VOLUM OMAGIAL - Facultatea de Ştiinţe ale Naturii şi Ştiinţe Agricole

Ovidius University Annals of Natural Sciences, Biology – Ecology Series Volume 14, 2010
SPATIO-TEMPORAL DYNAMICS OF PHYTOPLANKTON COMPOSITION AND
ABUNDANCE FROM THE ROMANIAN BLACK SEA COAST
Laura BOICENCO
National Institute for Marine Research and Development „Grigore Antipa”
300, Mamaia Bd., Constanta, 900581, Romania, e-mail: boicenco@alpha.rmri.ro
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Abstract: Based on more than 2,000 samples collected during 1996-2007, the paper deals with the taxonomic
and ecological composition, spatio-temporal development of phytoplankton blooms from waters of up to 50 m
depths laying on the Romanian Black Sea. The author identified 396 species, varieties and forms, and assessed a
density mean varying among 417 and 3,376∙10 3 cells∙l -1 . Bacillariophyta phylum, with a number of 157 taxa and
a density mean of minimum 186.4 (in 2000) and maximum 2,311.9∙10 3 cells∙l -1 (in 1997), was the most numerous
(39.6% of the total); Dinoflagellata was the second dominant group, represented in the communities with 85 taxa
(21.5%); density means ranged from 9.2 (in 2003) and 225.6∙10 3 cells∙l -1 (in 1997). Groups Chlorophyta and
Cyanobacteria represented only 19.4 and 12.9%, respectively, from the total number of species. Species showing
huge developments in the reference period were: the diatoms Skeletonema costatum, Cerataulina pelagica,
Nitzschia delicatissima, Chaetoceros socialis, Cyclotella caspia and dinoflagellates Prorocentrum minimum,
Heterocapsa triquetra and Scrippsiella trochoidea.
Keywords: taxonomic composition, ecological composition, phytoplankton blooms
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1. Introduction
The early 1990s seemed to be a new
beginning for the Black Sea ecosystem. After the
“Mnemiopsis era” describing the 8 th decade,
superimposed on the 20 years-long “eutrophication
era” started in the 1970s, signs of improvement of
its ecological state occurred, evidenced by a
reduction of the Danube river nutrient input, a
decrease in the frequency of hypoxia conditions, an
increase in fodder zooplankton biomass, and a
drop in M. leidyi’s abundance. The recovery of the
ecosystem was attributed partly to the collapsing
economy and agricultural production, and to some
protective measures taken to control anthropogenic
pollution in all the coastal countries.
Due to their short life cycles and quick
response to changes in their environment, the
phytoplankton was sensitive to these new shifts,
displaying a tendency to “normal” status before
eutrophication: decreased amplitude and frequency
of blooms, and a qualitative and quantitative
structure similar to the period 1960-1970 rather
than 1980-1990.
So, between 1991 and 1996, only six maximum
densities, higher than 10 6 cells·l -1 , were registered,
compared to 13 in the1980s; among them, only two
species produced ample bloom events: Prorocentrum
minimum (53.1 and 93.7·10 6 cells·l -1 in the summer of
1991 and 1995) and Microcystis pulverea (60.0·10 6
cells·l -1 in the spring of 1991) [1].
The range of algal groups was different from that
of 1970s and 1980s, but quite similar to that of 1960-
1970 with a reduction of non-diatom bloom amplitude
and increase of numerical density and especially
biomass of diatoms. The reduction of non-diatoms
coincided with decrease of nutrient stocks, especially
of phosphates, which reached concentrations of 2.55
µM·l -1 in 1991-1996, 2.8 times lower than in 1986-
1990 [1].
During 1995-1996, the Black Sea ecosystem
showed abrupt shifts in all trophic levels, from primary
producers to apex predators. This arose as a
manifestation of concurrent changes in its physical
climate induced by intensive warming of surface
waters, as well as abrupt increases in the mean sea
level and annual mean fresh water flux [2].
ISSN-1453-1267 © 2010 Ovidius University Press