Microbes and Plants - Freshwater Ecology: Concepts and Environmental Applications - page 150

3. The biomass, metabolic diversity, and
species diversity of Bacteria probably
exceeds that of any other group of
organisms on Earth. Understanding the
role of bacteria is central to attempts to
understand the aquatic environment.
4. Cyanobacteria are a significant
ecosystem component of many lighted
aquatic habitats. They can cause
problems related to large blooms and
associated toxic strains.
5. Algae constitute an important and
diverse group found in freshwaters and
form the basis of many aquatic food
webs. The importance of algae also
includes an intimate role in water
quality and use of diatoms in
paleolimnology to document historical
biological patterns over thousands of
years.
6. Protozoa are generally the primary
consumers of bacteria in aquatic
systems.
7. Fungi are responsible for much of the
degradation of particulate organic
material that occurs in freshwater, and
some groups are also commonly
parasitic on aquatic organisms.
8. The Bryophytes can be important in
some shallow aquatic habitats.
Formation and maintenance of high
latitude wetland communities by
Sphagnum in peat bogs has global
significance.
9. Plants can be classified as submerged,
floating, or emergent. Vascular plants
are dominant contributors to organic
matter in many shallow aquatic
ecosystems. The types of flowering
plants present define many wetlands.

Sidebar 8.4.
Invasion of Wetlands by Purple
Loosestrife

Purple loosestrife ( Lythrum salicaria ) is a
perennial that is invading many North Ameri-
can wetlands. It is an emergent plant with
beautiful purple flowers. Purple loosestrife can
reach some of the highest levels of biomass
and annual production reported for freshwater
vegetation (Mitsch and Gosselink, 1993). Un-
fortunately, the plant is a poor food source for
most waterfowl, and large stands with a high
percentage of cover possibly lower the num-
bers of nesting sites for ducks and other water
birds as well as provide additional cover for
predators. Purple loosestrife can outcompete
native plants and lower biodiversity (Malecki
et al., 1993). In wet areas that are used for hay,
it lowers the forage value. However, Anderson
(1995) suggested that the effects of purple
loosestrife have been overestimated and more
research should be done to quantify its im-
pacts on native ecosystems.
Lythrum salicaria occurs naturally in Europe
from Great Britain to Russia (Mal et al., 1992). It
was introduced to eastern North America in
the ballast of ships and as a medicinal plant
(Malecki et al., 1993). Loostrife has since be-
come a serious pest species around the Great
Lakes of North America and has spread across
Canada and the United States to the west coast.
Introductions have also occurred in Australia,
New Zealand, and Tasmania (Mal et al., 1992).
Several control strategies have been at-
tempted (Malecki et al., 1992), including herbi-
cides (which also harm other wetland species),
physical removal, burning, manipulation of wa-
ter levels to favor native species, use of native
insects, and introduction of exotic insects to
control the plant. There are concerns that in-
sects introduced as control agents will harm
native species. After tests for host specificity,
three insect species were released in the
United States as control agents (Piper, 1996).
Their efficiency in loosestrife control is not yet
known. Certainly, an understanding of wetland
ecology is crucial to assessing the impact of
and control options for this exotic invader.

QUESTIONS FOR THOUGHT

1. Do more types of viruses exist than
species of organisms on Earth?
2. Should separate taxonomic definitions
of species be used for microbes than
those that are used for animals?