species appear as floating entities in the water column with
their distribution and transport influenced by existing
currents and upwelling conditions.
Composition
Diatoms and dinoflagellates are examples of the more
dominant and diverse eukaryote algal components of estuaries and are joined in these waters by a variety of species
from other algal categories (Reynolds, 2007). Although a
variety of the prokaryote cyanobacteria taxa are present in
freshwater lakes and rivers, they have a more limited occurrence in estuaries. In general, freshwater species entering
an estuary are not very tolerant to the existing salinity
levels, which subsequently results in a phytoplankton community dominated by estuarine and marine species. In
addition to salinity, there are other environmental variables
that will influence the composition, abundance, and distribution of the phytoplankton in these waters (e.g., these
include existing temperatures, nutrient availability, light
intensity, predation, tidal exchange, among others). The
changing environmental conditions within an estuary will
generally favor a greater seasonal development and presence of several algal components, resulting in changing
patterns of dominance through the year and the presence
of background species. These changes result in seasonal
and annual patterns of species representation and dominance. A common seasonal response associated with
increasing temperatures from winter into spring is the
major development of diatoms occurring in this late
winter-early spring period. This growth is then typically
followed by a decrease in diatom development, followed
by increased concentrations among other taxa, with this
sequence repeated the following year.
Size
Sieburth et al. (1978) proposed a classification system for
various taxa within the plankton community based on
size. These categories and the range of their sizes
pertaining to the plankton constituents were picoplankton
(0.2–2.0 mm), nanoplankton (2–20 mm), microplankton
(20–200 mm), mesoplankton (200 mm to 2 mm), and
macroplankton (>2 mm). Many of the smaller
cyanobacteria are included in the picoplankton category,
whereas several representative dinoflagellates and diatoms are in the meso- and macroplankton categories.
For instance, among those included in the largest of the
phytoplankton taxa are the dinoflagellate Noctiluca
scintillans with a cell size of ca. 1 mm in diameter and
the diatom Ethmodiscus gazellae having cell diameters
up to 1–2 mm. However, these examples are the extreme
with the majority of the phytoplankton taxa in either the
nano- or microplankton size categories.
Distribution
Distribution patterns among the estuarine phytoplankton
species will vary from being globally cosmopolitan to
those more common to specific polar, temperate, of
tropical geographic regions. Species may be introduced
to other estuaries from currents within adjacent coastal
waters through tidal entry, or from ballast water released
from ships entering local harbors. These species may survive and eventually persist in these waters, or may perish
due to conditions not conducive to their survival. It is not
unusual for an invasive species to enter an estuary, survive,
and become a newly established resident of that estuary.
Trophic representation
Phytoplankton may also be classified according to their
trophic status. Autotrophs are the photosynthetic species,
capable of synthesizing inorganic material (CO 2 and
H 2 O) using light or chemical energy to produce organic
carbon. This is the dominant type of nutrition associated
with phytoplankton represented by species possessing
photosynthetic pigments (e.g., diatoms, cyanobacteria,
chlorophytes). Through this process they are a major
source of biomass and oxygen. The heterotrophs lack
these pigments and do not conduct photosynthesis, so they
obtain carbon products externally, such as by ingesting
(phagotrophy) other organisms, or their organic products.
This life style is common among many of the dinoflagellates which are capable of ingesting bacteria or other
organisms in the water column. The mixotrophs are
represented by autotrophic taxa that are also capable of
phagotrophy.
Reproduction
Reproduction among the phytoplankton is primarily by
binary fission, with sexual reproduction also common
among several of the categories (e.g., the dinoflagellates).
Included in the life cycle of many phytoplankton species is
the formation of cysts, a temporary resting stage which
may settle to the substrate of the estuary. Under favorable
conditions these resting cysts may later develop to active
developing cells that will continue growing and complete
the life cycle stages of the species. Favorable environmental conditions would enhance increased cell division of
these taxa resulting in greater abundance among the phytoplankton. Excessive patterns of growth will also produce high concentrations of the cells that may produce
an algal bloom. Due to pigments within the cells of these
algae, these blooms may impart a noticeable color to the
water’s surface (e.g., red tide). Based on the existing environmental conditions (e.g., available nutrients, favorable
temperatures, residency time within the estuary, etc.),
these blooms may be brief and involve a small area of
development or be long lasting (e.g., days, weeks) and
extend over a large surface area.
Environmental concerns
In contrast to phytoplankton’s beneficial contributions to
the waters as a food and oxygen source, they have also
been associated with unfavorable conditions associated
with algal bloom events. Following algal bloom development and the subsequent death of these cells, the cells
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their distribution and transport influenced by existing
currents and upwelling conditions.
Composition
Diatoms and dinoflagellates are examples of the more
dominant and diverse eukaryote algal components of estuaries and are joined in these waters by a variety of species
from other algal categories (Reynolds, 2007). Although a
variety of the prokaryote cyanobacteria taxa are present in
freshwater lakes and rivers, they have a more limited occurrence in estuaries. In general, freshwater species entering
an estuary are not very tolerant to the existing salinity
levels, which subsequently results in a phytoplankton community dominated by estuarine and marine species. In
addition to salinity, there are other environmental variables
that will influence the composition, abundance, and distribution of the phytoplankton in these waters (e.g., these
include existing temperatures, nutrient availability, light
intensity, predation, tidal exchange, among others). The
changing environmental conditions within an estuary will
generally favor a greater seasonal development and presence of several algal components, resulting in changing
patterns of dominance through the year and the presence
of background species. These changes result in seasonal
and annual patterns of species representation and dominance. A common seasonal response associated with
increasing temperatures from winter into spring is the
major development of diatoms occurring in this late
winter-early spring period. This growth is then typically
followed by a decrease in diatom development, followed
by increased concentrations among other taxa, with this
sequence repeated the following year.
Size
Sieburth et al. (1978) proposed a classification system for
various taxa within the plankton community based on
size. These categories and the range of their sizes
pertaining to the plankton constituents were picoplankton
(0.2–2.0 mm), nanoplankton (2–20 mm), microplankton
(20–200 mm), mesoplankton (200 mm to 2 mm), and
macroplankton (>2 mm). Many of the smaller
cyanobacteria are included in the picoplankton category,
whereas several representative dinoflagellates and diatoms are in the meso- and macroplankton categories.
For instance, among those included in the largest of the
phytoplankton taxa are the dinoflagellate Noctiluca
scintillans with a cell size of ca. 1 mm in diameter and
the diatom Ethmodiscus gazellae having cell diameters
up to 1–2 mm. However, these examples are the extreme
with the majority of the phytoplankton taxa in either the
nano- or microplankton size categories.
Distribution
Distribution patterns among the estuarine phytoplankton
species will vary from being globally cosmopolitan to
those more common to specific polar, temperate, of
tropical geographic regions. Species may be introduced
to other estuaries from currents within adjacent coastal
waters through tidal entry, or from ballast water released
from ships entering local harbors. These species may survive and eventually persist in these waters, or may perish
due to conditions not conducive to their survival. It is not
unusual for an invasive species to enter an estuary, survive,
and become a newly established resident of that estuary.
Trophic representation
Phytoplankton may also be classified according to their
trophic status. Autotrophs are the photosynthetic species,
capable of synthesizing inorganic material (CO 2 and
H 2 O) using light or chemical energy to produce organic
carbon. This is the dominant type of nutrition associated
with phytoplankton represented by species possessing
photosynthetic pigments (e.g., diatoms, cyanobacteria,
chlorophytes). Through this process they are a major
source of biomass and oxygen. The heterotrophs lack
these pigments and do not conduct photosynthesis, so they
obtain carbon products externally, such as by ingesting
(phagotrophy) other organisms, or their organic products.
This life style is common among many of the dinoflagellates which are capable of ingesting bacteria or other
organisms in the water column. The mixotrophs are
represented by autotrophic taxa that are also capable of
phagotrophy.
Reproduction
Reproduction among the phytoplankton is primarily by
binary fission, with sexual reproduction also common
among several of the categories (e.g., the dinoflagellates).
Included in the life cycle of many phytoplankton species is
the formation of cysts, a temporary resting stage which
may settle to the substrate of the estuary. Under favorable
conditions these resting cysts may later develop to active
developing cells that will continue growing and complete
the life cycle stages of the species. Favorable environmental conditions would enhance increased cell division of
these taxa resulting in greater abundance among the phytoplankton. Excessive patterns of growth will also produce high concentrations of the cells that may produce
an algal bloom. Due to pigments within the cells of these
algae, these blooms may impart a noticeable color to the
water’s surface (e.g., red tide). Based on the existing environmental conditions (e.g., available nutrients, favorable
temperatures, residency time within the estuary, etc.),
these blooms may be brief and involve a small area of
development or be long lasting (e.g., days, weeks) and
extend over a large surface area.
Environmental concerns
In contrast to phytoplankton’s beneficial contributions to
the waters as a food and oxygen source, they have also
been associated with unfavorable conditions associated
with algal bloom events. Following algal bloom development and the subsequent death of these cells, the cells
492
PHYTOPLANKTON