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The Cahaba River
Tips for Planning a Field Trip
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Pictured at top: Bluegill Sunfish
describes some of the Cahaba River's animals.
Mussels are freshwater
mollusks that have a shell separated into two symmetrical
valves. Inside these valves are a soft body and gills. Mussels
are very similar to clams.
42 mussel species were found in the Cahaba River. Their
populations once fueled a million-dollar industry in Alabama. Unfortunately, barely half
of these species (27 to be exact) are now found in the river. Eleven
of these mussel species are recognized as
U.S. Fish and Wildlife Service.
may be hard to notice in the river (they burrow down into the
sediment) they play an important role in the ecosystem. Mussels
filter river water, helping to keep it clean for other species and for
us. Many are a source of food for large animals that feed in the
river. Mussels are also important to us as an indicator of
the health of the river. Unfortunately, because many of our
rivers have been so
heavily damaged by damming and pollution, many of the nation's
and Alabama's mussel
species are extinct.
|Mussels have an
elaborate mating method that is truly bizarre.
The male mussel releases his sperm into the water to fertilize the female's
eggs. The fertilized eggs grow in the mom's gills until they are
mature. But the mother must make sure the
survive and find the proper habitat into which to settle.
Thus, she cannot just release them or they end up far downstream. This
is when unsuspecting fishes play a critical role. The female mussel
essentially tricks fishes into transporting her offspring to a new place in
the river. The female mussel will grow a fleshy lure on her body that
resembles a small meal for a large fish.
Some of the lures resemble
minnows, while others resemble crayfish. Mussels pack the lure
with larval mussels, and when a fish takes a bite, the packet of larvae explodes in the
fish's mouth and the larvae then attach to the
fish’s gills. Other mussels keep the lure close to their body, and
when the hungry fish approaches, the female squirts her larvae at the fish
and the young mussels attach to the fish's gills. Once secure inside
the fish, the young mussels continue to grow and eventually drop off when
the fish have unknowingly transported them to the proper habitat for the
mussels. This way the mussels are able to send their offspring
upstream against the current. The only problem with the fish-mussel
relationship is that when a fish species declines, so do the mussels
species that depend on it.
to see images of many mussel species found in the
Cahaba River. These images may help your students identify mussel
shells they find in the river on field trips.
When the file opens, click on the numbered slides
in the far left column to view the slides.
Above Picture: the Cahaba Shiner
Cahaba River is known
for its fish diversity. The river contains the greatest diversity
of fish species per mile than any other river in North America. There are 131
species of fishes found in the Cahaba River, and eighteen are endemic,
meaning they are found nowhere else in the world. The Cahaba shiner
was one of these endemic
fishes. Unfortunately, the Cahaba shiner is no longer found in the
Picture: Blue Shiner)
Many other fish species are no longer found in the
Cahaba River. Fish and other aquatic organisms are suffering
because of declining ecological conditions in our watersheds.
Chemicals (like heavy metals, fertilizers, pesticides) and sediments (silt
and sand) are being
dumped into rivers through
rainfall and runoff from cities. Blue shiners used to be one of the most
common minnows in the Cahaba and are now considered threatened under
the US Endangered Species List. Like many other of the unique
fishes in the Cahaba, these shiners have an unusual reproductive strategy. They are called
The Blue shiner females spray their eggs
into the crevices and cracks of of rocks, boulders,
wood, etc. This protects the eggs from predators. In rivers where
siltation is a problem,
sediment builds up in the crevices of rocks and the shiners have nowhere to lay their eggs.
Other fish species have declined in the Cahaba
River for different reasons. The Alabama
shad and Atlantic sturgeon used to migrate from the Gulf of Mexico to
the Cahaba River for
but are no longer able to reach their spawning habitats due to damming
on the major rivers below the Cahaba River.
Fishes come in an array of
sizes and shapes. Some fishes are slim, while some are a little
thicker. Some fishes' mouths are on the bottom of their heads, while
some have mouths more toward the center. The shape and size of a
fish correlates with what food it eats and where it lives in the
river. Fishes vary in their
eating habits. Most fishes are omnivorous, eating many kinds of
foods. Others are more specialized, eating only vegetation,
invertebrates, or other fish. Some fishes feed
on the bottom of the river (these are called bottom-feeders), and some fishes
dwell at the surface of the water to get their food.
|Invertebrates are animals lacking a
backbone and spinal cord. There is a tremendous diversity of
invertebrate species that live in our rivers and they are essential to
maintaining the health of the river's ecosystem. Every organism in
the river has a role in the ecosystem and is part of the river's food
chain. The invertebrates usually make up the lower regions of the
food chain since
they are some of the smallest organisms
Picture above: Dragonfly larvae
right: Aquatic invertebrates occupy the second-lowest tier
on the adjacent food pyramid.
Larger animals eat the invertebrates,
while the invertebrates eat detritus and microscopic plants and
animals. As organisms eat one another, energy and nutrients flow
through the ecosystem.
||Aquatic invertebrates can have
elaborate life cycles. The larval flies pictured at left go through three
to four very different stages during their lifetime, eventually
becoming flying adults that hardly resemble the larval stages.
|Aquatic insects live on, between, and under stones
and logs in rivers.
Though they are small, aquatic insects have developed certain adaptations
to live in fast moving waters. For example the blackfly
themselves to stones, and mayflies have small claws that allow them to
hang on to rocks when the current is strong. Aquatic insects can be found
in rivers of all temperatures, but they are especially common in temperate
rivers, such as the Cahaba River. They can even be found during the wintertime when the water is
at its coldest temperature.
are crustaceans like crabs, shrimp and lobsters. Crawfish are common invertebrates
|Crawfish, also known as
crayfish and crawdads to many people, are alive and well in the Cahaba
River, just as they are in other central, eastern, and southeastern parts
of the United States. There are 24 species of crawfish in the
Cahaba. Crawfish can be 10-150 mm long, and come
in various colors such as black, brown, red, blue, orange, and green. Crawfish
use their pincers to grab and tear-up
their food. They are
eating a variety of foods such as snails, insects, small fishes,
vegetation. Crawfish, as a group are are very versatile, but some
species require very narrow environmental conditions. They live
in areas of different temperatures and have a mixture of habitats. Crawfish
often dwell under rocks or in holes they dig.
Follow the link to pictures and descriptions of
common and important aquatic invertebrates. This pamphlet
can you and your students identify the types of invertebrates that you
will likely find when exploring your local stream or river.
Identification of Aquatic Invertebrates
Sources used: Draft Interim Report- Natural
U.S. Fish and Wildlife Service
Explore the Cahaba River- CRS Pamphlet
2717 7th Avenue S.
See References for other sources