VOLUM OMAGIAL - Facultatea de Ştiinţe ale Naturii şi Ştiinţe Agricole

Laura Boicenco / Ovidius University Annals, Biology-Ecology Series 14: 163-169
chlorophytes – 77 species (19.4%) and
cyanobacteries – 55 species (12.9%); the rest of
phyla (Chrysophyta, Euglenophyta, Cryptophyta),
with 12, 8 and 6 species, respectively, constitute
together only 6.6% of the total (Fig. 2).
Fig. 2. Taxonomic composition.
Ecologically, the phytoplankton represents a
combination of autochthonous species, comprising
euryhaline marine and brackish water forms (218),
and alochthonous forms, comprising fresh-brackish
and fresh water forms (178), reflecting the mixed
marine water masses and riverine fresh waters
which characterise the hydrologic regime of the
Romanian sector.
Table 2. Structure by ecologic groups.
Phylum MarineFreshbrackish brackish
Bacillariophyta 112 45
Dinoflagellata 83 2
Chlorophyta 0 77
Cyanobacteria 9 42
Chrysophyta 8 4
Euglenophyta 2 6
Cryptophyta 4 2
Total 218 178
Diatoms
During 1996-2007 the averaged data for the
whole Romanian littoral waters suggest that the
communities are dominated by diatoms, both in
terms of numeric density and biomass. The
multiannual mean of 833.5·10 3 cells·l -1 is 12.2
times higher than dinoflagellates (68.5·10 3
cells·l -1 ). The highest diatoms mean density -
2,311.9·10 3 cells·l -1 , achieved in 1997 was 10.2
times higher than that recorded for dinoflagellates
165
in the same year. The diatoms produced their highest
mean densities during summer; in the summer of 1997,
they exceeded 6 million cells per litre. When we were
able to collect samples in winter, e.g. in 1999, we
found out that many diatoms – such as S. costatum, C.
caspia, Ch. socialis, N. tenuirostris began to vegetate
in winter. So, we detected communities very well
constituted, higher than 10 6 cells∙l -1 . In five out of 12
springs investigated (1999, 2003, 2004, 2006 and
2007), the diatom populations were most abundant;
they progressively decreased toward summer and
autumn.
Table 3 shows the diatom species with the
highest densities in the Romanian Black Sea waters,
between 1991 and 2007.
Table 3. The highest densities of diatoms
(10 6 cells∙l -1 )
1996- 2001-
Species
2000 2007
Cyclotella caspia 10.5 78.6
Skeletonema costatum 24.4 37.3
Nitzschia tenuirostris 1.8 15.5
Cerataulina pelagica 8.2 10.0
Chaetoceros socialis 22.2 7.5
Skeletonema subsalsum 4.4 3.9
N. delicatissima 0.6 2.5
Small-sized diatom, Skeletonema costatum is an
omnipresent species in the communities identified not
only at the Romanian littoral but in whole Pontic
basin, producing most of the bloom events. Its
maximum level was registered in July 2002, off
Constanta (37.3∙10 6 cells∙l -1 ). Its second outburst
occurred in the shallow waters of Mamaia Bay (where
the sampling is carried out almost weekly); starting in
the second half of March 1998, the phytoplankton
communities were more and more abundant, attaining
the value of 24.3∙10 6 cells·l -1 on March, 31. We have
to remark that the communities from Mamaia Bay
were almost monospecific, being constituted up to
99.8% only by Skeletonema.
Eurythermal and euryhaline species,
Skeletonema vegetates abundant starting from winter,
not only in Mamaia Bay, where usually attain over
5∙10 6 cells∙l -1 , in January-March, but also in deeper
waters off Constanta, where its concentrations reached