A method commonly utilized by wildlife for withstanding poor environmental conditions is timing reproduction to match food availability. Most animals attempt to time the birth or hatching of their young when food is prevalent and temperatures are moderate. Brine shrimp take this to the extreme, by either giving live birth if conditions are suitable or creating eggs that can remain viable (un-hatched but alive) for hundreds, or thousands, of years. These tough, coated eggs are called cysts.
A female brine shrimp has a collection of unicellular shell glands within the uterus which control the amount of protective coating applied to an embryo. Generally, when environmental conditions are conducive to survival, only a thin coating is excreted around the embryo, forming an egg. This egg hatches within the uterus, and free-swimming nauplii emerge. This is called the ovoviparous method.
When conditions are unfavorable, a thick coating is applied, and cysts are produced. This is called the oviparous method, as the cysts hatch outside the body. Cysts are said to be in diapause, and remain un-hatched until favorable conditions return. The cyst shell is composed of chitin, the same material that makes up an insect exoskeleton, and surrounds a 4,000-cell embryo. When suitable conditions return, the embryo "reawakens" by processing lipoproteins that fill the cyst, providing energy. As it is re-hydrated, the embryo expands, bursts the shell, and wriggles free.
This modification of reproduction shows how influential environmental conditions are on brine shrimp. Variables such as food availability, water salinity, water temperature, dissolved oxygen levels, and photo-period all play a role in Artemia biology.