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Brine shrimp

The life cycle

Courtesy of the U.S. Geological Survey.

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). 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, and Artemia attempt to time cyst hatching with the highest food availability. This occurs when water temperatures reach 4 °C (48 °F), typically by February or March. The emerging nauplii feed on the abundant algae, providing energy for the 12-24 molting stages a brine shrimp goes through to reach maturity, a process that takes 2-3 weeks depending on food availability and temperature. The average adult will produce around 8 broods, generally a combination of both egg and cysts, and since 1995 the GSL population has produced around 2-4 generations per year.

The Utah Division of Wildlife Resources monitors the various age classes and finds that peak numbers of nauplii occur in mid-April to mid-May. Peak numbers of adults occur in late May, depleting the phytoplankton food source. The stress of a lack of food triggers cysts production in females, and as adults die off, there are fewer live young to replace them on the lake. Generally, December brings cold enough weather to decrease water temperatures to around 6 °C (42 °F) (UGS), and the last free-swimming shrimp are killed by the cold. Cyst densities increase throughout the fall, until thick mats of cysts occur on some portions of the lake, known as "streaks". Cysts also wash up on the shore.

What else happens when they run out of food?

Beyond playing a hand in the lifecycle of brine shrimp, food availability plays a role in the health and development of shrimp after they are born as well. Brine shrimp are passive filter feeders; this means that they do not select what goes into their mouth beyond flapping their appendages in the water. Because of this, 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, the specific species of brine shrimp that inhabits the Great Salt Lake is unable to produce a protein component without acquiring the amino acid tryptophan from their diet (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.

In 1997, a period of abundant precipitation raised the lake level and decreased the salinity level, allowing other varieties of phytoplankton to increase. The dominant form of algae in the lake changed from small phytoplankton to larger diatoms, which are simply too big for nauplii to eat (e.g., most of your grocery store just closed, and what little food is left is sufficient to feed all the children). The nauplii in the lake consumed a greater proportion of the available phytoplankton, because that was what would fit into their mouths. As they mature, mainly diatoms remained, with little other algae. The diatoms do not provide adequate amounts of tryptophan, and black spot disease develops in adults.