Biological Characteristics of the Polychaete Ficopomatus enigmaticus (Fauvel, 1923) from Mass Settlements in the Coastal Water Area of the Kerch Strait (Black Sea)

In September 2019, the polychaete Ficopomatus enigmaticus (Fauvel, 1923), formerly known as Mercierella enigmatica Fauvel, 1923, was found in mass colonial settlements in the coastal water area of the Kerch Strait near the Arshintsevskaya Spit. Brackish water bodies in India are considered by some researchers to be the initial natural range of this polychaete species. This species is currently known to be widely distributed along the coasts of the Atlantic, Pacific, and Indian oceans and along the coasts of the North, Mediterranean, and Caspian seas. Only a few isolated individuals of F. еnigmaticus have been found so far along the Crimean coast of the Black Sea, in the coastal zone of Sevastopol, and along the Karadag shores. The colonies described in this study do not constitute reef structures yet, but have already reached high population numbers. The colony has a diameter of 46 cm and comprises 1774 individuals. The settlements of F. еnigmaticus are true populations represented by individuals of different sizes, ranging in length from 2 to 39 mm. The populations include both males and females: males account for 56% and females account for 44% of the population. The fecundity of the worms expressed as the number of mature eggs per female depends on the body size and varies between 5800 eggs for the body size of 12 mm and 24 820 eggs for the body size of 29 mm. The present study describes the morphology of F. enigmaticus using scanning electron microscopy and identifies numerous sensory structures on the surface of the body, gills, and the pygidium for the first time. Judging from the presence of a mass settlement of the polychaete F. еnigmaticus in the coastal water areas of the Kerch Strait, it can be presumed that this species has become completely naturalized in the Black Sea. Since this species is eurybiontic, it can be assumed that it will invade the Sea of Azov and adjacent estuaries, river deltas, and coastal lakes successfully, which will have an inevitable effect on the life of the local species and the ecosystems in general.