Crustacea Decapoda from the Rhodes Island Area (Eastern Mediterranean): New Records and an Updated Checklist

: Decapod crustaceans are ecologically and commercially important members of marine communities. Faunal surveys constitute essential tools for the understanding of local diversity, especially in areas subjected to significant alterations of community composition due to climate changes, anthropogenic impacts, and biological invasions. Following a literature review and the study of new samples, we hereby update on the Crustacea Decapoda from the Rhodes Island area (Greece), situated in a key position in the eastern Mediterranean Sea. Published data yielded records of 120 species, whereas 28 taxa are recorded here for the first time from the study area. Among them, the collection of Liocarcinus bolivari widens its distribution to the eastern Mediterranean. Details on material examined and distributional/faunal remarks are provided for the species newly recorded and for some other native and alien species rarely reported from Rhodes. The present paper raises the local decapod biodiversity to 148 species, accounting for ~50% of the Hellenic Aegean decapod fauna and provides a useful baseline for analysing the long ‐ term changes in the local fauna and the westward spreading of Lessepsian species. Despite present advances, the lack of records of many common Mediterranean species may be still due to limited fieldwork in some habitats rather than a true absence. DNA Taxonomy the identity of the widely ‐ disjunct


Introduction
Decapod crustaceans are one of the most important groups in the marine ecosystem, not only from a biodiversity point of view, but also as fishery resources [1]. Despite of that, knowledge of decapods diversity and distribution, even in a "well-known" basin such as the Mediterranean Sea, is still an ongoing process. Moreover, in habitats diversified and heavily affected by biological invasions, faunal surveys are not only essential for improving knowledge of the local diversity, but also constitute an useful baseline for analysing long-term changes in the composition and functioning of the biota, and eventual biodiversity loss [2].
In fact, the warming of the Mediterranean Sea, and in particular of its eastern part [3][4][5], the temporary changes in the south Aegean water mass characteristics, that have considerably influenced the thermohaline circulation of the eastern Mediterranean (Eastern Mediterranean Transient) [6,7], along with anthropogenic impacts and biological invasions, considerably affect the distribution of marine organisms and their communities' structure and function both at a basin and at a local scale [8,9].
Rhodes is an island located in the southeastern Aegean Sea, close to the northwestern Levant Sea. The position of the island is interesting from the oceanographical and biological point of view, due to the intense hydrological phenomena of the surrounding marine area, such as the Rhodes gyre and the Asia Minor Current, while its pelagic and subtropical marine environment is favorable to the native thermophilic biota and to the tropical or subtropical alien biota as well [10,11].
This key position led to a flourishment of zoological studies, and the knowledge on the decapod crustacean diversity along the coasts of Rhodes Island has been the subject of several studies in the recent decades. In the first decapods checklist for the area, Lewinsohn [12], listed 45 marine species including those reported in previous literature. The local checklist was subsequently updated to 83 species by Kevrekidis & Galil [13], and lastly to 109 species by Corsini-Foka and Pancucci-Papadopoulou [14]. Since then, additional single species records were reported by various researchers as a result of intensification of biological surveys on previously undersampled habitats and of increasing interest and contribution of citizen scientists in observing and recording species (e.g., [15][16][17][18]). These last contributions raised the final list to 120 species.
Notwithstanding the efforts mentioned above, these numbers suggest that local biodiversity is still underexplored. We hereby update the current knowledge of the Rhodian decapod biota based on published literature and the study of new samples and provide new information on decapod distribution in the Aegean and the eastern Mediterranean Sea. Data reported on alien and native species rarely recorded in the area may assist in the overall assessment of the Hellenic and eastern Mediterranean biodiversity.

Study Area
The sea floor of Rhodes presents a very narrow continental shelf, with coastal areas characterized by a variety of intermingling substrates, spanning from sands and muds with or without Posidonia oceanica (Linnaeus) Delile patches or meadows to pebbly and rocky bottoms [19]. Greater depths are characterized by muddy substrates, and presence of several submarine canyons [19]. In the last decades, the area has been widely colonized by alien species (e.g., [20,21]).

Sampling
The material analysed here came from 20 sampling sites widely distributed along the Rhodes coastline and four trawling grounds (Table 1; Figure 1). Sampling areas were either chosen by us according to their proximity to the Hydrobiological Station of Rhodes (HSR) or according to the fishing areas exploited by local fishermen. The material was mostly obtained from May 2013 to November 2019, although it was later increased by additional samples from 2008 onwards. Samples altogether come from three different sources: (i) targeted activities carried out by the HSR; (ii) a COST Action TD1209-ALIEN Challenge held in 2014; (iii) the analysis of the by-catch of Italian commercial trawlers fishing for "red shrimps" off Rhodes. Shallow waters (0-3 m) were investigated by snorkelling, and the specimens were picked by hand or with the help of a hand net (HN). Hard and soft infralitoral grounds down to ~30 m were investigated with gill nets (GN) and trammel nets (TN) as well as with boat-seine with 8 mm mesh size in the cod-end (BS, Danish method), operated by a professional fishing vessel (length 10.8 m, engine power 53 Kw). Posidonia oceanica meadows down to ~20 m were sampled during night hours with an epibenthic sledge (ES), with a bag made of plankton net with 1 mm mesh size, towed from a fishing vessel (length 8.25 m, engine power 38 Kw). Sandy and muddy circalittoral bottoms (~80-200 m) were investigated only with shrimp traps (ST) (diameter 60-70 cm, mesh opening 20 mm), deployed by a fishing vessel (length 9 m, engine power 18.6 Kw). Finally, bathyal samples (~600-750 m) were obtained from Italian commercial bottom trawlers (BT), fishing with otter-board trawl nets with 50 mm mesh opening in the cod-end. Table 1. Sampling sites and trawling grounds shown in Figure 1, with coordinates (rounded to degrees and minutes) and depth range (in meters).

Laboratory Work
Samples obtained through the first two sources were sorted out from the material collected and subsequently photographed alive. Samples obtained from commercial trawlers were frozen onboard and subsequently delivered to the authors. Following identification, specimens were sorted by sex, keeping record of the presence of ovigerous females (ov), and measured. Measurements were taken to the nearest 0.1 mm with a digital caliper or by means of an ocular micrometer under stereomicroscope. Size is given as: (i) carapace length (CL), from rear margin of orbit to mid-dorsal posterior margin of carapace in shrimps, or from front margin (tip of rostrum) to posterior margin of carapace in crabs; (ii) shield length (SL), from front margin to posterior margin of cervical groove in hermit crabs.
Species identification was based on Zariquiey Álvarez [22], or on more recent specialistic reviews (references under single species). Updated nomenclature was based on World Register of Marine Species [23]. Voucher specimens, preserved in 80% ethanol, were deposited in the collections of the Hydrobiological Station of Rhodes (HSR, Greece) and of the Museum of Natural History of Verona (MSNVR, Italy).

New Records and Updated Checklist
We report here unpublished data for 39 taxa. Twenty-eight of them are new records for the Rhodes Island area [12][13][14], whereas the remaining 11 species, mainly non-indigenous, are rather common nowadays, despite the paucity of published records of their presence in the area.
Single records are briefly discussed in next section, with new records from Rhodes and alien species highlighted respectively with * (asterisk) and (A) after the species name.
Present data raise the number of decapod species known from the area to 148, accounting for 56 families. Among the species listed here, 126 are natives (86%), whilst 22 are alien (14%), with the latter species mostly distributed in the families Portunidae (7 taxa) and Penaeidae (6 taxa).
In the updated checklist (Table 2), references for the first record of each species are also provided.  [58]. Previously known from Rhodes area from a juvenile specimen (31 mm total length) collected by the "Thor" expedition [24].

Family POLYCHELIDAE Wood-Mason, 1875
Polycheles typhlops Heller, 1862 * Polycheles typhlops -Zariquiey Álvarez [22]: 209, Figure 86b; Galil [70]: 354, Figure 30.  [73] and García-Gomez [71] remarked that all the eastern Mediterranean specimens previously identified as A. laevis that they could re-examine did not belong to that species and most of them were A. breviaculeatus. Based on the present material, A. breviaculeatus is added to the fauna of Rhodes and the early record of A. laevis is considered a probable misidentification.
Pagurus cuanensis Bell, 1845 * - Figure 2G Pagurus cuanensis -Zariquiey Álvarez [22] Pirimela denticulata (Montagu, 1808) * - Figure 2H Pirimela denticulata -Zariquiey Álvarez [22]: 350, Figures 7a, 11d, 112a [58]. Noteworthy, in a study on the distribution in Greece of Portumnus latipes and its congeneric species Portunus lysianassa (Herbst, 1796), Chartosia et al. [77] did not find any of the two species in the three sites sampled in eastern Rhodes. Remarks: Native from Indo-Pacific, including Red Sea [78], this alien species was first recorded in the Mediterranean off Israel [79] and latter collected off Rhodes [47]. It is now established all around the island on rocky substrates with algal cover. Remarks: Native from Indo-Pacific, including Red Sea [78], this alien species has demonstrated a high invasive capacity, not only in the eastern Mediterranean, where it entered via the Suez Canal, but also in the western Atlantic, where it arrived with ballast waters [80]. First observed in Rhodes in 2004 [48], it is now established all around the island on rocky substrates with algal cover and is displayed in the HSR Aquarium [81]. Remarks: Native from western Indian Ocean, including Red Sea [78], this alien species is now abundant off Turkey and off Israel on sandy and muddy bottoms in 30-60 m depths, although it was collected down to 250 m [82]. First observed in Rhodes in 1996 [7], the species is only known so far from scattered specimens collected over a wide bathymetric range.  [49], and then from other localities in the eastern Mediterranean [84,85]. More recently, Galil et al. [83], from results of molecular analysis, reinstated the validity of Gonioinfradens giardi, a species previously considered a junior synonym of G. paucidentatus, and reported it from Israel, suggesting that previous Mediterranean records of the latter species should be referred to G. giardi. We keep here present specimens as G. giardi, although this should be confirmed by molecular data as they could not be unequivocably identified on the distinctive morphological characters illustrated in Galil et al. [83]. Remarks: Native from western Indian Ocean, including Red Sea [78], this alien species recently spread in the eastern Mediterranean (e.g., [86]). First observed in Rhodes in 2007 [51], it is now locally established, used as bait for fishing rod, and commonly displayed in the HSR Aquarium [81].

Family POLYBIIDAE Ortmann, 1893
Bathynectes maravigna (Prestandrea, 1839) * Figure 3E,F Bathynectes superbus -Zariquiey Álvarez [22]: 382, Figure 127g. Remarks: Known from eastern Atlantic and Mediterranean Sea [58]. Two females examined here (CL 19 mm, the other smashed) were parasitized by Sacculina (see figure 3F). Øksnebjerg [88], reported one specimen of B. maravigna from eastern Ionian Sea parasitized by Sacculina carcini Thompson, 1836. However, Polybiidae hosting S. carcini usually occur on shallow grounds in depths of less than 50 m, whereas B. maravigna is restricted to bathyal grounds, from 300 to 1000 m. Moreover, the present externae (4.6 and 4.8 mm in size) have the mantle opening placed at the top of a rather long papilla, less developed in S. carcini [88] (front-cover), and thus we suspect that these specimens do not belong to S. carcini.
Liocarcinus bolivari (Zariquiey Álvarez, 1948) * - Figure 3G,H Macropipus bolivari -Zariquiey Álvarez [22]: 375, Figure 127a [58]. Here, it is recorded for the first time in the eastern Mediterranean. Liocarcinus bolivari is closely related to Liocarcinus depurator (Linnaeus, 1758) and Liocarcinus vernalis (Risso, 1827). In addition to the morphological differences that allow separation of long-time preserved specimens [22], L. bolivari can be recognized at a glance in the field for the presence of dark bands on articles of walking legs ( Figure 3H), versus a uniform colour in L. depurator and L. vernalis, and the distal part of dactylus of the fifth pereopod, blue-violet only in L. bolivari and L. depurator.   [58]. The species is usually associated with floatsam (natural or artificial) and sea turtles in the pelagic realm [95] and was first collected in the Aegean in 2010 at Rhodes [14]. The present findings represent the second and third records of the species in the Aegean Sea.  [56,97]. As consequence of global warming, the species is currently expanding westwards to the central Mediterranean from the Levant Sea, which may have acted as refugium during the last glacial period [57]. Kinzelbach [56] reported Ocypode cursor from southern Aegean (including Rhodes) based on a specimen displayed at the HSR museum and another one from Karpathos Island.

Discussion
To date, a number of approximate 400 decapods have been listed in the Mediterranean Sea [98], of which about 24% are aliens [99], and less than 300 species are known from the Hellenic Aegean Sea (Authors' unpublished data), of which 25 are aliens [100]. In the present work, 28 species of decapods are reported for the first time for the Rhodes Island area, including eight deep-water species detected from material collected by "red-shrimp" bottom trawlers, six species discovered during snorkeling in shallow waters, twelve species obtained from night sampling with epibenthic sledge on Posidonia oceanica meadows, and two more species collected with shrimp traps on the continental shelf. The number of marine decapod species recorded for Rhodes (148) accounts now for about 50% of the Hellenic Aegean decapod fauna.
All the new records are native species with a wide distribution in the Mediterranean, with the exception of Liocarcinus bolivari, rarely recorded in the West and Central Mediterranean and here documented for the first time in the eastern Mediterranean, and Pachygrapsus transversus, although for the latter species also a human-mediated range extension may be involved. Among species already recorded from Rhodes, but only from a limited number of specimens, Ocypode cursor needs a mention, being the only decapod species listed in the Annex II (strictly protected fauna species) of the Convention on the Conservation of European Wildlife and Natural Habitats (Berne Convention). The uncontrolled development of mass tourism in the last decades and the unlimited use of the beaches [101] requires a monitoring of the local population of this crab in beaches heavily impacted by tourism activities, such as those of Prasonisi and Tsampika.
It is also worth a mention that when the coastal waters of the island were first investigated (about 50 years ago) for the presence of species of Indo-Pacific origin, no alien decapods were collected [12]. Nowaday twenty-two of the 148 species reported in the checklist are aliens and there is evidence that biological pollution is locally increasing at a steady rate, with several species becoming established, especially in the last decade. Also records of alien decapods in stomach contents of both native and alien fishes suggest they became a component of the local food web with effects on the whole biota. The local ratio alien vs native decapod species of 0.17 appears slightly higher than the 0.13 calculated for bony fishes [102]. This may be partially explained by the fact that fishes are not only more easily spotted due to their larger sizes and commercial value, but even more easily identified by various sea lovers, including non-professional ones like scuba divers and citizen scientists.
Finally, improving knowledge of diversity of the major marine groups, as also requested by the MSFD Annex I 2008/56/EC, provide data useful as descriptor of the environmental status of regions highly affected by the influx of alien species and contribute in monitoring possible changes in the diversity of marine biota [103]. Notwithstanding past and present research efforts, the list of the decapod biota of the Rhodes Island area is presumably far from being complete. Future surveys, carried out with as many professional fishing gears and scientific samplers as possible, and in different habitats, from shallow to deep waters, including areas all around the island, will presumably reveal the presence of many unrecorded native species and additional Lessepsian immigrants.
Funding: This research received no external funding.