Journal of Water Resource and Protection, 2011, 3, 245-252
doi:10.4236/jwarp.2011.34031 Published Online April 2011 (
Copyright © 2011 SciRes. JWARP
Increase in Straight and Coiled Cylindrospermopsis
raciborskii (Cyanobacteria) Populations under
Conditions of Thermal De-Stratification in a Shallow
Tropical Reservoir
Maria do Carmo Bittencourt-Oliveira1,2*, Ariadne do Nascimento Moura3,
Talita Caroline Hereman1,2, Enio Wocyli Dantas3,4
1Universidade de Sã o Paulo, ESALQ, De p. C i ênci as Bi ol ó gic as , Av. Pádua Dias, Piracicaba, Brazil
2Programa de Pós-Gra duação em Ciências Biol ó gic as, Área de Bi ol o gia Veget al,
UNESP-Rio Claro, Rio Claro, Brazil
3Universida de Fed eral Rural de Pern a m buco, Departamento de Biologia-Área de Botânica,
R. Dom Manuel de Medeiros, s/n, Dois Irmãos, Recife, Brazil
4Universidade Estadual da Paraíba - UEPB - Campus V, Centro de Ciências Biológicas e Sociais
Aplicadas-CCBSA, R. Monsenhor Walfredo Leal,487, Tambiá, João Pessoa, Brazil
In recent decades, there have been frequent occurrences of the cyanobacterium Cylindrospermopsis
raciborskii in northeastern Brazil. Little is known regarding the response of straight and coiled morphotypes
to environmental conditions such as light intensity and water temperature. Samples were collected at the
Mundaú reservoir (PE, Brazil) at six sampling depths in the dry and rainy season. Both morphotypes
exhibited seasonal and vertical differences in densities. The reservoir was stratified in the dry season, with a
predominance of the straight morphotype. The coiled morphotype exhibited greater densities in the lower
strata and prove to be more susceptible to light. There was evident thermal de-stratification in the rainy
season, with a predominance of the coiled morphotype in the surface layers. Thermal de-stratification favors
an increase in both morphotypes by providing adequate conditions for growth, such as low light intensity and
milder temperatures, which are characteristic of the winter season in the northeastern Brazil.
Keywords: Cyanophyta, Light, Morphotype, Northeastern Brazil, Mundaú Reservoir
1. Introduction
In recent decades, the occurrence of cyanobacterial
blooms, such as those of the genera Microcystis Kützing
ex Lemmermann, Anabaena Bory ex Bornet & Flahault
and Planktothrix Anagnostidis & Komárek, have become
a common event in different regions of the world and are
closely related to eutrophication processes in aquatic
ecosystems. The presence of cyanobacterium in freshwa-
ter ecossystems are often associated with eutrophic con-
ditions, CO2 availability and high temperatures [1] low
luminosity [2], alkaline pH [3], high concentrations of
nutrients, especially phosphorus [4] and a low N:P ra- tio
[5], and buoyancy regulation [6]. Such blooms alter the
ecological balance of these systems and give an un-
pleasant taste and smell to the water, thereby elevating
treatment costs. However, the greatest problem stems
from the fact that some species produce toxins
(cyanotoxins) and can cause serious public health prob-
lems. These toxins can accumulate in the food chain and
produce different symptoms of intoxication.
Cylindrospermopsis raciborskii (Woloszynska) See-
nayya et Subba Raju (Ordem Nostocales) is one of the
most worrisome bloom-forming species in Brazil due to
its extremely invasive nature and increasing occurrence.
Initially classified as having pan-tropical distribution
[7], C. raciborskii was soon recorded in subtropical
environments in Africa and the Americas as well as in
temperate regions, where it occurs in shallow lakes (for
more details see [8]. Massive populations of C.
raciborskii in a public water supply reservoir are
worrisome due to their capacity to produce hepatotoxins
(cylindrospermopsin) and neurotoxins (saxitoxins) [9].
C. raciborskii has multiple adaptation strategies, such
as resistance to herbivory, tolerance to low light intensity,
ability to migrate in the water column due to aerotopes,
storage and use of intracellular reserves and the capabil-
ity of fixing atmospheric nitrogen [10]. Populations with
straight and coiled trichomes have been observed occur-
ring simultaneously in different proportions in Australia
[8,11,12] and northeastern Brazil [13,14]. Although mo-
lecular investigations reveal that the straight and coiled
morphotypes pertain to the same species [11,15], it is not
yet clear how these morphotypes behave in response to
environmental conditions such as light intensity and wa-
ter temperature. In recent decades, the frequent occur-
rence of C. raciborskii in reservoirs and small lakes has
been recorded in different states of Brazil, especially in
the northeastern region of the country [13,16-21].
In stratified lakes, populations may reach peak density
in the epilimnion. With the data available in the literature,
however, it is not possible to generalize on vertical
movements or depths with light intensities that are more
adequate to the growth of this species [22].
Considering the scarcity of studies on populations with
straight and coiled trichomes that occur simultaneously
in their natural environment as well as the need for in-
formation on the behavior of these populations in nature,
the aim of the present study was to determine the spatial
and seasonal dynamics of these C. raciborskii morpho-
types in relation to light intensity and temperature in the
water column of a shallow eutrophic tropical reservoir.
2. Materials and Methods
2.1. Study Site
The Mundaú reservoir is located in the city of Garanhuns
(8°5540S to (8°5704S and 36°3040W to
36°2902W) 716 m above sea level in the state of Per-
nambuco (northeastern Brazil) (Figure 1). The reservoir
has a water accumulation capacity of approximately
1 968 600 m3, surface are of 4 km2 and mean deepness
around 11m. Its main purpose is to supply the public
drinking water, but it receives part the residential sewage
of the city [23]. The reservoir has pH ranging from alka-
line to neutral, with a high availability of phosphorus and
limited nitrogen [24]. The geographical region is
characterized by high temperatures and dry periods,
especially between October and March (summer); the
winter (April to September) is characterized by greater
precipitation and milder temperatures.
2.2. Site and Periods of Samplings and
Community Study
Spatial and seasonal variations in the population density
of the straight and coiled C. raciborskii morphotypes
were determined from collections made at a single
sampling site located near the central pelagic region of
the reservoir (8°5640S and 36°2926.2W) at six
sampling depths (surface, 0.5 m, 1.0 m, 2.0 m, 5.0 m
and 10.0 m) during the dry (October,06 and November,
06/2004) and rainy seasons (August, 17 and September,
21/2004; June, 07 and August, 20/2005), only one
sampling for each month. Maximal depth at this site
varied according to the season (dry-10 m or rainy-12 m),
with a mean of 11 m during our study.
Throughout the water column, samples were
collected with a van Dorn bottle and subsequently fixed
in 5% acetic Lugol solution for quantitative analysis.
Trichome counts were performed directly with the use
of a Fuchs-Rosenthal chamber and a binocular optical
microscope (Nikon, Japan). Whenever possible, a
minimal number of 450 trichomes were counted for
each morphotype in order to obtain a 5% error and 95%
level of confidence [25]. Morphological analysis
involved measurements of the length and width of the
vegetative cells (n = 1 800), heterocysts (n = 450) and
number of cells per trichome (n = 600) in both morp-
hotypes, with the aid of a micrometered ocular coupled
to the microscope.
2.3. Abiotic Analyses
Air temperature was measured with a common mercure
thermometer and water temperature was obtained using
an YSI field probe (model 556). Depth (m) was
determined with a bathymeter (Garmin, Fishfinder 100).
Light intensity was accessed using a photometer (LI-
COR, model LI-250) with an underwater cable and
spherical sensor. Precipitation during the sampling
months was obtained from the National Meteorology
Institute in the city of Caruaru [26].
2.4. Statistical Methods
The normality of the data was tested for the choice of
analyses of variance and correlation. Analysis of vari-
ance (ANOVA, 5% level of significance) was used with
normal data to determine the occurrence of seasonal and
vertical variations. Spearman’s correlation coefficient
Copyright © 2011 SciRes. JWARP
Figure 1. Map of study area; Mundaú reser voir, PE, nor theastern Brazil.
Mundaú reservoir
Sampling satation
500 m
(rs) was used to determine associations between abiotic
variables and morphotype density. Tukey test was used
to analyze temporal differences. The Statistica 2004 pro-
gram (StatSoft, Inc., Tulsa, OK, USA) was employed for
all analyses.
3. Results
During the study period, mean monthly air temperature
ranged from 21.6 to 23.1 in the rainy season and from
23.1 to 29.1 in the dry season. Figures 2 and 3 display
underwater light intensity, water temperature, straight
and coiled trichome density and precipitation.
Water temperature exhibited significant seasonal
differences (F = 20 832, p < 0.001). October/04 and
November/04, months of dry season, show statistical
differences of rainy months (Tukey, p < 0.05). The water
column was uniformity in October and November 2004,
in these months no significant difference was found for
light intensity (Figures 3(a), (b)).
During the months sampled, single-species blooms of
C. raciborskii (straight and coiled morphotypes) comp
osed the entire phytoplankton community, which is
common in this body of water.
Both morphotypes exhibited seasonal and vertical
differences in density (Fstraight = 5.232; Fcoiled = 10.894,
p < 0.001 and Fstraight = 5.579; Fcoiled = 9.913, p < 0.001,
respectively). Greater densities occurred in the rainy
season (5.3 and 4.3 x 107 trichomes mL1 or 2.7 and 2.4
× 109 cell mL1 for straight and spiraled morphotypes,
respectively, data not shown). There was a predomina-
nce of straight trichomes when light intensity was above
8 µmol m2·s1 and temperature was above 24. The
coiled morphotype had greater densities in this same
light intensity range but with the temperature below 24
ºC. There was a tendency toward the predominance
Copyright © 2011 SciRes. JWARP
b c d
Deth (m)
(106 trichomes. mL–1)
(106 trichomes. mL–1)
90 mm*
Deth (m)
(106 trichomes. mL–1)
140 mm*
Deth (m)
320 mm*
Deth (m)
(106 trichomes. mL–1)
110 mm*
21 22 23 24 25 26 27 28 2921 22 23 24 25 26 27 28 29
0 20 40 60 80 100
Water temperature ()
21 22 23 24 25 26 27 28 29
Water temperature ()Water temperature ()
Water temperature ()
21 22 23 24 25 26 27 28 29
Water temperature
Light intensity
Straight morphotype
Coiled morphotype
(μmol photons.m–2, s–1)
Light intensity
0 20 40 60 80 100
(μmol photons.m–2, s–1)
Light intensity
0 20 40 60 80 100
(μmol photons.m–2, s–1)
Light intensity
(μmol photons.m–2, s–1)
a Light intensity
0 20 40 60 80 100
Figure 2. Vertical variation in trichome density of straight and coiled C. raciborskii morphotypes in relation to water
temperature and underwater light intensity at the Mundaú reservoir in the rainy season; (a) August, 17/2004; (b) Septe mber,
21/2004; (c) June,07/2005; (d) August, 20/2005; * accumulated monthly rainfall.
(106 trichomes. mL–1) (106 trichomes. mL–1)
60 0
Deth (m)
Deth (m)
21 2223242526272829
2627 28 29
Water temperature () Water temperature ()
b a
(μmol photons.m–2, s–1)
Light intensity
0 20 40 60 80 100
(μmol photons.m–2, s–1)
Light intensity
0 20 40 60 80 100
Water temperature
Light intensity
Straight morphotype
Coiled morphotype
7 mm*
5 mm*
Figure 3. Vertical variation in trichome density of straight and coiled C. raciborskii morphotypes in relation to water
temperature and underwater light intensity at the Mundaú reservoir in the dry season (a) October, 06/2004; (b) November,
06/2004; * accumulated monthly rainfall.
Copyright © 2011 SciRes. JWARP
Copyright © 2011 SciRes. JWARP
Figure 4. Variation in vegetative cell size, mean and standard deviation values for straight and coiled Cylindrospermopsis
raciborskii morphotypes during rainy and dry season (a. length, b. width).
of coiled trichomes when light intensity was below 3
µmol m2·s1. The straight morphotype exhibited a
greater number of trichomes with heterocysts in
comparison to the coiled morphotype, which were only
found in October and November 2004 (dry season) and
in September 2004 (rainy season)( data not shown).
An analysis of the data on C. raciborskii between
different sampling depths and months reveals that the
densities of both morphotypes had a positive correlation
with light intensity (rsstraight = 0.372 and rscoiled = 0.399, p
< 0.001). Both morphotypes also had a negative
correlation with depth (rsstraight = 0.486 and rscoiled =
0.557, p < 0.001) .
The Mundaú reservoir was stratified in the dry season,
with higher temperatures and greater light intensity in the
surface layers (down to 1 m) and a predominance of the
straight morphotype. In the lower strata, the coiled mor-
photype exhibited greater densities, but with no signifi-
cant differences. The straight morphotype population
was tolerated to high light intensity (83.23 to 92.26
µmol m2·s1) and temperatures (25.5 to 28.0),
whereas the coiled morphotype was proved as more
susceptible to light intensity. The existence of strata with
different water densities may facilitate the permanence of
the coiled morphotype population in the lower layers of
the water column, which is more adequate to its
In the rainy season (winter), the reservoir remained
shallow (10 to 12 m), with evident thermal de-
stratification. Variations in temperature were lesser than
those found in the summer months and there was low
light intensity throughout the water column, with an
extreme reduction in light below the surface layers. The
general pattern of the populations under these cond-
itions was a predominance of the coiled morphotype at
higher depths (to 1 m), with the exception of September
2004, and there was a balance between the morphotypes
at greater depths, with a slight predominance alternating
between the two morphotypes. The coiled morphotype
population developed well under conditions of low light
intensity and milder temperatures, which are character-
istics commonly found in the winter months.
The mean length and width of the vegetative cells
were similar in both morphotypes, regardless of the
season and with no differences beyond the shape of the
trichome. In the straight morphotype, vegetative cells
measured 6.14 to 6.92 µm in length and 2.68 to 3.03 µm
in width. In the coiled morphotype, vegetative cells
measured 6.46 to 7.03 µm in length and 2.68 to 3.12 µm
in width (Figure 4). In straight morphotype the
heterocysts measured 6.73 to 7.09 µm in length and
2.79 to 3.01 µm in width; the number of cells per
trichome was 47 to 56 and in the coiled morphotype the
heterocysts measured 6.79 to 7.02 µm in length and
2.84 to 3.02 µm in width and the number of cells per
trichome was 49 to 59.
4. Discussion
According to [27], populations of cyanobacteria exhibit
considerable growth under conditions of high tempera-
ture, low N:P ratio and alkaline pH. However, the
dominance of one species or another depends on its
particular characteristics, survival strategy, nutritional
requirements and need for light. During the study period,
the Mundaú reservoir exhibited environmental character-
istics that allowed the occurrence of high densities of C.
raciborskii, such as high concentrations of phosphorus,
high temperature (above 21) and availability of light in
the epilimnion, but with an accentuated drop in the
metalimnion and hypolimnion.
In northeastern Brazil, the summer months are
characterized by low rainfall and high temperatures,
whereas rains occur during the winter months,
accompanied by a slight drop in temperature and lesser
light intensity. The highest density values were reached
in the rainy season due to the increase in the
concentration of nutrients carried by the rain as well as
the circulation of the mass of water, which stirs up the
sediment and suspends nutrients in the water column.
Among the rainy months, September had the greatest
densities of both the coiled and straight C. raciborskii
morphotypes. This was perhaps due to the higher
temperatures (22.8 to 24.1) in comparison to other
months in the rainy season. However, there was a more
uniform distribution of the C. raciborskii populations at
the different depths in the other months of this season
(August 2004; August and July 2005); at a depth of 10
meters trichome density was more than double that found
in September 2004. This difference at greater depths in
this month as well as the concentration of populations in
more surface layers (0 to 2 meters) may have been
influenced by the tendency toward stratification that
occurred in September.
According to [11], there is a clear difference in growth
rate between the two C. raciborskii morphotypes in
response to variations in temperature and light intensity.
The coiled morphotype tends to grow more quickly
under different environmental conditions than the
straight form due to its tolerance to high temperature and
low light intensity. It is believed to favor the dominance
of the coiled over the straight morphotype in tropical
ecosystems. However, the results observed in the
Mundaú reservoir contradict these findings. On the other
hand, the results are in agreement with a study by [28],
who compared the growth of the straight and coiled C.
raciborskii morphotypes under controlled light and
temperature conditions; the straight morphotype was
more tolerant to higher luminosity and temperature,
which led to faster growth rates, whereas the coiled
morphotype always exhibited slower growth, even at
lower temperatures and lesser luminosity; at high
temperatures and luminosity, the coiled population did
not develop well.
No akinetes were found in any other months sampled,
even when there were variations in temperature between
the rainy and dry seasons. In a shallow lake in France,
[29] found that the occurrence of C. raciborski blooms
depended mainly on climatic factors such as air tem-
perature, water temperature and light intensity. This
confirms the observations made by [30] that
temperatures between 22 and 23.5 favor the
germination of akinetes. The lack of akinetes in the
present study suggests the occurrence of factors
favorable to the maintenance of the trichomes
throughout the entire study period, as these cells
develop under adverse environmental conditions.
Monitoring a small, shallow reservoir (Solomon Dam,
Australia), [31] found that stable stratification
conditions during dry periods were favorable to the
expansion of C. raciborskii populations. In the Mundaú
reservoir, the uniformity in the temperature of the water
column and low luminosity associated to the drowning
effect promoted greater population development when
compared to months in which thermal stratification
occurred. Thermal de-stratification in the rainy season
favored the increase in the populations of both C.
raciborskii morphotypes by providing more adequate
conditions for their growth, namely, lesser light
intensity and milder temperatures, which are
characteristics of the winter months in the hinterland
region of the state of Pernambuco in northeastern Brazil.
The species Cylindrospermopsis raciborskii persisted
under a variety of temperature and light conditions,
demonstrating adaptability to environmental variables,
which has also been reported for other regions in the
world. Due to the potential toxicity stemming from the
occurrence of high densities of this species, there is an
accentuated need for monitoring water quality in this
5. Acknowledgements
This study was supported by grants from CNPq
(Brazilian Council for Research and Development-
MCBO: 300794/2004-5) and FAPESP (State of São
Paulo Research Foundation – MCBO: 2006/03878-6).
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