Fairy shrimp are found in vernal pools across the northeastern United States, typically spanning east of the Appalachians from South Carolina up to Maine. They are also found in Ohio, Michigan, Indiana, Alabama, and southwestern parts of Ontario, Canada. (Belk, et al., 1998; Bodie and Semlitsch, 1998; Dexter, 1946; Ferguson, 1939; Hay and Hay, 1889; McCafferty, et al., 2010)
Fairy shrimp are freshwater organisms found in small vernal pools isolated from other bodies of water, which usually dry up during the summer months. Suitable pools must be deep enough so that they don't freeze all the way through during winter months, which would kill the developing young. Fairy shrimp are also rarely found in water warmer than 20°C. The cyst-like eggs of fairy shrimp are very robust and can be transported by the wind (if the pool has dried up) or other organisms to other pools before hatching but, once hatched, young are confined to one pool. Vernal pools are suitable habitats for fairy shrimp because they usually lack predatory fish. (Dexter, 1946; Ferguson, 1939; Hay and Hay, 1889; Knight, et al., 1975; McCafferty, et al., 2010; Weaver, 1943)
Fairy shrimp are bilaterally symmetrical organisms with 20 body segments, from which 10 pairs of leaf-like swimming appendages (phyllopods) extend. The head is distinct from the thorax and has a pair of compound eyes. The segments posterior to the thorax form an elongated tail, the last segment of which bears an additional pair of phyllopodia. Individuals are most typically orange but may be translucent/white, blue, or green (depending on diet). Juveniles are similar in morphology to adults but are more orange in color. Males are typically larger than females with orange bodies and swimming appendages. They have a set of claspers emerging from around the head which are used for mating purposes. Females have much smaller heads than males and a smaller second set of antennae. Females also have an ovisac located below their swimming appendages. ("Fairy Shrimp", 2012; Dexter, 1946; Ferguson, 1939; )
Fairy shrimp eggs hatch and larvae begin to develop in the winter after pools in which they were laid fill back up with water; development continues until the pond begins to freeze again. After ponds melt in the spring, larvae undergo a series of molts and instars, adding body segments with each successive stage. Adult fairy shrimp have 20 body segments. Individuals grown in the lab at 6.5°C were reported to have an average growth rate of 0.13 mm per day. ("Fairy Shrimp", 2012; Castle, 1938; Dexter, 1946; Ferguson, 1939; Hay and Hay, 1889; Modlin, 1982; Prophet, 1963; Weaver, 1943)
Only one male and one female will mate at a time and males die shortly after copulation is completed. Little research has been done specifically on fairy shrimp mating behavior, but the behavior of a close relative, neglected fairy shrimp (Eubranchipus neglectus), has been better described. When males find females to mate with, they position themselves to use their claspers (on the second set of antennae) to grab on to females and inject their sperm. Although the mating process takes only minutes, males and females may remain clasped together for days. Males show a preference for larger females, likely due to their higher reproductive potential. ("Fairy Shrimp", 2012; Belk, et al., 1998; Feigenbaum and Switzer, 2007)
In years when the vernal pools refill with water later in the year (sometimes as late as March), female shrimp can become sexually mature in as little as two weeks after hatching. Females are considered sexually mature when they have eggs in their brood pouch, whereas the males must have well-developed claspers. Adult fairy shrimp are active during the spring. Breeding occurs once a year, typically in April and May, before pools dry up (at which time mature individuals die). Once they mate, females release their eggs into the water where they settle at the bottom of the vernal pool, typically lying dormant until October or November when the pools fill back up with water. There is debate in the literature as to whether fairy shrimp eggs must go through a period of desiccation and/or freezing before they are able to hatch. It has been documented that, in order to hatch in the wild, fairy shrimp eggs require a resting period of at least a few months. Eggs can, however, lie dormant for years if necessary. Females have been reported to produce between 22 and 44 eggs per clutch. Eggs may have thinner shells ("summer eggs") or thicker shells ("winter eggs"); eggs with thinner shells will typically hatch during the same season that they were laid while those with thicker shells will overwinter. It has been suggested that females are more likely to lay "summer eggs" when there is a shortage of males in the population. ("Fairy Shrimp", 2012; Avery, 1939; Brendonck, 1996; Dexter, 1946; Eldridge, 1990; McCafferty, et al., 2010; Modlin, 1982)
Female fairy shrimp spend time and energy developing the eggs before fertilization. There is no parental investment following egg laying as males die shortly after mating and females die when their vernal pools dry up. Eggs hatch and young develop after pools have filled again, without any parental care. (Avery, 1939; Dexter, 1946; Ferguson, 1939; Hay and Hay, 1889)
The lifespan of this species depends on environmental conditions. Fairy shrimp require water to stay alive and thus can only survive for as long as the vernal pools they inhabit remain filled. Vernal pools usually completely dry up by April or May, although some pools can stay filled for years at a time. Eggs do not hatch until the vernal pools are filled with water again, usually in October or November. Water temperature is another important factor determining life span; it has been observed, both in the wild and lab, that fairy shrimp can only survive for a few days in water warmer than 20-21°C. (Dexter, 1946; Ferguson, 1939; Knight, et al., 1975; Modlin, 1982)
Fairy shrimp are benthic, meaning that individuals spend the majority of their time on the bottom of their vernal pools. They are not generally very active and this, along with their coloration, can make them very hard to see. On cloudy days, they tend to remain near the bottom of the pools whereas on sunny days they can be found swimming near the top more frequently. They swim, ventral side up, by moving their appendages and, even when swimming, do not move very quickly. ("Fairy Shrimp", 2012; Dexter, 1946; Ferguson, 1939; McCafferty, et al., 2010; Modlin, 1985)
Individuals have a pair of compound eyes which they use to perceive their environments. Although no species-specific details were found, other anostracans are known to use chemorecption and mechanorecption to sense their environments and it is likely that this species does as well. (Tyson and Sullivan, 1979)
Fairy shrimp are benthic scrapers that use their appendages to scrape food off the bottoms of vernal pools, which is then filtered from the water. Their diet typically consists of benthic diatoms, filamentous algae (such as Draparnaldia glomer), desmids, platyhelminth eggs, and Arcella species. (Modlin, 1982; Modlin, 1985)
This species is not usually food for other organisms because the vernal pools in which they live do not support predatory fish that will survive the seasonality of these pools. In the rare cases where fairy shrimp are found in pools that do not dry up every year, they may be prey to some fish. While current literature has not investigated this species as a prey item specifically, other species of fairy shrimp (Order Anostraca) are eaten by waterfowl in the spring, as well as some amphibians (wood frogs and mole salamanders, specifically) and insect larvae. ("Fairy Shrimp", 2012; Eldridge, 1990)
The vernal pools in which these fairy shrimp are typically found contain a relatively high level of algae during the spring. Fairy shrimp are primarily algivores which may help to keep the relative levels of algae low. (Ferguson, 1939; Modlin, 1982; Modlin, 1985)
This species does not have any major economic importance for humans.
There are no known adverse effects of this species on humans.
As it has very specific habitat requirements, the protection of small wetlands where vernal pools exist is essential to its survival. (Bodie and Semlitsch, 1998; )
Nicholas Kirkpatrick (author), University of Michigan-Ann Arbor, Alison Gould (editor), University of Michigan-Ann Arbor.
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.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
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.
mainly lives in water that is not salty.
An animal that eats mainly plants or parts of plants.
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.
fertilization takes place within the female's body
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats plankton
Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).
breeding is confined to a particular season
remains in the same area
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sight to communicate
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