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Effects of temperature and nitrogen availability on the growth of invasive and native cyanobacteria

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Abstract

Rising temperatures are expected to favour the growth of bloom-forming cyanobacteria in temperate lakes, but may also change the composition of cyanobacterial communities. To predict future community and bloom dynamics, it is therefore important to understand how bloom-forming species respond to temperature. Cylindrospermopsis raciborskii (Woloszynska) Seenayya & Subba Raju is an invasive, toxin-producing, nitrogen-fixer that may benefit from warming. To understand how changing temperatures will influence its ability to compete against native North American bloom-formers, we characterized the thermal reaction norms and temperature traits of three C. raciborskii strains, four strains of Microcystis aeruginosa (Kützing) Kützing and one strain of Anabaena flos-aquae (Lyng.) Brèb. C. raciborskii strains had higher optimum temperatures and survived higher temperatures than toxic M. aeruginosa strains, but had no apparent advantage over the non-toxic M. aeruginosa strain or A. flos-aquae. M. aeruginosa strains and A. flos-aquae tolerated lower temperatures than C. raciborskii, suggesting that fitness differences at low temperature may be important in limiting the latter’s spread. Furthermore, we found that nutrient availability strongly influenced thermal reaction norm shape: nitrogen deprivation lowered growth rates and decreased both low- and high-temperature tolerance, but did not affect the optimum temperature in C. raciborskii.
PRIMARY RESEARCH PAPER
Effects of temperature and nitrogen availability
on the growth of invasive and native cyanobacteria
Mridul K. Thomas .Elena Litchman
Received: 18 April 2015 / Revised: 21 June 2015 / Accepted: 23 June 2015 / Published online: 30 June 2015
ÓSpringer International Publishing Switzerland 2015
Abstract Rising temperatures are expected to
favour the growth of bloom-forming cyanobacteria
in temperate lakes, but may also change the compo-
sition of cyanobacterial communities. To predict
future community and bloom dynamics, it is therefore
important to understand how bloom-forming species
respond to temperature. Cylindrospermopsis raci-
borskii (Woloszynska) Seenayya & Subba Raju is an
invasive, toxin-producing, nitrogen-fixer that may
benefit from warming. To understand how changing
temperatures will influence its ability to compete
against native North American bloom-formers, we
characterized the thermal reaction norms and
temperature traits of three C. raciborskii strains, four
strains of Microcystis aeruginosa (Ku
¨tzing) Ku
¨tzing
and one strain of Anabaena flos-aquae (Lyng.) Bre
`b.
C. raciborskii strains had higher optimum tempera-
tures and survived higher temperatures than toxic M.
aeruginosa strains, but had no apparent advantage
over the non-toxic M. aeruginosa strain or A. flos-
aquae.M. aeruginosa strains and A. flos-aquae
tolerated lower temperatures than C. raciborskii,
suggesting that fitness differences at low temperature
may be important in limiting the latter’s spread.
Furthermore, we found that nutrient availability
strongly influenced thermal reaction norm shape:
nitrogen deprivation lowered growth rates and
decreased both low- and high-temperature tolerance,
but did not affect the optimum temperature in C.
raciborskii.
Keywords Cylindrospermopsis Temperature
Functional traits Cyanobacteria Microcystis
Phytoplankton
Introduction
Global environmental change has led to rising tem-
peratures, which are a major source of stress in natural
environments, having already affected most ecosys-
tems on Earth (IPCC Fourth Assessment Report,
2007). Other stressors such as changing nutrient
Electronic supplementary material The online version of
this article (doi:10.1007/s10750-015-2390-2) contains supple-
mentary material, which is available to authorized users.
Handling editor: Judit Padisa
´k
M. K. Thomas E. Litchman
W. K. Kellogg Biological Station, Michigan State
University, Hickory Corners, MI 49060, USA
M. K. Thomas E. Litchman
Department of Zoology, Michigan State University,
East Lansing, MI 48824, USA
Present Address:
M. K. Thomas (&)
Department of Aquatic Ecology, Eawag: Swiss Federal
Institute for Aquatic Science and Technology,
Ueberlandstrasse 133, 8600 Duebendorf, Switzerland
e-mail: mridul.thomas@eawag.ch
123
Hydrobiologia (2016) 763:357–369
DOI 10.1007/s10750-015-2390-2
deposition rates and the spread of invasive species
interact with increasing temperatures, making predict-
ing ecosystem responses difficult (Vitousek et al.,
2002; Walther et al., 2009). In aquatic ecosystems, one
of the major predicted consequences of warmer
temperatures is an increase in frequency and severity
of HABs (harmful algal blooms), which in lakes are
caused mostly by toxic cyanobacteria (Paerl & Huis-
man, 2009). These blooms can release toxins in high
enough concentrations to pose a threat to human
health, and may be harmful to algae, zooplankton, and
fish, thereby having a negative impact on water quality
and ecosystem functioning (Chorus & Bartram, 1999).
Rising temperatures may stimulate growth of toxic
HAB species both directly and indirectly. Higher
temperatures stimulate cyanobacterial growth directly
because they are believed to have higher optimum
temperatures for growth than other groups of algae
(Tilman & Kiesling, 1984; Robarts & Zohary, 1987;
but see Lu
¨rling et al., 2013). The indirect benefit
occurs as a result of increased thermal stratification;
cyanobacteria can regulate their buoyancy and take
advantage of the high stability of the water column
(Jo
¨hnk et al., 2008; Paerl & Huisman 2009).
Lake warming may stimulate growth not only of
native species but also invasive cyanobacteria. These
have the potential to alter community structure and
dynamics in lakes as well as biogeochemical cycling
(Litchman, 2010). One such species is Cylindrosper-
mopsis raciborskii, a nitrogen-fixing toxic cyanobac-
terium spreading in temperate regions across the world
that is capable of altering local ecosystem processes
when dominant (Padisa
´k, 1997; Isva
´novics et al.,
2000). Recent phylogenetic evidence has suggested
that the species originated in the American tropics
(Moreira et al., 2015) and its distribution was once
thought to be restricted to the tropics and subtropics,
where it co-occurs with other bloom-formers such as
Microcystis aeruginosa and Anabaena sp. (Marinho &
Huszar, 2002; Molica et al., 2005; Soares et al., 2009;
Moisander et al., 2012). However, it has increasingly
been found in temperate regions, most recently in
Europe and North America (Hong et al., 2006; Conroy
et al., 2007; Kling, 2009). It possesses a number of
traits that likely make it an excellent competitor in
lakes, including nitrogen fixation, low-light tolerance,
buoyancy regulation, and strong competitive ability
for phosphorus (Padisa
´k, 1997; Isva
´novics et al.,
2000), the last of which is thought to be atypical for
nitrogen-fixers (Smith, 1983). It is also highly
successful under fluctuating nitrogen and phosphorus
regimes, a factor that likely contributes to its
success in dynamic environments (Posselt et al.,
2009; Moisander et al., 2012). Some strains of C.
raciborskii produce a variety of toxins, of which a
few have been shown to be allelopathic (Figueredo
et al., 2007; Rzymski et al., 2014). Others have been
implicated in human poisoning and cattle mortality
events (Saker & Griffiths, 2000). The reasons behind
its recent invasions into temperate water bodies are
as yet unclear, though lake warming has been
implicated (Briand et al., 2004; Wiedner et al.,
2007; Bonilla et al., 2012; Sinha et al., 2012).
However, it is not clear whether rising temperatures
will give it an advantage in competition with native
species, including other HAB-forming cyanobacteria
already adapted to local conditions. The effects of
temperature on the growth of C. raciborskii and its
native competitors are therefore factors that could
determine its invasiveness in temperate regions.
However, the mechanism by which warming might
favour it is unclear: warming may reduce mortality
by increasing temperature above the minimum a
species can tolerate (Wiedner et al., 2007), and it
can also change the difference in (positive) growth
rates between species.
One way to characterize the ability to compete
with different species is to examine growth rates
under different environmental conditions. Although
growth rate does not capture all aspects of resource
competition, increases in growth rate decrease R*in
either Monod or Droop equations and therefore
strongly contribute to competitive ability (Droop,
1973; Tilman, 1982; Litchman et al., 2015). Growth
rates across temperature may be characterized in
ectotherms by thermal reaction norms and temper-
ature traits that describe the reaction norms (King-
solver, 2009; Thomas et al., 2012). The traits we
consider here are the optimum temperature for
growth (the temperature at which population growth
rate is maximized), maximum persistence tempera-
ture (T
max
, the temperature above which population
growth rate becomes negative), minimum persis-
tence temperature (T
min
, the temperature below
which population growth rate becomes negative),
temperature niche width (the range of temperatures
over which population growth rate is positive), and
maximum growth rate.
358 Hydrobiologia (2016) 763:357–369
123
The temperature traits of C. raciborskii and its
competitors are likely to be important determinants of
the species’ invasion success, for the following
reasons: (1) rising temperatures are thought to have
contributed to its spread (Briand et al., 2004; Wiedner
et al., 2007; Bonilla et al., 2012), (2) cyanobacterial
blooms have been shown to increase the temperature
of the water bodies in which they occur by as much as
1.5°C (Kahru et al., 1993), and (3) differences in
species’ growth rates at different temperatures have
been experimentally shown to predict the outcomes of
cyanobacterial competition (Fujimoto et al., 1997;
Chu et al., 2007). C. raciborskii’s thermal reaction
norms have been examined in strains from Australia,
Europe, Asia, Africa, and South America (Saker &
Griffiths, 2000; Briand et al., 2004; Chonudomkul
et al., 2004; Mehnert et al., 2010). However, despite its
recent invasion into N. America and its potential to
disrupt local lake ecosystems, little is known about the
physiology of N. American strains of C. raciborskii,
especially in comparison with its local competitors.
Measurements of these temperature traits may help us
predict the future pattern of invasion and possible
ecosystem changes in temperate North American
lakes.
To address this, we examined the effect of temper-
ature on the growth rates of three recently isolated N.
American strains of C. raciborskii. We compared the
performance of C. raciborskii across temperatures
with that of four strains of M. aeruginosa, a non-fixer
that co-occurs with C. raciborskii, and which presum-
ably competes with it for resources such as light and
phosphorus (Conroy et al., 2007; Kormas et al., 2011).
C. raciborskii appears to be displacing M. aeruginosa
in some tropical and subtropical lakes (Chapman &
Schelske, 1997; Saker & Griffiths, 2001), indicating
that this competition may be ecologically important in
temperate lakes. We observed almost monospecific
blooms of C. raciborskii in a lake in Michigan
(Litchman et al., unpublished data), a region that
commonly experience blooms of M. aeruginosa.
Performance of C. raciborskii in lakes will also be
affected by nitrogen concentration, as nitrogen-fixers
are favoured under N-limited conditions (Smith,
1983). However, nitrogen fixation requires an invest-
ment of cell resources and, therefore, there is likely to
be a fitness cost of N-fixation. As enzyme reaction
rates increase exponentially with temperature, the
resources devoted to N-fixation may vary with
temperature as well, leading to changes in the shape
of the thermal reaction norm and differences in
performance under nitrogen limitation. To better
understand how N-availability and temperature will
interactively affect C. raciborskii, we characterized its
thermal reaction norm under both N-replete and
N-free conditions. For comparison, we also estimated
growth rates under N-free and N-replete conditions in
a common HAB-forming N-fixer, Anabaena flos-
aquae. Interactions between important environmental
variables including temperature, nutrients, and light,
are likely to prove important to predicting C. raci-
borskii invasion and the dynamics of phytoplankton
communities (Sinha et al., 2012).
Materials and methods
Strains used
We tested three strains of Cylindrospermopsis raci-
borskii (Indiana Lake Lemon, Florida D, and Florida
E, hereafter referred to as IN, FL-D, and FL-E,
respectively), four strains of Microcystis aeruginosa
(Gull B-00, Gull K-00, Bear AC-02, Bear AG-02) and
a single strain of Anabaena flos-aquae UTEX 1444 for
growth responses to temperature. The three C. raci-
borskii strains are not known to produce any toxins.
M. aeruginosa Bear AC-02 lacks the mcyA gene
necessary for toxin production, while the remaining
three M. aeruginosa strains (Gull B-00, Gull K-00,
Bear AG-02) and A. flos-aquae UTEX 1444 possess
this gene and produce microcystins detectable in lab
assays. The C. raciborskii and M. aeruginosa strains
are recent isolates, with Microcystis aeruginosa Gull
B-00 and K-00 being isolated in 2000, M. aeruginosa
Bear AC-02 and AG-02 in 2002, Cylindrospermopsis
raciborskii strain D in 1999 and C. raciborskii strain
IN in 2006. C. raciborskii strain E was isolated in the
decade prior to our experiments, though the precise
time of isolation is unknown. The relatively recent
isolation increases the likelihood that their growth
responses are reflective of performance in natural
environments. The A. flos-aquae strain has been
maintained in laboratory culture since 1967, making
it highly likely that adaptation to laboratory condi-
tions has altered its physiology; we therefore do not
compare A. flos-aquae with the other two species
except in the context of nitrogen fixation.
Hydrobiologia (2016) 763:357–369 359
123
Florida C. raciborskii strains were obtained from
Dr. Julianne Dyble-Bressie, NOAA (isolated from
Lake Dora, Florida) and the Indiana strain was
obtained from Dr. Carole Lembi, Purdue University
(isolated from Lake Lemon, IN). M. aeruginosa
strains were obtained from Dr. Alan Wilson, Auburn
University and isolated from Gull Lake and Bear Lake
in Michigan. A. flos-aquae UTEX 1444 was obtained
from the UTEX Culture Collection of Algae.
Culture conditions
Non-axenic cultures of every strain were grown in
autoclaved 250-ml conical flasks containing approx-
imately 100 ml WC medium (Guillard, 1975). Sepa-
rate cultures of A. flos-aquae and the three C.
raciborskii strains were maintained in N-replete
(1 mmol N L
-1
, in the form of NaNO
3
) and N-free
WC medium, bringing the total number of cultures to
12. Each culture was maintained in a growth chamber
at 20°C under cool white fluorescent lights (EcoLux
20 W). All growth chambers used during the exper-
iment were set to a 14:10 light/dark cycle, with a light
intensity of approximately 100 lmol photons
m
-2
s
-1
. This has been shown to be saturating for
most phytoplankton species (Litchman, 2000) and is
consistent with past data on these species (e.g. Briand
et al., 2004). Cultures were shaken every day by hand
and diluted regularly to keep them in exponential
growth phase.
Experiment
To measure the thermal reaction norms of all the
strains in our study, we measured their population
growth rates at six temperatures after acclimation to
these conditions. Growth rates were estimated from
measurements of chlorophyll-afluorescence (excita-
tion wavelength: 436 nm, emission wavelength:
680 nm) in 24-well microplates over 5 days using a
SpectraMax M5 microplate reader (Molecular
Devices, Sunnyvale, CA). Before the experiment, we
tested the efficacy of this method by showing that
chlorophyll-afluorescence correlated strongly with
cell density for all three species above a fluorescence
value of 1 (relative fluorescence units, RFU), though
the chlorophyll content per cell/colony differed
between species.
Cultures were allowed to acclimate for a minimum
of three days in growth chambers maintained at a light
level of 100 lmol photons m
-2
s
-1
and 6 different
temperatures (15, 20, 25, 30, 35, and 40°C). Prelim-
inary tests indicated that growth rate remained
consistent after this acclimation period at almost all
temperatures. This is not the case at extreme temper-
atures (15 and 40°C, as well as 35°C in the case of
Microcystis) where growth rate is negative and
populations may never truly acclimate. We did not
extend the acclimation period further to avoid driving
cultures at these extreme temperatures extinct. We
began the assay by diluting the cultures to between 1
and 2 RFU in Greiner Bio-One CELLSTAR 24-well
microplates (Monroe, NC). Each culture was trans-
ferred to two microwells on each of two microplates at
every temperature (four replicates for every treatment
combination). The microplates were then returned to
the growth chambers and chlorophyll-afluorescence
was measured every 24 h for 5 days. Before each
measurement, microplates were agitated by the
microplate reader to ensure that settling did not skew
the results. Each well was divided into a 3 93 grid
and 20 fluorescence measurements were made at each
point, with the mean of all 180 measurements being
used for further calculations. The microplates were
returned to the growth chambers immediately after the
measurements.
Calculation of specific growth rate
For each well, the linear regression of the natural log
of chlorophyll fluorescence against day number was
examined visually, and data points from the end of the
growth period were removed if log-fluorescence
plateaued before the end of the assay (i.e. culture
was no longer experiencing exponential growth). This
occasionally occurred when a culture became extre-
mely dense or sparse, at which point it had either
exhausted its nutrient supply or was beyond the range
in which the instrument registered a linear relationship
between chlorophyll fluorescence and biomass. The
slope of the resulting regression is the specific growth
rate (day
-1
) of the well culture. The initial cell
densities used appear to be too low for accurate
measurement of negative population growth rates, as
fluorescence levels quickly dropped below the lower
detection limit for several cultures at 15, 35, and 40°C.
Therefore, we have less confidence in these
360 Hydrobiologia (2016) 763:357–369
123
measurements than in those involving positive growth.
Moreover, due to the rapid decline to below the
detection limit, negative growth rate estimates are
likely to be underestimates (i.e. the actual rates may be
more negative). As this may be a source of bias, when
growth rates were negative at both 35 and 40°C, the
40°C measurements were excluded from further
calculations of temperature traits and from the figures.
All growth rate measurements from our experi-
ments are included in Supplementary information
(Online Resource 1).
Thermal reaction norm characterization
and temperature trait estimation
The thermal reaction norm of each strain was charac-
terized as in Thomas et al. (2012) and Boyd et al.
(2013), using the equation:
fTðÞ¼aebT 1Tz
w=2

2
"#
;ð1Þ
where specific growth rate fdepends on temperature,
T, as well as parameters z,w,a, and b.wis the
temperature niche width, while the other three possess
no explicit biological meaning. We fit (1) to the
growth data for each strain using maximum likelihood
to obtain estimates for parameters z,w,a, and
b(parameter estimates included in Online Resource
2). We then used the reaction norm equation to
numerically estimate four further traits of interest: the
optimum temperature for growth, T
max
,T
min
, and
maximum growth rate. For each culture, Eq. (1) was
fit to the data from all temperatures, except where
growth was negative at both 35 and 40°C. In these
cases, the data for 40°C were omitted during the fitting
procedure.
We also estimated confidence intervals on the
temperature traits using a parametric bootstrapping
approach. For each strain, we fitted (1) to the growth
rate measurements and extracted the residuals from
this fit. We then performed 1,000 residual bootstraps, a
procedure in which the residuals are randomly ‘reas-
signed’ to the original growth rate estimates and added
to them, thereby generating a slightly different thermal
reaction norm. During each iteration, we refitted (1) and
re-estimated the reaction norm parameters (z,w,a,b)
as well as the derived traits. Examining the distribu-
tion of these parameters and traits over the 1,000
bootstraps allows us to quantify the uncertainty in our
estimates, which we can then use to generate 95%
confidence intervals and examine differences between
strains.
Data analysis was performed using R 2.15.2 (R
Core Team, 2012).
Results
Growth in N-replete medium
The three species exhibited strong differences in
their thermal reaction norms (Fig. 1). The optimum
temperatures of the three C. raciborskii strains
ranged from approximately 30 to 33°C (Figs. 1,2;
Table 1). A. flos-aquae had an optimum above 36°C
while M. aeruginosa exhibited clear differences
between strains. The three toxic M. aeruginosa
strains had optima of 28–29°C while the single non-
toxic strain Bear AC-02 was estimated to growth
fastest at 34°C. The species exhibited a similar
hierarchy in T
max
, with A. flos-aquae able to tolerate
higher temperatures than C. raciborskii, and M.
aeruginosa exhibiting the lowest high-temperature
tolerance. However, M. aeruginosa and A. flos-
aquae had lower T
min
s than the C. raciborskii strains
(except for M. aeruginosa strain Bear AG-02).
Maximum growth rate differed strongly between
species, ranging from 0.56 to 0.67 day
-1
in C.
raciborskii, 0.29 to 0.62 day
-1
in M. aeruginosa and
1.48 day
-1
in A. flos-aquae (Table 1). The growth
rates obtained in this study agree well with previ-
ously measured rates for the same strains of M.
aeruginosa (Wilson et al., 2006).
The three C. raciborskii strains exhibited relatively
little variation in their thermal reaction norms,
although the northern strain IN had the lowest
optimum temperature of the three and the highest
measured growth rates at 20 and 25°C (Figs. 1,2;
Table 1). M. aeruginosa showed larger differences in
temperature response between strains. Bear AG-02
exhibited the poorest low-temperature tolerance, with
an estimated T
min
above 15°C. The non-toxic Bear
AC-02 exhibited an optimum temperature and T
max
more than 5°C higher than the other strains as well as a
maximum growth rate 50% greater. A. flos-aquae had
the highest estimated optimum temperature and T
max
of all strains measured (Fig. 2).
Hydrobiologia (2016) 763:357–369 361
123
Effects of N-deprivation at different temperatures
N-deprivation increased the T
min
(i.e. reduced the low-
temperature tolerance) of all three C. raciborskii
strains (Fig. 1; Table 1); we did not have
measurements at sufficiently low temperatures to
draw conclusions about its effect on the T
min
of A.
flos-aquae. It also slightly decreased the T
max
(i.e.
reduced high-temperature tolerance) in C. raciborskii,
but had no detectable effect on A. flos-aquae (Fig. 1;
Table 1). It exhibited inconsistent effects on the
optimum temperature and on average had no effect
on this (Figs. 2,3). N-deprivation decreased the
optimum in strain FL-D, increased it in strain IN,
and did not change it in strain FL-E or A. flos-aquae.
N-deprivation did decrease the measured growth
rates of C. raciborskii and A. flos-aquae at most
temperatures, by as much as 0.4 d
-1
;italsoreduced
their estimated maximum growth rates (Figs. 3,4;
Table 1). However, there were considerable differences
in its effects across strains and temperatures. C.
raciborskii FL-E experienced little to no reduction in
growth rate at 20 and 25°C, while all other strains
experienced decreases ranging from 0.1 to 0.25 day
-1
.
The largest difference between strains occurred at 35°C,
with C. raciborskii FL-IN experiencing no detectable
reduction in growth while the other three strains
experienced reductions of 0.25–0.4 day
-1
.Differences
occurred at 15 and 40°C as well, but since we have less
confidence in negative growth rate measurements for
reasons explain in the ‘Materials and methods’ section,
we do not draw conclusions from them.
Fig. 1 Specific growth rates (day
-1
)ofC. raciborskii,M. aeruginosa and A. flos-aquae between 15 and 40°C, as well as curve fits to
the data based on Eq. (1). Error bars indicate standard errors from four replicates
Fig. 2 Optimum temperatures for growth (°C) of all strains.
Optima of N-fixers are shown in both N-replete and N-free
media. Error bars represent 95% confidence intervals estimated
by parametric bootstrapping
362 Hydrobiologia (2016) 763:357–369
123
Discussion
Cyanobacteria are believed to have higher optimum
temperatures for growth than other groups of phyto-
plankton (Robarts & Zohary, 1987), though a recent
study has suggested that chlorophytes possess simi-
larly high optima (Lu
¨rling et al., 2013). The predom-
inance of cyanobacteria when lakes are at their
warmest is therefore likely due to a combination of
high-temperature optima and traits that are beneficial
under stratified conditions, such as buoyancy regula-
tion (Huisman et al., 2004; Paerl & Huisman, 2009).
As a number of cyanobacterial species are capable of
buoyancy regulation, including the three species
considered in this study (Reynolds et al., 1987;
Padisa
´k, 1997), differences in temperature response
and nutrient competitive abilities may be more
important in determining the outcomes of competition
between them. Differences in temperature response
have been shown to successfully predict the outcomes
of competition in cyanobacteria in experiments (Chu
et al., 2007) as well as in the field, especially in
combination with N:P supply ratio and the species’
nutrient traits (Fujimoto et al., 1997).
The optimum temperatures of the three species
tested in this study were high and within the range
reported for cyanobacteria previously: between 28
and 37°C. The optima of the three C. raciborskii
strains ranged from 30 to 33°C in N-replete medium,
highly similar to estimates from other isolates.
Though C. raciborskii strains from a number of
countries in South America, North America, Europe,
Australia, and Asia have now been measured, there is
little variation in Topt and no apparent geographical
pattern in its distribution (Saker & Griffiths, 2000;
Briand et al., 2004; Chonudomkul et al., 2004;
Mehnert et al., 2010). This might suggest a lack of
local adaptation to temperature differences, but it is
important to note that measurements in each of these
studies were performed under slightly different con-
ditions, particularly in terms of irradiance. For
example, Briand et al. (2004) estimated optima
between 29 and 31°C for ten other strains of this
species from multiple continents, using an irradiance
level of 30 lmol photons m
-2
s
-1
and a 16:8 h
light/dark cycle. Saker & Griffiths (2000) measured
seven Australian strains, also with optima largely
around 30°C, but used an irradiance level of 50 lmol
photons m
-2
s
-1
and a 12:12 h light/dark cycle.
Chonudomkul et al. (2004) measured 24 strains from
Thailand and Japan and found optima in the range of
30–35°C, using an irradiance level of 40 lmol
photons m
-2
s
-1
and a 12:12 h light/dark cycle.
Given the small amount of apparent variation in Topt,
it appears that adaptation to local temperature condi-
tions may be weak at best, though it is difficult to
conclude this with confidence due to the differences in
experimental methods.
Table 1 Temperature traits of the cyanobacterial strains with 95% confidence intervals estimated by parametric bootstrapping
Species Strain Nitrogen
added
Optimum
temperature
(°C)
T
min
(°C) T
max
(°C) Niche
width (°C)
Maximum
growth rate
(day
-1
)
C. raciborskii IN Yes 29.9 [29.4, 30.4] 15.3 [14.9, 15.6] 39.9 [39.7, 40.1] 24.5 [24.2, 24.9] 0.57 [0.56, 0.58]
C. raciborskii IN No 33.2 [32.7, 33.6] 16.4 [14.9, 17.4] 39.1 [39.0, 39.2] 22.8 [21.8, 24.3] 0.52 [0.50, 0.54]
C. raciborskii FL-D Yes 32.6 [32.0, 33.2] 14.9 [13.0, 15.9] 39.9 [39.8, 40.1] 25.1 [24.1, 26.8] 0.67 [0.65, 0.70]
C. raciborskii FL-D No 29.6 [28.9, 30.3] 17.7 [17.3, 18.1] 38.6 [38.3, 38.9] 20.9 [20.6, 21.2] 0.41 [0.39, 0.43]
C. raciborskii FL-E Yes 31.5 [30.6, 32.1] 15.2 [14.0, 15.9] 39.8 [39.6, 40.0] 24.6 [23.9, 25.8] 0.56 [0.53, 0.58]
C. raciborskii FL-E No 31.6 [30.6, 32.4] 17.4 [16.0, 18.2] 39.4 [39.0, 39.7] 22.0 [21.2, 23.3] 0.34 [0.31, 0.38]
A. flos-aquae UTEX 1444 Yes 36.4 [36.0, 36.7] -13.2 [-15.2, 10.5]
a
41.4 [41.2, 42.0] 54.7 [31.1, 56.6]
a
1.48 [1.34, 1.60]
A. flos-aquae UTEX 1444 No 35.9 [35.3, 36.2] -10.9 [-16.1, 12.6]
a
41.7 [41.4, 42.5] 52.6 [29.6, 57.7]
a
1.07 [1.00, 1.13]
M. aeruginosa Gull B-00 Yes 28.3 [27.9, 28.7] 14.0 [12.8, 14.8] 34.2 [34.1, 34.3] 20.3 [19.4, 21.4] 0.38 [0.37, 0.40]
M. aeruginosa Gull K-00 Yes 28.8 [28.2, 29.3] 14.0 [11.7, 15.2] 34.3 [34.1, 34.4] 20.3 [19.1, 22.5] 0.41 [0.39, 0.44]
M. aeruginosa Bear AC-02 Yes 34.1 [32.6, 34.8] -6.8 [-17.7, 39.6]
a
39.4 [39.1, 70.8] 46.2 [23.3, 57.0]
a
0.62 [0.55, 0.69]
M. aeruginosa Bear AG-02 Yes 28.0 [27.5, 28.5] 16.4 [15.8, 16.8] 33.9 [33.7, 34.0] 17.5 [17.1, 18.1] 0.29 [0.28, 0.30]
a
These point estimates of T
min
and niche width are inaccurate for these strains due to a lack of measurements at sufficiently low
temperatures; however, the 95% confidence intervals overlap reasonable trait estimates
Hydrobiologia (2016) 763:357–369 363
123
Anabaena flos-aquae exhibited the highest opti-
mum temperature of 36°C, towards the higher end of
the 27–39°C range of estimates for this species
(Uehlinger, 1981; Novak & Brune, 1985). The three
toxic Microcystis aeruginosa strains exhibited optima
around 28°C, while the non-toxic strain Bear AC-02
possessed an optimum of 34°C. These measurements
are slightly more extreme than estimates from earlier
studies, which are between 30 and 32°C (Nalewajko &
Murphy, 2001; Imai et al., 2009), possibly indicating
important intraspecific variability. Some of these
optima are higher than the temperatures these species
are likely to experience in their natural environments,
a pattern that has been observed in earlier studies of
phytoplankton and other taxa (Barker, 1935; Karentz
& Smayda, 1984; Kingsolver, 2009; Thomas et al.,
2012). These are likely to be adaptive responses to
environmental temperature variation, given the phys-
iological constraints that these phytoplankton experi-
ence (i.e. an exponential increase in maximum growth
rate with temperature and skewness of thermal
tolerance curves). An eco-evolutionary model of
phytoplankton growth in the ocean found that the best
strategy under typical patterns of temperature varia-
tion was to have an optimum several degrees above the
mean temperature (Thomas et al., 2012). Variability in
the temperature environment may select for higher
optima, as growth rates decrease more rapidly above
the optimum temperature than below it (Martin &
Huey, 2008). Our findings support the high-tempera-
ture preference of subtropical and temperate
cyanobacteria (Reynolds, 2006), which implies that
rising lake temperatures will promote cyanobacterial
dominance (Paerl & Huisman, 2009; Kosten et al.,
2012).
Maximum growth rates of C. raciborskii grown on
nitrate have ranged from 0.3 to 1.3 day
-1
in previous
studies (Saker & Griffiths, 2000; Shafik et al., 2001;
Briand et al., 2004; Mehnert et al., 2010). This places
the N. American strains (0.56–0.67 day
-1
, Fig. 1;
Table 1) at the lower end of the range, below
measured Australian and Hungarian strains (Saker &
Fig. 3 Specific growth
rates of N-fixers under
N-replete (filled points) and
N-free (hollow points)
conditions at all
temperatures. Error bars
indicate the standard error of
the mean
364 Hydrobiologia (2016) 763:357–369
123
Griffiths, 2000; Shafik et al., 2001) but above a number
of European, American and African strains (Briand
et al., 2004; Mehnert et al., 2010). However, our
earlier caveats about differences in experimental
methods in these studies apply here as well. Variation
in T
max
is limited, with all studies finding values
between 35°C and just above 40°C (Saker & Griffiths,
2000; Briand et al., 2004; Chonudomkul et al., 2004).
However, T
min
exhibited notable differences, with the
three C. raciborskii strains in our study dying at 15,
unlike in earlier studies. These previous studies found
that C. raciborskii can tolerate temperatures between
10 and 15°C (Briand et al., 2004; Chonudomkul et al.,
2004; Mehnert et al., 2010). The consistency of these
earlier findings across geographical regions suggests
that their difference to our findings do not reflect strain
differences, but an interaction between temperature
and irradiance. The irradiance we used was consider-
ably higher than that used in earlier studies; our
experiments were conducted at 100 lmol pho-
tons m
-2
s
-1
, approximately the optimum light inten-
sity at intermediate temperatures, as determined by
Briand et al. (2004) and Shafik et al. (2001) at 25 and
27°C. Irradiance level has been shown to alter the
response to temperature in many phytoplankton,
including C. raciborskii (Dauta et al., 1990; Kehoe
et al., 2015), which suggests that the inability of the C.
raciborskii strains in our study to survive at extreme
temperatures is likely due to the different light
environments used in the two studies. Alternatively,
the differences may be indicative of local adaptation to
more variable temperature conditions; ecotypic dif-
ferences have previously been suggested to explain
intraspecific variation in light response in this species
(Piccini et al., 2011; Pierangelini et al., 2014).
Climate change and C. raciborskii
Our data suggest that climate change is likely to favour
the invasive C. raciborskii over the native temperate
cyanobacterium M. aeruginosa in temperate North
America. A. flos-aquae performed better than both
these species, but because it has been maintained in
laboratory cultures since 1967, this may be due to
adaptation to laboratory conditions, which leads to
important changes in physiology and genome archi-
tecture (Swan et al., 2013), making the comparison
unreflective of performance differences in natural
environments. However, its temperature response
does inform our understanding of the constraints on
adaptation to high temperatures under highly favour-
able growth conditions. Therefore, we restrict discus-
sion of A. flos-aquae to the effect of N-deprivation on
thermal reaction norm shape, as the cost of nutrient
deprivation is more likely to be conserved. However,
if the temperature response has not changed signifi-
cantly since its isolation, our results would lead us to
predict that warming will facilitate the invasion of
subtropical A. flos-aquae strains in temperate lakes.
Microcystis aeruginosa strains tolerated low tem-
peratures better than C. raciborskii, with estimated
T
min
s around 14°C. This low-temperature advantage
of M. aeruginosa may be an important factor in
limiting the invasion of C. raciborskii; if lakes spend a
greater proportion of time above the C. raciborskii
T
min
of 15–18°C, it may strongly favour their invasion
and growth. This 15–18°C threshold corresponds
closely with the 15–17°C range identified as crucial
to favouring the growth of lake populations of C.
raciborskii (Wiedner et al., 2007), providing a strong
link between physiological tolerance and performance
in natural environments. Above 20°C, the three C.
raciborskii strains had higher growth rates than the
toxic M. aeruginosa strains. The non-toxic M. aerug-
inosa strain Bear AC-02 experienced comparable
growth rates at to C. raciborskii at all temperatures,
Fig. 4 The difference in specific growth rate (day
-1
)of
N-fixers between N-replete and N-free conditions at all
temperatures. Error bars indicate standard error of the
difference between growth rates
Hydrobiologia (2016) 763:357–369 365
123
suggesting that there might be a trade-off between
toxin production and growth rate or high-temperature
performance in M. aeruginosa. As our study was not
designed to test this difference and lacked statistical
power in this regard, any difference between toxic and
non-toxic strains may be purely coincidental. How-
ever, the potential implications for such a trade-off are
important: it would suggest that higher summer
temperatures may favour non-toxic strains over toxic
ones. Therefore, we hope that this question will be
addressed more rigorously with carefully designed
experiments.
The performance of a cyanobacterial species in the
20–30°C range may be a useful indicator of future
success and invasibility in temperate regions, because
phytoplankton communities are frequently dominated
by cyanobacteria at these temperatures, and interme-
diate-sized lakes are expected to spend a greater
proportion of the year in this temperature range in
the future (de Stasio et al., 1996; Magnuson et al.,
1997). This invasion may alter lake ecosystems and
communities through a variety of pathways—changes
in nitrogen supply (as a result of N-fixation), changes
in phosphorus concentration (as C. raciborskii is an
excellent phosphorus competitor), changes in the light
environment (due to its shade tolerance), altered
zooplankton community abundance and composition
(as a result of changes in toxin load and type) (Padisa
´k,
1997; Isva
´novics et al., 2000). Each of these can alter
the selective environment and may lead to both
ecological and evolutionary changes in the local
community (Litchman et al., 2010). The outcomes of
competition between these species in lakes will
depend on other factors as well, including nutrient
and light response.
Interactions between these factors and the role of
natural cycles in environmental variables may prove to
be important in drive dynamics in natural systems. For
example, our study (and most studies of this kind) used
constant temperature and binary light/dark conditions,
while taxa in natural environments experience daily
cycles in both temperature and light intensity. Espe-
cially due to the highly nonlinear effects of temper-
ature and light on growth rate (Litchman, 2000;
Kingsolver, 2009; Edwards et al., 2015), the effects of
interacting, cycling variables may be highly complex.
Early examinations of the effects of fluctuating light
have found strong influences on growth rate, but at
most a weak interaction with temperature, possibly
making the job of prediction easier (Litchman, 2000;
Shatwell et al., 2012). Many important questions
remain unresolved, however. Most importantly, can
measurements made under constant conditions be used
to accurately predict growth under fluctuating condi-
tions? Current models appear to have some predictive
power, but do an inadequate job of capturing the effect
of fluctuations on growth (Litchman, 2000). The
development of better models that account for phys-
iological acclimatization should therefore a priority,
as they could guide us in developing experiments and
assays to collect more useful data, with the goal of
improving forecasts of phytoplankton dynamics in
natural systems.
Effects of N-deficiency
N-deficiency showed inconsistent effects on the
growth of nitrogen-fixers. It reduced low-temperature
tolerance (increased T
min
) and high-temperature tol-
erance (decreased T
max
) in all C. raciborskii strains.
This suggests that eutrophication may favour spread
and dominance of C. raciborskii by altering their
response to environmental temperatures. If true, this
leads to the testable prediction that C. raciborskii
should be found in lakes with higher nutrient concen-
trations earlier in the season (i.e. at lower tempera-
tures) than those with lower nutrient concentrations. It
further points towards a physiological mechanism by
which a combination of eutrophication and warming
will have a strongly interactive effect on the success of
the species, and may have already done so. However,
the fact that N-deprivation altered optimum temper-
atures and growth rates in an unpredictable manner
(Fig. 2; Table 1) indicates that predicting the outcome
of the interaction will be challenging, and will likely
require more extensive experiments with measure-
ments across a range of nutrient concentrations.
Conclusion
Our study indicates that warming of temperate lakes is
likely to favour C. raciborskii over the native M.
aeruginosa due to C. raciborskii’s inability to survive
at low temperatures and higher growth rates at warmer
temperatures. M. aeruginosa currently has a strong
advantage in temperate North American lakes due to
its ability to tolerate colder temperatures. By
366 Hydrobiologia (2016) 763:357–369
123
beginning its growth earlier in the season than C.
raciborskii, it may have access to nutrients at a time
when the latter is unable to grow, thereby negating the
strong nutrient competitive abilities of C. raciborskii.
However, warming above the 15–18°C temperature
range will strongly favour C. raciborskii; the presence
of this temperature threshold suggests that a nonlinear
transition between Microcystis-dominated and Cylin-
drospermopsis-dominated communities is a possibil-
ity. Management of nutrient pollution in lakes may
also play an important rule in delaying or preventing
C. raciborskii’s spread, due to the effect of N-depri-
vation on T
min
. Understanding the nature of the
interaction between nutrients, light, and temperature,
particularly under fluctuating conditions, will likely
improve our ability to predict C. raciborskii invasion
as well as the composition and dynamics of phyto-
plankton communities.
Acknowledgements We thank Carole Lembi and Julianne
Dyble-Bressie for providing us with C. raciborskii cultures,
Alan Wilson for M. aeruginosa cultures, and G. G. Mittelbach,
J. A. Lau, and C. A. Klausmeier for useful comments on the
manuscript. This research was in part supported by the NSF
grants (DEB 06-10531 and DEB 08-45932) to E.L., a grant by
the J.S. McDonnell Foundation to C. Klausmeier and E. L. and
an MSU College of Natural Science fellowship to M.K.T. This is
Kellogg Biological Station Contribution No. 1711.
References
Barker, H. A., 1935. The culture and physiology of the marine
dinoflagellates. Archiv fu
¨r Mikrobiologie 6: 157–181.
Bonilla, S., L. Aubriot, M. C. S. Soares, M. Gonza
´lez-Piana, A.
Fabre, V. L. M. Huszar, M. Lu
¨rling, D. Antoniades, J.
Padisa
´k & C. Kruk, 2012. What drives the distribution of
the bloom-forming cyanobacteria Planktothrix agardhii
and Cylindrospermopsis raciborskii? FEMS Microbiology
Ecology 79: 594–607.
Boyd, P. W., T. A. Rynearson, E. A. Armstrong, F. Fu, K.
Hayashi, Z. Hu, D. A. Hutchins, R. M. Kudela, E. Litch-
man, M. R. Mulholland, U. Passow, R. F. Strzepek, K.
A. Whittaker, E. Yu & M. K. Thomas, 2013. Marine
phytoplankton temperature versus growth responses from
polar to tropical waters - Outcome of a scientific commu-
nity-wide study. PLoS ONE 8: e63091.
Briand, J.-F., J.-F. Humbert, C. Leboulanger, C. Bernard & P.
Dufour, 2004. Cylindrospermopsis raciborskii
(Cyanobacteria) invasion at mid-latitudes: selection, wide
physiological tolerance, or global warming? Journal of
Phycology 40: 231–238.
Chapman, A. D. & C. L. Schelske, 1997. Recent appearance of
Cylindrospermopsis in five hypereutrophic Florida lakes.
Journal of Phycology 33: 191–195.
Chonudomkul, D., W. Yongmanitchai, G. Theeragool, M.
Kawachi, F. Kasai, K. Kaya & M. M. Watanabe, 2004.
Morphology, genetic diversity, temperature tolerance and
toxicity of Cylindrospermopsis raciborskii (Nostocales,
Cyanobacteria) strains from Thailand and Japan. FEMS
Microbiology Ecology 48: 345–355.
Chorus, I. & J. Bartram, 1999. Toxic Cyanobacteria in Water: A
Guide to Their Public Health Consequences, Monitoring,
and Management. E & FN Spon, London.
Chu, Z., X. Jin, N. Iwami & Y. Inamori, 2007. The effect of
temperature on growth characteristics and competitions of
Microcystis aeruginosa and Oscillatoria mougeotii in a
shallow, eutrophic lake simulator system. Hydrobiologia
581: 217–223.
Conroy, J. D., E. L. Quinlan, D. D. Kane & D. A. Culver, 2007.
Cylindrospermopsis in Lake Erie: testing its association
with other cyanobacterial genera and major limnological
parameters. Journal of Great Lakes Research 33: 519–535.
Dauta, A., J. Devaux, F. Piquemal & L. Boumnich, 1990.
Growth rate of four freshwater algae in relation to light and
temperature. Hydrobiologia 207: 221–226.
de Stasio, B. T., D. K. Hill, J. M. Kleinhans & N. P. Nibbelink,
1996. Potential effects of global climate change on small
north-temperate lakes: physics, fish, and plankton. Lim-
nology and Oceanography 41: 1136–1149.
Droop, M. R., 1973. Some thoughts on nutrient limitation in
algae. Journal of Phycology 9: 264–272.
Edwards, K. F., M. K. Thomas, C. A. Klausmeier & E. Litch-
man, 2015. Light and growth in marine phytoplankton:
allometric, taxonomic, and environmental variation. Lim-
nology and Oceanography 60: 540–552.
Figueredo, C. C., A. Giani & D. F. Bird, 2007. Does allelopathy
contribute to Cylindrospermopsis raciborskii (Cyanobac-
teria) bloom occurrence and geographic expansion? Jour-
nal of Phycology 43: 256–265.
Fujimoto, N., R. Sudo, N. Sugiura & I. Yuhei, 1997. Nutrient-
limited growth of Microcystis aeruginosa and Phormidium
tenue and competition under various N:P supply ratios and
temperatures. Limnology and Oceanography 42: 250–256.
Guillard, R. R. L., 1975. Culture of phytoplankton for feeding
marine invertebrates. In Smith, W. L. & M. H. Chantey
(eds), Culture of Marine Invertebrate Animals. Plenum
Press, New York: 29–60.
Hong, Y., A. Steinman, B. Biddanda, R. Rediske & G. Fah-
nenstiel, 2006. Occurrence of the toxin-producing
cyanobacterium Cylindrospermopsis raciborskii in Mona
and Muskegon Lakes, Michigan. Journal of Great Lakes
Research 32: 645–652.
Huisman, J., J. Sharples, J. M. Stroom, P. M. Visser, W. E. A.
Kardinaal, J. M. H. Verspagen & B. Sommeijer, 2004.
Changes in turbulent mixing shift competition for light
between phytoplankton species. Ecology 85: 2960–2970.
Imai, H., K.-H. Chang & S. Nakano, 2009. Growth responses of
harmful algal species Microcystis (Cyanophyceae) under
various environmental conditions. In Obayashi, Y., T.
Isobe, A. Subramanian, S. Suzuki & S. Tanabe (eds),
Interdisciplinary Studies on Environmental Chemistry –
Hydrobiologia (2016) 763:357–369 367
123
Environmental Research in Asia. Terrapub, Tokyo:
269–275.
IPCC Fourth Assessment Report, 2007. Climate Change 2007:
the physical science basis. In Solomon, S., D. Qin, M.
Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor &
H. L. Miller (eds), Contribution of Working Group I to the
Fourth Assessment Report of the Intergovernmental Panel
on Climate Change. Cambridge University Press,
Cambridge.
Isva
´novics, V., H. M. Shafik, M. Pre
´sing & S. Juhos, 2000.
Growth and phosphate uptake kinetics of the cyanobac-
terium, Cylindrospermopsis raciborskii (Cyanophyceae) in
throughflow cultures. Freshwater Biology 43: 257–275.
Jo
¨hnk, K. D., P. M. Visser, J. Huisman, J. M. Stroom, J. Sharples
& B. Sommeijer, 2008. Summer heatwaves promote
blooms of harmful cyanobacteria. Global Change Biology
14: 495–512.
Kahru, M., J. M. Leppanen & O. Rud, 1993. Cyanobacterial
blooms cause heating of the sea surface. Marine Ecology
Progress Series 101: 1–7.
Karentz, D. & T. J. Smayda, 1984. Temperature and seasonal
occurrence patterns of 30 dominant phytoplankton species
in Narragansett Bay over a 22-year period (1959–1980).
Marine Ecology Progress Series 18: 277–293.
Kehoe, M., K. R. O. Brien, A. Grinham & M. A. Burford, 2015.
Primary production of lake phytoplankton, dominated by
the cyanobacterium Cylindrospermopsis raciborskii,in
response to irradiance and temperature. Inland Waters 5:
93–10.
Kingsolver, J. G., 2009. The well-temperatured biologist. The
American Naturalist 174: 755–768.
Kling, H. J., 2009. Cylindrospermopsis raciborskii (Nostocales,
Cyanobacteria): a brief historic overview and recent dis-
covery in the Assiniboine River (Canada). Fottea 9: 45–47.
Kormas, K. A., S. Gkelis, E. Vardaka & M. Moustaka-Gouni,
2011. Morphological and molecular analysis of bloom-
forming Cyanobacteria in two eutrophic, shallow
Mediterranean lakes. Limnologica 41: 167–173.
Kosten, S., V. L. M. Huszar, E. Be
´cares, L. S. Costa, E. van
Donk, L.-A. Hansson, E. Jeppesen, C. Kruk, G. Lacerot, N.
Mazzeo, L. de Meester, B. Moss, M. Lu
¨rling, T. No
˜ges, S.
Romo & M. Scheffer, 2012. Warmer climates boost
cyanobacterial dominance in shallow lakes. Global Change
Biology 18: 118–126.
Litchman, E., 2000. Growth rates of phytoplankton under fluc-
tuating light. Freshwater Biology 44: 223–235.
Litchman, E., 2010. Invisible invaders: non-pathogenic invasive
microbes in aquatic and terrestrial ecosystems. Ecology
Letters 13: 1560–1572.
Litchman, E., P. de Tezanos Pinto, C. A. Klausmeier, M.
K. Thomas & K. Yoshiyama, 2010. Linking traits to spe-
cies diversity and community structure in phytoplankton.
Hydrobiologia 653: 15–28.
Litchman, E., K. F. Edwards & C. A. Klausmeier, 2015.
Microbial resource utilization traits and trade-offs: impli-
cations for community structure, functioning, and biogeo-
chemical impacts at present and in the future. Frontiers in
Microbiology 6: 254.
Lu
¨rling, M., F. Eshetu, E. J. Faassen, S. Kosten & V. L. M.
Huszar, 2013. Comparison of cyanobacterial and green
algal growth rates at different temperatures. Freshwater
Biology 58: 552–559.
Magnuson, J. J., K. E. Webster, R. A. Assel, C. J. Bowser, P.
J. Dillon, J. G. Eaton, H. E. Evans, E. J. Fee, R. I. Hall, L.
R. Mortsch, D. W. Schindler & F. H. Quinn, 1997.
Potential effects of climate changes on aquatic systems:
Laurentian great lakes and Precambrian Shield region.
Hydrological Processes 11: 825–871.
Marinho, M. M. & V. L. M. Huszar, 2002. Nutrient availability
and physical conditions as controlling factors of phyto-
plankton composition and biomass in a tropical reservoir
(Southeastern Brazil). Archiv fu
¨r Hydrobiologie 153:
443–468.
Martin, T. L. & R. B. Huey, 2008. Why ‘‘suboptimal’’ is opti-
mal: Jensen’s inequality and ectotherm thermal prefer-
ences. The American Naturalist 171: E102–E118.
Mehnert, G., F. Leunert, S. Cires, K. D. Jo
¨hnk, J. Rucker, B.
Nixdorf & C. Wiedner, 2010. Competitiveness of invasive
and native cyanobacteria from temperate freshwaters under
various light and temperature conditions. Journal of
Plankton Research 32: 1009–1021.
Moisander, P. H., L. A. Cheshire, J. Braddy, E. S. Calandrino,
M. Hoffman, M. F. Piehler & H. W. Paerl, 2012. Faculta-
tive diazotrophy increases Cylindrospermopsis raciborskii
competitiveness under fluctuating nitrogen availability.
FEMS Microbiology Ecology 79: 800–811.
Molica, R. J. R., E. J. A. Oliveira, P. V. V. C. Carvalho, A. N. S.
F. Costa, M. C. C. Cunha, G. L. Melo & S. M. F.
O. Azevedo, 2005. Occurrence of saxitoxins and an ana-
toxin-a(s)-like anticholinesterase in a Brazilian drinking
water supply. Harmful Algae 4: 743–753.
Moreira, C., A. Fathalli, V. Vasconcelos & A. Antunes, 2015.
Phylogeny and biogeography of the invasive cyanobac-
terium Cylindrospermopsis raciborskii. Archiv fu
¨r
Mikrobiologie 197: 47–52.
Nalewajko, C. & T. P. Murphy, 2001. Effects of temperature,
and availability of nitrogen and phosphorus on the abun-
dance of Anabaena and Microcystis in Lake Biwa, Japan:
an experimental approach. Limnology 2: 45–48.
Novak, J. T. & D. E. Brune, 1985. Inorganic carbon limited
growth kinetics of some freshwater algae. Water Research
19: 215–225.
Padisa
´k, J., 1997. Cylindrospermopsis raciborskii (Woloszyn-
ska) Seenayya et Subba Raju, an expanding, highly adap-
tive cyanobacterium: worldwide distribution and review of
its ecology. Archiv fu
¨r Hydrobiologie Supplementband
Monographische Beitra
¨ge 107: 563–593.
Paerl, H. W. & J. Huisman, 2009. Climate change: a catalyst for
global expansion of harmful cyanobacterial blooms.
Environmental Microbiology Reports 1: 27–37.
Piccini, C., L. Aubriot, A. Fabre, V. Amaral, M. Gonza, A.
Giani, C. C. Figueredo, L. Vidal, C. Kruk & S. Bonilla,
2011. Genetic and eco-physiological differences of South
American Cylindrospermopsis raciborskii isolates support
the hypothesis of multiple ecotypes. Harmful Algae 10:
644–653.
Pierangelini, M., S. Stojkovic, P. T. Orr & J. Beardall, 2014.
Photosynthetic characteristics of two Cylindrospermopsis
raciborskii strains differing in their toxicity. Journal of
Phycology 50: 292–302.
368 Hydrobiologia (2016) 763:357–369
123
Posselt, A. J., M. A. Burford & G. Shaw, 2009. Pulses of
phosphate promote dominance of the toxic cyanophyte
Cylindrospermopsis raciborskii in a subtropical water
reservoir. Journal of Phycology 45: 540–546.
R Core Team, 2012. R: A Language and Environment for Sta-
tistical Computing. R Foundation for Statistical Comput-
ing, Vienna.
Reynolds, C. S., 2006. The Ecology of Phytoplankton. Cam-
bridge University Press, Cambridge.
Reynolds, C. S., R. L. Oliver & A. E. Walsby, 1987.
Cyanobacterial dominance: the role of buoyancy regula-
tion in dynamic lake environments. New Zealand Journal
of Marine and Freshwater Research 21: 379–390.
Robarts, R. D. & T. Zohary, 1987. Temperature effects on
photosynthetic capacity, respiration, and growth rates of
bloom-forming cyanobacteria. New Zealand Journal of
Marine and Freshwater Research 21: 391–399.
Rzymski, P., B. Poniedziałek, M. Kokocin
´ski, T. Jurczak, D.
Lipski & W. Wiktorowicz, 2014. Interspecific allelopathy
in cyanobacteria: Cylindrospermopsin and Cylindrosper-
mopsis raciborskii effect on the growth and metabolism of
Microcystis aeruginosa. Harmful Algae 35: 1–8.
Saker, M. L. & D. J. Griffiths, 2000. The effect of temperature
on growth and cylindrospermospsin content of seven iso-
lates of Cylindrospermopsis raciborskii (Nostocales,
Cyanophyceae) from water bodies in Northern Australia.
Phycologia 39: 349–354.
Saker, M. L. & D. J. Griffiths, 2001. Occurrence of blooms of the
cyanobacterium Cylindrospermopsis raciborskii (Wolos-
zyn
´ska) Seenayya and Subba Raju in a north Queensland
domestic water supply. Marine & Freshwater Research 52:
907–915.
Shafik, H. M., S. Herodek, M. Pre
´sing & L. Vo
¨ro
¨s, 2001. Factors
effecting growth and cell composition of cyanoprokaryote
Cylindrospermopsis raciborskii (Wołoszyn
´ska) Seenayya
et Subba Raju. Archiv fu
¨r Hydrobiologie Supplementband
Algological Studies 140: 75–93.
Shatwell, T., A. Nicklisch & J. Ko
¨hler, 2012. Temperature and
photoperiod effects on phytoplankton growing under sim-
ulated mixed layer light fluctuations. Limnology and
Oceanography 57: 541–553.
Sinha, R., L. A. Pearson, T. W. Davis, M. A. Burford, P. T. Orr
& B. A. Neilan, 2012. Increased incidence of Cylindros-
permopsis raciborskii in temperate zones - Is climate
change responsible? Water Research 46: 1408–1419.
Smith, V. H., 1983. Low nitrogen to phosphorus ratios favour
dominance by blue-green algae in lake phytoplankton.
Science 221: 669–671.
Soares, M. C. S., M.I. de A. Rocha, M. M. Marinho, S. M. F.
O. Azevedo, C. W. C. Branco & V. L. M. Huszar, 2009.
Changes in species composition during annual cyanobac-
terial dominance in a tropical reservoir: physical factors,
nutrients and grazing effects. Aquatic Microbial Ecology
57: 137–149.
Swan, B. K., B. Tupper, A. Sczyrba, F. M. Lauro, M. Martinez-
Garcia, J. M. Gonzalez, H. Luof, J. J. Wright, Z. C. Landry,
N. W. Hanson, B. P. Thompson, N. J. Poulton, P. Sch-
wientek, S. G. Acinas, S. J. Giovannoni, M. A. Moran, S.
J. Hallam, R. Cavicchioli, T. Woyke & R. Stepanauskas,
2013. Prevalent genome streamlining and latitudinal
divergence of planktonic bacteria in the surface ocean.
Proceedings of the National Academy of Sciences of the
United States of America 110: 11463–11468.
Thomas, M. K., C. T. Kremer, C. A. Klausmeier & E. Litchman,
2012. A global pattern of thermal adaptation in marine
phytoplankton. Science 338: 1085–1088.
Tilman, D., 1982. Resource Competition and Community
Structure. Princeton University Press, Princeton, NJ.
Tilman, D. & R. L. Kiesling, 1984. Freshwater algal ecology:
taxonomic trade-offs in the temperature dependence of
nutrient competitive abilities. In Klug, M. J. & C. A. Reddy
(eds), Current Perspectives in Microbial Ecology: Pro-
ceedings of the Third International Symposium on
Microbial Ecology. American Society for Microbiology,
Washington, D.C.: 314–319.
Uehlinger, V. U., 1981. Experimental studies of the autecology
of Aphanizomenon flos-aquae. Archiv fu
¨r Hydrobiologie
Supplementband Algological Studies 60: 260–288.
Vitousek, P. M., S. Ha
¨ttenschwiler, L. Olander & S. Allison,
2002. Nitrogen and nature. Ambio 31: 97–101.
Walther, G.-R., A. Roques, P. E. Hulme, M. T. Sykes, P. Pys
ˇek,
I. Ku
¨hn & M. Zobel, 2009. Alien species in a warmer
world: risks and opportunities. Trends in Ecology & Evo-
lution 24: 686–693.
Wiedner, C., J. Ru
¨cker, R. Bru
¨ggemann & B. Nixdorf, 2007.
Climate change affects timing and size of populations of an
invasive cyanobacterium in temperate regions. Oecologia
152: 473–484.
Wilson, A. E., W. A. Wilson & M. E. Hay, 2006. Intraspecific
variation in growth and morphology of the bloom-forming
cyanobacterium Microcystis aeruginosa. Applied and
Environmental Microbiology 72: 7386–9.
Hydrobiologia (2016) 763:357–369 369
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... The decrease in abundance of cyanobacteria after Sep. 17 was related to the decrease in temperature. Numerous studies have shown that the growth rate of Microcystis is temperaturedependent with optima usually at 25 C or greater (Richard et al., 1987;Thomas and Litchman, 2016). ...
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... This may be caused by the strong correlation between the month of sampling and temperature, especially because we collected mosses at the beginning and the end of the growing season, which was characterized by a 4°C difference on average. While we are not aware of any study testing the effect of temperature on total moss-associated cyanobacterial biomass, but temperature has been shown to be positively correlated with cyanobacterial biomass in lakes (Cremona et al., 2018) and in cultures (Thomas & Litchman, 2016). Moreover, temperature can affect the composition of the moss microbiome and the relative abundance of cyanobacteria. ...
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... Even though it is not yet clear how phytoplankton will respond globally to the increase in temperature, it is evident that a possible consequence is the reduction of diversity, favoring the growth of different cyanobacteria species, for instance, Planktothrix sp. and Microcystis sp., which have better survival strategies in new climatic conditions [52][53][54]. ...
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... The dominance of this group can have major impacts in water quality, cause increased turbidity because of high biomass (Scheffer et al. 1997) and potential toxicity (Carmichael 1994). The strong association of group III with water temperature shown in the RDA is related to the metabolism of these organisms, which at favorable temperatures can promote an increase in growth rates (Robarts and Zohary 1987;Thomas and Litchman 2016) and helps with regulation of its flotage, an important competitive ability to access resources such as nutrients and light (Padisak 1997;Reynolds et al. 1987). ...
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Conference Paper
Full-text available
Tilman, D. and R.L. Kiesling. 1984. Freshwater algal ecology: taxonomic tradeoffs in the temperature dependence of nutrient competitive abilities. In: M.J. Klug and C.A. Reddy, eds., Current Perspectives in Microbial Ecology. Amer. Soc. Microbiology, Washington, D.C.
Book
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this book aims to give background information as well as practical guidance. Chapters 2 and 3 provide the background for understanding the behaviour of cyanobacteria and their toxin production in given environmental conditions. Chapter 4 reviews the evidence regarding health impacts, primarily for public health experts establishing national guidelines or academics identifying and addressing current research needs. Chapters 5-7 provide guidance on safe practices in the planning and management of drinking water supplies and recreational resorts. Readers who access the book with specific questions regarding prevention of cyanobacterial growth or their removal in drinking water treatment will find Chapters 8 and 9 of direct relevance. Guidance on the design and implementation of monitoring programmes is given in Chapter 10, and Chapters 11-13 provide field and laboratory methods for monitoring cyanobacteria, their toxins and the conditions which lead to their excessive growth.
Article
Temperature provides a powerful theme for exploring environmental adaptation at all levels of biological organization, from molecular kinetics to organismal fitness to global biogeography. First, the thermodynamic properties that underlie biochemical kinetics and protein stability determine the overall thermal sensitivity of rate processes. Consequently, a single quantitative framework can assess variation in thermal sensitivity of ectotherms in terms of single amino acid substitutions, quantitative genetics, and interspecific differences. Thermodynamic considerations predict that higher optimal temperatures will result in greater maximal fitness at the optimum, a pattern seen both in interspecific comparisons and in within‐population genotypic variation. Second, the temperature‐size rule (increased developmental temperature causes decreased adult body size) is a common pattern of phenotypic plasticity in ectotherms. Mechanistic models can correctly predict the rule in some taxa, but lab and field studies show that rapid evolution can weaken or even break the rule. Third, phenotypic and evolutionary models for thermal sensitivity can be combined to explore potential fitness consequences of climate warming for terrestrial ectotherms. Recent analyses suggest that climate change will have greater negative fitness consequences for tropical than for temperate ectotherms, because many tropical species have relatively narrow thermal breadths and smaller thermal safety margins.