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International Journal of Marine Science 2013, Vol.3, No.15, 121-127
http://ijms.sophiapublisher.com
122
Sevastopol
bay (st.1) evidenced that over a year the
estimates could differ nearly 8 times as large (Figure 1).
Figure 1 Seasonal dynamics of the microzooplankton grazing
(g) on phytoplankton (1), the ratio of grazing to phytoplankton
growth rate (g/µ), (2) and phytoplankton biomass (3) in the
surface waters of the Sevastopol bay (A), Quarantine bay (B)
and in the open coastal waters near Kruglaya bay (C) in
2006~2007
Maximums (1.6~1.7 d
-1
) were registered in June 2006,
when an intensive bloom of
Chaetoceros
spp. was
fading away, and in May 2007, prior to another
outbreak of these diatoms. Minimums (0.2~0.3 d
-1
)
were measured from October 2006 till February 2007.
The records from st.3 located in the open coastal sea
water next to the Kruglaya bay (Figure 1C) show
similar seasonal variation. In the Quarantine bay (st.2),
the microzooplankton grazing activity intensified to the
peaks ranged between 1.4~1.6 d
-1
in June 2006 and in
May 2007. Noteworthy, it was only slighter lesser
(1.1~1.5 d
-1
) during November~December 2006
(Figure 1B). The facts that phytoplankton biomass in
the Quarantine bay has been 2~2.5 times as large as in
the Sevastopol bay and at the Kruglaya bay region and
that
Chaetoceros
spp., the favorite prey item for the
microzooplankton, dominated in the rich phyto-
plankton production can account for these late
autumn~early winter maximums.
In summer 2010, the sea water was 4
℃
warmer than
usual; according to the records, in the phytoplankton
biomass near the shores of Sevastopol and village
Katsiveli dinoflagellates prevailed for most time of the
year. In the samples collected near Sevastopol the
small-celled
Skeletonema costatum
, the abundance of
which were as large as to conform to a bloom level
(2~3 × 10
6
cells/L), dominated only in February. In
March, the predatory pressure of microzooplankton
increased to 0.5 d
–1
in the Sevastopol bay and to 0.7 d
-1
in the open coastal water area neighboring the
Kruglaya bay (Figure 2). In May, at the intensive
growth period of
Emiliania huxleyi
(2.2×10
6
~2.5×10
6
cells/L) and at low total phytoplankton biomass
(30~70 mg C/m
3
), the specific microzooplankton
grazing rate decreased to 0.2 d
-1
in the Sevastopol bay
and to 0 d
-1
near Kruglaya bay; from June to August it
was again increasing in these two locations to 0.6~0.8
and 0.8~1.1 d
-1
, correspondingly. Simultaneously, the
portion of small forms of mixotrophic dinoflagellates,
namely
Prorocentrum cordatum
and
P. micans
,
responsible for larger values of summer phytoplankton
biomass has increased (70% of the total biomass) in
the microplankton. In the Quarantine bay, over the
observation period the phytoplankton loss due to
microzooplankton grazing inconsiderably fluctuated
between 0.4~0.7 d
-1
.
In 2010, lowest estimates of phytoplankton biomass
and microzooplankton grazing impact were registered
near the shore of village Katsiveli. During the year,
the microzooplankton predatory pressure varied in the
narrow range of 0~0.5 d
-1
(Figure 3) reducing to