First record of the hydrozoan Podocorynoides minima in the Romanian Black Sea waters

The paper reports the first finding of hydromedusa of Podocorynoides minima (Trinci, 1903) in the plankton samples collected in the summer of 2020 in nearshore, coastal and offshore waters of the Romanian Black Sea shelf. Distribution and abundances of the new incoming species are presented. Different hypotheses on introduction pathways and factors that might ensure or hinder its successful spreading in the Black Sea are discussed. The results point out a climate-driven opportunity and a potential free ecological niche for the species settlement, but also highlight the impediments due to competition pressure. While the polyp stage has not yet been found, this evinces once again the paradigm of this species regarding the cryptic existence of its benthic phase confirmed by the worldwide studies. It also stresses the importance of detection of medusa of the new species even in the absence of the polyp, as a sign of more profound ecological changes that might occur in the Black Sea in the near future.