Their possession of accessory pigments, such as phycoerythrin, enable several cyanobacteria species to carry out
photosynthesis at depths that receive only green light and
where, in addition, nutrients are more abundant than at the
surface (as in the case of surface waters rapidly depleted
following spring algal proliferations). Cyanobacterial pigments, as well as mycosporin-like amino acids, are
involved in their capacity to resist ultraviolet radiation in
surface waters, giving them another advantage over some
phytoplankton (Castenholz et al., 2000).
The cyanobacteria are poorly grazed by zooplankton
due to their production of mucilage layers (Mur et al.,
1999; Goleski et al., 2010). Recent data reveal that
cyanobacteria have adopted a mode of defense depending
on grazer pressure (i.e., they are able to modify their
defense reaction according to the actual risk of grazing)
(Gomes et al., 2012). The synthesis of different toxins by
many cyanobacterial blooms gives them a selective
advantage, since some zooplanktonic predators are susceptible to these toxins and thus avoid eating
cyanobacteria (Jacquet et al., 2004; Oliver et al., 2010).
The biology and ecology of cyanobacteria have been
extensively studied throughout the world during the two
last decades due to their expansion and proliferation in
most aquatic environments (Pearl and Otten, 2013). Several inner ecophysiological strategies allow the
cyanobacteria to exploit anthropogenic modifications of
aquatic environments (specifically nutrient overenrichment and hydrologic alterations). Thus when conditions of light and water column stability are favorable,
cyanobacteria may proliferate creating a competitive
advantage over other species of phytoplankton (Smith
and Bennet, 1999; Peter et al., 2002). Because benthic
cyanobacteria are the principal colonizers of the interface
between sediments and water, they can affect fluid flow
dynamics and structure formation in biofilms and microbial mats. Therefore, they greatly influence the sedimentary dynamics of peritidal depositional systems as noted
by Vincent et al. (2000) and Noffke et al. (2003).
Cyanobacteria status in estuarine ecosystems
Due to their salinity gradients, estuaries provide a large
variety of aquatic habitats for native populations of
marine, brackish, and freshwater planktonic species
(Telesh, 2004). The spatial zoning and functional characteristics of estuaries result in biologically active zones
with high concentrations of bacteria and microalgae
(Golubkov et al., 2001). Further, the microbial communities of estuarine ecosystems are susceptible to rapid
changes in response to the flux of environmental conditions. Thus, the flux of dissolved and suspended organic
and inorganic material, in addition to hydrological variations, significantly affects microbial abundance, diversity,
and activity in the estuarine ecosystems (Bouvy et al.,
2010).
Given sufficient nitrogen inputs, estuarine and coastal
marine environments can be driven by phosphorus
limitation which contributes to greater far field nitrogen
enrichment and eutrophication at greater distances
(Howarth et al., 2011). Nutrient loading from coastal
watersheds and upstream systems typically deliver higher
quantities of nutrients than those entering from coastal
ocean waters (Galloway et al., 2004; Fennel et al., 2006).
In estuarine waters with salinities greater than
8–10 ppt, planktonic cyanobacteria capable of
N-fixation are largely absent (Howarth and Marino,
2006; Marino et al., 2006; Howarth and Paerl, 2008).
A decrease in planktonic N-fixation in estuaries has been
attributed in part to high levels of sulfates in seawater,
making the assimilation of molybdenum (an element
required for N-fixation) difficult. This leads to slow potential growth rates of N-fixing cyanobacteria (heterocystus
cyanobacteria, where N-fixation occurs only in heterocyst
cells) exposed to grazing by zooplankton and benthic animals (Chan et al., 2006).
Cyanotoxicity and cyanobacterial blooms
A notable increase in occurrence and intensity of
cyanobacteria toxic blooms has been observed worldwide
over the last several decades (Eiler and Bertilsson, 2004;
Pearson and Neilan, 2008; Rinta-Kanto et al., 2009). For
major cyanobacterial genera involved in harmful blooms,
the optimal growth rates and bloom potentials have
increased with higher water temperatures; thus global
warming may be playing a key role in the expansion and
persistence of bloom-forming cyanobacterial taxa (Pearl
and Fulton, 2006).
A recent study by Pearl et al. (2013) showed how
cyanobacterial surface blooms may locally increase surface water temperatures due to light energy absorption
via an array of photosynthetic and photoprotective pigments (chlorophylls, carotenoids, and phycobilins). This
represents a positive feedback mechanism by which
cyanobacterial bloom species can optimize their growth
rates leading to competitive dominance over eukaryotic
phytoplankton. Global warming, therefore, may enhance
cyanobacterial dominance in the plankton as reported by
Bonilla (2012).
Cyanobacterial blooms are complex microbial assemblages, consisting of many representatives from characterized phyla (Pope and Patel, 2008; Li et al., 2011; Wilhelm
et al., 2011). The morphological features of organisms
within a bloom appear as associative microbial assemblages analogous to biofilms (Zehr et al., 1995; Reid
et al., 2000; Omoregie et al., 2004; Burke et al., 2011).
The initiation, maintenance, and subsequent decline of
cyanobacteria blooms depend to a large extent on the
availability of nitrogen (N) and phosphorus (P) (Levich,
1996). It also depends on the ratios of N and P, selecting
for organisms capable of fixing atmospheric nitrogen over
those lacking this physiology (Klausmeier et al., 2004).
Among the harmful cyanobacteria species cited elsewhere, the most common toxin producing cyanobacteria
N 2 -fixing genera are Anabaena, Aphanizomenon,
170
CYANOBACTERIA
photosynthesis at depths that receive only green light and
where, in addition, nutrients are more abundant than at the
surface (as in the case of surface waters rapidly depleted
following spring algal proliferations). Cyanobacterial pigments, as well as mycosporin-like amino acids, are
involved in their capacity to resist ultraviolet radiation in
surface waters, giving them another advantage over some
phytoplankton (Castenholz et al., 2000).
The cyanobacteria are poorly grazed by zooplankton
due to their production of mucilage layers (Mur et al.,
1999; Goleski et al., 2010). Recent data reveal that
cyanobacteria have adopted a mode of defense depending
on grazer pressure (i.e., they are able to modify their
defense reaction according to the actual risk of grazing)
(Gomes et al., 2012). The synthesis of different toxins by
many cyanobacterial blooms gives them a selective
advantage, since some zooplanktonic predators are susceptible to these toxins and thus avoid eating
cyanobacteria (Jacquet et al., 2004; Oliver et al., 2010).
The biology and ecology of cyanobacteria have been
extensively studied throughout the world during the two
last decades due to their expansion and proliferation in
most aquatic environments (Pearl and Otten, 2013). Several inner ecophysiological strategies allow the
cyanobacteria to exploit anthropogenic modifications of
aquatic environments (specifically nutrient overenrichment and hydrologic alterations). Thus when conditions of light and water column stability are favorable,
cyanobacteria may proliferate creating a competitive
advantage over other species of phytoplankton (Smith
and Bennet, 1999; Peter et al., 2002). Because benthic
cyanobacteria are the principal colonizers of the interface
between sediments and water, they can affect fluid flow
dynamics and structure formation in biofilms and microbial mats. Therefore, they greatly influence the sedimentary dynamics of peritidal depositional systems as noted
by Vincent et al. (2000) and Noffke et al. (2003).
Cyanobacteria status in estuarine ecosystems
Due to their salinity gradients, estuaries provide a large
variety of aquatic habitats for native populations of
marine, brackish, and freshwater planktonic species
(Telesh, 2004). The spatial zoning and functional characteristics of estuaries result in biologically active zones
with high concentrations of bacteria and microalgae
(Golubkov et al., 2001). Further, the microbial communities of estuarine ecosystems are susceptible to rapid
changes in response to the flux of environmental conditions. Thus, the flux of dissolved and suspended organic
and inorganic material, in addition to hydrological variations, significantly affects microbial abundance, diversity,
and activity in the estuarine ecosystems (Bouvy et al.,
2010).
Given sufficient nitrogen inputs, estuarine and coastal
marine environments can be driven by phosphorus
limitation which contributes to greater far field nitrogen
enrichment and eutrophication at greater distances
(Howarth et al., 2011). Nutrient loading from coastal
watersheds and upstream systems typically deliver higher
quantities of nutrients than those entering from coastal
ocean waters (Galloway et al., 2004; Fennel et al., 2006).
In estuarine waters with salinities greater than
8–10 ppt, planktonic cyanobacteria capable of
N-fixation are largely absent (Howarth and Marino,
2006; Marino et al., 2006; Howarth and Paerl, 2008).
A decrease in planktonic N-fixation in estuaries has been
attributed in part to high levels of sulfates in seawater,
making the assimilation of molybdenum (an element
required for N-fixation) difficult. This leads to slow potential growth rates of N-fixing cyanobacteria (heterocystus
cyanobacteria, where N-fixation occurs only in heterocyst
cells) exposed to grazing by zooplankton and benthic animals (Chan et al., 2006).
Cyanotoxicity and cyanobacterial blooms
A notable increase in occurrence and intensity of
cyanobacteria toxic blooms has been observed worldwide
over the last several decades (Eiler and Bertilsson, 2004;
Pearson and Neilan, 2008; Rinta-Kanto et al., 2009). For
major cyanobacterial genera involved in harmful blooms,
the optimal growth rates and bloom potentials have
increased with higher water temperatures; thus global
warming may be playing a key role in the expansion and
persistence of bloom-forming cyanobacterial taxa (Pearl
and Fulton, 2006).
A recent study by Pearl et al. (2013) showed how
cyanobacterial surface blooms may locally increase surface water temperatures due to light energy absorption
via an array of photosynthetic and photoprotective pigments (chlorophylls, carotenoids, and phycobilins). This
represents a positive feedback mechanism by which
cyanobacterial bloom species can optimize their growth
rates leading to competitive dominance over eukaryotic
phytoplankton. Global warming, therefore, may enhance
cyanobacterial dominance in the plankton as reported by
Bonilla (2012).
Cyanobacterial blooms are complex microbial assemblages, consisting of many representatives from characterized phyla (Pope and Patel, 2008; Li et al., 2011; Wilhelm
et al., 2011). The morphological features of organisms
within a bloom appear as associative microbial assemblages analogous to biofilms (Zehr et al., 1995; Reid
et al., 2000; Omoregie et al., 2004; Burke et al., 2011).
The initiation, maintenance, and subsequent decline of
cyanobacteria blooms depend to a large extent on the
availability of nitrogen (N) and phosphorus (P) (Levich,
1996). It also depends on the ratios of N and P, selecting
for organisms capable of fixing atmospheric nitrogen over
those lacking this physiology (Klausmeier et al., 2004).
Among the harmful cyanobacteria species cited elsewhere, the most common toxin producing cyanobacteria
N 2 -fixing genera are Anabaena, Aphanizomenon,
170
CYANOBACTERIA