DYNAMICS OF SIZE SPECTRUM OF NOCTILUCA SCINTILLANS IN THE BLACK SEA

Abstract

Size spectra for Noctiluca at different seasons and various depths of the Black Sea are presented. These data make it possible to estimate the “age spectrum” of the populations and, on this basis, to reach conclusions on reproductive activity of cells in different habitats. The proportion of cells smaller than 0.5 mm is shown as minimum at noon and maximum at 6 p.m. – 9 p.m. These observations suggest that, in the Black Sea; the division of Noctiluca cells takes place during the dark time of the day (it is confirmed by observations already made in the North Sea). The following seasonal changes in population size spectra have been observed. The biggest proportion of small cells (60 – 84%) occurs in March at all investigated depths. This is consistent with Noctiluca spring bloom start. In April the main peak in the abundance of small cells sinks to a depth of more than 60 m. In August, 45% of cells in the surface layer are < 0,5 mm. This fact is difficult to explain because of inactive reproduction of Noctiluca at this period.