Brine shrimp are small aquatic organisms found globally, often recognized from popular science kits. They survive in environments too harsh for most other life by employing unique biological strategies. Their unusual life cycle and ability to enter a state of suspended animation make them a subject of scientific interest.
Classification and Natural Habitat
The brine shrimp belongs to the genus Artemia, a group of aquatic crustaceans classified within the class Branchiopoda. Adult brine shrimp grow up to 15 millimeters long and have a segmented body. They use numerous leaf-like appendages for swimming, feeding, and respiration.
Brine shrimp are primarily found in hypersaline environments, such as inland salt lakes and coastal salt flats, which have extremely high salinity. These habitats, like the Great Salt Lake in Utah, often have salt concentrations ten times higher than typical seawater. They rarely occur in the open ocean because they lack defense mechanisms against predators like fish.
Their ability to tolerate salinity levels between 2.5% and 25% allows them to occupy an ecological niche free of competitors. This osmotolerance, coupled with the capacity to synthesize efficient respiratory pigments, enables survival in conditions of high salt and low oxygen that would be lethal to most other aquatic life.
The Unique Biology of Dormant Cysts
The brine shrimp’s primary survival mechanism involves producing dormant embryos known as cysts. When environmental conditions become adverse, such as high salinity, low oxygen, or desiccation, the female switches from producing live young to encapsulated embryos. This metabolic suspension is called cryptobiosis, or “hidden life,” which halts the embryo’s development.
The embryo inside the cyst is metabolically inactive, having arrested its development within a protective shell at the gastrula stage. This robust shell allows the cysts to withstand complete desiccation, chemical exposure, and extreme temperatures for many years. For instance, in a dry, oxygen-free state, the cysts can survive temperatures ranging from -190°C to briefly above boiling point.
The cysts enter a state of diapause, an internal, pre-programmed arrest of development. Diapause must be terminated for the embryo to resume development, often achieved by the dehydration and rehydration that occurs when cysts are re-immersed in water. Once rehydrated with sufficient oxygen, the embryo’s metabolism resumes, and the cyst hatches into a free-swimming larva, called a nauplius, typically within 24 hours.
Primary Uses in Science and Aquaculture
The ability to produce and store dormant cysts has made brine shrimp a valuable resource in several human industries. Their primary application is in aquaculture, where freshly hatched nauplii are used as a live food source for the larval stages of commercially important fish and crustaceans. The cysts can be stored indefinitely and hatched on demand, providing a convenient, nutritious, and readily available food supply.
The first and second-stage nauplii are valuable because they contain large yolk reserves and are rich in nutrients. Over 2,000 metric tons of dry Artemia cysts are marketed globally each year, often harvested from locations like the Great Salt Lake. Brine shrimp are also sold commercially as novelty pets, famously marketed as “Sea-Monkeys.”
Brine shrimp also serve as a model organism in scientific research, particularly for toxicology testing. Their quick reaction to toxins and ease of cultivation make them a cost-effective tool for assaying the toxicity of chemical compounds. Scientists have used the cysts to study the effects of radiation and extreme conditions, including sending them into space on missions like Apollo 16 and 17.