ideal model for demonstrating the impact of non-indigenous species on ecosystem services (Lodge et al., 2012). Monitoring the spread of invasive species and their impact on native communities is essential for effective conservation practices (see International Union for Conservation of Nature (IUCN) Red List criteria; http://www. iucnredlist.org/). The crayfish genus Procambarus Ortmann, 1905 (Cambaridae), is highly diverse, with over 167 species native to North and Central America (Hobbs, 1984; Crandall & De Grave, 2017; Lyko, 2017). Many species of Procambarus have been intentionally introduced to regions outside their native range (primarily for aquaculture or for the pet trade sector), where they are considered as invasive species in the wild (Savini et al., 2010). One of the most popular farmed species of Procambarus is the red swamp

crayfish, Procambarus clarkii (Girard, 1852), first recorded in Europe in southern Spain in 1973 (Ackefors, 1999; Souty-Grosset et al., 2006), from where the species has spread to aquatic habitats across the entire Iberian Peninsula and large portions of northwestern and central Europe (Kouba et al., 2014). Procambarus clarkii has so far been recorded from sixteen different European territories (Souty-Grosset et al., 2016). The species, which has been described as a ‘paradigmatic’ invader of freshwater ecosystems (Aquiloni et al., 2010), was first recorded in Italy from the Piedmont region in the early 1990’s (Delmastro, 1992), and subsequently introduced to the entire Italian Peninsula and to the island of Sardinia (Aquiloni et al., 2010). The first record of an established population of Procambarus clarkii in Sicily dates back to 2002 from the Lake Preola e Gorghi Tondi Nature Reserve in the province of Trapani in western Sicily (D’Angelo & Lo Valvo, 2003). A second population of the same species was recorded nine years later at the

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Invasion by non-indigenous freshwater decapods of Malta and Sicily, central Mediterranean Sea

A. D EID UN ET AL.

MAT ERI AL S AND MET HO DS Reports of a crayfish species apparently new to the Maltese Archipelago were communicated to the authors over social media in July 2016. This discovery prompted us to embark during summer 2016 to spring 2017 a systematic census of all the major watercourses and large freshwater reservoirs in the Maltese Archipelago followed by a spot check in two localities on the island of Malta (Bahrija, Ghajn Zejtuna; Fig. 1) in February 2018 to verify the putative occurrence of Procambarus clarkii on a site as reported by members of the public. Each targeted watercourse and reservoir was comprehensively surveyed for the occurrence of crayfish individuals by two observers walking along the margin of the entire length of the watercourse. This was achieved through a semi-quantitative assessment coupled the diel and nocturnal observation of possible trophic relationships involving the crayfishes. Individuals were either sampled directly by hand or through the deployment of baited traps where individuals were not encountered during the first visit to a particular location (see Crandall, 2016). Farmers and owners of freshwater reservoirs as well as individuals importing aquatic species for commercial purposes in Malta were unofficially interviewed on condition of anonymity. Crayfish individuals were encountered at all the major freshwater sites visited. Observations on the behaviour and ecological interactions of the monitored crayfishes were made throughout the day at each of the surveyed sites by workers stationed at concealed locations. Faunal species preyed upon by or preying upon the monitored non-indigenous crayfish species were identified in situ through visual examination. Because P. clarkii had been previously recorded from the western half of Sicily, a survey of rivers and streams on the eastern half of Sicily was undertaken at the same time as the Malta survey Identification of species followed Holdich & Vigneux (2006) and the same Malta sampling methodology adopted.

RE SULT S Maltese Archipelago The 2016–17 surveys recorded specimens of Procambarus clarkii and Procambarus virginalis (Fig. 1 and Supplementary material Figs. S2, S3, Table S1. Both species of Procambarus spp. were observed to prey and feed on the gastropod Cornu aspersum (Müller, 1774), tadpoles of the painted frog Discoglossus pictus Otth, 1837 and of Bedriaga’s frog Pelophylax bedriagae Camerano, 1882, adults of the western mosquito fish Gambusia affinis (S. F. Baird & Girard, 1853), adults of the scarlet darter nymph Crocothemis erythrae (Brulle, 1832), and larvae of the lesser drone fly Eristalinus taeniops (Wiedemann, 1818). Most of the feeding by both crayfish species took place early in the morning, with the crayfishes also observed scavenging under reeds and vegetation but in a largely inactive state later during the day. When disturbed, individuals of Procambarus sp. were observed to retreat in the mud by beating the abdomen backwards. 2


the species are very popular in the aquarium trade in Australia (Beatty et al., 2005). The main goal of this study was to determine the occurrence and distribution of non-native decapods in aquatic ecosystems in the Maltese Archipelago, given that these had never been comprehensively investigated and that they represent a high ecological risk. We also made preliminary observations on the ecology of Procambarus clarkii in the Maltese Archipelago and update the known distribution of non-indigenous crayfish species in Sicily. Our study also aimed to set the baseline for monitoring these invasive species in the Maltese Archipelago and their impact on local freshwater habitats. It also adds to our knowledge understanding of the spread of these non-indigenous species across the world.

Rosamarina Reservoir in the province of Palermo, northwestern Sicily (Di Leo et al., 2014). Despite a number of attempts to eradicate these population, the species still thrives in the area. A citizen science campaign (the Sicilian Procambarus Working Group, or SPwg) is also involved in tracking the spread of the genus in Sicilian freshwater sites (Faraone et al., 2017). The first record of Procambarus clarkii from Malta was documented from a valley between September 2016 to spring 2017 (Vella et al., 2017). The invasive potential of the species is also acknowledged through its inclusion, along with forty-eight other species (including Procambarus virginalis Lyko, 2017 (Cambaridae) and Pacifastacus leniusculus (Dana, 1852) (Astacidae), as of August 2017, in the Invasive Alien Species (IAS) list slated for direct intervention by Regulation 1141/2016 of the European Union. The invasive potential of Procambarus virginalis (known as marmorkrebs in Malta), is impressive given its obligate parthenogenetic reproduction, which is unique for a decapod species (Scholtz et al., 2003). In Europe, the species first appeared in Germany in the 1990’s through the aquarium trade, where it is still a popular species (Chucholl & Wendler, 2017). The species has since spread to large swathes of Europe, including Italy (Vojkovská et al., 2014) and, most recently, Romania (Pârvulescu et al., 2017). The species has also been recorded in Madagascar (Jones et al., 2009) and Japan (Faulkes et al., 2015). The Galician or narrow-clawed crayfish Pontastacus leptodactylus (Eschscholtz, 1823) (Astacidae) (see updated classification in Crandall & De Grave, 2017) has a widespread distribution, known from most of continental Europe, eastern Russia, and even the Middle East. It is considered indigenous to the eastern portion of its current range, having been introduced in the past to western Europe (Machino & Holdich, 2006). This species complex prefers fresh running water (rivers) but can also be found in standing fresh water (lakes) and brackish water (lagoons and estuaries) and its populations have declined in western areas in recent years due to crayfish plague (Aphanomyces astaci Schikora, 1906) as well as competition with other crayfish species (Gherardi & SoutyGrosset, 2010). The bamboo shrimp Atyopsis moluccensis (De Haan, 1849) has a broad distribution, extending from Sri Lanka to Thailand, Malaysia, Indonesia, and the Philippines, inhabiting fast-flowing rivers, frequently in upland areas (De Grave et al., 2013). The species is common in ornamental aquarium inventories. The Australian redclaw Cherax quadricarinatus von Martens, 1868 is native to freshwater habitats in tropical northern Australia and Papua New Guinea, even though its popularity in aquaculture (mainly due to its large size and suitability for farming) has resulted in its translocation around the world (Ahyong & Yeo, 2007). As a result of this trade, the species has established wild populations in South Africa, Swaziland, Israel, Singapore, Mexico, and Puerto Rico (du Preez & Smit, 2013 and references therein) as well as from eastern Slovenia in central Europe (Jacklic & Vrezec, 2011). The species has also been previously reported from confined systems (e.g., rearing facilities) on Sicily by a number of authors (e.g., D’Agaro et al., 1999; Marino et al., 2014). The signal crayfish Pacifastacus leniusculus (Eschscholtz, 1823) is native to the Pacific Northwest of the United States and is considered a major invasive species in many parts of Asia, Europe, and elsewhere in the United States (Larson et al., 2012 and references therein). The species has been introduced in Scandinavia to compensate for declines in populations of the native European crayfish Astacus astacus (Linnaeus, 1758) (Soderback, 1995). The common yabby Cherax destructor Clark, 1936 is native to eastern Australia from southern Queensland and the Northern Territories to Tasmania. The taxonomic status of the species, which probably represents a species complex, is still under debate (Souty-Grosset et al., 2006). Although it is listed by the IUCN as a vulnerable species, wild populations seem to have expanded into new habitats created by reservoirs and farm dams. Blue forms of

N O N - I N D I G E N O US D E C APO D INVAS IO N OF MALTA AND S ICI LY

Wied Qlejgha watercourse, respectively, on the dates specified in Supplementary material Table S1 and Fig. S7.

A number of mammals, notably the long-tailed field mouse (Apodemus sylvaticus) (Linnaeus, 1758), the brown rat (Rattus norvegicus) (Berkenhout, 1769), and the North African hedgehog (Erinaceus algirus) (Lereboullet, 1842), were observed to prey on individuals of Procambarus spp. in shallow, restricted water where the crayfishes were easily accessible from land. Bedriaga’s frog (Pelophylax bedriagae), a non-native species which is abundant at Ghajn il-Papri in Gozo (Sciberras & Schembri, 2006), was also recorded from a second pond, il-Hofra, on the island of Gozo, where it has been present since 2010. The frog was observed feeding on numerous sub-adults of Procambarus virginalis and on subadults of Procambarus clarkii at Ta’ Sarraflu pond, Gozo. The common chameleon Chamaeleo chamaeleon (Linnaeus, 1758) and the praying mantis Mantis religiosa (Linnaeus, 1758) occasionally preyed on Procambarus individuals along the margins of these ponds. Malta’s Environmental and Resources Authority (ERA) has been alerted about the localities supporting the five reported nonindigenous crayfish species NICS and a preliminary eradication programme has been started. This programme is supplemented by the unilateral collection of crayfishes by the public through the use of traps, to be used as fishing bait, even though this practice is forbidden within the revised European Union’s Regulation 1141/2016 on IAS. This practice unearthed the occurrence of yet another non-indigenous crayfish species in Malta, the signal crayfish Pacifastacus leniusculus (Dana, 1852), of which an estimated few hundred individuals were captured at Wied Qlejgha (Supplementary material Table S1 and Fig. S4). Three additional non-indigenous decapod species were found during our surveys. One specimen of the bamboo shrimp Atyopsis moluccensis (Supplementary material Fig. S5) and 50 specimens (20 collected) of the narrow-clawed crayfish Pontastacus leptodactylus (Supplementary material Fig. S6) were recorded on October 2016 from the same water reservoir at Pembroke, island of Malta), which was also inhabited by individuals of Procambarus virginalis. Individuals of the Australian redclaw crayfish Cherax quadricarinatus were observed in the Nadur pond (six individuals) and in the

Sicily Our survey also resulted in new records of P. clarkii (Fig. 2) from Sicily (Table 1), extending the previous western distribution of the species to the east of the island. Also observed was the occasional sale of P. clarkii at the main fish market in Catania. A new non-indigenous crayfish species was reported from Sicily. Four individuals of the common yabby, Cherax destructor (Supplementary material Fig. S8) were captured by one of us (GI) on 8 August 2017 (Table 1). The specimens consisted of two males (total length 115 mm, 45 g and 105 mm, 30 g, respectively) and two females (145 mm, 119 g and 130 mm, 94 g, respectively). All specimens were deposited in Museo Civico di Storia Naturale di Comiso, Ragusa, Italy (MSNC 4558).

DI SC US SI O N The introduction of non-indigenous crayfish species into European markets was driven by the need to compensate for the decline in indigenous crayfish species, such as the European crayfish Astacus astacus. The decline in their numbers, at least in Italy, had been since the late nineteenth century, mainly due to outbreaks of the crayfish plague (Ninni, 1865). The introduction of P. clarkii (as Cambarus clarkii) was recommended as one of the species for intentional introduction to the Italian market in view of its resistance to epidemics (Aquiloni et al., 2010). The adoption of some form of measures to limit non-indigenous species spread is especially important considering that some of the Maltese localities harbouring the Procambarus species are also known as some (e.g., the Bahrija [Malta] and Wied il-Lunzjata [Gozo] watercourses) of the last haunts for critically-endangered aquatic species, including the brachyuran crab Potamon fluviatile (Herbst, 1785) (Potamidae) and frog Discoglossus pictus (Otth, 1837), the only amphibian indigenous to Malta. Another important 3


Figure 1. Distribution of the records of non-indigenous decapod species reported from the Maltese Archipelago; 1, Ghajn Zejtuna; 2, Bahrija; 3, Fiddien/ Wied Qlejgha; 4, Wied l-Isperanza; 5, Pembroke (all in Malta); 6, Nadur; 7, Ghajn il-Papri; 8, Il-Hofra; 9, Wied il-Lunzjata; 10, Sarraflu (all in Gozo).

A. D EID UN ET AL.

Table 1. New records of Procambarus clarkii and Cherax destructor from Sicily, Italy. Reference number in Figure 2

Location (province)

Coordinates

Year of record

1

Santa Rosalia Reservoir (Ragusa)

36.974803°N, 14.776731°E

2015

2

Venetico artificial ponds (Messina)

38.195686°N, 15.384248°E

2015

3

Margi Stream (Siracusa)

37.214115°N, 14.891158°E

2015

4

San Leonardo River (Siracusa)

37.342701°N, 15.081742°E

2015

5

Gornalunga River (Catania)

37.388865°N, 15.078404°E

2016

6

Simeto river mouth (Catania)

37.400072°N, 15.064382°E

2016

7

Costanzo Stream (Siracusa)

37.252467°N, 14.912453°E

2016

8

Costanzo Stream (Siracusa)

37.257818°N, 14.920217°E

2017

Our study reports the first Malta record of wild populations of Procambarus virginalis, Pacifastacus leniusculus, Pontastacus leptodactylus, Cherax quadricarinatus, and Atyopsis moluccensis, and the first Sicily record of Cherax destructor. Procambarus virginalis is expected to share most of the traits mentioned above for Procambarus clarkii, rendering the adoption of eradication programmes for all five non-indigenous crayfish species even more pressing. The invasive Pacifastacus leniusculus was implicated in the collapse of a federally-listed three-striped stickleback species pair on Vancouver Island, Canada (Behm et al., 2009), whilst, the species is reported as having led to the competitive displacement of native populations of the white-clawed crayfish Austropotamobius pallipes (Lereboullet, 1858) in the UK (Dunn et al., 2009). Cherax quadricarinatus, like Procambarus clarkii, is reported as being capable of establishing naturalised, breeding populations in introduced areas, even producing offspring, and, at least in South Africa, as a carrier of a non-indigenous temnocephalan flatworm parasite, which might infect local freshwater decapods (du Preez & Smit, 2013). Cherax destructor is an r-selected species considered a highrisk species by Tricarico et al. (2010) due to its high resistance to environmental extremes, its ability to cope with global warming, and its severe impacts on other species and habitats, as implied by its epithet. We also document the possible biological control of Procambarus clarkii by a number of mammals, which unfortunately is offset by the high reproductive potential of the crayfish. Aquiloni et al. (2010) also documented the predation by the European eel Anguilla anguilla (Linnaeus, 1758) on Procambarus clarkii.

consideration is the invasive potential of these non-indigenous crayfishes and that these species apparently managed to persist the arid summer of 2016, when many transient freshwater bodies on the islands dried up. The crayfishes reproduced in the autumn, as evidenced by the occurrence of egg-bearing females and of subadult stages in autumn 2016 and 2017 with the onset of the wet season. A flood triggered by heavy rainfall in early February 2018 was observed to extend the local distribution of Procambarus clarkii on the islands, underscoring the behavioural plasticity of the species. Jaklič & Vrezec (2011) reported the persistence of populations of C. quadricarinatus in water bodies having a temperature as high as 41 °C, with the majority of sexually mature individuals being restricted to water bodies with temperatures of 21 °C to 31 °C. Besides the Bahrija and Wied il-Lunzjata ponds, the Fiddien and Wied il-Qlejgha ponds should also be priorities for management measures by local authorities because of the large populations of at least three non-indigenous crayfish species (Procambarus clarkii, Cherax quadricarinatus and Pacifastacus leniusculus), which might be attributed to the easy accessibility by the public and to the persistence of pockets of freshwater throughout the year. The high invasive potential of P. clarkii has led the species to being regarded as an r-selected species (Gherardi, 2006), characterised by early maturity at small body size, rapid growth rates, large numbers of offspring at a given parental size, and relatively short life spans. It is also plastic in its life cycle, able to disperse widely and to tolerate environmental extremes. It displays generalist and opportunistic feeding habits, consuming macrophytes and preying on amphibians (Gherardi, 2006). 4


Figure 2. Updated distribution of Procambarus clarkii on Sicily (A and B circles, records by D’Angelo & Lo Valvo, 2003 and Di Leo et al., 2014; circles, new records). The triangle indicates the site of the first record of Cherax destructor for the island.

N O N - I N D I G E N O US D E C APO D INVAS IO N OF MALTA AND S ICI LY trade should also be introduced in order to enable more effective monitoring of the entry of non-indigenous species.

We were unable to use molecular tools for taxonomic identification. This shortcoming advises caution, especially with respect to Procambarus virginalis, whose genetic identity is confounded by possible hybridization (Martin et al., 2010), and to Pacifastacus leniusculus, which might represent a species complex rather than a single species (Larson et al., 2012). The introduction of Pacifastacus leniusculus to a watercourse in eastern Sicily is putatively attributed to the opening of commercial culturing facilities for C. quadricarinatus at the same location given the popularity of this species in aquaculture (D’Agaro et al., 1999; Marino et al., 2014), with C. destructor being apparently erroneously imported for farming, only to be partially discarded through release into the wild once the misidentification was detected. The non-indigenous crayfish species documented herein belong to three different families (Cambaridae, Astacidae, and Parastacidae) and originate in widely-disparate geographical regions, including southeastern and northwestern United States and northern Australia. The putative ecological impact of these crayfishes is compounded by a putative ecotoxicological effect. Some studies (e.g., Bellante et al., 2015) have shown that P. clarkii is involved in the transfer of toxins and heavy metals to higher trophic levels. The trade of aquarium species and the marketing of crayfishes for fish and human food are the principal pathways responsible for the introduction and establishment of non-native crayfishes in Europe (Kouba et al., 2014). Crayfishes can also be inadvertently introduced as live bait for angling purposes. We observed Procambarus individuals in watercourses and water reservoirs that are not connected to the watercourse network on the islands. This disparate distribution across the Maltese Archipelago of the four non-indigenous species reported suggests that the species have been released repeatedly into the wild, at least in the isolated reservoirs, making escape into the wild as an introduction pathway highly unlikely. This is supported by the species being imported for the aquarium trade as well as being so far featured in the menu of one restaurant in Sliema, Malta. At least three other non-indigenous species (Procambarus virginalis, Atyopsis moluccensis, and Pontastacus leptodactylus) in the same water reservoir at Pembroke, Malta. While Pontastacus leptodactylus is being intentionally introduced for human consumption in some countries, we consider it highly likely that it was introduced to Malta through the aquarium trade given the unpopularity, as yet, of the consumption of crayfish as food in Malta. An introduction for human consumption cannot be completely discounted given the absence of a bright colouration in this species, which reduces its value for the aquarium trade when compared to other non-indigenous crayfishes. Atyopsis moluccensis is a popular aquarium freshwater shrimp, both in aquarium shops and on online catalogues (Lipták & Vitázková, 2015). It survives in small aquaria, it has an appealing colouration, and is non-aggressive. Contrary to the non-indigenous crayfishes, the shrimp is not considered to pose a significant risk to native aquatic ecosystems due its non-persistence outside water, thus making its survival during the dry season only possible in artificial bodies of water, including ponds and reservoirs. The semi-arid nature of the central Mediterranean, where watercourses and valleys are generally characterised by seasonal water flows only, are not expected to pose a similar hurdle to the persistence of the non-indigenous crayfishes due to their ability to survive prolonged periods of drought. The development of a facility for the commercial farming of crustaceans on the island of Malta is also being considered by a private enterprise, rendering the adoption of a precautionary approach even more pressing, including the adoption of stringent stocking provisions to ensure complete isolation of the cultured individuals from natural ecosystems. Better regulation of the importation of freshwater (and marine) species for the aquarium

SUPPL EMENTARY MAT ER IAL

ACKNOWLEDGMENTS We thank Jeffrey Sciberras, Miguel Vassallo, Johann Spagnol, and Nick Dobbs for their assistance in the field work, as well as Antonino and Francesco di Maiuta, two Catania, Sicily fishermen for invaluable information concerning sales of the red crayfish in the Catania, Sicily fish market and to Agatino Reitano, Vincenzo Cerruto, Salvatore Todaro, and Piero Armenia for their contribution during field research in Sicily. We are also grateful to David Diacono for assisting in the identification of A. moluccensis, as well as Darrin Stevens and other ERA (Environment and Resources Authority) staff for their guidance on European and Maltese legislation concerning the control of invasive alien species.

REFERENCES Ackefors, H.A. 1999. The positive effects of established crayfish introductions in Europe. In: Crayfish in Europe as alien species (How to make the best of a bad situation?) (F. Gherardi & D.M. Holdich, eds.). Crustacean Issues, 11: 49–62. Ahyong, S.T. & Yeo, D.C. 2007. Feral populations of the Australian redclaw crayfish (Cherax quadricarinatus von Martens) in water supply catchments of Singapore. Biological Invasions, 9: 943–946. Aquiloni, L., Brusconi, S., Cecchinelli, E., Tricarico, E., Mazza, G., Paglianti, A. & Gherardi, F. 2010. Biological control of invasive populations of crayfish: the European eel (Anguilla anguilla) as a predator of Procambarus clarkii. Biological Invasions, 12: 3817–3824. Beatty, S., Morgan, D. & Gill, H. 2005. Role of life history strategy in the colonisation of Western Australian aquatic systems by the introduced crayfish Cherax destructor Clark, 1936. Hydrobiologia, 549: 219–237. Behm, J.E., Ives, A.R. & Boughman, J.W. 2009. Breakdown in postmating isolation and the collapse of a species pair through hybridization. American Naturalist, 175: 11–26. Bellante, A., Maccarone, V., Buscaino, G., Buffa, G., Filiciotto, F., Traina, A., Del Core, M., Mazzola, S. & Sprovieri, M. 2015. Trace element concentrations in red swamp crayfish (Procambarus clarkii) and surface sediments in Lake Preola and Gorghi Tondi natural reserve, SW Sicily. Environmental Monitoring and Assessment, 187(7) [doi: 10.1007/ s10661-015-4613-4]. Chucholl, C. & Wendler, F. 2017. Positive selection of beautiful invaders: long-term persistence and bio-invasion risk of freshwater crayfish in the pet trade. Biological Invasions, 19: 197–208. Clark, E. 1936. The freshwater and land crayfishes of Australia. Memoirs of the National Museum, 10: 5–57, pls. 1–11.

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Supplementary material is available at Journal of Crustacean Biology online. S1 Table. Summary of all records made in the Maltese Archipelago for the non-indigenous decapod species recorded. S2 Figure. Specimen of Procambarus clarkii caught at Fiddien, island of Malta. S3 Figure. Two voucher specimens of Procambarus virginalis from a water reservoir in Pembroke, island of Malta. S4 Figure. Specimens of Pacifastacus leniusculus from Wied Qlejgha watercourse, island of Malta. Photo by David Gove. S5 Figure. Dorsal view of the single individual of Atyopsis moluccensis from the island of Malta. S6 Figure. Dorsal view of a number of individuals of Pontastacus leptodactylus from the island of Malta. S7 Figure. Dorsal (A) and ventral view (B) of a dead specimen of Cherax quadricarinatus photographed at Nadur, island of Gozo. S8 Figure. Dorsal view of one of the four individuals of Cherax destructor from Sicily, Italy.

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