especially liver cancer (Backer and McGillicuddy, 2006).
As this toxin and other related toxins can affect the nervous
system, there has been a suggestion that some neurological diseases such as Parkinson’s disease or dementia
may also be related to some of the toxic and bioreactive
compounds originating from this HAB group (Ibelings
and Chorus, 2007). Among the CyanoHAB group are also
some species that attach to seagrass, corals, or sediment,
such as Lyngbya which is also capable of producing
a wide array of toxic or potentially toxic compounds,
including Lyngbyatoxin and saxitoxin.
Although this entry is focused on planktonic HABs, for
the sake of completeness, it is important to mention
macroalgal HABs. Macroalgae also dominate the flora of
many shallow estuaries, lagoons, and upper embayments,
coral reefs, and rocky intertidal/subtidal habitats especially in polluted environments. A well-documented
example of such a bloom occurred in 2008, when the
macroalgal species Enteromorpha prolifera (also called
Ulva prolifera or sea lettuce) occurred at the venue of
the Olympic Games sailing competition, almost
blanketing the water with filamentous scum (Hu et al.,
2010). Blooms of this magnitude in this region had not
previously been observed but have since reoccurred on
a near annual basis associated with expanding aquaculture
industries and eutrophication. It has been estimated that
the cost associated with the management of the
E. prolifera event in 2008 was greater than $100 million.
Ecology and dynamics of HABs
For decades, HABs have been studied in all areas of the
globe, but there is still much that is not well understood
regarding the underlying processes behind the development or outbreak of species or species groups. In the
simplest terms, the success of HABs lies at the intersection
of their physiological adaptations of the HABs, the environmental conditions, interaction with co-occurring
organisms, and physical dynamics of the water body.
Physiological adaptations
In order to grow and make new biomass, algae need to
have the necessary materials and energy to make new
biomass. The classic paradigm of algal blooms is that of
microscopic “plants” or primary producers, dependent
on light and the uptake of dissolved nutrients. However,
as noted above, many HABs (the diatoms being the primary exception) may both engage in photosynthesis but
may also graze on particles, including bacteria,
cyanobacteria, other algae, or even bits of fish tissue. This
complex nutrition or mixotrophy (the mix of different
modes of nutrition) imparts advantages to organisms
under conditions of low light (when photosynthesis would
be reduced), under low nutrients (when inorganic nutrient
uptake may be limited), or under conditions of imbalanced
nutrient supply. Some species only use mixotrophy as
a supplement, while others rely exclusively or nearly so
on mixotrophic nutrition (Burkholder et al., 2008).
Some of these “algae” in fact do not make their own chlorophyll at all, but rather borrow their chloroplasts from the
food they eat, a process termed kleptochloroplasty. Most
all the major groups of eukaryotic phytoplankton, including most HABs, engage in mixotrophy to some extent
(Flynn et al., 2013). Importantly, when an organism undertakes primary production (photosynthesis) and grazing,
the two processes provide “more than the sum of the parts”
in terms of benefits to the organisms (Mitra and Flynn,
2010), and thus these modes of nutrition have important
consequences for understanding HAB success and in
modeling the flow of energy and materials in microbial
food webs (Flynn et al., 2013).
In addition to the complex nutrition of mixotrophy, the
development of specific algal species may be a function
of availability of specific nutrient forms. Using sources of
nutrients not available to competitors may impart an advantage for certain species or species groups (Glibert and
Burkholder, 2011). Many HABs have the ability to utilize
organic forms of nitrogen and phosphorus, but mechanisms
may vary. Some species have species enzymes for transport
or metabolism of certain forms of organic nitrogen or phosphorus, while other species have the capability for the
breakdown of organic compounds at the cell surface
(Glibert and Legrand, 2006). Yet other species appear to
be stimulated when complex organic molecules are provided in conjunction with inorganic nutrients. For example,
in mesocosm experiments, Granéli et al. (1985) showed that
dinoflagellate populations, including Prorocentrum minimum, were stimulated by inorganic nitrogen only when
added in combination with humic acids.
Furthermore, the mechanisms for nutrient acquisition
and the extent of dependence by a HAB on mixotrophy or
on specific dissolved nutrient forms depend not only on
the species, but also prevailing environmental factors such
as temperature or light (Glibert and Burkholder, 2006).
Thus, a given suite of nutrients may have different impacts
in different sites and at different times. Smayda (2002) has
suggested that different HAB dinoflagellates can be classified into a matrix, based on preferences organized by
a nearshore/offshore gradient in decreasing nutrients,
reduced mixing, and increasing light. In this matrix, estuarine species are defined as the dinoflagellates that are better
adapted to low-light high-nutrient waters, but oceanic species are better adapted to high-light low-nutrient waters.
Many algae, including HABs, also have complex life
cycles and behaviors that have important implications
for their occurrence, distribution, and dynamics. Among
life cycle stages for some algae are benthic cysts or other
resting stages that give cells capability to withstand hostile
or unfavorable environmental conditions. The metabolic
switch from resting stages to motile stages often occurs
for a population at or around the same time, allowing
actively dividing cells to initiate a bloom. These cysts or
spores provide a recurrent seed source or inoculum
for planktonic populations, and this characteristic may
be a critical factor in determining not only the geographic
distribution of species but also their eventual abundance.
ALGAL BLOOMS
9
As this toxin and other related toxins can affect the nervous
system, there has been a suggestion that some neurological diseases such as Parkinson’s disease or dementia
may also be related to some of the toxic and bioreactive
compounds originating from this HAB group (Ibelings
and Chorus, 2007). Among the CyanoHAB group are also
some species that attach to seagrass, corals, or sediment,
such as Lyngbya which is also capable of producing
a wide array of toxic or potentially toxic compounds,
including Lyngbyatoxin and saxitoxin.
Although this entry is focused on planktonic HABs, for
the sake of completeness, it is important to mention
macroalgal HABs. Macroalgae also dominate the flora of
many shallow estuaries, lagoons, and upper embayments,
coral reefs, and rocky intertidal/subtidal habitats especially in polluted environments. A well-documented
example of such a bloom occurred in 2008, when the
macroalgal species Enteromorpha prolifera (also called
Ulva prolifera or sea lettuce) occurred at the venue of
the Olympic Games sailing competition, almost
blanketing the water with filamentous scum (Hu et al.,
2010). Blooms of this magnitude in this region had not
previously been observed but have since reoccurred on
a near annual basis associated with expanding aquaculture
industries and eutrophication. It has been estimated that
the cost associated with the management of the
E. prolifera event in 2008 was greater than $100 million.
Ecology and dynamics of HABs
For decades, HABs have been studied in all areas of the
globe, but there is still much that is not well understood
regarding the underlying processes behind the development or outbreak of species or species groups. In the
simplest terms, the success of HABs lies at the intersection
of their physiological adaptations of the HABs, the environmental conditions, interaction with co-occurring
organisms, and physical dynamics of the water body.
Physiological adaptations
In order to grow and make new biomass, algae need to
have the necessary materials and energy to make new
biomass. The classic paradigm of algal blooms is that of
microscopic “plants” or primary producers, dependent
on light and the uptake of dissolved nutrients. However,
as noted above, many HABs (the diatoms being the primary exception) may both engage in photosynthesis but
may also graze on particles, including bacteria,
cyanobacteria, other algae, or even bits of fish tissue. This
complex nutrition or mixotrophy (the mix of different
modes of nutrition) imparts advantages to organisms
under conditions of low light (when photosynthesis would
be reduced), under low nutrients (when inorganic nutrient
uptake may be limited), or under conditions of imbalanced
nutrient supply. Some species only use mixotrophy as
a supplement, while others rely exclusively or nearly so
on mixotrophic nutrition (Burkholder et al., 2008).
Some of these “algae” in fact do not make their own chlorophyll at all, but rather borrow their chloroplasts from the
food they eat, a process termed kleptochloroplasty. Most
all the major groups of eukaryotic phytoplankton, including most HABs, engage in mixotrophy to some extent
(Flynn et al., 2013). Importantly, when an organism undertakes primary production (photosynthesis) and grazing,
the two processes provide “more than the sum of the parts”
in terms of benefits to the organisms (Mitra and Flynn,
2010), and thus these modes of nutrition have important
consequences for understanding HAB success and in
modeling the flow of energy and materials in microbial
food webs (Flynn et al., 2013).
In addition to the complex nutrition of mixotrophy, the
development of specific algal species may be a function
of availability of specific nutrient forms. Using sources of
nutrients not available to competitors may impart an advantage for certain species or species groups (Glibert and
Burkholder, 2011). Many HABs have the ability to utilize
organic forms of nitrogen and phosphorus, but mechanisms
may vary. Some species have species enzymes for transport
or metabolism of certain forms of organic nitrogen or phosphorus, while other species have the capability for the
breakdown of organic compounds at the cell surface
(Glibert and Legrand, 2006). Yet other species appear to
be stimulated when complex organic molecules are provided in conjunction with inorganic nutrients. For example,
in mesocosm experiments, Granéli et al. (1985) showed that
dinoflagellate populations, including Prorocentrum minimum, were stimulated by inorganic nitrogen only when
added in combination with humic acids.
Furthermore, the mechanisms for nutrient acquisition
and the extent of dependence by a HAB on mixotrophy or
on specific dissolved nutrient forms depend not only on
the species, but also prevailing environmental factors such
as temperature or light (Glibert and Burkholder, 2006).
Thus, a given suite of nutrients may have different impacts
in different sites and at different times. Smayda (2002) has
suggested that different HAB dinoflagellates can be classified into a matrix, based on preferences organized by
a nearshore/offshore gradient in decreasing nutrients,
reduced mixing, and increasing light. In this matrix, estuarine species are defined as the dinoflagellates that are better
adapted to low-light high-nutrient waters, but oceanic species are better adapted to high-light low-nutrient waters.
Many algae, including HABs, also have complex life
cycles and behaviors that have important implications
for their occurrence, distribution, and dynamics. Among
life cycle stages for some algae are benthic cysts or other
resting stages that give cells capability to withstand hostile
or unfavorable environmental conditions. The metabolic
switch from resting stages to motile stages often occurs
for a population at or around the same time, allowing
actively dividing cells to initiate a bloom. These cysts or
spores provide a recurrent seed source or inoculum
for planktonic populations, and this characteristic may
be a critical factor in determining not only the geographic
distribution of species but also their eventual abundance.
ALGAL BLOOMS
9