ON THE INVASION OF THE GENUS MARENZELLERIA (POLYCHAETA, SPIONIDAE) REPRESENTATIVES INTO THE CASPIAN SEA BASIN

In 2018, in the bottom fauna of the Caspian Sea, single specimens of a previously unknown species of polyhaetes were discovered. Since 2019, pelagic larvae of this species have been recorded in zooplankton samples. These worms are also found in the nutrition of migratory and semi-migratory fish species. According to morphological features, this polychaete species is identified as Marenzelleria arctia , an Arctic species dominating in the Gulf of Finland and probably invaded the Caspian along the Volga-Caspian invasion corridor.

Mass appearance of the Ponto-Caspian invader Pontogammarus robustoides in the River Tisza catchment: bypass in the southern invasion corridor?

The river Danube is the backbone of the ‘southern invasion corridor’, one of the most important passages for the spread of Ponto-Caspian invaders in Europe. However, not all of these species used the passive or active upstream movement in the main channel to reach the upper sections and tributaries, some found detours. Mass occurrences of the Ponto-Caspian peracarid, Pontogammarus robustoides (Sars, 1894) were recorded at 17 sites along the entire Hungarian section of the River Maros, for the first time in the River Tisza catchment and also in Hungary. Those populations are found ca. 707 km upstream from the closest known and confirmed locality in the lower Danube section. We confirmed their identity by DNA barcoding and showed that all individuals fit in with the lower Danube population, thus identifying the source of this introduction. The most likely vector allowing the jump dispersal of the species is fish stocking in the Romanian section of the River Maros, which − combined with downstream drift to the Serbian Danube section and the relatively busy ship traffic between Belgrade and Vienna − might provide the opportunity to bypass the dispersal barrier represented by the unregulated Middle Danube and open the way towards Western Europe.

A minimalist macroparasite diversity in the round goby of the Upper Rhine reduced to an exotic acanthocephalan lineage

The round goby, Neogobius melanostomus, is a Ponto-Caspian fish considered as an invasive species in a wide range of aquatic ecosystems. To understand the role that parasites may play in its successful invasion across Western Europe, we investigated the parasitic diversity of the round goby along its invasion corridor, from the Danube to the Upper Rhine rivers, using data from literature and a molecular barcoding approach, respectively. Among 1666 parasites extracted from 179 gobies of the Upper Rhine, all of the 248 parasites barcoded on the c oxidase subunit I gene were identified as Pomphorhynchus laevis. This lack of macroparasite diversity was interpreted as a loss of parasites along its invasion corridor without spillback compensation. The genetic diversity of P. laevis was represented by 33 haplotypes corresponding to a haplotype diversity of 0·65 ± 0·032, but a weak nucleotide diversity of 0·0018 ± 0·00015. Eight of these haplotypes were found in 88·4% of the 248 parasites. These haplotypes belong to a single lineage so far restricted to the Danube, Vistula and Volga rivers (Eastern Europe). This result underlines the exotic status of this Ponto-Caspian lineage in the Upper Rhine, putatively disseminated by the round goby along its invasion corridor.

Non-native fish in Belarusian and Polish areas of the European central invasion corridor

This is the first comprehensive review to examine the role of the central European invasion corridor on fish introductions into Belarusian and Polish inland waters (Dnieper-Bug-Vistula-Oder-Elbe-Spree-Havel). Historical and recent data were assessed, including the results of a 2003–2008 survey along the Belarusian and Polish sections of the corridor. Since the eighteenth century, at least six fish species of Ponto-Caspian origin have spread via the corridor and migrated westwards to the Baltic basin, with five species found in recent surveys, namely the monkey goby Neogobius fluviatilis, round goby N. melanostomus, racer goby N. gymnotrachelus, tubenose goby Proterorhinus marmoratus and the white eye-bream Abramis sapa. Four other non-native species were also found within the corridor — the Amur sleeper Perccottus glenii, gibel carp Carassius gibelio, brown bullhead Ameiurus nebulosus and the topmouth gudgeon Pseudorasbora parva. Their presence is related to numerous accidental introductions to many localities in Belarus and Poland, rather than from using the corridor as an invasion route. One species, the ninespine stickleback, Pungitius pungitius, has migrated from the Baltic basin to the Black Sea drainage systems.