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Blooms Like It Hot

DOI:10.1126/science.1155398
Authors:
Hans Paerl at University of North Carolina at Chapel Hill
Hans Paerl
Jef Huisman at University of Amsterdam
Jef Huisman
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Abstract

A link exists between global warming and the worldwide proliferation of harmful cyanobacterial blooms.
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RNA pieces in the spliceosome, has a domain
V counterpart, containing a 2-nucleotide
bulge located 5 base pairs away from an AGC
triad (10). Formation of an analogous metal-
binding platform in this region of U6 (11) may
explain the apparent ability of spliceosomal
RNAs to retain catalytic activity in the com-
plete absence of the many protein components
that usually accompany splicing (12). A
domain V-like element could have played a
major role during the RNA world era of evolu-
tion, serving as the catalytic center for RNA
cleavage, transesterification, and polymeriza-
tion reactions.
The new structure provides a powerful
starting point for future investigations of
group II introns and the spliceosome. The
lack of electron density for domain VI,
which is important for the first step of splic-
ing in many group II introns, and the
absence of exons from the structure preclude
us from seeing how these elements dock
onto the surface created by domains I to V.
Thus, the structural details of substrate
recognition and catalysis remain undefined.
The nature of the conformational change
known to separate the two steps of splicing
(13) also remains unclear. Finally, it will be
important for our understanding of group II
intron self-splicing to capture the structures
of the other intermediates along the splicing
pathway and to pursue experiments that link
features of these structures with functionally
defined interactions.
References
1. A. M. Pyle, Ribozymes and RNA Catalysis (Royal Society
of Chemistry, Cambridge, UK, ed. 2, 2008).
2. A. M. Pyle, A. M. Lambowitz, The RNA World (Cold Spring
Harbor Laboratory, Cold Spring Harbor, NY, ed. 3, 2006).
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320, 77 (2008).
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10.1126/science.1156721
www.sciencemag.org SCIENCE VOL 320 4 APRIL 2008
57
CREDITS: (TOP) HANS PAERL/UNIVERSITY OF NORTH CAROLINA; (BOTTOM) SATELLITE PHOTO, DIGITALGLOBE
PERSPECTIVES
N
utrient overenrichment of waters by
urban, agricultural, and industrial
development has promoted the
growth of cyanobacteria as harmful algal
blooms (see the figure) (1, 2). These blooms
increase the turbidity of aquatic ecosystems,
smothering aquatic plants and thereby sup-
pressing important invertebrate and fish habi-
tats. Die-off of blooms may deplete oxygen,
killing fish. Some cyanobacteria produce tox-
ins, which can cause serious and occasionally
fatal human liver, digestive, neurological, and
skin diseases (1–4). Cyanobacterial blooms
thus threaten many aquatic ecosystems,
including Lake Victoria in Africa, Lake Erie in
North America, Lake Taihu in China, and the
Baltic Sea in Europe (3–6). Climate change is
a potent catalyst for the further expansion of
these blooms.
Rising temperatures favor cyanobacteria
in several ways. Cyanobacteria generally
grow better at higher temperatures (often
above 25°C) than do other phytoplankton
species such as diatoms and green algae (7, 8).
This gives cyanobacteria a competitive advan-
tage at elevated temperatures (8, 9). Warming
of surface waters also strengthens the vertical
stratification of lakes, reducing vertical mix-
ing. Furthermore, global warming causes
lakes to stratify earlier in spring and destratify
later in autumn, which lengthens optimal
growth periods. Many cyanobacteria exploit
these stratified conditions by forming intra-
cellular gas vesicles, which make the cells
buoyant. Buoyant cyanobacteria float upward
when mixing is weak and accumulate in dense
surface blooms (1, 2, 7) (see the figure). These
surface blooms shade underlying nonbuoyant
phytoplankton, thus suppressing their oppo-
nents through competition for light (8).
Cyanobacterial blooms may even locally
increase water temperatures through the
intense absorption of light. The temperatures
of surface blooms in the Baltic Sea and in
Lake IJsselmeer, Netherlands, can be at least
1.5°C above those of ambient waters (10, 11).
This positive feedback provides additional
competitive dominance of buoyant cyanobac-
teria over nonbuoyant phytoplankton.
Global warming also affects patterns of
precipitation and drought. These changes in
the hydrological cycle could further enhance
cyanobacterial dominance. For example,
more intense precipitation will increase sur-
face and groundwater nutrient discharge into
water bodies. In the short term, freshwater dis-
charge may prevent blooms by flushing.
However, as the discharge subsides and water
residence time increases as a result of drought,
nutrient loads will be captured, eventually pro-
moting blooms. This scenario takes place
when elevated winter-spring rainfall and
flushing events are followed by protracted
periods of summer drought. This sequence of
A link exists between global warming and
the worldwide proliferation of harmful
cyanobacterial blooms.
Blooms Like It Hot
Hans W. Paerl
1
and Jef Huisman
2
CLIMATE
1
Institute of Marine Sciences, University of North Carolina
at Chapel Hill, Morehead City, NC 28557, USA. E-mail:
hpaerl@email.unc.edu
2
Institute for Biodiversity and
Ecosystem Dynamics, University of Amsterdam, 1018 WS
Amsterdam, Netherlands. E-mail: jef.huisman@science.
uva.nl
Undesired blooms. Examples of large water bodies
covered by cyanobacterial blooms include the Neuse
River Estuary, North Carolina, USA (top) and Lake
Victoria, Africa (bottom).
Published by AAAS
on April 4, 2008 www.sciencemag.orgDownloaded from
4 APRIL 2008 VOL 320 SCIENCE www.sciencemag.org
58
PERSPECTIVES
events has triggered massive algal blooms in
aquatic ecosystems serving critical drinking
water, fishery, and recreational needs. At-
tempts to control fluctuations in the discharge
of rivers and lakes by means of dams and
sluices may increase residence time, further
aggravating cyanobacteria-related ecological
and human health problems.
In addition, summer droughts, rising sea
levels, increased withdrawal of freshwater for
agricultural use, and application of road salt as
a deicing agent have led to rising lake
salinities in many regions. Several common
cyanobacteria are more salt-tolerant than
freshwater phytoplankton species (12, 13).
This high salt tolerance is reflected by increas-
ing reports of toxic cyanobacterial blooms in
brackish waters (2, 6).
Some cyanobacteria have substantially
expanded their geographical ranges. For
example, Cylindrospermopsis raciborskii—
the species responsible for “Palm Island mys-
tery disease,” an outbreak of a severe hepati-
tis-like illness on Palm Island, Australia (4)—
was originally described as a tropical/subtrop-
ical genus. The species appeared in southern
Europe in the 1930s and colonized higher lat-
itudes in the late 20th century. It is now wide-
spread in lakes in northern Germany (14).
Similarly, the species was noted in Florida
almost 35 years ago and is now commonly
found in reservoirs and lakes experiencing
eutrophication in the U.S. southeast and mid-
west (2). It is adapted to the low-light condi-
tions that typify eutrophic waters, prefers
water temperatures above 20°C, and survives
adverse conditions through the use of special-
ized resting cells (14). These bloom character-
istics suggest a link to eutrophication and
global warming.
More detailed studies of the population
dynamics in cyanobacterial blooms are needed.
For example, competition between toxic and
nontoxic strains affects the toxicity of
cyanobacterial blooms (15). Furthermore,
viruses may attack cyanobacteria and mediate
bloom development and succession (16). It is
unclear how these processes are affected by
global warming. What is clear, however, is that
high nutrient loading, rising temperatures,
enhanced stratification, increased residence
time, and salination all favor cyanobacterial
dominance in many aquatic ecosystems. Water
managers will have to accommodate the effects
of climatic change in their strategies to combat
the expansion of cyanobacterial blooms.
References
1. J. Huisman, H. C. P. Matthijs, P. M. Visser, Harmful
Cyanobacteria (Springer, Dordrecht, Netherlands, 2005).
2. H. W. Paerl, R. S. Fulton III, in Ecology of Harmful Marine
Algae, E. Graneli, J. Turner, Eds. (Springer, Berlin, 2006),
pp. 95–107.
3. I. Chorus, J. Bartram, Toxic Cyanobacteria in Water
(Spon, London, 1999).
4. W. W. Carmichael, Human Ecol. Risk Assess. 7, 1393
(2001).
5. L. Guo, Science 317, 1166 (2007).
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Shelf Sci. 71, 580 (2007).
7. C. S. Reynolds, Ecology of Phytoplankton (Cambridge
Univ. Press, Cambridge, 2006).
8. K. D. Jöhnk et al., Global Change Biol. 14, 495 (2008).
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559, 401 (2006).
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11. B. W. Ibelings, M. Vonk, H. F. J. Los, D. T. van der Molen,
W. M. Mooij, Ecol. Appl. 13, 1456 (2003).
12. L. Tonk, K. Bosch, P. M. Visser, J. Huisman, Aquat. Microb.
Ecol. 46, 117 (2007).
13. P. H. Moisander, E. McClinton III, H. W. Paerl, Microb.
Ecol. 43, 432 (2002).
14. C. Wiedner, J. Rücker, R. Brüggemann, B. Nixdorf,
Oecologia 152, 473 (2007).
15. W. E. A. Kardinaal et al., Aquat. Microb. Ecol. 48, 1 (2007).
16. M. Honjo et al., J. Plankton Res. 28, 407 (2006).
10.1126/science.1155398
I
n 2006, Yamanaka and colleagues (1) dis-
covered that mouse fibroblasts could be
reprogrammed to a pluripotent, embry-
onic stem (ES) cell–like state by the simple
introduction of four transcription factors,
Oct4, Sox2, Klf4, and c-Myc. This finding has
since been reproduced (2–6) and extended to
human fibroblasts using the same cocktail of
genes (7, 8) or one composed of Oct4, Sox2,
Nanog, and Lin28 (9). These so-called “in-
duced pluripotent stem cells” (iPS cells)
appear similar to ES cells in that they can give
rise to all the cells of the body and display fun-
damental genetic and morphologic ES cell
characteristics (see the figure). The concept of
an iPS cell brings together decades of work in
the fields of ES cell biology and nuclear
reprogramming that predicted it might be pos-
sible to impose pluripotency upon a somatic
cell (10). iPS cells not only have the potential
to produce patient-specific stem cells, but
they also provide a platform to study the biol-
ogy of pluripotency and cell reprogramming.
In Science Express, Aoi et al. (11) broaden the
application of iPS cell methodology to murine
epithelial cell types, highlighting differences
when compared with reprogramming of
fibroblasts. And on page 97 of this issue,
Viswanathan et al. (12) address the role of one
of the reprogramming factors, Lin28, in regu-
lating microRNAs (miRNAs) in ES cells. The
findings of Viswanathan et al., and recent
work by Benetti et al. (13) and Sinkkonen et al.
(14), advance our knowledge of the little-
understood roles of miRNAs in ES cells.
Collectively, these studies take us closer to
understanding how ES cells maintain an
undifferentiated, self-renewing, and pluripo-
tent state, and to defining how pluripotency
can be imposed on other cell types.
To date, fibroblasts and mesenchymal
stem cells have been used to generate iPS cells
(1–9). A next step is to determine whether
other cell types are susceptible to reprogram-
ming. Toward this end, Aoi et al. produced iPS
cells from two epithelial cell populations,
adult mouse hepatocytes and gastric epithelial
cells, by expressing Oct4, Sox2, Klf4, and
c-Myc. Like iPS cells generated from fibro-
blasts (iPS-fibroblast), those from primary
hepatocytes (iPS-Hep) and gastric epithelial
cells (iPS-Stm) were pluripotent and gave rise
to adult and germline chimeras. However,
iPS-Hep and iPS-Stm differ from iPS-fibro-
blast cells in several important respects, indi-
cating that the dynamics of reprogramming
may not be equivalent in these cell types. For
instance, although c-Myc was used, iPS-Hep
and iPS-Stm cell–derived chimeric mice did
not display the c-Myc–dependent tumori-
genicity observed in iPS-fibroblast–derived
chimeric mice. In addition, iPS-Hep and iPS-
Stm cells could be generated using less strin-
gent selection conditions. Thus, epithelial cell
types may be more prone to reprogramming
than fibroblasts.
How do these differences inform us about
the mechanism of reprogramming? Given that
ES cells are an epithelial population, charac-
terized by cell adhesion (mediated by the
membrane protein E-cadherin), one possibil-
ity is that epithelialization is an event required
The requirements for reprogramming different
somatic cell types to a pluripotent state may
not be equivalent.
Deconstructing Pluripotency
Anne G. Bang and Melissa K. Carpenter
DEVELOPMENT
Novocell Inc., 3550 General Atomics Court, San Diego, CA
92121, USA. E-mail: mcarpenter@novocell.com
Published by AAAS
on April 4, 2008 www.sciencemag.orgDownloaded from
... Further gradients exist within each region, both in air temperature and other drivers, such as urbanization, agriculturalization, and industrialization, that could be the source of this residual signal. Nonetheless, warming air temperature leads to warmer water temperature, which in turn is known to influence water quality (e.g., O'Reilly et al., 2015;Paerl and Huisman, 2008;Shuvo et al., 2021). ...
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We provide the first comprehensive analysis of spatial heterogeneity in water quality across the Canadian nearshore regions of the Laurentian Great Lakes (LGL) with periodic sampling in the ice-free seasons from 2000 to 2019 for 24 water quality variables from 52 nearshore sites. We asked: (1) What is the extent, range, and magnitude of spatial heterogeneity in water quality conditions across the nearshore of the Canadian Great Lakes? and (2) How do features of anthropogenic development, sub-basin characteristics, anticipated coastal circulation, and weather influence water quality conditions in the nearshore of the Canadian Great Lakes? Principal Components Analysis explained 42% of the variation in water quality across the Canadian Great Lakes, with high spatial heterogeneity both within and among lakes, ranging from oligotrophic conditions in Lake Superior to eutrophic conditions in Lake Erie. Lakes Erie and Ontario generally had higher concentrations of chloride, chlorophyll a, and nutrients while higher silicate concentrations were observed in Lake Superior. Consistent patterns of degraded water quality were observed in Areas of Concern, such as Hamilton Harbour, Bay of Quinte, Nipigon Bay, and near Thunder Bay. Across the nearshore of the Canadian Great Lakes, regions with warmer air temperatures, in addition to urbanized and agricultural landscapes, were associated with deteriorated water quality. Our study highlights the importance of improving management practices across urban and agricultural landscapes, particularly in consideration of climatic change cumulatively degrading water quality conditions in the highly biologically, culturally, and socioeconomically important nearshore regions of the LGL.
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... Rising temperatures and thermal stratification can favor cyanobacteria growth allowing them to outcompete other phytoplankton groups (Fadel et al., 2015;Wagner and Adrian, 2009). They often bloom and dominate aquatic ecosystems during dry season when water temperature rises as they outcompete other groups such as diatoms and green algae at higher temperatures (Paerl and Huisman, 2008). Some species use gas vesicles to float upward during stratified conditions and accumulate in dense surface blooms shading nonbuoyant diatoms and green algae and suppressing them through competition for light (Jöhnk et al., 2008). ...
... Over the last decades, many studies have demonstrated that cyanobacterial blooms are promoted by higher temperatures and nutrient loadings (Burford et al., 2020;Davis et al., 2009;Fadel et al., 2019;Jöhnk et al., 2008;Paerl and Huisman, 2008;Slim et al., 2014). Changing climatic conditions are predicted to increase the frequency and toxicity of cyanobacterial blooms (O'Neil et al., 2012). ...
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... In Taihu, under the situation of an increase in internal loading, although the eutrophication of lakes has increased, there is no significant increase in nutrient input. During the cyanobacteria outbreak season, the death and decomposition of algae can easily lead to hypoxia on the sediment surface, and many benthic macroinvertebrates will suffocate [52,53]; however, in the cold season, macroinvertebrates will not be disturbed by more pollutants. For multiyear changes, these two effects are superimposed on macroinvertebrates in different seasons in one year. ...
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Potentially toxic Cyanobacteria, like Microcystis, form a serious threat in recreational waters and drinking-water reservoirs. We monitored the population dynamics of toxic and non-toxic Microcystis strains using rRNA of the internal transcribed spacer region in combination with DGGE to determine whether there is a seasonal succession of toxic and non-toxic Microcystis genotypes in freshwater lakes and, if so, whether this succession can explain seasonal dynamics of the toxin microcystin. We studied 3 lakes in The Netherlands, all dominated by Microcystis during summer. Coexistence of several genotypes was observed in all lakes. The seasonal succession in a deep, stratified lake started with a population consisting of several toxic genotypes at the onset of the bloom, which changed into a population dominated by non-toxic genotypes at the end of the bloom. In this lake, the genotype succession clearly accounted for the observed microcystin dynamics. In 2 unstratified lakes, we also observed a seasonal replacement of Microcystis genotypes; however, the relation between genotype succession and microcystin dynamics was less conspicuous, since toxic strains dominated throughout the bloom period. A seasonal succession of different Microcystis genotypes might often be a key mechanism determining microcystin concentrations in Microcystisdominated lakes. Therefore, factors driving the succession of toxic and non-toxic genotypes deserve further study.
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Fuzzy modeling of cyanobacterial surface waterblooms: Validation with NOAA-AVHRR satellite images
Article
  • Oct 2003
Surface waterblooms of toxic cyanobacteria (scums) interfere with the use of lakes, for instance in the production of drinking water or for recreation. Routine monitoring data are not sufficient for early warning due to the large temporal and spatial variability in the occurrence of surface waterblooms, and the time lag between the formation of the scum and the availability of relevant information for risk management. We combined a "traditional" dynamic simulation model based upon differential equations with fuzzy logic to describe the three main conditions governing surface waterbloom formation: (1) a preexisting population of cyanobacteria, (2) buoyancy of the cells, and (3) stability of the water column. The attributes and membership functions of the fuzzy model were based on earlier field studies of diel changes in buoyancy and vertical distribution of cyanobacteria. The model was applied without further calibration to the large lake IJsselmeer (1200 km(2)) in the Netherlands, and we validated the model output using 12 years of NOAA-AVHRR (National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometers) satellite images on which surface blooms are discernible as an enhanced vegetation index or increased surface water temperature. Existing surface blooms were predicted with high accuracy, but additional blooms were also predicted. A statistical test (Cohen's Kappa) showed that correct predictions of the absence or presence of surface blooms were highly unlikely to have occurred by chance only. The model can be used to predict the occurrence of surface waterblooms in advance on the basis of the long-term weather forecast, leaving time for appropriate management of the problem. The lake management has expressed interest in converting the present model into a fully operational-online-early warning system.
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Testing the Sensitivity of Phytoplankton Communities to Changes in Water Temperature and Nutrient Load, in a Temperate Lake
Article
  • Apr 2006
Freshwater lakes are biologically sensitive to changes in the surrounding environment and the impacts that such changes have on their water quality are of considerable ecological, recreational and economic importance. In this study the phytoplankton community model, PROTECH, was used to experiment with the effects of elevated temperatures and increased nutrient load on phytoplankton succession and productivity. The response of a phytoplankton community to combined incremental changes in these drivers was analysed, in order to elucidate the resulting ecological changes. Annual mean phytoplankton biomass increased with increases in temperature and nutrient loading, although the latter had the larger effect. The phenology of the dominant phytoplankton taxa changed with increasing water temperature; the three spring blooming species all peaked earlier in the year. The simulated summer bloom of Anabaena became earlier in the year and the Chlorella bloom later. The increased phytoplankton biomass was largely dominated by the cyanobacterium Anabaena, which was especially prevalent during the summer bloom. This resulted in a progressive loss of phytoplankton biodiversity with increasing water temperature and nutrient supply. Model experimentation showed that whilst both factors greatly affected the community, the changes to nutrient loading generally had the greater effect and that at low nutrient levels the effect of water temperature change was reduced considerably. Finally, the model predicted that cyanobacteria have the potential to dominate the phytoplankton community, with clear consequences for water quality, and that this dominance was at its greatest when high water temperatures were combined with high nutrient loads.
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