Response to salinity and temperature changes in the alien Asian copepod Pseudodiaptomus marinus introduced in the Black Sea

SEASONAL AND INTERANNUAL DYNAMICS OF THE ABUNDANCE OF THE BLACK SEA ALIEN SPECIES <i>PSEUDODIAPTOMUS MARINUS</i> SATO, 1913 (COPEPODA, CALANOIDA, PSEUDODIAPTOMIDAE) IN THE CRIMEAN COASTAL WATERS: INFLUENCE OF THE TEMPERATURE FACTOR

Observation on the occurrence of the Black Sea alien species Pseudodiaptomus marinus were initiated since this species was reported in the coastal waters of Crimea, in 2016. Current study is focused on the 170-500 µm microplankton fraction represented by nauplii and the first copepodite stages. These data were complemented by the mesoplankton fraction abundance contributed by copepodite stages II-V and adults. Samples were collected by plastic bottles at the sea surface and by Juday and Apstein plankton nets in the upper 10 m layer. Nauplial stages of P. marinus were observed during the first three years after species invasion, in September, at the sea surface temperature range from 21.1 to 25.5 C. From 2019 to 2020, specimens appeared in July, at temperatures from 25.8 to 26.0C. The presence of specimens in samples has been observed by the end of November or December, at sea surface temperature of 13.1 or 8.6C, respectively. The maximal abundance was observed in the inner part of the Sevastopol Bay. The correlation value of 0.7-0.9 was estimated between the abundance and sea surface temperature throughout the year. Inter-annual variations of the abundance were associated with an integrative indicator of temperature (in particular, the sum of active temperatures).

Pseudodiaptomus marinus Sato, 1913 in the Black Sea: morphology, genetic analysis, and variability in seasonal and interannual abundance

Calanoid copepod Peudodiaptomus marinus Sato, 1913 was first recorded in Sevastopol Bay in the northern Black Sea in September 2016. We performed regular observations of this new invasive species between October 2016 and December 2018. We conducted bi-weekly plankton sampling at three stations located within or adjacent to Sevastopol Bay. This is the first paper to combine (i) a detailed morphological study, (ii) molecular genetic analysis, and (iii) an investigation of P. marinus seasonal dynamics and interannual abundance variability in the coastal Black Sea. Our morphological research showed similarities between Pseudodiaptomus specimens and existing P. marinus illustrations and descriptions. Our morphological analysis results were confirmed using molecular genetic studies. Based on the genetic variability of ITS2 and cytb, we found that all investigated specimens from Sevastopol Bay belonged to P. marinus. Investigations of P. marinus seasonal and interannual abundance variability showed the same seasonal patterns throughout the studied period, with a higher seasonal abundance from October to November and one pronounced density peak in autumn. The highest abundances (2,000 ind m^–3 at the mouth of the bay and more than 5,000 ind m^–3at its centre) were recorded in November 2018. In the samples, we found adults of both sexes, including ovigerous females, copepodites I–V, and nauplii, suggesting that the species reproduce in Sevastopol Bay. Our research indicated that P. marinus is a new non-indigenous species (NIS) in the Black Sea, and we will discuss a possible vector of its introduction into this basin.