EXERCISE 13
Benthic Fauna of Streams
Stream invertebrates are well adapted to the
running water environment. The dominant taxa
in headwater streams include the immature
stages of the insect orders Ephemeroptera
(mayflies), Plecoptera (stoneflies), Trichoptera
(caddisflies), Megaloptera, Coleoptera (beetles),
and certain Diptera. Many other types of
invertebrates, attached and planktonic algae,
rooted vascular plants, and various vertebrates
also are common in streams of higher order. All
of these organisms have certain traits that enable
them to maintain their position and survive in
rapidly flowing waters. Some mayflies (e.g.,
Heptageniidae) have become dorsoventrally
flattened. Although they inhabit very rapid
water, these mayflies live close to the substrate
where the water velocity is nearly zero
(Fig. 5.3). Many caddisflies (e.g., Limnephilidae)
build elaborate cases that not only protect them
from predators but also serve as ballast against
the current or as attachment points on rocks.
Others (Hydropsychidae) build intricate nets on
submersed rocks and logs to catch food particles
that are being transported downstream. Certain
dipteran larvae (e.g., Blepharoceridae) have
specialized suckers that are used to attach to the
substrate. The common black fly larvae
(Simuliidae) spin silk pads and attach themselves
to rock surfaces by this means. [See Hynes (1970)
for extensive treatment of this SUbject.]
The wide variety of microhabitats available to
stream organisms will become apparent as you
investigate stream ecosystems. Rock surfaces,
plant surfaces, leaf debris, logs, backwaters, silty
or sandy sediments, crevices in gravel, organic
debris dams, and other spaces in the stream all
provide special habitats for different organisms.
The patchy distribution and abundance of
organisms in a given stretch of stream is partially
dependent on the availability of these microhabitats. Thus, any sampling of the benthic fauna
must take this spatial heterogeneity into account.
This patchiness adds both to the fascination as
well as to the difficulty of research on streams.
Stream insects playa role in the processing of
organic matter [see Cummins (1974) and
Cummins et al. (1984)]. Streams in forested
regions depend on allochthonous inputs of
organic matter for much of the consumer
productivity [see Fisher and Likens (1973)].
Many of the insects mentioned above are well
adapted to utilize terrestrial organic matter as
food. Ingested detrital particles are either
assimilated by the organisms or egested and
utilized as a food source by other consumers.
Bacterial colonization of these organic particles
may increase the food value of the detritus by
increasing the nitrogen content. Many of
the invertebrates themselves become sources of
food for other carnivorous invertebrates or
vertebrates.
The types and distributions of benthic macroinvertebrates also have been used widely as indicators quality. The distribution of certain
macro invertebrates and microorganisms can be
quite specific because many organisms often
have narrow physiological tolerance ranges
[e.g., Shidecek, (1973)]. Colonization of many
different artificial substrata has been used in
comparative analyses of water quality among,
199
Benthic Fauna of Streams
Stream invertebrates are well adapted to the
running water environment. The dominant taxa
in headwater streams include the immature
stages of the insect orders Ephemeroptera
(mayflies), Plecoptera (stoneflies), Trichoptera
(caddisflies), Megaloptera, Coleoptera (beetles),
and certain Diptera. Many other types of
invertebrates, attached and planktonic algae,
rooted vascular plants, and various vertebrates
also are common in streams of higher order. All
of these organisms have certain traits that enable
them to maintain their position and survive in
rapidly flowing waters. Some mayflies (e.g.,
Heptageniidae) have become dorsoventrally
flattened. Although they inhabit very rapid
water, these mayflies live close to the substrate
where the water velocity is nearly zero
(Fig. 5.3). Many caddisflies (e.g., Limnephilidae)
build elaborate cases that not only protect them
from predators but also serve as ballast against
the current or as attachment points on rocks.
Others (Hydropsychidae) build intricate nets on
submersed rocks and logs to catch food particles
that are being transported downstream. Certain
dipteran larvae (e.g., Blepharoceridae) have
specialized suckers that are used to attach to the
substrate. The common black fly larvae
(Simuliidae) spin silk pads and attach themselves
to rock surfaces by this means. [See Hynes (1970)
for extensive treatment of this SUbject.]
The wide variety of microhabitats available to
stream organisms will become apparent as you
investigate stream ecosystems. Rock surfaces,
plant surfaces, leaf debris, logs, backwaters, silty
or sandy sediments, crevices in gravel, organic
debris dams, and other spaces in the stream all
provide special habitats for different organisms.
The patchy distribution and abundance of
organisms in a given stretch of stream is partially
dependent on the availability of these microhabitats. Thus, any sampling of the benthic fauna
must take this spatial heterogeneity into account.
This patchiness adds both to the fascination as
well as to the difficulty of research on streams.
Stream insects playa role in the processing of
organic matter [see Cummins (1974) and
Cummins et al. (1984)]. Streams in forested
regions depend on allochthonous inputs of
organic matter for much of the consumer
productivity [see Fisher and Likens (1973)].
Many of the insects mentioned above are well
adapted to utilize terrestrial organic matter as
food. Ingested detrital particles are either
assimilated by the organisms or egested and
utilized as a food source by other consumers.
Bacterial colonization of these organic particles
may increase the food value of the detritus by
increasing the nitrogen content. Many of
the invertebrates themselves become sources of
food for other carnivorous invertebrates or
vertebrates.
The types and distributions of benthic macroinvertebrates also have been used widely as indicators quality. The distribution of certain
macro invertebrates and microorganisms can be
quite specific because many organisms often
have narrow physiological tolerance ranges
[e.g., Shidecek, (1973)]. Colonization of many
different artificial substrata has been used in
comparative analyses of water quality among,
199