Population dynamics of the copepod invader Oithona davisae in the Black Sea

Abstract

During 2013-2016 in Sevastopol Bay, seasonal and interannual dynamics of the population density, age and sex composition, fecundity, and mortality of males and females of Oithona davisae were studied. A maximum population number (up to 554 ind × 10$^{3}$ m$^{-3}$) was registered at the end of summer?end of autumn. In this period, the nauplii and early copepodite stages constituted up to 95% of the Oithona davisae population. During 1-2.5 cold winter?spring months, the population consisted only of females, who were not numerous. The phase of latent population development was recorded from April until July-August, with a high share of ovigerous females, maximum clutch size, and high egg production rate but low population density, which may be due to predator pressure from lobate ctenophores. The average share of adult males amounted to 32% at the end of spring and 27% at the beginning of winter, while the share of dead males reached maximum values (20.7%) during the winter degradation period for the population. On the basis of the studied successions of the population's developmental stages, from ovigerous females through nauplii and early copepodites to adults, the number of generations produced by Oithona davisae during the reproductive period (10-11) was determined.