Environmental Engineering Reference
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Likens 2010). This is an ecologically important group, providing a high nutrient food for
zooplankton. Chryptomonads frequently dominate the phytoplankton assemblages of
the Great Lakes. While populations may at times opportunistically increase with favor-
able conditions, aided by high production rates, they are typically year-round residents.
They are able to grow at low light levels so that maximum population densities may occur
at depth, resulting in deep chlorophyll maxima in some lakes. Diel vertical migrations
(DVMs) may also occur (Likens 2010).
Division Euglenophyta—Euglenoids: Euglenoids represent a large and diverse group of
which only a few are planktonic (Figure 15.8). They are typically lagellated on one end,
and most are colorless and nonphotosynthetic (Likens 2010) or photosynthetic and faculta-
tive heterotrophs. They are most often found in shallow water that is rich in organic mat-
ter (e.g., polluted lakes or farm pounds). Most euglenoids live in freshwaters (Suthers and
Rissik 2009) with only a few marine species reported.
Division Phaeophyta—Brown Algae: Brown algae are well-known, predominantly marine
species, the largest of which is kelp. Other examples include seaweeds such as the genus
Sargassum , which form loating mats and are the most prominent species in the area
known as the Sargasso Sea, which is in the middle of the North Atlantic Ocean. The few
freshwater forms are attached, not planktonic.
Division Chrysophytes—Chrosophytes: These are commonly known as the golden-brown
algae due to the presence of the pigment fucoxanthin in addition to chlorophyll. The groups
are made up primarily of free-swimming, unicellular freshwater forms. Interestingly,
while they are predominately phototrophs, in the absence of light or with the abundance of
dissolved food nearly all of this group are facultative heterotrophs.
Division Haptophyta—Golden Algae: These are also referred to as golden algae, which
are lagellated (typically two slightly unequal lagella) and include some of the most com-
mon marine algae (Wehr and Sheath 2003). One of the well-known members of this group
is Prymnesium parvum , which produces toxins that have resulted in massive ish kills in
Texas ish hatcheries and reservoirs.
Division Bacillariophyta—Diatoms: Diatoms are one of the more important, diverse, and
abundant groups of phytoplankton. They are particularly dominant in cold, nutrient-rich
waters. A distinguishing characteristic of diatoms is their cell wall (frustule) composed of
silicon dioxide (Figure 15.9). Thus, in addition to other nutrients, diatoms require silica for
growth. The frustules are composed of two parts (valves) that it together, and diatoms are
Euglena
gracilis
Phacus
Trachelomonas
FIGURE 15.8 Examples of Euglenophyta. (Courtesy of Dr. Morgan L. Vis, Professor of Environmental &
Plant Biology, Ohio University Algae Home Page http://www.ohio.edu/plantbio/vislab/algaeindex.htm.)
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