BRINE SHRIMP BACKGROUND INFORMATION
WHAT IS A BRINE SHRIMP?
Brine shrimp are small animals that live in very salty waters. The adult brine shrimp Artemia is an extremely well known animal because of its importance as a food source for fish raised in home aquariums and in laboratories. One can buy brine shrimp at practically any pet store. Dried brine shrimp cysts look like a powdery brown substance but in reality the substance is thousands of eggs surrounded by protective cases. When added to water, these cysts will hatch into shrimp within a few hours.
Brine shrimp live in salty waters around the world and they can be found in the Great Salt Lake and Mono Lake in the United States. Geologic core samples show that brine shrimp have been present in the Great Salt Lake area for at least 600,000 years.
CLASSIFICATION
Kingdom – Animalia
Phylum – Arthropoda
Class – Crustacea
Order – Anostraca
Genus & species – Artemia salina
ANATOMY
Brine shrimp are small crustaceans, just a centimeter in size when full grown. Crustaceans are a group of animals whose skeletons are on the outside of their bodies. They live in saltwater and breathe through gills, just like fish. They have many pairs of legs, and their bodies are jointed, like a human’s elbows or knees. Crustaceans use feelers for touching, feeling and smelling.
Although brine shrimp are not really shrimp, they are called brine shrimp because of their shrimp-like shape and because they live in very salty water which is called brine.
Brine shrimp have a head, middle (thorax) and a tail (abdomen). They usually move around on their backs, upside down with their flat-legs above. The eleven pairs of flat-legs are used as filters, paddles, and as gills. On the front of the head are three black eyes. There are also two small antennae that feel the environment ahead.
In the male the second antennae develop into large, hooked claspers that they use to hold on to females during mating. Various pigments from the phytoplankton that the shrimp eat give hues of blue, green, and red to the otherwise transparent body. The males often have a more translucent body than the females. The females often have a bundle of eggs in a brood-pouch halfway along the body.
MATING and LIFE CYCLE
When the brine shrimp mate they pair up into tandem pairs where the female is in the front and the male behind. They go around together in this position and swim for many hours and even days. Some colonies have only females and these eggs develop without being fertilized. Eggs can hatch very soon if conditions are favorable or lie quiet for a years. Such “resting” eggs are called cysts and have hard brown shells and can be dried and kept for years before being hatched in salt water.
In the United States, in areas such as the Great Salt Lake, the brine shrimp's yearlong life cycle usually begins in early spring. After hatching, the larvae will shed its exoskeleton 15 times before it reaches the adult form, a process which usually takes 2-3 weeks. Adults begin to die around October and most will be gone by December. In Great Salt Lake, the adult shrimp typically die from lack of food or low temperature during December. Although, live brine shrimp have been observed in the lake at a water temperature of 3 degrees Celsius (37*F), they cannot reproduce at that temperature.
If conditions are perfect, the female can live as long as 3 months and produce as many as 300 live nauplii or cysts every 4 days. However, difficult conditions usually limit the population to two or three generations per year. The females often have a bundle of eggs in a brood-pouch halfway along the body which is usually brown/red in color. The larvae remain in the brood-pouch for some time before being liberated when conditions are favorable to their survival. If there is not enough oxygen or food, or it is too cold, or if there is too much salt the female will release the eggs as cysts. Cysts burst and the embryo leaves the shell after 15 or 20 hours in salty water at 25 degrees C (77 *F). For the first few hours, the embryo hangs beneath the cyst shell, still enclosed in the hatching membrane.
Whether baby brine shrimp hatch from a cyst or are born live in its first free- swimming period it is called a nauplius (plural: nauplii). These young are active, with short bodies, no limbs, but large antennae, used for swimming. The “nauplius” larvae become adults after a succession of molts where they lose their outer shell in order to grow.
The rate at which it develops through the rest of the stages in its life cycle is affected by salinity, water temperature, and food availability. The algae on which brine shrimp feed is most abundant at the end of winter when water temperatures reach at least 4 °C (48 °F), typically by February or March. Brine shrimp attempt to time cyst hatching with this time so the emerging nauplii can feed on the abundant algae.
HABITAT
Brine shrimp are adapted to sub-tropical countries which are hot like Morocco (in North Africa), Iran (in the Middle East) and California. The lakes they live in are slightly alkaline and have a pH that is above 7.0 (neutral). Brine shrimp can survive in salt lakes where the salinity (saltiness) may be quite high, sometimes the water in the lakes evaporates completely during the dry season and become flat white “salt pans”. Brine shrimp can survive in water with salinities ranging from 30–330 grams/liter (3% to 33% salinity). These water bodies are salty enough that predators and competitors cannot survive so the brine shrimp have the water all to themselves except for a few species of bacteria and algae, which provide food for them.
EATING AND THE FOOD CHAIN
Brine shrimp are passive filter feeders; this means that they do not select what goes into their mouth. They flap their 11 pairs of feathery-legs to sweep the particles in the water backwards along the front of their body and filter their food out of the water. The particles are caught in strainers formed by the bristles on the inner edges of the legs and are then transferred forward into the mouth. Because they cannot choose their food, they are dependent upon high quality food being readily available: it would be similar to walking into the grocery store and not being able to choose what you were given. On top of this, brine shrimp need the amino acid tryptophan (like the tryptophan in your Thanksgiving turkey). Without tryptophan, nauplii show appendage deformities, and adults are covered in black spots that signify malnutrition. Once again, it is similar to the grocery store, and you can only eat what you are handed, but in order to be healthy, you require a balanced diet.
Food chains begin with the sunshine and a green plant. The brine shrimp food chain starts with a single celled plant called algae. These microscopic green plants are found in the water and in large numbers. The number of algae may double every day and they grow most in bright lights and with lots of mineral nutrients. The reason that you may not see the algae easily is that they are very small and brine shrimp eat them up almost as fast and they can reproduce!
Although adult shrimp feed primarily on phytoplankton (algae) suspended in the water they will eat their own fecal pellets (poop) when algae become less abundant. They may also graze on diatoms that live on their old exoskeleton parts released from their many molts.
A variety of birds feed on brine shrimp to fuel their long migrations. Eared grebes, Wilson's phalaropes, Red-necked phalaropes forage almost exclusively on brine shrimp during staging, or preparation for migration. Without this food source, their long migrations would not be possible. Flamingoes, stilts, greves and avocet birds fly in to the salt lake just to eat brine shrimp. Fish also like brine shrimp but sometimes the water is too salty for fish to live there. Without the predatory fish and birds the brine shrimp numbers are often high. There may be a hundred adult shrimp in a liter of water. Humans are the greatest threat to brine shrimp in the Great Salt Lake.
The brine shrimp industry began on Great Salt Lake during the 1950's when adult shrimp were harvested to be used as fish food in the aquarium trade in the United States. The harvest of cysts in 1995-96 and 1996-97 was about 15 million pounds gross weight (about half is suitable for final product). Because of its characteristics and its short life span the brine shrimp has been useful to a variety of researchers in genetics, histology, toxicology, radio biology, biochemistry, molecular biology, and ecology as well as a food supply for the aquaculture industry. Because the cysts are also very small and require no food, they were chosen as test organisms for the early space experiments. Cysts housed both within and outside the U.S. Apollo and the U.S.S.R. Cosmos spacecraft helped scientists determine the effects of ultraviolet radiation on living cells.
ADAPTATIONS
It is remarkable enough that the cysts should be able to survive for years when dried out, but this is not the limit of their tolerance. By drying them in a high vacuum, practically every trace of water can be removed and then the chemical processes of life are brought to a complete standstill. If such dried eggs are cooled to the temperature of liquid air, around -190 *C/-350 *F, they will still hatch when returned to salt water at a normal temperature. Moreover, if they are fully dry, a small portion will even survive for 2 hours in temperatures of 105*C/221*F which is like being boiled alive without the water!
The adults, too, are unusual in their tolerance of harsh conditions. They can be found in water so full of salt that crystals form around the edge of the pool or in water 100 times less salty. Although they can live in less salty water like sea water, they do not and are only found in water that is super salty like salt pans or salt springs, probably because the extremely salty water is too concentrated for their predators to survive.
Animals have to keep the concentration of salt steady in their bodies. In the process of filter feeding brine shrimp ingest a lot of salt water. They keep their internal salt concentrations lower than the surrounding salt water by absorbing salt in their digestion canal and expelling the surplus salt through special gills in their limbs.
BACKGROUND QUESTIONS FOR BRINE SHRIMP LAB
1. Where do brine shrimp live?
2. Name the brine shrimp’s:
Kingdom:
Phylum:
Class:
3. What is the brine shrimp’s scientific name (its genus and species)?
Genus and species:
4. How big are brine shrimp?
5.
· What would happen to the population of brine shrimp in the Great Salt Lake if the salinity increased? If it decreased? Use examples from your hatching experiment to support your answer.
· Under what conditions would it be least likely for the brine shrimp to survive? Support your conclusion with results from your investigation.
· Why does salinity fluctuate in the Great Salt Lake? Why are brine shrimp suited to this habitat?
Finally, ask students:
· In the salinity experiment, you tried to hold temperature constant. What if you wanted to see if temperature affects the hatching of brine shrimp eggs? Briefly outline an experiment you could conduct to determine this, indicating the independent and dependent variables, as well as the variables to be kept constant. Try to design a tight experiment, keeping in mind how you felt the salinity experiment could have been done better.
BRINE SHRIMP LAB IDEAS
Have students work in small groups to develop a question about brine shrimp survival they want to answer. For example, students could investigate questions such as:
· What happens if you transfer the hatched shrimp to water of different salinities? Do the shrimp survive?
· How big a salinity change can they stand?
· Does temperature affect the hatching of brine shrimp eggs?
· Does acid rain affect brine shrimp?
· Is the best salinity for hatching also the salinity in which the shrimp are most likely to thrive once hatched?
· Do they do better in environments with different substrates?
Charbonneau 2012