2.2. Laboratory microcosm studies
Examination of the influence of nitrate and phosphate additions on
the phytoplankton community structure was performed annually in
May–June in the coastal laboratory of Southern Branch of the Institute
of Oceanology (Gelendzhik). Water for the experiments was taken
from the sea surface on the shelf station of the standard section (the
depth on this station was 50 m). Water was sampled in 5-L bottles
with simultaneous filtration through two layers of net (mesh size —
180 μm) to remove zooplankton. To determine the structure of the natural phytoplankton community at the start of the experiments,
phytoplankton was concentrated from 2 L of unfiltered water using
the inverse-filtering camera (nuclear filterwith mesh size 1 μm). Experiments
were carried out in 0.5-L Erlenmeyer flasks. The volume of culture
medium was 200 mL in all experiments. The final concentration
of nutrients in the sample after their addition was 12–14 μM and
1 μM, for nitrates and phosphate, respectively. A full factorial design 22
was used for the experiment; examples of this type of experiment can
be found in other studies (Maksimov, 1980). There are 4 variants in
the scheme of this experiment: 1 – without nutrients addition; 2 –
only nitrogen addition; 3 – only phosphorus addition; 4 – nitrogen
and phosphorus additions simultaneously. Each variant was assessed
in duplicate or triplicate, the Student t-test used to compare different
variants in the experiments and significance set at 5%.