Microbes and Plants - Freshwater Ecology: Concepts and Environmental Applications - page 140

flagellates (class Phytomastigophora) and the colorless flagellates (class
Zoomastigophora). The Phytomastigophora includes several groups previ-
ously discussed (e.g., dinoflagellates, chrys-
ophytes, euglenoids, and flagellated green
algae).
The Zoomastigophora includes several
important human parasites (e.g., try-
panosomes and Leishmania ) and many free-
swimming forms. The heterotrophic
nanoflagellates are in this group. They are
very small flagellates that are often the most
important consumers of pelagic bacteria and
can serve a vital role in nutrient cycling.
The subphylum Sarcodina includes the
protozoa that move by protoplasmic flow
and pseudopodia (extensions of the proto-
plasm; e.g., Amoeba ). The movement of
amebae illustrates the process. The Sarco-
dina are more often associated with benthos
and sediments than open freshwaters. Two
species can cause meningitis in human swim-
mers. The Sarcodina are also important mi-
crobial predators.
The subphylum Ciliophora includes the
ciliates. These protozoa have more than four
cilia. The group contains the familiar Para-
mecium and other free-swimming genera.
The common attached organism Vorticella
is also a member of this group.

Sidebar 8.3.
Diatoms in Forensics

Diatoms can be used as a tool to determine if
drowning is a cause of death and where a
drowning or other crimes occurred. When a
person dies by drowning, one of the last things
they do is take a breath of water. The water
enters the lungs and bursts some of the alve-
oli (site of contact between blood and atmo-
sphere). Diatoms in the water enter the blood-
stream and are circulated through the body
until the heart stops. When a forensic scientist
searches for the cause of death, a tissue sam-
ple can be digested in strong acid or with en-
zymes and the diatom frustules will remain be-
hind (Timperman, 1969). If diatom frustules are
in the tissues (particularly the bone marrow),
the person likely died from drowning (Ludes
et al., 1996). If the person was not breathing
when he or she entered the water (i.e., he or
she was already dead), no diatom frustules will
be found deep within the organs. The tech-
nique is useful enough that the establishment
of routine monitoring programs for diatoms has
been recommended in areas where frequent
drowning cases occur (Ludes et al., 1996).
The method can establish location of drown-
ing or trace suspects to a particular place
because specific diatoms occur in known ar-
eas. In one case, a Finnish man was assaulted
and thrown into a ditch. Five years later, the
corpse was discovered and diatoms found in
the lungs and bone marrow were the same
species as those occurring in the ditch. Inves-
tigators concluded that the death was caused
by drowning in the ditch where the body was
found (Auer, 1991). In another case, a group of
teenagers assaulted two boys who were fish-
ing in a pond and attempted to drown them.
The boys escaped and the teenagers were ap-
prehended. Investigation confirmed that the
teenagers had been at the pond because
the residue found on their shoes contained the
same diatom community as the pond mud
(Siver et al., 1994).

FUNGI

Fewer species of fungi occur in aquatic
habitats than in terrestrial habitats. None-
theless, they are very important in the degra-
dation of detritus (leaf litter and woody
debris) that enters streams and lake mar-
gins. Without the activity of fungi and bac-
teria, these carbon sources would probably
remain unavailable to many invertebrates
(Arsuffi and Suberkropp, 1989; Suberkropp
and Weyers, 1996).

Aquatic Fungi
More than 600 species of fungi occur in
freshwaters (Wong et al., 1998), including
those of the Labyrinthulomycetes (slime