New data on aquatic alien invertebrates in the Ukrainian Danube Delta with special emphasis on the first records of the trumpet ram’s-horn, Menetus dilatatus (Gould, 1841)

Abstract

Studies of alien aquatic invertebrates in 2021–2022 covered fresh marine and transitional waters mostly within the boundaries of the Danube Biosphere Reserve. As a result of these studies, important new findings of six species of aquatic macroinvertebrates were obtained: Menetus dilatatus (Gould, 1841) is first indicated for the Danube Basin, and three marine species ( Arcuatula senhousia (Benson, 1842), Polydora cornuta Bosc, 1802 and Streblospio gynobranchiata Rice & Levin, 1998) for the first time for Ukrainian Danube Delta. For two species ( Pectinatella magnifica (Leidy, 1851) and Ferrissia californica (Rowell, 1863)), new localities were found within the delta. In the case of M. dilatatus , the pathway of entry into the Danube Delta is an absolute mystery. The most likely pathway of dispersal of this species is natural dispersion, both along the river network and associated with waterfowl, however, the large distance between the Danube Delta and the nearest locations in Western Ukraine makes direct transportation unlikely. In all probability, the similarity of this species with local species leads to the formation of cryptic populations, not identified by researchers, which may be intermediate stages of species expansion towards the Northern Black Sea area.