Oithona davisae : Naturalization in the Black Sea, Interannual and Seasonal Dynamics, and Effect on the Structure of the Planktonic Copepod Community

— Naturalization of the invasive copepod Oithona davisae is examined based on long-term (2003–2014) routine observations of zooplankton in Sevastopol Bay (the Black Sea). The study analyzes inter-annual and seasonal variability of the species and their impact on the native copepod community. The invasion of O. davisae and their undoubted dominance in terms of abundance have been shown to alter the community structure, while not causing a decline in abundance of native species, except the earlier Black Sea invader Acartia tonsa . A significant decline in A. tonsa numbers over the phases of establishment and naturalization of O. davisae indicates competition between the species. It has been demonstrated that O. davisae have gained a competitive advantage over A. tonsa , which ensured the rapid spread of the former across the Black Sea, acclimatization to the new habitat, and successful competition over native species.