Inventory of alien and cryptogenic species of the Dodecanese (Aegean Sea, Greece): collaboration through COST action training school

The Dodecanese region has a high prevalence of marine alien species due to its close proximity to the Suez Canal and associated Suez shipping lanes, as well as its location at biogeographical border between sub-tropical and tropical biota. This region is therefore very important for the early detection of alien species entering the Mediterranean Sea via the Suez Canal and it is imperative that monitoring of alien species is continued in order to assess the levels of biological invasion. We present results of marine alien surveys, carried out in April 2014 on the island of Rodos. Surveys were performed by a team of marine taxonomic experts and students as part of an EU wide training school, coordinated by the COST Action TD1209 “Alien Challenge”. A variety of survey methods were employed to cover a number of coastal habitats. These included: rapid assessment surveys of epibiota on artificial structures in harbours, rapid assessment snorkelling surveys of biota on sublittoral bedrock, and quantified fishing surveys (both boat-seine and trammel net fishing methods). A total of 33 alien and cryptogenic species were recorded across all the survey techniques. Of these species, 9 represented first records for Rodos: the foraminiferan Amphisorus hemprichii , the polychaetes Branchiomma bairdi , Dorvillea similis , Hydroides dirampha and Pseudonereis anomala , the molluscs Aplysia parvula , Chama pacifica and Septifer cumingii , and the bryozoan Hippopodina feegeensis . Of note the record of the Lessepsian invader Dorvillea similis represents the second record in the Mediterranean Sea. Alien fish species represented a small but notable proportion of the diversity, biomass and number of individuals in fishing catch of both fishing methods. All alien fish species observed were already known to be present in Rodos. The addition of species firstly recorded in this study brings the total number of marine alien and cryptogenic species in the Dodecanese region up to 129 species. The vast majority of these alien species have entered unaided via the Suez Canal, but an increasing number have been introduced through hull fouling or ballast water transfer from shipping. The results highlight the value of conducting marine alien surveys with teams of a diverse range of taxonomic expertise, both in its scientific output and student training.


Introduction
Invasive alien species (IAS) threaten biodiversity, ecosystem services, human health, well-being and the economy . The European Commission highlights the importance of Information Systems  to support European policies on IAS, especially the new Regulation 1143/2014, and specifically effective early warning, rapid response, prevention, and control of IAS. The COST Action TD1209 "ALIEN Challenge" aims to enhance gathering and sharing of knowledge on IAS through a network of experts (www.cost.eu/COST_Actions/fa/Actions/TD1209) engaged in a variety of activities. Training schools provide a mechanism within the framework of COST for capacity building and knowledge exchange. The first training school of the COST Action "ALIEN Challenge" focused on marine survey skills and alien species identification. The island of Rodos, Greece has excellent local facilities [Hydrobiological Station of Rhodes (HSR) of the Hellenic Centre for Marine Research] and was chosen as the location for the training school.
Located in the eastern Mediterranean region, the island of Rodos (in the Dodecanese islands complex) is heavily affected by climate change and intensification of human activities and is strongly impacted by biological invasions (Raitsos et al. 2010;Pancucci-Papadopoulou et al. 2012;Tsiamis 2012). In fact, its subtropical environment is favorable to native thermophilic biota (Papaconstantinou 2014) and also to tropical or subtropical alien biota (Corsini-Foka et al. 2014). The vast majority of aliens occurring in the wider Dodecanese area are warm-water species, mainly of Red Sea/Indo-Pacific origin and many of them are well established and integrated in the shallow water biocommunities and food web (Zenetos et al. 2009a(Zenetos et al. , 2011Pancucci-Papadopoulou et al. 2012).
The training school lasted three days, including introductory lessons on biological invasions, field work, laboratory work and a dissemination event for local stakeholders. The aim of the present work is to disseminate the outcome of the surveys conducted during the training school. Surveys were performed with various techniques along the coasts of the island, allowing (1) identification of alien species, (2) assessment of their distribution, and (3) update of the list of alien species occurring in the wider area. Cryptogenic species, defined as "species that cannot be reliably demonstrated as being either introduced or native" (Carlton 1996) and pseudoindigenous species, defined as "introduced species that are mistakenly considered as native (indigenous or endemic) to a location" (Carlton 2009) were taken into account, according to a precautionary approach.

Materials and methods
The first training school of the COST Action "ALIEN Challenge" was hosted by the Hellenic Centre for Marine Research (HCMR) in Rodos. There were 19 trainees and 13 trainers. Survey was performed on the 10 th of April 2014, following a day of intensive training by the trainers Elizabeth Cook (EJC), Melih Ertan Çinar (MC), Carlo Froglia (CF), Daniel Golani (DG), Stelios Katsanevakis (SK), Sami Lakkis (SL), Helen Roy (HR), Elena Tricarico (ET), Konstantinos Tsiamis (KT), Ante Zuljevic (AnZ), Argyro Zenetos (AZ), Maria Corsini-Foka (MCF), with expertise on marine macrophytes, polychaetes, molluscs, decapods, plankton, fish, alien management, European policies and legislation on IAS. The trainees were divided into 8 groups led by at least one trainer. Four different methods were used by the groups at various locations in the city of Rodos and the surrounding coastline.

Area of study
The island of Rodos (in the Dodecanese Archipelago) is situated in the southeastern Aegean Sea, at the limits of the northwestern Levantine Sea (Figure 1). This is an interesting oceanographic position, due to the intense hydrological phenomena of the surrounding marine area (Napolitano et al. 2000;Pancucci-Papadopoulou et al. 2012).
Seawater temperature and salinity at the surface (date 10/04/2014) were approximately 18.5-19 o C and 39.2 psu respectively; air temperature was 18-20 o C and winds of 2-3 on the Beaufort scale with a South-Southeast direction (http://poseidon.hcmr.gr).

Experimental fishing: Boat-seine method
The boat-seine method is a traditional technique which has been used in the Greek coastal fishery until it was prohibited in June 2010, when the European Council Regulation (EC) No. 1967No. /2006 was applied across Greek territorial waters. Special permission was granted to allow the use of this technique for the scientific and educational purposes of the training school. Bottom seine fishing is an ideal method for this type of scientific survey because it takes a short amount of time and targets the fish assemblage at the depth range usually colonized by alien species in the area (Corsini-Foka  . It was expected to obtain a larger biomass and a wider spectrum of species than those achieved with the trammel net method, so enabling the ratio of alien/native species to be assessed. The boat-seine method (Danish method) was conducted off Karakonero (Station A), a small embayment on the South-southeast of Rodos' town ( Figure 1; Table 1). The Karakonero fishing ground was chosen because of the absence of currents, the proximity to the HSR and the satisfactory yields it can produce in terms of quantity and diversity of organisms, according to local information from fishermen. The area is characterized by soft, sandy to muddy bottoms, interrupted by hard substrata and Posidonia oceanica meadows. A 12-m professional trawling fishing boat was hired to collect the samples. Trawl mesh size increased from 8 mm at its lower bound (cod end), to 11 mm, 12 mm, 32 mm and finally 1 m at its upper bound end. Fishing took place during the daytime at a depth of 20-40 m. The weather conditions were favourable, but unfortunately the trawl nets were partially destroyed during the operation by a rock or a metal object probably used for anchorage and the yield was confined to a few kilograms. A second haul was therefore not possible. Nevertheless, specimens collected were immediately transported either in styrofoam boxes or live in seawater and were introduced into aquarium tanks at the facilities of the HSR. Fish samples were identified measured with calipers (0.1 mm accuracy) and weighed (0.1 g accuracy).
Material was also photographed.

Experimental fishing: Trammel net
The second fishing method used trammel nets. This type of fishing is also traditional in Greece, applied all year round whenever the weather is suitable, supporting many families throughout the coastal areas of the country.
Trammel net fishing took place at Faliraki, Station B ( Figure 1; Table 1). The area is characterized by soft, sandy bottom, interrupted by hard substratum and was chosen based on prior knowledge on its diversity and abundance of organisms. A 12-m professional fully equipped fishing boat was hired for the sampling at this site. Knot to knot mesh sizes of inner and outer nets were 32 mm and 130 mm respectively. Approximately, 3000 m of these nets were deployed in late afternoon on the 9 th April 2014 at depths of 7-19 m and retrieved in the early morning of the 10 th April 2014. All specimens were placed in plastic containers and transported to the facilities of the HSR. Fish samples were identified and weighed (0.1 g accuracy). Material was also photographed.  Table 1) by a team of 4-6 surveyors based on the rapid assessment survey technique (Ashton et al. 2006;Nall et al. 2015). A period of between 1-2 hours was spent surveying a wide variety of submerged structures at each site. All specimens were collected from a maximum depth of 0.5 m by hand. Specimens were either collected directly by hand or chisels were used to scrape encrusting organisms from the various substrates. These substrates typically included, submerged/floating ropes, boat fenders, tyres, electricity cables, pontoons, boat hulls and steel marina dock piles. Samples were preserved in 4 % formaldehyde and sea water and were transferred to HSR for further identification to species level, where possible.

Hard bottom sampling by snorkelling
Snorkelling was employed to collect benthic epifauna and flora taxa from depths of 0-2 m, on rocky substratum, at two sites: the Three Windmills station (Station H; Figure 1) and Faliraki (Station C; Figure. 1) ( Table 1). Samples were preserved in 4 % formaldehyde and sea water and some specimens were kept alive in portable, aerated aquariums and transferred to HSR for further identification down to species level where possible. Herbariums were also created, for flora identification. In situ underwater photos were taken in addition to ex situ photographs at the laboratories of HSR.
Species identification of common alien species was supported by the use of taxonomic literature and aided and confirmed by the expert trainers. Trainers also alerted participants to the occurrence of alien species not widely included in the literature and provided appropriate references for their identification.

Alien, cryptogenic and pseudoindigenous species
A total of 33 alien and cryptogenic species were sampled (7 macrophytes, 18 invertebrates and 8 fish species), of which 28 are of Indo-Pacific/Red Sea origin (Table 2). Nine species were completely new records for Rodos Island. The finding of the polychaete, Dorvillea similis (Crossland, 1924), represents the second record for the Mediterranean; the polychaete, Branchiomma bairdi (McIntosh, 1885), is new to Greek and Aegean waters; two other polychaetes, Hydroides dirampha Mörch, 1863 and Pseudonereis anomala Gravier, 1900, are (Table 2).
Detailed descriptions of the above mentioned alien foraminiferan, polychaetes, bryozoan and mollusc new to Greek waters and/or Dodecanese are given below, with notes on their distribution in the Mediterranean waters.
The fouling bryozoan Amathia verticillata (Delle Chiaje, 1822) was first recorded in Greek waters (including Dodecanese Islands, Rodos and Chalki) in the 1970s (Castritsi-Catharios and Kiortsis 1984). Amathia verticillata was first described in the Tyrrhenian Sea (Naples) under the name Hydra verticillata Delle Chiaje, 1822, and it was considered a native to the Mediterranean Sea, thus not accounted for in Mediterranean alien lists (Zenetos Table 2. Alien and cryptogenic species collected during COST Action samplings (see Table 1 (Galil and Gevili 2014). Here it is provisionally classified as 'pseudoindigenous' and has been included within the list. Station H, sampled by snorkelling, was the richest in term of alien species diversity (15 species), followed by Station C, where 13 alien species were collected by hand; a high number of alien species were also obtained using the boat-seine and trammel net techniques at Stations A and B, where 8 and 9 species were registered respectively ( Table 2). Notes: The test is discoidal and the circular and annual chambers are subdivided by septula into two separate layers of chamberlets. The apertures are located at the test periphery between the chamberlets in a double row.

Remarks on new findings for
Amphisorus hemprichii has often been confused with flat modifications of Marginopora vertebralis Quoy and Gaimard, or with microspheric Sorites orbiculus (Forskål, 1775) (Langer and Hottinger 2000). It is an epiphytic species reported in seagrasses, coralline red and filamentous green algae, and it hosts dinoflagellate symbionts (Leutenegger 1984). This species lives in high-energy environments showing a maximum depth distribution between 20 and 30 m and tolerates a wide range of temperatures (14-38 o C).
Distribution: It is a cosmopolitan species found in the Atlantic, Pacific and Indian Oceans and the Red Sea (Langer and Hottinger 2000). In the eastern Mediterranean it is known from Egypt (Samir et al. 2003) and southern coasts of Turkey (Meriç et al. 2008). So far, A. hemprichii has not been recorded in previous studies of alien Foraminifera distribution in the Aegean Sea (Koukousioura et al. 2010). Gravier, 1900 (Anellida, Polychaeta) ( Figure 3A)

Pseudonereis anomala
Pseudonereis anomala Gravier, 1900: 191-197, figures 50-52, pl.12;Çinar and Ergen, 2005 . It is abundant in the shallow-water hard bottom benthic habitats of the region and has been accepted as an invader species . This is the first record of the species from the Dodecanese Islands. (Crossland, 1924)  Notes: Incomplete specimen, with anterior end, 6 mm long, 0.9 mm wide, with 22 chaetigers. Body pale brownish, without colour markings ( Figure 3B). Prostomium almost rounded, slightly longer than wide; with two reddish, large eyes. Two antennae with seven joints. Palps stout, slightly shorter than antennae ( Figure 3B). Distribution: It is a Lessepsian invader that abundantly occurs among algae on the Levantine coast of Turkey (Çinar 2009). It is the second time this species has been recorded in the Mediterranean Sea.  Distribution: This species was first reported from Cyprus [Çinar, 2005[Çinar, (cited as B. boholense Grube, 1878] and the Levantine coast of Turkey (Çinar 2009) and then found along the coasts of Italy (Strait of Messina, Brindisi Harbour, Sicily and Gulf of Naples), Malta and Spain (Mediterranean) (Arias et al. 2013). The finding of B. bairdi reported here documents the first occurrence of this alien in the Greek waters and the Aegean Sea, although it has been previously recorded at the extremity of the Northeastern Levantine Sea, at Göcek and Fethiye in Turkey (Çinar 2009).  radii and spines brownish. Thorax 5.2 mm long, 2 mm wide, with 7 chaetigers. Abdomen 29.5 mm, with 40 chaetigers. Branchial crown 7.5 mm long, with 42 radioles. Peduncle plus operculum 8 mm long; funnel with 44 radii possessing pointed tips; verticil with 16 spines, similiar in shape and size; tips of spines T shaped, flattened. Reproduction: Specimen with oocytes in abdominal coelomic cavity; 50-60 µm in diameter. Distribution: This species was originally described from the St. Thomas, West Indies (Caribbean Sea, West Atlantic Ocean) (Mörch, 1863). It has been known to be present in Mediterranean Sea for more than one century, described as Eupomatus lunulifer in the Gulf of Naples by Claparède (1870), which was then synonymized with H. dirampha by Zibrowius (1971). The species is now widely distributed in tropical regions, and occurs in the western and eastern Mediterranean Sea (see Çinar 2006). This is the first finding of H. dirampha in the Dodecanese Islands.
Proximal margin slightly concave or straight with two lateral condyles pointing proximally. Adventitious avicularium positioned disto-laterally to orifice and oriented transversely above distal part of orifice; mandible triangular, crossbar complete (Figure 4). In specimen, adventitious avicularium always single and generally zooids without avicularia. However, the specimens collected from the Philippines were characterised by a pair of proximo medially pointing avicularia located at the distal part of the orifice (Tilbrook 1999). The length of the avicularia collected from different localities is variable among specimens (Levinsen 1909). In the Rodos specimens, the rostrum did not include a long, thin terminal part. Distribution: Hippopodina feegeensis is a circumtropical species. It forms encrusting sheets on artificial substrates, coral rubble and basalt cobbles of intertidal pools (Hayward 1988). This species it is commonly reported from coral substrate and/or reef environments (Winston 1986). It is widely distributed in the Indo-Pacific region and Red Sea, but also occurs in the tropical western Atlantic as well (Powell 1969a). This species was introduced to the Mediterranean Sea via the Suez Canal and firstly reported from the Israeli coast within the Mediterranean Sea (Powell, 1969b) and then from the Greek coast (Milos) . This is the first record of H. feegeensis in the Dodecanese Islands and the third time this species is being recorded in the Mediterranean Sea. Notes: Small aplysiid species, head well developed, with oral tentacles at the front of the head, on either side of the mouth, and smaller auriculate rhinophores just above the eyes. Short parapodia fused near the tail and enclosing the mantle cavity. Dorsal mantle quite thin, with an oval foramen through which a flat fragile shell is observed. Tail well developed. Reddish-brownish in colour, mottled whitish (often big white spots are formed by clusters of smaller white spots). Black eyes inside a whitishpinkish circular area. Purplish borders of foot, parapodia and mantle foramen (sometimes interrupted by whitish bands), as well as tips of oral tentacles and rhinophores. Internal anatomy of the specimens not observed, although they have been sent to Ángel Valdés (Pomona, California) for subsequent molecular analysis. Distribution: Aplysia parvula is currently considered a circumtropical species, being both recorded in the Indo-Pacific region and Red Sea, and in the whole Atlantic Ocean. Since 1959, it also colonized the Mediterranean, with multiple records from its eastern (e.g. Swennen 1961;Bebbington 1975;Danin 1971, 1988), central (e.g. Bebbington 1975;  Cattaneo 1982;Perrone 1983; Jaklin 1998) and western (e.g. Ballesteros et al. 1986;Ballesteros and Templado 1987) parts. However, worldwide specimens identified as such may belong to a still unsolved complex of cryptic species. Therefore, its assignment as a cryptogenic species is mostly due to uncertainties regarding its taxonomic status. Relationships with the native putative sister species Aplysia punctata (Cuvier, 1803) and possible spreading pattern are widely debated for the Mediterranean Sea population (e.g. Zenetos et al. 2010;Crocetta 2012;Crocetta et al. 2015a).

Fish catches
In the single boat-seine haul carried out at Station A, a total number of 1579 fish specimens were caught, with a biomass of 43.3 kg (Table 3). Centracanthidae (Spicara spp.) and Sparidae [Boops boops (Linnaeus, 1758)] dominated both in term of specimen number (1350) and biomass (32.7 kg). In the net, also two native species of cephalopods were present (7 individuals, 2.31 kg total weight). Alien fish species represented 19 % of the total fish diversity (21 native, 5 alien), and comprised 3 % of total fish specimens counted but 11 % of the total fish biomass, due to the presence of 20 individuals of Fistularia commersonii Rüppell, 1838 with a weight of 4.2 kg. Three alien invertebrates were also observed (Table 3).
In the trammel net applied at Station B, alien fish species represented 22 % of total fish diversity (18 native, 5 alien), 17.3 % of total fish specimens and 19.8 % of total fish biomass (Table 3).
Total fish species encountered along the two fishing techniques used were 31 native and 8 alien, while 2 native and 6 alien invertebrates were observed (Table 3). All alien species collected during the fishing survey were previously known to be present in the area of Rodos.

Alien marine macrophytes
Alien marine macrophytes constitute a significant element of Rodos benthic vegetation. Most of the alien taxa observed were common species and exhibited high abundancies. In the Three Windmills station (Station H), the alien red macroalga Hypnea spinella (C. Agardh) Kützing was monopolizing the upper rocky sublittoral zone, indicating an aggressive invasive behavior. Nevertheless, no new alien macroalgal taxa for the Island of Rodos were detected, probably due to intense algal studies that have taken place in the island during the last decade (Tsiamis 2012).

Review of alien and cryptogenic species in the Dodecanese complex
A review of alien species in the waters of the Dodecanese Islands (March 2015) was performed. Species in previous inventories were removed if, according to Zenetos et al. (2012), they have extended their distribution range from the Atlantic via Gibraltar unaided. By including records of species recently published and the 6 new findings reported in the present work, the list of aliens reaches 129 species, the great majority of which (66 %) are established (Supplementary material Table S1). Phytoplanktonic species are included with some reservation. The cyanobacterium Trichodesmium erythraeum Ehrenberg ex Gomont, 1893, which has a wide distribution in tropical and subtropical waters has a limited distribution in the Mediterranean (Israel, Turkey, Greece, Italy) (Guiry and Guiry 2015;Spatharis et al. 2012;Çinar et al. 2011). Hence its alien status is questionable.
The vast majority of the aliens introduced in the area are tropical species of Indo West Pacific/Indian Ocean/Red Sea/tropical Atlantic origin. Of the alien species known to be present in the Dodecanese Islands, approximately 60 % were introduced via the Suez Canal unaided (Lessepsian migration), whilst approximately 25 % of introductions occurred via shipping (9% introduced by shipping via Suez) ( Table  S1). Thirteen of the species listed are considered cryptogenic, while the occurrence of five species, namely the red macroalgae Asparagospis armata Harvey and Sarconema scinaioides Børgesen, the bivalve Acar plicata (Dillwyn, 1817), the gastropod Alvania dorbignyi (Audouin, 1826) and the fish Iniistius pavo (Valenciennes, 1840), is questionable.
The single A. armata record from Rodos Island is based only to a tetrasporophyte specimen (Koussouris et al. 1973). Since the tetrasporophyte of A. armata is indistinguishable from the tetrasporophyte of the sister species A. taxiformis, Rodos record of A. armata should be considered as questionable. Regarding S. scinaioides, there is no confirmed record from Rodos Island. According to Tsiamis (2012), the species was transferred from Rodos to Athens in the early 1970s for agar extraction experiments, but the original source site in Rhodes Island remains unknown and despite numerous samplings around the Island during the recent years (Tsiamis 2012) the species was never detected.
According to one of the authors (F. Crocetta), the presence of Acar plicata is hereby considered questionable because the depth declared by Tzomos et al. (2010) clearly suggests a misidentification for the similar native species Acar clathrata (Defrance, 1816), a common species in the circalittoral from the Dodecanese. As observed also by the same author, the specimen figured by Tenekides (1989) as A. dorbignyi is a misidentification for the native Alvania colossophilus Oberling, 1970. The absence of further records of I. pavo since 2004, and based on its resemblance with the native Xyrichtys novacula (Linnaeus, 1758), its presence in Dodecanese is also considered (by M. Corsini-Foka) as questionable.

Discussion
The surveys, which took place as an integral part of the training workshop, provided the golden opportunity to record 33 alien and cryptogenic species, 9 of which were unknown to Rodos Island. The newly recorded species included the polychaete Dorvillea similis reported for the second time in the Mediterranean Sea and the bryozoan Hippopodina feegeensis, considered casual in the eastern Mediterranean . Furthermore, they enabled the first record of the polychaete Branchiomma bairdi for the whole Aegean Sea and Greece, the first record of the foraminifer Amphisorus hemprichii for Greece and the addition of two polychaetes (Pseudonereis anomala, Hydroides dirampha) and one gastropod (Aplysia parvula) to the Dodecanese alien biota, filling gaps on their known distribution. The occurrence of the molluscs Septifer cumingii Récluz, 1849 and Chama pacifica Broderip, 1835 observed in Rodos confirms the wide distribution of these two species, already known from the nearby islands of Astypalaia and Karpathos respectively (Zenetos et al. 2011;Crocetta and Russo 2013).
Furthermore, the surveys provided the opportunity to monitor the occurrence and abundance of previously recorded alien species in the coastal waters of the island of Rodos and to investigate sites, which have been generally poorly studied until now. The alien species outlined in the updated list of the Dodecanese, are mostly thermophilic, the majority (80% of the total) of Indo-Pacific/Red Sea origin. Most of the marine aliens known in the Dodecanese region appeared to have reached the area via progressive migration from the Suez Canal (Golani 2010;Pancucci-Papadopoulou et al. 2012;Corsini-Foka and Pancucci-Papadopoulou 2012), however in the last few years the frequency of introductions as a result of shipping has increased Katsanevakis et al. 2013). For example, shipping and general maritime traffic have been blamed as a possible vector for the recent introduction of two new alien crabs, Actaeodes tomentosus (H. Milne Edwards, 1834), and Xanthias lamarckii (H. Milne Edwards, 1834) to Rodos and the nearby area .
The marine alien species recorded in the Dodecanese to date represent 52 % of the total marine aliens occurring in Greek waters (247 species, cf. ELNAIS 2015;present work) and about 13 % of marine alien species recorded in the Mediterranean (1020 species; Gerovasileiou et al. in press). The high number of alien macrophytes inventoried in the Dodecanese, further classify this marine region as one of the most biologically polluted of the Aegean Sea (Tsiamis 2012). In relation to alien zoobenthic organisms, the picture has changed in recent years: in fact, in contrast to the past, where decapods and stomatopods dominated over molluscs , today the number of alien species in the area appears to be equally shared between molluscs and crustaceans (decapods and stomatopods).
All the 29 alien bony fishes recorded in the study area are Lessepsian immigrants and have enriched the Hellenic ichthyofauna, with the addition of 8 families (Papaconstantinou 2014). The family Tetraodontidae, which has contributed with 5 new species to the area, is the one most successful in bioinvasions (Corsini-Foka 2010).
The results of the present study from Rodos match the geographic distribution of Red Sea (Lessepsian) fish immigrants in the Mediterranean, as presented by Golani (1998Golani ( , 2010, namely, an east-west gradient of number of species. At the most eastern coast of the Mediterranean, the coast of Israel, there are 88 Lessepsian fish species; two additional Lessepsian fish species have been found so far only in Lebanon (Bariche 2011;Bariche and Heemstra 2012). Turan et al. (2014) andBilecenoğlu et al. (2014) listed 65 Lessepsian fish species in the Turkish Mediterranean coast and 29 occur in the Dodecanese Islands (see Table S1). Thirteen such species have reached the central Mediterranean waters of Tunisia and Sicily (Bradai et al. 2004;Ben Souissi et al. 2014 The composition of fish species obtained by both types of fishing activities (boat-seine and trammel net) showed a ratio of aliens to native species of approximately 1:4 and did not differ from results obtained from previous studies carried out in recent years, with the same techniques, around the island (Corsini-Foka and Pancucci-Papadopoulou 2010). In terms of biomass, catches were low and results confirmed that alien fish species show a higher impact in the shallower waters on sandy habitat, where trammel net method is used, compared to the lightly deeper waters on Posidonia oceanica, where the boat-seine sampling was performed . The characteristic predominance of Centracanthidae and Sparidae by the boat-seine technique both in terms of density and biomass obtained in this work has been already discussed ). Among the 29 alien fish registered in the area, only 8 species were encountered in our surveys (all common to the area). Siganus luridus and S. rivulatus have economic value since their early stages of colonization (Corsini-Foka 2010), while F. commersonii is now marketable, due to its local abundance. Other fishes caught in nets, as Pteragogus trispilus Randall, 2013, Sargocentron rubrum (Forsskål, 1775 and Stephanolepis diaspros Fraser-Brunner, 1940 are currently discarded (small size, unpalatable). The alien mullid Upeneus pori Ben-Tuvia and Golani, 1989, elsewhere abundant in the Levantine waters (Gücu et al. 2010), is regularly present today in coastal fishery of Rodos, more common than the congeneric alien Upeneus moluccensis (Bleeker, 1855), but it does not seem to reach a biomass comparable to the native commercially important mullids, Mullus barbatus barbatus Linnaeus, 1758 or Mullus surmuletus Linnaeus, 1758. Although only one specimen of the highly toxic fish L. sceleratus was captured in our surveys, the abundance of this species in the area continues to be devastating both to biodiversity and fisheries, with an ecological and socio-economic impact in the region , similarly to other eastern Mediterranean locations (Rousou et al. 2014).
Other alien fish of economic value in the area, but not captured in the present samplings, are Sphyraena chrysotaenia Klunzinger, 1884 and Etrumeus golanii DiBattista, Randall and Bowen, 2012. Schools of S. chrysotaenia are commonly caught in boat seine nets (cf. Kalogirou et al. 2012) and trammel nets, while schools of the pelagic E. golanii are captured with purse-seines in the wider region (Çinar et al. 2011;Corsini-Foka et al. 2014 In the Dodecanese, a region belonging to the biogeographic "Lessepsian Province" of the Mediterranean Sea (Por 1990), the majority of records of aliens and information on their establishment have been from Rodos. Rodos Island is regularly studied and monitored through various research programs. Although the current number of alien records from Rodos is significantly higher than that reported for the rest of the Dodecanese Archipelago, a large number of inputs obtained through ELNAIS since 2007  provided knowledge of alien species presence and distribution in the complex underwater habitats of the Hellenic seas, including the smaller islands of the Dodecanese. The resulting picture of alien distribution in the area reflects clearly the Levantine character of Kastellorizo, where a higher number of alien species was registered compared to the other small islands of the Archipelago. Many records from Kastellorizo were provided by citizen scientists (Zenetos et al. 2011. In terms of marine xenodiversity in Rodos, alien macrophytes and fish are about 10 % and 11 % of total number of species known in their respective groups (Tsiamis 2012;Papaconstantinou 2014), alien crustaceans (Decapoda and Stomatopoda) are 18 % of total number of species registered (Corsini-Foka and Pancucci-Papadopoulou 2012), while alien molluscs account approximately 6 % of total number of species (MCF, unpublished data).
A large number of the listed alien species are considered invasive or potentially invasive in the Mediterranean Sea . As already suggested in Corsini-Foka and Pancucci-Papadopoulou (2012), monitoring of the biota in this geographically crucial region that is subjected to invasions and considered biopolluted (Pancucci-Papadopoulou et al. 2011), is imperative.
It is also worth mentioning that, during the training school, a species of Polychaete new to science, Myrianida rodosensis Çinar, 2015, was discovered and described by Çinar (2015).
The expertise available in this COST Action "ALIEN Challenge" training school covered a wide, but not complete, range of marine taxa. The results of the surveys therefore have a propensity mainly for macroalgae, polychaetes, molluscs, decapods and fishes, while other taxa such as cnidarians, tunicates or others, not included in expertise, were not reported in the results. It is worth to mention also that trainees were graduate or postgraduate students or employees, most with a general marine biology background, few specialized taxonomically in a specific group of marine organisms.
To conclude, and taking into consideration the above, the participation of experts of a number of different marine taxa as well the attendance of the training school by experienced trainees, were imperative for the positive outcome of the surveys that took place in Rodos. The surveys, which focused on a variety of ecosystems throughout the coastal environment revealed a substantial number of new sightings of alien species and highlights what can be achieved in a short time by a team with a wide range of taxonomic expertise. Furthermore, the concluding stakeholder event provided means of presenting the results of the surveys to members of the local community including people from local trades such as fishing and tourism and politicians. The willingness of the local community to disseminate the findings more widely through production of identification guides  in collaboration with the HSR was appreciated by all on the training school.