The non-native copepod Oithona davisae (Ferrari F.D. and Orsi, 1984) in the Western Black Sea: seasonal and annual abundance variability

Abstract

A new cyclopoid copepod species, Oithona davisae was discovered during regular monitoring along the western coast of the Black Sea in 2009–2012. In the short period since its discovery off the Bulgarian Coast, O. davisae populations have increased to become one of the dominant zooplankters, contributing up to 63.5–70.5 % of total mesozooplankton numbers in the Varna Bay and adjacent open sea waters. This species thrived in early autumn with a maximum density of 43818 ind.m -3 in the eutrophic Varna Bay, but seasonal and annual abundance fluctuated widely during the investigation period. Temperature variability, changes in the phytoplankton community composition, and decreased abundance of gelatinous plankton were investigated as possible drivers for rapid increase in the new established population O. davisae in the Black Sea.