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Copyright ©2000-06
P.D. Schreuders
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Biota
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The Biosphere
This
crayfish project can be seen as a representation of the biosphere that we call
Earth. As with every living system, there needs to be an important balance that
allows the cycle of life to continue. By understanding the balances between
nitrogen compounds, oxygen, and the survival of the crayfish, it allows the
students taking part in this project to more clearly recognize how each human
behavior affects the grand scheme of human existence.
The
biosphere is composed of many ecosystems that encompass the biotic and abiotic
components of the environment. The interactions between biotic and abiotic
components involves the community of living organisms, the hydrosphere (water),
the lithosphere (solid earth and soils), and the atmosphere (air).
Within
the biosphere, there are ecosystem processes that include energy flow and
nutrient cycles. Energy flow processes include food consumption, the primary
production of food through photosynthesis, and energy losses within the food
chain. The nutrient cycles that occur in a biosphere include the water cycle,
the nitrogen cycle, and the process of the production and consumption of oxygen
and carbon dioxide.(see cycles for more
information)
This
crayfish project is viewed as an ecological study where the tank environment is
modeled after a biosphere. Through observations of the tank and analysis of
collected data, the students see what conditions are necessary to sustain life
within a sealed system. Also, large-scale environmental predictions and
problems can be investigated and possible solutions can be tested, as the tank
is a simple representation of a biosphere on earth.
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Crayfish - General Information
 Crayfish are small, lobster-like
animals belonging to the Class Crustacea and the Order Decapoda (Groves, 1985). While over 500 species of crayfish exist in the world, and over 330 of
these are found in the United States (Holdich, 2002), the two most common
species of crayfish that are farmed in the United States are Procambarus
clarki and Procambarus actus actus (Harrell). The smallest known
crayfish reaches a length of one inch at maturity, while the largest can be up
to 16 inches (LaCaze, 1968). The crayfish's body consists of three main
sections: the head, the thorax, and the abdomen. Its body is divided into
twenty different segments (Groves, 1985). The colors of crayfish include light
cream, yellow, blue, red, green, and black (LaCaze, 1968). Crayfish have four
pairs of walking legs, which are its main method of transportation. The
crayfish cannot swim like other crustaceans, such as shrimp, can. When crayfish
are startled, they spread their fan-like tail and rear abdomen and propel
themselves backwards at high speeds (Groves, 1985).
Chitin
composes the majority of the exoskeleton of the crayfish (Groves, 1985). In
order to grow, the crayfish must shed this exoskeleton in a process known as
molting (Huner, 1994). Crayfish normally molt approximately eleven times before
they reach maturity, growing a 1/4 to 1/2 of an inch with each molt (Harrell).
Growth and molting are ultimately dependant upon the amount of calcium
available to the crayfish in the water. During molting, the calcium from the old
exoskeleton is stored in two gastroliths in the crayfish's stomach. These
deposits are used during the formation of the new exoskeleton. In addition to
growth, crayfish can regenerate lost limbs. They can lose appendages either
voluntarily, to escape a predator or a tight crevice, or involuntarily. The new
appendage, however, is not as good as the first (Groves, 1985).
Crayfish
are freshwater animals, but can tolerate brackish waters with low salinities
(3-9 ppt) (Huner, 1994). They normally live in "hides," small holes
or shelters where they can effectively defend themselves against predators,
including other crayfish (Groves, 1985). Some crayfish burrow underground for
part or the entirety of their lives (LaCaze, 1968). Crayfish will leave their
hides to forage for food, reproduce, and molt, but are vulnerable when they do
and return to their hides as quickly as possible (Groves, 1985). Crayfish
prefer pH values ranging from 5.8 ? 9, but optimally around 7 (Harrell; Groves,
1985). The total of both alkalinity and water hardness should be greater than
50 ppm for optimum growth conditions (Huner, 1994). Crayfish prefer a minimum
dissolved oxygen content in water of 6 ppm (Groves, 1985) and begin to exhibit
oxygen stress at 3 ppm. At 2 ppm, the crayfish will start to climb out of the
water to breath atmospheric oxygen. Crayfish can tolerate temperatures from 2
to 32 åm, but grow optimally around or above 22 åm (Huner, 1994).
 Crayfish
are opportunistic omnivores,
eating both dead and fresh animal and plant matter (Groves, 1985). Crayfish
consume both aquatic and terrestrial plants, and, when given the choice, do
have preferences among plants. They also consume zooplankton, insects, other
invertebrates, and each other. As crayfish mature, they move away from a diet
rich in animal matter to a more vegetarian one (Moloney, 1993). Crayfish are
not active predators (LaCaze, 1968), but also do not actively seek dead matter
to feed on (Groves, 1985). Crayfish use their antennae to examine food sources,
as well as their second and third pair of walking legs (Moloney, 1993).
Crayfish feed almost nocturnally, beginning at midday and feeding into the
early morning (Groves, 1985).
Crayfish
normally mate starting at the end of September through November. The male
crayfish hunts the female and attacks her. If she escapes, he hunts and attacks
her again. When he catches her for good, they mate in a slow process. This
mating ritual can cause death to the female crayfish and mutilation to both
(Groves, 1985). During gestation, the female stores the eggs inside of her body
for the first half of incubation, and outside of her body for the second half.
When the eggs are visible on the outside of the female's body, she is said to
be "in berry." Once the eggs hatch, the young must undergo two molts
before they can leave their mother. Once the second molt is complete, however,
they will not be able to return to her (Huner, 1994). Females generally burrow
during gestation for protection (LaCaze, 1968).
References:
Groves, Roy E. The Crayfish: Its Nature and Nurture. Farnham: Fishing News Books Ltd, 1985.
Harrel, Reginal M. "Crawfish Culture in Maryland." Crawfish Aquaculture Workbook Series. College Park: Maryland Sea Grant Extension, University of
Maryland System.
Holdich, D. M., 2002, Biology of Freshwater Crayfish, Nottingham, University of Nottingham
Huner, Jay V, Editor. Freshwater Crayfish Aquaculture. New York: Food Products Press, 1994.
LaCaze, Cecil. "Crawfish Farming." Rev. 1968. National Agricultural Library. Source Unknown
Moloney, John. Feeding in Freshwater Crayfish. Launceston: Aquaculture Sourcebook publication, National Key Center for Aquaculture, University of Tennesse, 1993.
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Crayfish - Different Species
Crayfish, also called crawfish, crawdads, or mudbugs,
are closely related to the lobster. More than half of over 500 species
worldwide inhabit North America, particularly Kentucky (Mammoth Cave) and in
the Mississippi basin of Louisiana. Crayfish also live in New Zealand,
Europe, East Asia, and
throughout the world. The United States, supporting about 330 species, is considered the crayfish capitol of the world. 4
Crayfish are in the subphylum Crustacea, class Malacostraca, and order Decapoda, constituting
the superfamilies Astacidae and Cambaridae (Northern
Hemisphere) and Parastacidae (Southern Hemisphere in Australia,
New Zealand, South America, and Madagascar). Most crayfish live in
freshwater, a few in salt water, and even some in underwater caverns. Their color and size vary with species, diet, and age. Most are red, some
green, brown, tan, or blue with black or orange markings in various
combinations. Most juveniles are light tan and turn deep red as they
mature. Most adult species in the United States average 2-6 inches in
length. One of the largest species, Astacopsis gouldi in Australia,
may reach 15 inches and weigh up to 3.5 kg5. Maryland is a host to
ten different species of crayfish Cambarus acuminatues, Cambarus
bartonii bartonii, Cambarus diogenes, Cambarus dubius, Fallicambarus
uhler, Orconectes limosus, Orconectes obscurus, Procambarus
acutus acutus, and Procambarus clarki.2
Procambarus clarki is of the family Cambariidae and is commonly known as the red
crayfish. This crayfish originated in the swamps of Louisiana and has now been
relocated to other parts of the country, including Maryland. Most of the
Maryland crayfish enjoy water temperatures around 15 to 30o C and
will thrive in any water that is not heavily polluted, although the red
crayfish tends to be found in areas that have harder water. This crayfish can
range in sizes up to 20 cm and they have been found to be very aggressive even
towards there own species. The red crayfish diet consists of mainly vegetal
plants.1
Orconectes limosus and Orconectes obscurus are among a
species of crayfish known as Orconectes. This species is considered to be the
most common type of crayfish in North America. It is very difficult to make a
distinction between species of crayfish, but the Orconectes can be identified
by red-brown marks that reside on the abdomen. As in the red crayfish both O.
limosus and O. obscurus prefer the same type of vegetable
diet. It has been noted in laboratory experiments that most species of crayfish
will turn cannibalistic if there are inadequate food sources. They also
are most comfortable in water with temperatures of 15 to 30o C and
generally good water quality. The general size range for this species is
also around 15 to 20 cm. Generally most freshwater crayfish species in Maryland
tend to have the same water quality, diet, and similar overall habitats. 2
There may be many other species that have not yet been recorded. Because
of the similarities in appearance between species, the identification of
crayfish can be difficult. Many resources are available to aid in the
identification process including The Handbook of Crayfish of Ontario.3
References:
1 Collicutt, D., Crayfish! Online http://www.naturenorth.com/fall/crayfish/wcray.html, Accessed 11 May 2002.
2 Crandall, K. and J. Fetzner, Updated 6 Jan 2002, Welcome to the Crayfish Home Page, Online http://zoology.byu.edu/crandall_lab/crayfish/crayhome.htm,
Accessed 11 May 2002.
3 Crocker, D.W., and D.W. Barr, 1968, The Handbook of Crayfish of Ontario, Ontario, University of Toronto Press.
4 Holdich, D. M., 2002, Biology of Freshwater Crayfish, Nottingham, University of Nottingham.
5 Jones, D. and G. Morgan, 1994, A field guide to Crustaceans of Australian Waters. Sydney, Reed.
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Freshwater Clams
Freshwater clams prefer to live in streams and many can be found in one place. This
species can usually tolerate degraded water conditions. They are distinguished
by the characteristic two shells attached to an external hinge which encloses
the body of the clam. Also, they have no eyes or distinct head and a soft, fleshy
body known as a foot can be seen extending from the bottom of its body. A
freshwater clams size is usually around 3/4 inch and are generally rounder than
mussels are. They are filter feeders so they prey on bacteria, phytoplankton,
zooplankton and detritus. Some species of fish eat freshwater clams and mammals
such as raccoons eat clams as well.
Having clams in your tank can help filter your water. The clams feed on the bacteria
that may make your water dirty, so the crayfish are only left with clean and
pure water. Each clam is able to filter about fifteen gallons of water a day.
References:
http://www.chebucto.ns.ca/Science/SWCS/ZOOBENTH/bivalvia.html
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Snails
Snails
live in a variety of environments including freshwater and saltwater and
terrestrial environments. They have non segmented, soft, slimy bodies and have
a shell on their back to protect their body and when in danger or in hot
weather that could dry them up, they retract themselves into their shells for
protection. They are mollusks and are closely related to shellfish, their
scientific name is Helix Aspersa.
Snails
can be helpful to your tank ecosystem. They can be eaten by the crayfish for a
good source of protein and calcium (from the shells). They also eat detritus
and other things that may contribute to the turbidity of the tank water. They
consume algae, limiting the ability of its growth as too much algae is a bad
thing. However, snails consume oxygen and release carbon dioxide and solid
waste, so adding them to your system must be coordinated with the amount of
oxygen production and nitrogen/carbon dioxide consumption you plan to have in
your tank.
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Alfalfa
Alfalfa,
or Medicago sativa, is a leguminous, terrestrial plant. As a legume,
it has rhizomes on its roots that are the site for atmospheric nitrogen
fixation (Tortora et al., 1997). Alfalfa can grow up to 3 feet tall, and looks
much like a large clover (Ibrahim, 1996). Alfalfa is native to western Asia and
the eastern Mediterranean (Raintree, 2001), but can be grown in North America.
The taproot of alfalfa can reach lengths of 50 feet when the plant is twenty
years or older, and is known to reach lengths of six feet in as little as five
months. (EB, 2001). Alfalfa produces violet flowers that grow in racemes and
produce cork-screw shaped pods containing seeds. Alfalfa is rich in nutrients
including calcium, carotene, and Vitamin K (Ibrahim 1996).
Alfalfa
can be used in the tank for a process called assimilation. During assimilation,
Nitrate is used by the plant to produce proteins and nucleic acids producing
food for the crayfish and lowering the nitrate level in the tank. Also, photosynthesis will occur in
the plants and will provide oxygen for the crayfish and remove carbon dioxide
from the tank as well.
It is
recommended that the alfalfa be kept out of the crayfish's reach so it can
grow. This can be done by creating a shelf in the tank or by creating a raft
containing alfalfa to float above the water.
References:
Ibrahim, Sam. "Alfalfa." http://www.agric.gov.ab.ca/crops/special/medconfi/ibrahimb.html (1996) [Accessed 28 March 2001]
Tortora, Gerard, Berdell Funke, and Christine
Case. Microbiology: An Introduction (6th ed.). Benjamin/Cummings: City. 1997
EB: "alfalfa" Encyclop_dia Britannica Online. http://search.eb.com/bol/topic?eu=5727&sctn=1 [Accessed 28 March 2001].
Raintree: "Alfalfa" http://www.rain-tree.com/alfalfa.htm [Accessed 28 March 2001]
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Anacharis
 There are
several species of anacharis plants, including Egeria densa. They are
native to the cool subtropical or warm temperate regions of South America, Brazil,
Uruguay, and Argentina. They have leaves with rounded tips, in whorls of three
to four, and these leaves can be as long as one inch. They live in slow-flowing
or still waters, including ponds, lakes, rivers, and even ditches. Anacharis
grows easily, but their abundant growth is sometimes considered a nuisance and
they are sometimes called "water weed." (NAP, 2001)
Anacharis
is a common underwater plant that can serve as a great food source for your
crayfish. Also, anacharis consumes the carbon dioxide (via photosynthesis) that is
produced by the crayfish's respiration and produces oxygen for the crayfish to
consume. Anacharis also assimilates nitrate and turns it into proteins that are
consumed by the crayfish.
References:
NAP: "Egeria, Anacharis (Egeria densa) Planch." Nonindigenous Aquatic and Semi-Aquatic Plants in Freshwater Systems. http://www.aquatl.ifas.ufl.edu/mcplntlk.html [Accessed 28 March 2001]
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It's green! It's slimy! It's alive! It's...
Filamentous Algae!
We've all seen
it. Growing like green fur on rocks or other surfaces in streams and rivers,
filamentous algae is the stuff we have to be careful not to slip on when we're
wading! While it may look gross, filamentous algae is actually a really
important part of aquatic ecosystems, and an integral part of an algal turf
scrubber. Let's find out why!
What exactly is filamentous algae?
The term "algae" refers to a diverse group of organisms that ranges in size
from the microscopic (phytoplankton) to the macroscopic (seaweed). Like plants,
algae is photosynthetic, harnessing the power of sunlight to produce its own
food. Unlike plants, algae does not have true roots, stems, or leaves. "Filamentous algae" is a category of multi-celled algae that forms long chains or
branches. Some species of filamentous algae are epiphytic, which means they attach themselves to submerged surfaces using root-like structures.
A diagram of the basic structure of filamentous algae.
In many ecosystems, algae is a primary producer, which means it forms the base of many food chains. For example, in some woodland streams, filamentous algae is eaten by
crayfish, which in turn are eaten by raccoons, which in turn may be eaten by an
animal at the top of the food chain, like a mountain lion.
How does filamentous algae reproduce?
Different kinds of filamentous algae reproduce in different ways. Some reproduce asexually, simply by cell division (i.e. Tribonema, Oedogonium). Some reproduce sexually through conjugation (i.e. Spirogyra) or through oogamous reproduction, where the algae forms
distinct gametes (i.e. Coleochaete, Vaucheria). (http://www.msu.edu/course/bot/423/algallist3var.html)
Why is filamentous algae an integral part of an algal turf scrubber?
To grow,
filamentous algae doesn't just need sunlight. It also needs nutrients such as
nitrogen and phosphorus. Algae growth is very responsive to nutrient inputs; it
removes dissolved nutrients from its surroundings in a very efficient manner.
For this reason, filamentous algae is grown in algal turf scrubbers. Polluted
water (water with too many nutrients such as nitrates and organic phosphorus)
is sent through the scrubber, and the filamentous algae absorbs and metabolizes
the excess nutrients. Bacteria that live inside mats of filamentous algae can
also help convert these nutrients to less toxic forms (for example, nitrate to
nitogen gas). By absorbing and converting the nutrients in the polluted water,
the scrubber lowers the biochemical oxygen demand, or BOD, of the water. The
lower the BOD of the water, the more dissolved oxygen is availible for animals
like insects and fish.
Diagram of some of the biochemical conversions that occur in an algal turf scrubber.
The filamentous
algae is also important because it serves as the sole food source for the
crayfish that live in the algal turf scrubber. By eating the algae, the
crayfish are converting a product of limited material/dietary use (the algae)
to a product of many material/dietary uses (the protein of the crayfish). In
turn, the algae absorb the wastes produced by the crayfish, and the cycle
continues. The end result is that pollution goes in and crayfish come out!
References:
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Java Moss
 Java Moss, or Vesicularia dubyana, is used in aquariums for ground cover or as an ornamental plant. It is particularly useful in providing a place for fish to lay eggs, the dark green foliage providing the perfect hiding place for spawning. Java moss propagates by dividing existing clumps, which can function as separate entities. Java moss grows in temperatures of 20-30 °C and pH and water hardness do not affect its growth. It can even tolerate slightly brackish waters. Java moss clings to rocks and gravel and quickly creates a thick mat (Norwood, 1999). Java moss is an excellent food source and will be consumed quickly by the crayfish. Java moss also harbors colonies of microorganisms that aid in nitrification. Java moss also photosynthesizes, creating oxygen for the crayfish and removing carbon dioxide from their environment. Java moss also produces proteins that are consumed by the crayfish from nitrate in a process called assimilation.
References:
Norwoord, Clint. "Java Moss." http://www.petfish.net/jmoss.htm Petfish (1999). [Accessed 28 March 2001]
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Duckweed
The family of duckweeds (botanically, the Lemnaceae) are the smallest flowering plants. These plants grow floating in still or slow-moving fresh water around the globe, except in the coldest regions. The growth of these high-protein plants can be extremely rapid. Lemna is one of the best known of this group and has been the subject of much research. Researchers are using these plants to study basic plant development, plant biochemistry, photosynthesis, the toxicity of hazardous substances, and much more. Genetic engineers are cloning duckweed genes and modifying duckweeds to inexpensively produce pharmaceuticals. Environmental scientists are using duckweeds to remove unwanted substances from water. Aquaculturalists find them an inexpensive feed source for fish farming.
References:
Cross, J.W. (2002). The Charms of Duckweed. http://www.usra.edu/~jwcross/duckweed.htm (25 July 2002).
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