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International Journal of Marine Science 2013, Vol.3, No.15, 121-127
http://ijms.sophiapublisher.com
126
During abnormally warm year 2010, the biomass of
phytoplankton at the studied locations was relatively
low. Generally, the largest contribution was due to
dinoflagellates with specific growth rate less in 2~3
times in comparison with diatoms (Stelmakh et al.,
2010). The average phytoplankton loss due to
microzooplankton grazing during warm months of
2010 was significantly (nearly two times) lower
compared to warm seasons of 2006 and 2007.
Presumably, the scarcity of prey and the half reduced
diatom portion in the phytoplankton assemblage could
account for the decline in the specific rate of
microzooplankton impact.
As soon as phytoplankton growth rates exceeded the
rate of mortality due to microzooplankton grazing,
phytoplankton bloom started. As our observations
indicate, difference between the two rates was largest
at the peak of blooming. Near Sevastopol,
phytoplankton blooms emerged when g/µ ratio was
estimated between 33% and 80%, i.e., 50% on the
average.
At the studied areas of the Black Sea the primary
production grazed by microzooplankton varied widely
over the year, yielding the annual average of 65%.
This means that microzooplankton removes most of
the yearly primary production in the region, leaving to
mesozooplankton the lesser portion of microalgal
production. For comparison, in nutrient-rich coastal
waters of the World Ocean is 10% on the average
(Calbet and Landry, 2008).
3 Conclusion
In the studied areas at Sevastopol and Katsiveli
(southern Crimea, Black Sea), the specific rate of
microzooplankton grazing depended on the quantity
and the quality of available phytoplankton;
Chaetoceros
spp. and
Skeletonema costatum
have
been the favorite preys. Phytoplankton blooms in the
region were usually caused by diatoms. Blooming
started when the average ratio between the rates of
phytoplankton loss due to microzooplankton predation
and phytoplankton growth reached approximately
50%. It was estimated that the annual consumption of
phytoplankton by the microzooplankton in the
sampling areas reached 65%. The recent observations
prove the crucial role of microzooplankton in the
matter and energy transfer from phytoplankton to
higher trophic levels in the coastal Black Sea.
4 Data and Methods
During 2006~2007 and 2010, 86 daily surveys were
made at the examined locations. Three sampling
stations were situated near of the coast of Sevastopol
and two were located near village Katsiveli, southern
Crimea’s shore (Figure 5). Station 1 (44°37.25′N,
33°30.43′E) was located in the Sevastopol bay at a
distance of 50 m from the shore; st. 2 (44°36.50′N,
33°29.53′E) in the Quarantine bay, 30 m off the shore;
st. 3 (44º37.20′N, 33º29.50′E) was positioned near the
Kruglaya bay at a distance of 500 m from the shore.
Stations 4 and 5 (44°39.18′N, 33°97.93′E and
44°39.04′N, 33°98.03′E, correspondingly) were
situated in the Blue bay, 200~250 m from the coast.
Except for st.3 where the depth was 30 m, the depth at
other stations varied between 15~18 m.
Figure 5 Location of sampling stations
The rates of phytoplankton growth and loss as result
of microzooplankton grazing were determined using
dilution procedure (Landry and Hasset, 1982). The
major advantage of this method is that it assesses the
rate of total phytoplankton growth along with the rate
of microzooplankton grazing on the phytoplankton.
Samples of seawater (12~15 L) were taken from the
sea surface (~ 0.5 m depth) early in the morning using
Niskin bottle.