Alexander S. Mikaelyan

Structure of plankton phytocoenoses in the shelf waters of the northeastern Black Sea during the Emiliania huxleyi bloom in 2002–2005

It is shown that, in 2002–2005, the mass development of the coccolithofore Emiliania huxleyi on the Gelendzhik shelf occurred annually and in May–June its abundance reached 1.5 × 106 cells/l. In 2004–2005, the bloom of E. huxleyi was accompanied by a mass development of the diatom alga Chaetoceros subtilis var. abnormis f. simplex (0.6–0.9 × 106 cells/l); for the first time, it was registered as a dominating form of the Black Sea phytoplankton. Small flagellates and picoplankton algae played a noticeable role in the phytoplankton throughout the entire period of the studies. Meanwhile, in the early summer period, the bulk of the biomass consisted of coccolithophores (50–60%), while, in the late summer period, diatomaceous algae dominated (50–70%). Among the ecological factors that favor the coccolithophore development one may note the microstratification of the upper mixed layer at a high illumination level and high temperature in the surface waters (18–21°C). The terrigenous runoff during the rainy period had a negative effect on the E. huxleyi development, while storms dispersed the population over the upper mixed layer. The wind-induced near-shore upwelling stimulated the development of diatoms.

Alternation of diatoms and coccolithophores in the north-eastern Black Sea: a response to nutrient changes

In many regions phosphorus limits coccolithophore growth, whereas nitrogen generally controls development of diatoms. We tested the hypothesis that a change in nutrient composition defines the alternation of these algae. Data on phytoplankton, nutrients, chlorophyll and primary production were obtained in May–June from 2002 to 2012. Coccolithophore bloom dynamics were analysed using satellite images of particular inorganic carbon (PIC). In some years coccolithophore bloom occupied the sea interior and has spread on shelf areas. Most frequently blooms occurred in the coastal waters and were absent in the deep basin. Diatoms and coccolithophores interchangeably prevailed in phytoplankton. In the coastal waters, high biomass of diatoms corresponded to the increased ammonium. In the deep basin, PIC was positively correlated with phosphate and negatively with the sea air temperature in February indicating that the bottom-up flux of pycnocline waters during winter convection is the main driver of coccolithophore bloom. In the coastal zone, high concentrations of phosphate and PIC corresponded to high precipitation periods. Thus, independent from origin, phosphorus might have determined the development of coccolithophores both in the coastal and deep waters. In general, diatoms predominated in phytoplankton at high nitrogen:phosphorus ratio, whereas coccolithophores at low.

Chlorophyll “a” content in cells of Antarctic phytoplankton

Material was collected from the Weddell Sea and the Bransfield Strait in January/April 1989. Data on size-taxonomic composition and biomass of phytoplankton communities and Ch1 concentration were obtained to estimate the chlorophyll “a” (Ch1) cell content. Single cell fluorescence measured microscopically was used as a relative index of cellular Ch1 content of individual species. The relationship between the species composition of the algal communities and the ratio of phytoplankton carbon∶Ch1 concentration (C∶Ch1) was found. Due to changes in species composition the average C∶Ch1 ratio in March/April (56) was half that in January/February (115). The C∶Ch1 ratio ranged from 24 to 215 (mean=101) in the upper mixed layer and from 14 to 69 (mean=37) in the pycnocline region. The distribution of cellular Ch1 within individual species showed lower heterogeneity in the mixed layer in comparison with that in the pycnocline and below. Below the mixed layer, populations consisted partly of dead cells with very low pigment content, while other cells had greatly increased cellular Ch1. At several stations this cellular Ch1 increase led to the formation of a deep Ch1 maximum.

Database on phytoplankton of the Black Sea

A large amount of data is needed to study the variations occurring in ecosystems during long time periods over a vast basin. This evident statement appears to be hardly realized in practice, especially in biological studies based on sample processing to the level of species performed by a specialist. Despite the extremely labor consuming processing of such samples, which greatly limits the amount of material obtained, the difficulties of coordinating the formats of the sample processing by different researchers, the differences in identification of species, and the different interpretations of the calculations of the volumes of alga cells create additional problems. All this is fully related to phytoplankton data in general and to the Black Sea in particular.