Artemia salina

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Geographic Range

The brine shrimp is found in inland salt water bodies such as the Great Salt Lake in northern Utah, on the rocky coast south of San Francisco, and in the Caspian Sea. They also occur in many other bodies of water with any salt content, including the intermountain desert region of the western United States, salt swamps near any coast, and many man-made saltpans around the world. (Grzimek, 1972; Pennak, 1989)

Habitat

Artemia salina have a remarkable resistance to change and are able to live in a wide variety of water salinity. All contain some salt content ranging from seawater (2.9-3.5%) to the Great Salt Lake (25-35%), and they can tolerate up to a 50% salt concentration, which is almost saturated. Some are found in salt swamps just inland of the dunes at the seashore, but never in the ocean itself, because there are too many predators. They also inhabit man-made evaporation ponds, used to obtain salt from the ocean. Their gills help them to deal with the high salt content by absorbing and excreting ions as necessary and producing a concentrated urine from the maxillary glands. The temperature of the water also varies greatly from around six to 37 deg C, with the optimal reproduction temperature at about 25 deg C or room temperature. One advantage of their salty location means that they have very few predators, but the disadvantage is their diet is limited. (Banister, 1985)

Physical Description

An adult Artemia salina is usually about 8-10 mm but can reach up to 15 mm depending on its environment. It has an elongated body divided into at least 20 segments and attached to its trunk are approximately 10 sets of flat, leaf-like appendages called phyllopodia that beat in a regular rhythm. The adults can be pale white, pink, green, or transparent and usually live for a few months. They have compound eyes set on stalks and reduced mouthparts.

Artemia salina is in the order Anostroca, literally meaning "no shell," which classifies the shrimp with other species that have no carapace (a hard, bony outer covering). Its subclass Brachiopoda literally means "gill foot," referring to the fact that the gills are on the outer side of the limb bases. (Banister, 1985; Najarian, 1976)

  • Range length
    8 to 15 mm
    0.31 to 0.59 in
  • Average length
    8-10 mm
    in

Reproduction

In the Great Salt Lake studies have shown that many males are present and reproduction occurs when a male clasps a female with his large second antennae and fertilizes her eggs, producing diploid zygotes. Then she lays the eggs in a brood sac in the water. Parthenogenesis, or reproduction without fertilization, is also common among A. salina, particularly in Europe. Parthenogenesis is common when males are not present. During parthenogenesis, a female lays unfertilized eggs that will develop into female offspring. These eggs can be either diploid, tetraploid, or octoploid. Artemia salina eggs will only hatch if environmental conditions are right. The temperature must be around 30 deg C, the water supply plentiful, and the salt concentration not too high. If these conditions are not met, fertilized eggs are deposited as cysts and remain dried and surrounded by a thick shell until they are ready to develop, possibly up to 50 years. The cyst may be immersed in water several times before it will hatch and some require sustained hydration for at least 36 hours to ensure that the population is not wiped out when insufficient rain falls. A brine shrimp takes about one week to mature from a nauplii larva to an adult and then lives for several months and can reproduce up to 300 new nauplii every four days. (Banister, 1985; Captain's Universe, 1996; Najarian, 1976)

  • Parental Investment
  • no parental involvement

Behavior

The oddest behavior of A. salina is that they swim up-side down as compared to the majority of aquatic animals. This is a result of positive phototaxis, which means the brine shrimp is attracted to the light, and in nature it is found with its appendages pointed upward, because the sun is the natural light source. A specimen placed on a dissecting scope with a base light source would flip over so that it was swimming "normally." Also, because the brine shrimp are attracted to the light, they rise toward the surface during the day and sink again at night. High intensities of light, however, create a negative phototaxis response and drive the shrimp away. Newborn A. salina demonstrate positive geotaxis, observable when nauplii sink to the bottom after they hatch, because of the effect of gravity.

The same rhythmic movement of the phyllopodia that moves their food anteriorly is the brine shrimp's means of locomotion. They beat their appendages to propel themselves through the water toward the food, without much regard for the rest of the environment. (Grzimek, 1972; Pennak, 1989)

  • Key Behaviors
  • motile
  • aestivation

Food Habits

Artemia salina live on photosynthetic green algae, one type is Dunaliella. They obtain food by either filtering small particles with fine slender spines on the legs as they swim or by grazing on bottom mud and scraping algae off rocks with quick movements of their appendages. After the algae is captured, a feeding current moves it anteriorly to the mouth via a central median food groove, utilizing the regular rhythm of the phyllopodia, or leaf-like appendages. (Banister, 1985; Pennak, 1989)

Economic Importance for Humans: Positive

Brine shrimp are useful in toxicity tests and for education purposes because they reproduce quickly and their environment is easy to replicate. They are used to teach students the proper technique to observe live specimens and how to design experiments to determine behavior, means of obtaining food, and most optimal environment for reproduction and development.

Both the eggs and adults are used as feed for coral, larval fish and other crustacea, because of their low cost and ease of use. They cost about $7 per pound and their prime selling time is May to July, but they can be produced at any time of year in a laboratory. (Grzimek, 1972)

  • Positive Impacts
  • pet trade
  • research and education

Economic Importance for Humans: Negative

The brine shrimp does not adversely affect humans, because it is not bothersome or poisonous.

Conservation Status

There is no threat for the brine shrimp, because it reproduces quickly. It is easy to find, and the cost to catch and culture them is low. (Grzimek, 1972)

Other Comments

Artemia salina is the scientific name for Sea Monkeys. These popular, odd looking creatures are advertised as an easy to care for pet that grows quickly and does not have a very long life span.

Brine shrimp are not closely related to the shrimp we eat. One interesting point in their evolution is that their ancestors are fresh-water specimens including the fairy shrimp, which do not adapt well to any change in ions or temperature of the water.

Artemia salina may have become a general name for the many different species. (Banister, 1985)

Contributors

Renee Sherman Mulcrone (editor).

Sara Emslie (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parthenogenic

development takes place in an unfertilized egg

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

References

Banister, K. 1985. Encyclopedia of Aquatic Life. New York: Facts on File, Inc..

Captain's Universe, 1996. "Artemia salina, Saltwater Brine Shrimp" (On-line). Accessed (Date Unknown) at http://www.captain.at/artemia/index.php?p=1.

Grzimek, B. 1972. Grzimek's Animal Life Encyclopedia, Vol. 1 "Lower Animals". New York: Van Nostrand Reinhold Co..

Lagasse, P. 1993. Columbia Encyclopedia "Brine Shrimp".

Marty, S. 1996. The Brine of Life. Canadian Geographic: 50-52.

Najarian, H. 1976. Sex Lives of Animals Without Backbones. New York: Charles Scribner's Sons.

Pennak, R. 1989. Fresh-Water Invertebrates of the United States. Canada: John Wiley and Sons, Inc..