Journal of Environmental Protection, 2013, 4, 36-44
Published Online November 2013 (
Open Access JEP
Seasonal Succession of the Plankton and Microbenthos
in a Hypertrophic Shallow Water Reservoir at Modra
(W Slovakia)
Marta Illyová1, František Hindák2, Alica Hindáková2, Eva Tirjaková3, Ján Machava4
1Institute of Zoology, Slovak Academy of Sciences, Dúbravská Cesta 9, Bratislava, Slovakia; 2Institute of Botany, Slovak Academy
of Sciences, Dúbravská Cesta 9, Bratislava, Slovakia; 3Department of Zoology, Faculty of Natural Sciences, Comenius University,
Bratislava, Slovakia; 4Catholic University in Ružomberok, PF, Hrabovská Cesta 1, Ružomberok, Slovakia.
Received September 2nd, 2013; revised October 1st, 2013; accepted October 26th, 2013
Copyright © 2013 Marta Illyová et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The seasonal development of the phytoplankton, phytobenthos, zooplankton, and microbenthos in a high eutrophised
intravilan water reservoir was studied. Finally, 25 genera with 44 species of Cyanobacteria/Cyanophytes and 67 genera
with 102 species as well as infraspecific taxa of different groups of microscopic algae were identified. The phytoplank-
ton in most parts of the water basin was strongly dominated by green colonial alga Golenkiniopsis longispina. From
October until December a cyanophyte species Aphanocapsa delicatissima with typical cell dimensions of picoplankton/
was found in large amounts/predominated. As early as spring, a plankton bloom in all its components was observed. At
that time, also a high concentration of total phosphorus was recorded, which in the second half of April dropped rapidly.
The concentration of chlorophyll-a increased from 162.7 μg/L in March to 2322 μg/L in September. Massive occur-
rence of benthic protozoa in the plankton, as a consequence of anoxia, has been observed. Further, the detritivore and
omnivore ciliate species Coleps hirtus dominated in the microbenthos. Altogether 74 of ciliate taxa were detected. Their
abundance and biomass reached peak in April, but these steadily decreased from May until the end of the year. Extreme
values of zooplankton density (54,016 ind/L) were recorded in spring followed by a sudden fall in summer and autumn.
The contribution of rotifers (Brachionus spp., Filinia longiseta) in the total zooplankton density and biomass was 98%.
Relatively a low species richness of crustaceans (4 Cladocera and 3 Copepoda) was observed.
Keywords: Cyanobacterial Water Blooms; Eutrophication; Ciliates; Zooplankton; Shallow Ponds
1. Introduction
Cultural eutrophication is the Earth’s most widespread
water quality problem. It causes harmful algal blooms,
fish kills and many related problems in fresh waters that
are adjacent to areas with large human populations [1].
The small size and shallow water bodies are less stable
than larger lakes, and thus very sensitive to any human
intervention. Pollution from agriculture and sewage is
recognized as having a significant negative impact on
water quality and aquatic biota [2], besides the fish stock
[3]. The biological reaction of aquatic system to nutrient
enrichment is the eutrophication, the eventual cones-
quence of which is the development of primary produc-
tion to nuisance proportions [4]. Free dissolved phospho-
rus and nitrogen are important nutrients for photosyn-
thetic organisms [5], mainly for cyanobacterial blooms [6,
7]. Eutrophication causes considerable changes in bio-
chemical cycles and biological communities [8]. Com-
munity interaction in pelagic food webs is affected by
large scale of physical, chemical and biological processes
and are govern by nutrient limitation, competition, pre-
dation and other ecological forces [9,10]. In shallow wa-
ters, trophic level interactions are complicated by detritus
pathways and influences from the sediments [11].
In this paper we describe the seasonal development of
phytoplankton, algal picoplankton, cyanobacterial bloom,
ciliates and metazooplankton in small hypertrophic urban
reservoir in 2009 and try to elucidate some interactions
between food web components.
Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
2. Material and Methods
The water basin which is situated within the area of
Modra (town in W Slovakia, 48˚18'55.28''N, 17˚19'2.4''E)
was originally built and created as a flood control reser-
voir for the town. The access path and the drive-way for
the fire truck machinery to the basin as well as the con-
crete edges along the whole circumference of its area are
clear evidence of this reality “Figure 1”. However, for
the past decades, it has served as a fishpond. The water
basin lies at an altitude of 144 meters and its surface
covers 0.55 hectares. The maximum depth of this reser-
voir, at high level water conditions, is 2 meters and it has
neither regular direct inflow nor outflow. Due to this fact,
the only way how the water basin obtains water is from
snow-melt during winter and spring seasons and from
rainfall throughout the year. Furthermore, a certain
amount of nutrition gets into the basin from local people
by feeding the fish.
Our research was carried out from February to De-
cember 2009. During this investigation period samples
were taken at monthly intervals. The physical and chemi-
cal water parameters are as follows: water temperature
(˚C), pH, oxygen content (mg·L) and oxygen saturation
(%). All the parameters were measured near the surface
in situ by a multi-functional instrument WTW 80 1i ac-
cording to relevant working methods and processes. The
content of dissolved phosphorus (TRP) (μg/L) was evalu-
ated according to standard analytical techniques (STN
EN ISO 6878); total phosphorus (TP) and total nitrogen
(TN) were determined by a spectrophotometer DR 2800;
and the chlorophyll-a concentration was evaluated by
means of the standard method (ISO 10260:1992). Phyto-
plankton samples were taken by plankton net in mesh
size of 10 µm. Cyanobacteria and algae were determined
merely from fresh samples, diatoms were defined from
permanent slides as well. For the determination of photo-
trophic microorganisms several monographs were used
Ciliophora were studied in plankton and benthos.
Plankton samples were collected from a single spot in the
studied basin, using a take-off apparatus placed on a 3-
meter long telescopic pole, while benthic samples were
taken from four sampling sites. The analysis of samples
was conducted in vivo by means of a light microscope
within 8 hours after sample collection. Taxonomically
difficult species were examined also in protargol-im-
pregnated slides whose preparation followed the protocol
as described by Foissner [18]. Quantitative evaluation of
ciliate abundances included enumerating of active cili-
ates in 10 subsamples, each with a volume of 10 µL. The
obtained data were consequently recalculated to 1 mL.
The estimation of the total biomass was based on the
mean biomass values for particular species as given in
Figure 1. Water reservoir in Modra; right bottom (Photo F.
the determination atlases of Foissner et al. [18-22].
The metazooplankton samples for the qualitative
analysis were taken by vertical tows from the bottom by
a plankton net (70 μm mesh size). The qualitative sam-
ples were taken with a 2 L Patalas sampler from various
depths of the basin (surface, middle and bottom). The
entire water volume (10 L) was filtered through a net of
70 μm mesh size and preserved with 4% formalin. The
zooplankton density (ind/L) was assessed in a 1 mL
Sedgwick-Rafter chamber. The biomass (g/m3) was es-
tablished as wet weight and it was calculated from the
recorded average body lengths and the body length/bio-
mass ratio using tables assembled from several biblio-
graphic sources [23-27].
3. Results
3.1. Physical and Chemical Variables
In the season of 2009, high annual mean values of nitro-
gen, phosphorus and chlorophyll-a were recorded “Table
1”. It is notable that during the first months of our inves-
tigation, from end of March until May, low values of
oxygen were recorded due to respiration having been in
process during the night before “Figure 2”. For instance,
in March 27 the value for oxygen was 6.07 mg/L and in
April 03 we even witnessed oxygen of 4.25 mg/L. Over
the entire period of our research, high pH values were
measured in the water basin peaking in April with pH
10.81 and in May with pH 10.42. The concentration of
total reactive phosphorus (TRP) in the water reached
42.7 μg/L after the ice melted (February 25). The maxi-
mum value of TRP was recorded in early March “Figure
3”. Although the highest inflow concentration of TRP,
1240.8 μg/L was supposed on April 08, it occurred ear-
lier, in April 03 with a high value of TRP concentration
652 μg/L. Meanwhile, in the course of April this value
was gradually decreasing and at the end of the month
(April 29) it reached 180 μg/L. In the second half of the
Open Access JEP
Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
Table 1. Annual average values and ranges for selected
variables in 2009.
Variable (unit) Mean Minimum Maximum
Water temperature (˚C) 16.6 1.3 26
pH value 9.34 8.06 10.81
Oxygen (mg/L) 12.88 4.24 25.97
Oxygen (%) 131 7.5 315
SRP (μg/L) 310.77 14.38 1244.80
Total phosphorus (μg/L) 614 75 1550
Total nitrogen (mg/L) 9.51 0.56 22.85
BOD5 (mg/L) 7.49 5.15 9.67
CHSK (mg/L) 147.8 23.7 534.3
SO4 (mg/L) 93.5 60.4 141.7
NO3 (mg/L) 5.8 0.32 16.2
Cl (mg/L) 45.14 0.62 227
Na (mg/L) 21.2 18.3 25.4
K (mg/L) 31.5 22.9 37.1
Mg (mg/L) 20.8 14.5 31.1
Ca (mg/L) 31.4 10.1 82
Chlorophyll-a (μg/L) 947.3 208.3 2322.4
Conductivity (mS/cm) 553 460 802
Figure 2. Seasonal development of oxygen (mg/L) in 2009.
vegetation season, from August and November, the TRP
values tended to be low “Figure 3”. During the season
the concentration of chlorophyll-a was increasing
strongly ranging from the lowest values in March 162.7
μg/L up to maximum values in September 2322 μg/L;
high values over 1000 μg/L also persisted in October as
well as in November.
3.2. Phytoplankton
Centric diatoms Stephanodiscus hantschii and Cyc-
TRP μg/L
Figure 3. Seasonal development of soluble reactive phos-
phorus (TRP) (μg/L) in 2009.
lostephanos invisitatus together with cyanobacteria Mi-
crocystis ichtyoblabe and Aphanizomenon gracile domi-
nated the phytoplankton from early spring (March-April)
and this fact had a major effect on the colour of the water
which appeared to be brown greenish. At the end of April
and in May the mass development of the green colonial
alga Golenkiniopsis longispina was manifested and the
colour of water changed into green or dark green. Spo-
radically and usually in small numbers also some other
chloroccalean algae were observed from the genera
Scenedesmus, Oocystella, Monoraphidium, and species
Coenococcus planctonicus, Dictyosphaerium tetrachoto-
mum, Kirchneriella obesa, Lagerheimia longiseta, L.
wratislaviensis, Micractinium pusillum, Pediastrum bor-
yanum, Pseudodictyosphaerium minutum, Scenedesmus
pectinatus, Siderocelis ornata, Siderocystopsis fusca and
Tetraedron caudatum [28].
It was interesting to see and it should certainly be
pointed out that some groups of algae, e.g. diatoms, des-
mids or algal flagellates were almost missing in summer
and autumn. Only occasionally a green neustonic film,
caused by Chlamydomonas debaryana, was formed at
the edge of the reservoir or Euglena viridis was concen-
trated at the bottom of the reservoir. Periphyton was
composed of filamentous microorganisms from cyano-
bacteria Homoeothrix janthina, Oscillatoria janus, O.
princeps, Phormidium tenue, Calothrix fusca, from green
algae Oedogonium sp., Aphanochaete repens and zyg-
nematophycean algae from the genera Mougeotia, Spi-
rogyra and Zygnema. The cyanobacterial water bloom
started to be obvious and evident from May. At the be-
ginning it was dominated by the colonies of Microcystis
ichtyoblabe, later on (from July to early August) by a
rare nostocalean species, Cylindrospermopsis raciborskii.
Terminal heterocytes were formed very rarely; thus the
majority of filaments resembled similar species—Raph-
idiopsis mediterranea. From August until the end of the
season in December colonies of chroococcal cyanobacte-
rium Aphanocapsa delicatissima with cells of picoplank-
tic size (1 - 2 µm in diameter) dominated very strongly.
Taxa Microcystis botrys, M. aeruginosa and Anabaenop-
sis milleri ranked among the group of accompanying
Open Access JEP
Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
species of cyanobacterial water blooms.
3.3. Ciliates and Microbenthos
Totaly 74 taxa of ciliates were identified during the year
2009 [29]. The highest species richness of ciliates was
recorded in March (12). On the other hand, the lowest
number of species (5 - 8 species) was observed during
the second half of the year. The seasonal changes in
biomass and abundance of ciliates are shown in “Figure
4”. Cell abundance ranged from 305 to 10,570 ind/mL.
The mean ciliate number was 2595 ind/mL. Biomass
ranged from 2870 to 296,690 mg/mL, averaging 71,491
mg/mL. At the beginning of the vegetation season, i.e. in
March, the community structure was stabilized with an
average density of 300 - 400 ind/mL and a moderate
domination of members of the genus Vorticella. In April,
a boom of ciliate growth was noticed (over 10,000
ind/mL), which was primarily the result of a mass occur-
rence of the prostomatid Coleps hirtus. Also Pseudovor-
ticella natans was recorded during early spring at a rela-
tively high abundance (400 ind/mL). Moreover, a few
large ciliate species, such as Linostomella vorticella and
Paramecium caudatum were observed. In May, the cili-
ate density in the plankton dropped approximately to
2500 ind/mL. Coleps hirtus fell back, but the bacterivo-
rous Cinetochilum margaritaceum, which feeds also on
small aglae, became dominant. Some benthic species,
Spirostomum teres and Holophrya teres, were noted in
the plankton. This is a consequence of anoxia in the ben-
thos, and this phenomenon became very conspicuous in
June when the ciliate density in the plankton (6000
ind/mL) was several times higher than that in the benthos
(1000 ind/mL). During this period there was a compara-
tively poor species spectrum (5 - 8 species) with Coleps
hirtus and Cinetochilum margaritaceum being dominant
both in the plankton and in the benthos. In the July
plankton, there was an overall decrease of ciliate densi-
ties (1200 ind/mL), but the number of species in-
creased moderately to 12. The community was equable
and no species was dominanting over other ones. Small
bacterivorous species, such as Ctedoctema acanthocryp-
tum, Cyclidium glaucoma and Cinetochilum margarita-
ceum are characteristic for this period.
Species of algal and cyanobacterial diet, especially,
Frontonia leucas and Halteria grandinella began to oc-
cur in the summer communities. Further, algivorous and
bacteriovorous species (Pseudocohnilembus pusillus,
Cinetochilum margaritaceum) replaced the predatory
species in benthos. Frontonia leucas was the most domi-
nant algivorous species in the summer months, but dis-
appeared in September when the bacteriovorous species
Dexiotricha tranquilla became dominant both in the
plankton and in the benthos. As concerns predatory
abundance ind/
biomass mg/10
abu nda nce
bioma ss
Figure 4. Seasonal development of abundance (ind/mL) and
total biomass (mg·103 m/L) of ciliates in 2009.
gymnostomate ciliates, members of the genus Actinobo-
lina occurred mainly in spring and summer. At the same
time, a high abundance of colonial peritrichous ciliates of
the genus Epistylis (E. chrysemydis and E. enzii) was
recorded mostly in the benthos. By contrast, typical
planktobionts such as Rimostrombid ium, Limnostrombi-
dium, Tintinidium and Hastatella were noted only rarely
and at low abundance.
3.4. Metazooplankton and Rotifers
The season of changes in biomass and abundance of
zooplankton are showen in “Figure 5”, the changes in
biomass of rotifers, cladocerans and copepods in “Figure
6”. The abundance of the zooplankton ranged during the
sampling period from 102 ind/L up to 54,016 ind/L. The
metazooplankton was dominated by rotifers, which con-
tributed 98% of its total density and 91.6% of the total
zooplankton biomass. Accordingly, it can be stated that
the seasonal dynamics of the abundance of total net zoo-
plankton copies the seasonal dynamics of the abundance
of rotifers. As early as March, a very unusual abundance
of rotifers was recorded (15,680 ind/L). Moreover, this
high density production kept increasing and in April
reached extremely high values (53,712 ind/L) with the
dominance of the genus Polyarthra (92%). Although in
April the biomass of rotifers was high, it reached its
maximum level in July. We started to witness a species
dominance of Brachionus budapestinesis (57%) and
Filinia longiseta (36%). In the second half of the vegeta-
tion season a considerable drop of rotifers was observed
Figure 5”. While at the beginning of autumn the domi-
nance of B. budapestinensis (85%) was still prevailing, in
November only two species (Keratella quadrata and
Cephalodella gibba) of a very low abundance were
The proportion of cladocerans to total quantity was
considered low and their ratio to the total biomass indi-
Open Access JEP
Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
abundance ind/
biomass g/m
bioma ss
Figure 5. Seasonal development of abundance (ind/L) and
total biomass (g/m) of net zooplankton in 2009.
relative biomass
Figure 6. Seasonality of biomass (%) proportions of all
groups of net zooplankton in 2009.
cated 1.4%; however, during the autumn months their
relative biomass increased due to a regress of rotifers
Figure 6”. The most important cladoceran species was
Alona rectangula with abundance ratio from 2 ind/L to
44 ind/L. In addition to Alona, also a rare occurrence of
Chydorus sphaericus was observed. The contribution of
copepods in a total zooplankton biomass came to 7%.
Throughout the whole season the copepods were present
mostly as nauplii and small copepodites, adult being rare
(Acanthocyclops trajani).
4. Discussion
There are some evidence about the high eutrophication of
water body in the reservoir: 1) cyanobacterial bloom and
high chlorophyll-a content as a consequence of a high
phosphorus content; 2) changes in species composition of
planktonic communities, decrease of quantity and species
biodiversity at all plankton communities and microben-
thos; 3) anoxia at the bottom of reservoir indicated by
protozoan community.
1) The bloom of filamentous cyanobacteria in the half
of the summer is an indication of the eutrophic to the
hypertrophic state of the Modra reservoir. For example,
Cylindrospermopsis raciborskii which is adapted to low
light conditions is able to fix atmospheric nitrogen [30].
The small reservoir at Modra can be described as a typi-
cal pond with massive technical modification and with
no original macrovegetation [31]. It can be assumed that
its water is rich in nutrients and tied to sediments what is
very typical for all small water basins and fishponds [3],
or urban lakes [32]. The high concentration of chloro-
phyll-a and the dominance of cyanobacteria as well as of
green algae (namely Chlorococcales) over the vegetation
period indicated a high trophic level in the water basin
and the high rate of primary production. It is generally
agreed that if there is a sufficient source of nutrients in
water, phosphorus particularly, an excessive phytoplank-
ton production occurs cf. [33]. Phosphorus is often found
to be the limiting nutrient in inland fresh waters [10,34].
Values in excess of 30 μg/L ortho-phosphate phosphorus
(PO4-P) in river waters and in excess of 20 μg/L total P
(Ptot) in lakes are considered by the Irish EPA to lead to
eutrophication [35].
However, as far as spring we measured and recorded
far higher values for the reactive as well as total phos-
phorus concentration which largely determined the ex-
cessive production of phytoplankton. This corresponds
well with the findings published by [36] that found out a
linear correlation between TP and the maximum phyto-
plankton biomass at the beginning of vegetation season.
In spring, in addition to diatoms, a proliferation of cyano-
bacteria from the genus Microcyctis was observed at
Modra. For the period of winter the green colour of water
showed itself through the ice which is not an unusual
phenomenon. The production of cyanophytes below the
ice at the temperature of 3˚C was also observed by
Maršálek [37], or by Kiss and Genkal [38]. The high val-
ues of phosphorus remained until the middle of April
which was followed by a sudden drop presumably due to
consumed phosphorus at the massive phytoplankton de-
velopment. This manifested itself also with high values
of alkaloids, as they increase the values of pH in their
surroundings even to 9 - 11 by their metabolic activities
2) During the period of our investigation 25 genera
with 44 species of cyanophytes and 67 genera with 102
species as well as infraspecific taxa of different groups of
microscopic algae were identified [28]. Five are the first
records from the territory in the Slovak Republic cf. [39],
i.e. two species of cyanobacteria: Synechococcus muci-
cola Joosten, Synechocystis endophytica (G. M. Smith)
Joosten, and three species of green algae: Nautococcus
mamillatus Korshikov, Bicuspidella incus Pascher, Des-
matractum indutum Pascher [28]. However, the phyto-
plankton diversity was generally lower in comparison
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Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
with other eutrophic waters in Western Slovakia cf. [40].
Eutrophication causes considerable changes in bio-
chemical cycles and biological communities [8]. In the
Modra reservoir, the response of planktonic and benthic
ciliates on the phytoplankton development was mani-
fested as a change in the ciliate community structure [29].
The omnivorous species were replaced by algivorous and
bacterivorous ones. Ciliates seem to be very flexible in
reaction to environmental changes since many of them
are capable to alter their food sources upon the offer
within a relatively short time. Dias and D’ Agosto [41]
found out that Frontonia leucas feeds especially on dia-
toms in oligotrophic waters and only rarely consumes
bacteria and cyanobacteria. However, the diet of this
species changes when saprobiological level increases. In
Modra, abundance of F. leucas raised in summer after a
massive development of cyanobacteria and green algae
especially Golenkiniopsis. Due to the high feeding activ-
ity, this ciliate species could play a key role in reduction
of water bloom [42]. These authors also showed that
Halteria grandinella is another good candidate for re-
duction of water bloom, as it consumed over 70% of all
cyanobacteria which were engulfed by ciliates. These
findings are supported also by our observations in that H.
grandinella and also F. leucas co-occurred in the period
with a maximum developed cyanobacterial water-bloom.
Also Vörösváry [43] recorded an increased occurrence of
algivorous and bacterivorous species, especially from the
genera Chilodonella, Colpidium, Stylonychia, Coleps,
Paramecium and Frontonia as well as of species living
on organic remnants (Spirostomum) in a stream with wa-
ter bloom due to the pollution by sewage waters. Thus,
these taxa can be potentially used in suppression of water
bloom. Peritrichous filter feeders, which often occur at
high abundances in benthos, could be also highly effec-
tive in elimination of water bloom [44].
The hypertrophic conditions of the water body in
Modra were documented also by the net zooplankton
community: the extremely high abundance of the rotifers
in spring and extremely low planktonic crustaceans. The
extreme abundance of rotifera at the beginning of the
vegetation season draw the parallel between them and the
maximum values in spring which is the typical standard
for pond ecosystems [3]. The maximum density of roti-
fers in April reproduces a massive increase of diatoms
and colonial green algae as the majority of species pre-
sent in water are herbivorous filter feeders. Sládeček [45]
in his research make a reference to a very eutrophic
fishpond with abundance as high as 23,900 ind/L. High
abundance values of rotifers in spring (over 30,000 ind/L)
were also observed in naturally eutrophic two arms in the
Morava River floodplain [46]. The spring phase of rotifer
development was followed by a rapid drop in its density
which is quite typical for the summer season [47]. From
August on, no rotifer development was spotted and the
quantity of these species dropped significantly most
likely due to the existence of cyanobacteria. One of the
most undesirable aspects of cyanobacteria is an eventual
production of toxins [33]. As Dumont [48] states, the ex-
tra cellular substances of cyanobacteria are toxic for ro-
tifers so they repress their development. At that time the
species typical for self-purification reservoirs of sewage
(Brachionus budapestinensis and Filinia longiseta) ruled
in the rotifer community, so did the ones which are the
indicators of deteriorating saprobic conditions in waters
After a spring development of algae we suppose the
increase of density of filter feeder planktonic crustaceans
[49], e.g. large cladocerans grazers and herbivorous co-
pepods (Eudiaptomus). Large grazers are able to control
phytoplankton biomass even under hypereutrophic con-
dition (up to 1600 μg/L) [50]. But despite the reach food
source in the water basin in Modra, there were neither
herbivore copepods observed at all, nor large filter feed-
ers from the genus Daphnia; moreover, we did not even
record the species Bosmina longirostris. It can be ex-
plained by the lack of edible food here. The typical net
zooplankton species for eutrophic water and fishponds
are small cladocerans Bosmina longirostris and B. core-
goni, and a high abundance of cyclopoid copepods
Thermocyclops and Eudiaptomus [3,32,51]. Our findings
documented the occurrence of only two small cladocer-
ans Alona rectangula and Chydorus sphaericus, which
were observed in plankton in a small abundance. Both
species were spotted in plankton of extremely hypertro-
phic water bodies by Sládeček and Sládečková [52]. The
poor abundance of planktonic crustaceans was most
likely due to cyanobacteria which strongly proliferated as
far back as the beginning of the vegetation season and
were less edible for filter feeders than small algae. Par-
ticularly, the larger colonial and filamentous cyanobacte-
ria cannot serve as food source for zooplankton because
of its parameters [49] as well as its eventual toxicity [33].
Mayer et al. [32] also recorded a significant decrease in
zooplankton biomass over the summer development of
cyanobacteria which, as they claim, was determined by
changes in food source and the increase of water tem-
3) We assume that the direct consequence of the high
production of phytoplankton was the excessive consump-
tion of oxygen near the bottom of the basin which led to
anoxia. Presumably, the adverse conditions (anoxia) at
the bottom of the basin contributed to the occurrence of
some benthic species, e.g. Spirostomum teres and Holo-
phrya teres, in the plankton. Moreover, ciliate densities
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Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic
Shallow Water Reservoir at Modra (W Slovakia)
in the June plankton (6000 ind/mL) were several times
higher than those in the benthos, which is a rare phe-
nomenon in the protozoan communities. Also Finlay [53]
noted that ciliates can migrate from the benthic zone into
the water column depending on the oxygen content.
Moreover, he argued that species bigger than 150 µm,
such as Loxodes and Spirostomum, do not migrate. How-
ever, we observed high abundances of Spirostomum teres
not only in the benthos but also in the plankton during
May. This essentially supports Finlay’s migratory theory
also for this species.
5. Conclusion
The seasonal development of the phytoplankton, phyto-
benthos, zooplankton and microbenthos of a highly eu-
trophised intravilan water reservoir was investigated. The
cyanobacterial bloom and high chlorophyll-a content, as
a consequence of a high phosphorus concentration, in-
fluenced the seasonal dynamic of the plankton and mi-
crobenthos communities. The highest concentration of
TRP was recorded from March to early April. Subse-
quently the boom of the planktonic communities oc-
curred in that ciliates and rotifers reached the highest
abundance and biomass, and the green colonial alga Go-
lenkiniopsis longispina manifested a mass development.
The cyanobacterial water bloom, composed mainly from
the colonies of Microcystis ichtyoblabe, started in May
without any significant influence on the planktonic com-
munities of the reservoir. However, the colonies of
chroococcal picoplanktic cyanobacterium, with cells 1 -
2 µm in diameter, dominated very strongly during the
summer. Consequently the densities of ciliates and other
zooplankton dropped significantly. Paced plankton sank
to the bottom and started to decompose, which resulted
in oxygen depletion. As a consequence of anoxia, the
massive and multiple occurrences of benthic protozoa in
the plankton were observed in June. The ciliate densities
in the plankton were several times higher than those in
the benthos. From August on, in the second half of the
vegetation season, a considerable drop in abundance of
planktonic invertebrates was observed, most likely due to
the presence of cyanobacteria.
6. Acknowledgements
This study was supported by APVV, project No. 0566-07,
VEGA projects No. 1/0600/11 and 2/0113/13. This pub-
lication is the result of the project implementation:
Comenius University in Bratislava Science Park sup-
ported by the Research and Development Operational
Programme funded by the ERDF Grant number: ITMS
26240220086. The study was also supported by the pro-
ject ITMS: 26240220049.
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