Microbes and Plants - Freshwater Ecology: Concepts and Environmental Applications - page 135

and another trails behind. Many members of
the group are able to ingest other organisms.
Some have no photosynthetic pigments, and
some exist as predators, ingesting small cells.
Some dinoflagellates have complex life cy-
cles and are able to assume a variety of forms,
including spores, ameboid forms, and flagel-
lated cells (Burkholder and Glasgow, 1997).
In addition, some species of dinoflagellates in-
gest small unicellular algae and utilize them as
chloroplasts. The dinoflagellates form a group
that does not fit comfortably in the old classi-
fication system of plants or animals.
The toxic dinoflagellate Pfisteria pisci-
cida has caused concern recently. This or-
ganism is found in estuaries and has caused
fish kills in the Chesapeake Bay. Pfisteria pis-
cicida can harm humans and swimming ad-
visories are publicized when the organism is
known to be present. Nutrient pollution
transported via freshwaters to the estuary
probably exacerbates blooms of this toxic
alga (Burkholder and Glasgow, 1997).

in lakes, methods that lyse the cells and release
toxins should be avoided (Lam and Prepas, 1997).
Copper treatments commonly used on algal
blooms release most toxins present within 3
days, but lime (calcium hydroxide) will remove
algae without immediate release of toxins
(Kenefick et al., 1993). The toxins are remarkably
stable once they enter drinking water and can
be removed only by chlorination and activated
charcoal. Chlorination of drinking water rich in
organics may be problematic because it may
form chlorinated hydrocarbons (known carcino-
gens). Methods for controlling cyanobacterial
blooms will be discussed in Chapter 17.
Given the intense blooms of cyanobacteria
that can form in some lakes, the ecological im-
portance of these toxins in terms of ecosystem
and community properties is likely underappre-
ciated. The cyanobacterial toxins are known to
affect food crop (bean) photosynthesis when
they are present in irrigation water (Abe et al.,
1996). They can also modify zooplankton com-
munities (Hietala and Walls, 1995; Ward and
Codd, 1999), reduce growth of trout (Bury et al.,
1995), interfere with development of fish and am-
phibians (Oberemm et al., 1999), and presumably
affect numerous other organisms. However,
some animals may actually prefer water con-
taining toxic algae even though it is toxic to them
(Rodas and Costas, 1999). The toxins can also be
bioconcentrated by clams (Prepas et al., 1997).
A note of caution should be made related to
cyanobacterial toxins. Some companies in the
United States provide dietary supplements made
from cyanobacteria (blue-green algae). It is wise
to ascertain that the genera of algae used in
these supplements are not toxic (e.g., it has not
been demonstrated that Spirulina produces tox-
ins but Aphanizomenon can do so), and that
quality control procedures are used to ensure
that toxic genera are never present. If the gen-
era in the product have strains known to pro-
duce toxins, verification that tests for cyanobac-
terial toxins are conducted routinely (Schaeffer
et al., 1999) with negative results is advisable
before any of the products are consumed.
Other groups of algae (the dinoflagellates
and the diatoms) have toxic species or strains
but cause problems more rarely in freshwa-
ters. Cases of fish poisoning have been related
to dinoflagellate blooms (similar to the marine
red tide) in freshwater lakes or reservoirs. The
factors that lead to blooms of these toxic algae
are poorly understood.

Euglenophyceae
The euglenoids have pigments similar to
those of the green algae but are always uni-
cellular and generally motile. They are found
most commonly in eutrophic situations, in-
cluding shallow sediments. Euglenophytes are
capable of ingesting particles. A flexible pro-
tein sheath covers the cell, and ameboid cell
movement can occur. Additionally, many cells
have a single flagellum that can be used for
locomotion. Characteristic features include a
red photosensitive spot in one end and nu-
merous chloroplasts in the cell (Fig. 8.8).

Chlorophyceae and Charophyceae, Green
Algae and Relatives
These algae range from simple single-celled
organisms to complex multicellular assem-
blages (Fig. 8.9). They are found in all surface
aquatic habitats from damp soil and wetlands
to the benthos of rapidly flowing streams and
the plankton of large lakes, and they are the
most diverse freshwater algae group.
Some of the species are found mainly in
oligotrophic habitats, whereas others are
common in eutrophic habitats. Unicellular