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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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