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International Journal of Marine Science 2014, Vol.4, No.17: 160-165
http://ijms.sophiapublisher.com
164
(Stelmakh et al., 2013). N.V. Morozova-Vodyanitskaya
(Morozova-Vodyanitskaya, 1957) described a spring
bloom she observed in deep- and shallow-water areas
of the Black Sea in April 1952; at some locations the
abundance of
Pontosphaera huxleyi
(
E. huxleyi
)
amounted to 1 million (and more) cells per litre.
Presumably, the intensive autumn and spring
coccolithophore blooms were provoked not only by
abiotic factors but by biotic interactions in the
plankton, too.
In May 2013, the temperature and light in the sea
surface favoured intensive multiplication of the
coccolithophore; nutrients were sufficient and
therefore could not have been a growth-limiting factor.
High values of phytoplankton specific growth rate
measured in the bloom are not casual; they rather
represent the actual tempo of
E. huxleyi
growth. The
investigations conducted on
E. huxleyi
culture (
Tyrrell
and Merico,
2004
) and our own data allow concluding
that the recent estimates of specific growth rate agree
with the maximum admitted for this coccolithophore.
The relatively low microzooplankton predatory
pressure on the phytoplankton in the blooming Black
Sea water (g/µ ratio 34 % on the average) can indicate
beginning of the bloom. Earlier it was stated that in
marine ecosystems under food deficiency
herbivorous
protists are not likely to be able to prevent the
initiation and development of mass blooms when
conditions are favorable for rapid phytoplankton
growth
(Sher and Sher, 2009)
.
It is very probable that
in the Black Sea in May 2013 phytoplankton mortality
due to grazing has been limited by both quantity and
quality of the prey organisms. Extremely low
chlorophyll-
а
estimates measured in the blooming sea
water suggest prey deficiency, and the taxonomic
structure of phytoplankton evidence poor quality of
the prey. Usually,
E. huxleyi
are a prey of minor
interest to microzooplankton grazers (
Tyrrell and
Merico, 2004
) that is, probably, due to the ability of
this
coccolithophore
to
generate
DMPS
(
dimethylsulfoniopropionate)
. For example, laboratory
investigations point out that the rate of
microzooplankton grazing decreased when strains of
E.
huxleyi
with high DMPS lyase activity were used
(Strom et al, 2003). Five species (including ciliates
and heterotrophic dinoflagellates) showed lower
feeding rates on
E. huxleyi
strains with high DMPS
lyase activity than on low-lyase strains. However, the
heterotrophic dinoflagellate
Oxyrrhis marina
eagerly
grazed on all the tested strains without showing a
decrease in the consumption rate, i.e., the grazing rate
did not depend on DMPS lyase activity. As
DMSP (20
µM) was added to laboratory cultures of ciliates,
Strombidinopsis
acuminatum
and
Favella sp.
, and the
dinoflagellate
Noctiluca scintillans
it resulted in a
28–75% decrease in the feeding rates
on prey
dinoflagellates
Gymnodinium simplex
,
Heterocapsa
triquetra
and
Prorocentrum micans
(Fredrickson and
Strom, 2009).
The evidence given in this publication and previously
(Stelmakh, 2013) suggests that high phytoplankton net
growth rates and low g/µ percent ratios can warn of
the beginning
E. huxleyi
bloom. The pertinent records
show that in a dying out diatom bloom net growth rate
of the phytoplankton usually dropped to zero or even
below, and g/µ ratio was not lesser than 80% and
more.
4 Conclusions
The bloom of coccolithophore
E. huxleyi
that was
observed in the Black Sea in May 2013 has emerged
primarily owing to favorable environmental factors.
Therefore a specific growth rate of the phytoplankton
was the maximal or near-maximal. We suppose that
high phytoplankton net growth rate and low values of
g/µ ratio indicate that
E. huxleyi
bloom is beginning
and will, probably, only enhance.
Acknowledgements
We are grateful to our associates from IBSS – I.I. Babich,
engineer, who measured phytoplankton biomass and identified
species and N.Yu. Rodionova, who measured the content of
nutrients.
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