{'fraction_non_alphanumeric': 0.030660377358490566, 'fraction_numerical': 0.016872278664731497, 'mean_word_length': 4.921589688506982, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
First survey of shallow-water Amphipoda along the Georgian Black Sea coast reveals new faunistic records and the unexpected Atlantic invader Melita nitida

We present findings from the first survey of shallow-water amphipods conducted along the Black Sea coast in Georgia. Eight species from five families were identified, all but one being new for the Georgian fauna. Most are usual inhabitants of the Black and Mediterranean seas; however, we report the first record of the invader Melita nitida in this region. This species, originating from North America, was previously known in Europe only on the Atlantic and Baltic coasts. Its discovery in the Black Sea implies either jump dispersal or that its distribution is more widespread than is currently recognized. Given that the total number of species reported in Georgia is lower than that reported for the other countries that neighbour the Black Sea, we anticipate the discovery of new taxa in future surveys. Our study highlights the importance of faunistic exploration in previously overlooked regions for detecting potentially cryptic invasions and corroborating biogeographical patterns.


Material and Methods
Material was collected from six localities along the Georgian Black Sea coast between the 2 nd and 5 th of August 2019 (see Results) (Table 1, Fig. 1). We aimed to cover a broad diversity of habitats, including seashores, river mouths and adjacent saline lagoons. Amphipods were collected with standard hand nets (0.5 mm mesh size) and fixed in 96% ethanol in the field. Specimens were examined under a Nikon SMZ1000 stereomicro-scope and identified using appropriate keys (Ruffo et al., 1993;Grintsov & Sezgin, 2011;Krapp-Schickel & Sket, 2015). Photographs were taken with a Nikon D90 camera equipped with an AF Tamron 70-300 mm F/4-5.6 lens, a Raynox DCR-250 macro attachment, and a Delta DRF-14 flash.

Results
Eight species belonging to five families were identified ( Table 1.

Discussion
Our study is the first survey dedicated to the exploration of shallow-water amphipods along the Black Sea coast in Georgia. We identified seven new species for the fauna of this country. Based on the present data and published data, the Georgian Black Sea coastal fauna consists of 12 species from 8 distantly related families, revealing a high degree of phylogenetic diversity (Copilaş-Ciocianu et al., 2020).  Biogeographically, the species composition is similar to that of the other countries that border the Black Sea. The autochthonous Ponto-Caspian elements are represented by C. curvispinum, E. ischnus and P. robustoides (Derzhavin, 1924;Birstein, 1935). In the current study, we identified the last species from two new sites but did not collect C. curvispinum and E. ischnus. These three species are widely distributed throughout the Ponto-Caspian realm and are successful invaders throughout freshwater and brackish water habitats in Europe (Arbačiauskas et al., 2011). Intriguingly, we did not encounter C. curvispinum and P. robustoides in the brackish Paliastomi Lake, where both have been previously reported. The only amphipod sampled was M. nitida, suggesting an increase in salinity. It is possible that the Ponto-Caspian species retreated towards the less saline river inflows. All of the remaining species that are known to inhabit the Georgian coastline are recent immigrants, being either typical Mediterranean/Atlantic elements (Ruffo et al., 1993) or cosmopolitan species.
Our most important finding is the discovery of M. nitida, a species never before reported from the Mediterranean or Black Sea. A native of the North American Atlantic coast, it was introduced to Europe by shipping, where it currently inhabits the Atlantic and Baltic shores (Normant-Saremba et al., 2017). Its occurrence in Georgia is puzzling; it suggests either jump dispersal or a broader-than-recognized, cryptic distribution in the Mediterranean area. We found this species at three locations, ranging from the sea to the brackish Paliastomi Lake and its outflow, in accordance with its resilience to salinity changes (Normant-Saremba et al., 2017). Males, females and juveniles were collected, indicating the existence of viable populations. A very similar species, M. mirzaja-ni Krapp-Schickel & Sket, 2015, was recently described from the Bandar-e Anzali port on the Caspian Sea in Iran (Krapp-Schickel & Sket, 2015). Its recent appearance but unknown origin is intriguing. Both M. nitida and M. mirzajani dwell in similar habitats of decreased salinity and high anthropogenic influence. They are also very similar morphologically, the main difference involving the setosity of the flagellum of the second antenna in males. Given these similarities, we suggest that M. mirzajani might be a junior synonym of M. nitida. Future studies employing DNA barcoding and detailed morphological analyses are needed to clarify this issue.
Although our study significantly increased the number of coastal species in Georgia from 5 to 12, this number is considerably lower than those for other Black Sea neighbouring countries and probably represents a fraction of the total diversity. However, the eastern Black Sea shelf is the narrowest part of the shelf and slopes abruptly below the 200 m depth limit of the oxygenated water level (Barale, 2008). Given these limiting conditions, the eastern coast might indeed harbour a reduced diversity. Nevertheless, it is clear that more species await discovery, and we emphasize the need for further research.