undergo bacterial decomposition resulting in reduced oxygen levels in the water column, often resulting in hypoxic
or anoxic conditions and accompanied by fish mortalities.
This condition occurs more frequently in the smaller and
shallow regions of estuaries and tidal river sections.
Other bloom-forming algae also produce toxins harmful
to animals and humans.
Summary
Phytoplankton represent a diverse microscopic algal community of major ecological importance in estuaries and
other water-based ecosystems. They produce oxygen
through the process of photosynthesis and represent a basic
food source for microscopic fauna essential to various
pelagic food webs. They are also recognized as frequently
producing large surface concentrations of cells referred to
as algal blooms that are often associated with degraded
water quality conditions. Included among the phytoplankton are species that are potential toxin producers.
Bibliography
Reynolds, C., 2007. Ecology of Phytoplankton. New York:
Cambridge University Press.
Sieburth, J. M. N., Smetacek, V., and Lenz, J., 1978. Pelagic ecosystem structure: heterotrophic compartments of the plankton and
their relationship to plankton size fractions. Limnology and
Oceanography, 23, 1256–1263.
Tomas, C. R. (ed.), 1997. Identifying Marine Phytoplankton.
San Diego: Academic Press.
Cross-references
Algal Blooms
Cyanobacteria
Invasive Species
Phytoplankton
Phytoplankton Blooms
Toxic Blooms
PHYTOPLANKTON BLOOMS
Edward J. Phlips
Fisheries and Aquatic Sciences Program (SFRC),
University of Florida, Gainesville, FL, USA
Definition
A “phytoplankton bloom” is a major peak in biomass of
planktonic algae or cyanobacteria.
Description
Despite the relatively simple character of the term
“phytoplankton bloom,” its applications and the meaning
of the elements of the definition are in practice subject to
a range of interpretations (Smayda, 1997). In most
cases the term “phytoplankton” refers to photoautotrophic
species that spend a significant portion of their life
suspended in the water column (Reynolds et al., 2006);
however, there are exceptions to this most common usage.
For example, blooms can involve strictly heterotrophic
dinoflagellates, such as Pfiesteria piscicada, or
mixotrophic algae that alternate modes of growth between
photoautotrophy and other nutritional modes (e.g.,
phagotrophy, osmotrophy) (Burkholder et al., 2008). The
definition of “major” is also subject to varied interpretations. It can refer to annually recurring peaks in biomass,
e.g., “spring bloom,” or to events that deviate significantly
from a prescribed average condition. Therefore, what is
defined as a bloom in one ecosystem may not be considered a bloom in another. Even the term “phytoplankton”
can be subject to variations in interpretation, such as the
appearance of high concentrations of meroplankton (i.e.,
species of algae that spend much of their life associated
with the benthos) into the water column due to
wind-induced resuspension. It is also important to
distinguish between the terms “phytoplankton bloom”
and “high primary productivity.” High primary productivity refers to high rates of photosynthesis or growth. While
phytoplankton blooms are generally associated with
periods of elevated primary productivity, high primary
productivity does not always result in high biomass due
to the influence of loss processes (e.g., grazing, dilution,
sedimentation).
The requisites for the formation of phytoplankton
blooms include all factors that affect “gain” and “loss”
processes, since blooms can only develop when biomass
gains outweigh losses. The main “gain” processes are
photosynthesis and growth which require the presence of
adequate amounts of essential resources, including photosynthetically active radiation (i.e., PAR) and nutrients
(i.e., carbon, phosphorus, nitrogen, other macro- and
micronutrients, and in the case of species like diatoms silica) (Phlips, 2002; Reynolds, 2006). “Loss” processes
include respiration, release of fixed carbon from cells, grazing, dilution/export of biomass, sedimentation of
cells outside the euphotic zone, and cell death (i.e.,
programmed and disease related). Other physical and
chemical factors play a modulating role in “gain” and “loss”
processes, either by modifying the availability of growth
resources or impacting the ecophysiology of the organisms
themselves. For example, pH affects the availability of inorganic carbon and temperature regulates metabolic activity.
Historically, one of the most common uses of the
term phytoplankton bloom has been in relation to the
phenomenon of “spring blooms,” which refer to peaks in
phytoplankton biomass associated with the annual arrival
in the spring of optimal light and nutrient conditions for
phytoplankton growth in the surface mixed layer of many
temperate marine ecosystems. Over the past few decades,
research on phytoplankton blooms has increasingly
focused on harmful algal blooms (i.e., HABs) and
the impacts of anthropogenic sources of nutrients.
Although phytoplankton blooms are a feature of many
marine ecosystems around the world, even independent
of human influences, intense accumulations of biomass
of certain species can have disruptive consequences
PHYTOPLANKTON BLOOMS
493
or anoxic conditions and accompanied by fish mortalities.
This condition occurs more frequently in the smaller and
shallow regions of estuaries and tidal river sections.
Other bloom-forming algae also produce toxins harmful
to animals and humans.
Summary
Phytoplankton represent a diverse microscopic algal community of major ecological importance in estuaries and
other water-based ecosystems. They produce oxygen
through the process of photosynthesis and represent a basic
food source for microscopic fauna essential to various
pelagic food webs. They are also recognized as frequently
producing large surface concentrations of cells referred to
as algal blooms that are often associated with degraded
water quality conditions. Included among the phytoplankton are species that are potential toxin producers.
Bibliography
Reynolds, C., 2007. Ecology of Phytoplankton. New York:
Cambridge University Press.
Sieburth, J. M. N., Smetacek, V., and Lenz, J., 1978. Pelagic ecosystem structure: heterotrophic compartments of the plankton and
their relationship to plankton size fractions. Limnology and
Oceanography, 23, 1256–1263.
Tomas, C. R. (ed.), 1997. Identifying Marine Phytoplankton.
San Diego: Academic Press.
Cross-references
Algal Blooms
Cyanobacteria
Invasive Species
Phytoplankton
Phytoplankton Blooms
Toxic Blooms
PHYTOPLANKTON BLOOMS
Edward J. Phlips
Fisheries and Aquatic Sciences Program (SFRC),
University of Florida, Gainesville, FL, USA
Definition
A “phytoplankton bloom” is a major peak in biomass of
planktonic algae or cyanobacteria.
Description
Despite the relatively simple character of the term
“phytoplankton bloom,” its applications and the meaning
of the elements of the definition are in practice subject to
a range of interpretations (Smayda, 1997). In most
cases the term “phytoplankton” refers to photoautotrophic
species that spend a significant portion of their life
suspended in the water column (Reynolds et al., 2006);
however, there are exceptions to this most common usage.
For example, blooms can involve strictly heterotrophic
dinoflagellates, such as Pfiesteria piscicada, or
mixotrophic algae that alternate modes of growth between
photoautotrophy and other nutritional modes (e.g.,
phagotrophy, osmotrophy) (Burkholder et al., 2008). The
definition of “major” is also subject to varied interpretations. It can refer to annually recurring peaks in biomass,
e.g., “spring bloom,” or to events that deviate significantly
from a prescribed average condition. Therefore, what is
defined as a bloom in one ecosystem may not be considered a bloom in another. Even the term “phytoplankton”
can be subject to variations in interpretation, such as the
appearance of high concentrations of meroplankton (i.e.,
species of algae that spend much of their life associated
with the benthos) into the water column due to
wind-induced resuspension. It is also important to
distinguish between the terms “phytoplankton bloom”
and “high primary productivity.” High primary productivity refers to high rates of photosynthesis or growth. While
phytoplankton blooms are generally associated with
periods of elevated primary productivity, high primary
productivity does not always result in high biomass due
to the influence of loss processes (e.g., grazing, dilution,
sedimentation).
The requisites for the formation of phytoplankton
blooms include all factors that affect “gain” and “loss”
processes, since blooms can only develop when biomass
gains outweigh losses. The main “gain” processes are
photosynthesis and growth which require the presence of
adequate amounts of essential resources, including photosynthetically active radiation (i.e., PAR) and nutrients
(i.e., carbon, phosphorus, nitrogen, other macro- and
micronutrients, and in the case of species like diatoms silica) (Phlips, 2002; Reynolds, 2006). “Loss” processes
include respiration, release of fixed carbon from cells, grazing, dilution/export of biomass, sedimentation of
cells outside the euphotic zone, and cell death (i.e.,
programmed and disease related). Other physical and
chemical factors play a modulating role in “gain” and “loss”
processes, either by modifying the availability of growth
resources or impacting the ecophysiology of the organisms
themselves. For example, pH affects the availability of inorganic carbon and temperature regulates metabolic activity.
Historically, one of the most common uses of the
term phytoplankton bloom has been in relation to the
phenomenon of “spring blooms,” which refer to peaks in
phytoplankton biomass associated with the annual arrival
in the spring of optimal light and nutrient conditions for
phytoplankton growth in the surface mixed layer of many
temperate marine ecosystems. Over the past few decades,
research on phytoplankton blooms has increasingly
focused on harmful algal blooms (i.e., HABs) and
the impacts of anthropogenic sources of nutrients.
Although phytoplankton blooms are a feature of many
marine ecosystems around the world, even independent
of human influences, intense accumulations of biomass
of certain species can have disruptive consequences
PHYTOPLANKTON BLOOMS
493