Biota of Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 179

Since habitat types are a component of the indicators of aquatic health, such as relected in the
RBPs and indices of biotic integrity, as discussed in Chapter 7, organizations and state agencies
have identiied native macroinvertebrates and their feeding and habitat classiication to aid in those
assessments. For example, the Georgia Environmental Protection Division (Georgia EPD 2007)
provides a common taxa list that includes feeding and habitat types as part of a guide to conducting
macroinvertebrate biological assessments in Georgia. The guide, An Introduction to the Aquatic
Insects of North America by Merritt and Cummings (1998), is also a commonly used source of
habitat types associated with speciic macroinvertebrate species.
6.3.2 S treaM V ertebrateS
There are a variety of vertebrates (kingdom Animalia, phylum Chordata) that live in or depend on
rivers and streams for food, water, and cover. These include a variety of mammals (class Mammalia),
such as beavers; a variety of birds (class Aves) such as ducks, geese, egrets, and others; reptiles (class
Reptilia) such as snakes, lizards, and alligators; amphibians (class Amphibia) such as frogs and
salamanders; and ish (class Osteichthyes, for bony ish).
All vertebrates may be adversely impacted by processes such as eutrophication, habitat modii-
cation, and other impacts on their aquatic environment. Many of the vertebrate populations are in
decline and their population densities and distributions can serve as indicators of aquatic health.
As an example, amphibian populations are declining around the world. Amphibians are particu-
larly sensitive to pollution and changes in their environment since they have an aquatic larval stage,
and lack a protective epidermis. Chemicals, for example, can often be readily transferred through
their semipermeable skin, making them susceptible to pollution. Population declines prompted the
president and Congress in 2000 to undertake a national amphibian research and monitoring initia-
tive (ARMI; http://armi.usgs.gov/index.asp) to measure, develop, and understand the response to the
effects of environmental change on amphibians.
In addition, many avian species depend on the riparian zone of streams and rivers. While ripar-
ian zones comprise only about 1% of avian habitats in the western United States, these areas are
used by more avian species than any other habitat in the United States (Knopf 1985).
While other vertebrates are important components of the aquatic environment as indicators of
aquatic health, in this section we will primarily concentrate on ish. Fish are perhaps most com-
monly used in metrics for aquatic health, as discussed in Chapter 7. Also, similar to other aquatic
vertebrates, the diversity of ish species is declining. As of 2008, there are 139 ish species listed as
threatened or endangered.
The characteristics and habitat of ish are often relected in their anatomy (see Figure 6.17). Most
ish have ins that aid in their movement, which are located along the centerline on the top (dorsal
side), or along the bottom (ventral side) in the pelvic or anal region. Exceptions are the lampreys
(Petromyzontidae), which lack paired ins. The dorsal and ventral ins primarily add stability when
swimming. The caudal or tail in provides locomotion, while ins along the side and in the pectoral
area add stability and aid in side-to-side movement. In some unusual ish such as the “walking cat-
ish,” which is an invasive species in the United States, the pectoral in is used to aid in navigation
on land. The number and location of the ins and in rays, and the presence and structure of spines
are commonly used in ish identiication.
Most ish also have scales, which overlap and provide a protective barrier. Another important
protective barrier is ish slime, produced by the secretions of slime cells.
Respiration is generally through gills, which, in some ish, are covered by an opercular lap that may
open and close to aid in pumping water over the gills. Internally, most ish also have a hollow, gas-illed
bladder (swim or air bladder) that is used to aid in swimming by maintaining a neutral buoyancy in water.
In some ish, such as the African lungish, the swim bladder is also used in respiration.
In addition to sight and smell, one of the ish's primary sense organs is the lateral line, which
detects underwater vibrations and is capable of determining the direction of their source. The