Brine shrimp, also known as sea monkeys or Artemia, are tiny crustaceans that inhabit saline waters around the world Their small size belies their huge ecological and economic importance But exactly how small are brine shrimp? Let’s take a closer look at the size range of these little critters.
A Shrimp By Any Other Name
Brine shrimp go by many names, including sea monkeys, artemia, or scientific name Artemia franciscana They belong to a group called anostracans, containing “fairy shrimp” and other similar creatures. There are multiple brine shrimp species, but Artemia franciscana is the most common
Some key facts about brine shrimp:
- Crustaceans (related to shrimp, lobsters, crabs)
- Thrive in high salinity waters
- Important food source for birds, fish, and shellfish
- Harvested for commercial sale as fish food
Now let’s get into the nitty gritty details on their size.
Measuring Up: How Long do Brine Shrimp Grow?
Fully grown adult brine shrimp reach 8-10 millimeters (0.3-0.4 inches) in length. That’s roughly the size of a small match head.
To give some perspective on just how tiny that is:
- A dime is 18 mm wide
- A pencil eraser is 6 mm tall
- An M&M candy is 13 mm wide
So brine shrimp are seriously diminutive creatures, even compared to other small items. Their miniscule size belies the huge role they play in ecosystems worldwide.
Life Stages and Growth
Brine shrimp go through several life stages, each with distinct sizes:
- Eggs (cysts): 200-300 micrometers (0.2 mm)
- Nauplii: 0.4 – 0.5 mm after hatching
- Adolescents: 0.5 – 0.8 mm
- Adults: 8-10 mm full grown
After hatching from tiny eggs, brine shrimp exist as nauplii for their first few days to weeks of life. At this stage they are barely visible to the naked eye, around 0.5 mm.
They then transition to a juvenile or adolescent stage around 0.5-0.8 mm length. This stage lasts around 2-3 weeks as they grow and develop.
Finally, they reach mature adulthood at 8-10 mm long within 4-8 weeks after hatching. Their growth then levels off, and life span is 6-10 months.
Why So Small? Evolutionary Explanations
Brine shrimp fill an important niche in hypersaline waters where not much else can survive. But what evolutionary factors lead to their tiny size, even as full grown adults?
Some possible explanations:
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Limited nutrients – Less food availability in brine pools selects for smaller organisms.
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Oxygen exchange – Smaller body size enables sufficient oxygen absorption through their carapace.
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Predator avoidance – Makes them less visible to predators like fish and birds.
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Reproductive success – Their small size allows production of more offspring.
So in the harsh brine pool environment, being tiny gives brine shrimp key survival and reproductive advantages. Their importance comes not from individual size, but collective abundances.
Abundance Makes Up for Size
Brine shrimp occur in absolutely massive numbers in salt lakes and ponds. For example:
- There can be 2,500-3,000 brine shrimp per liter of water.
- Hundreds of billions to several trillion brine shrimp populate sites like Mono Lake in California.
- Up to 500 metric tons are harvested annually in the Great Salt Lake for commercial use.
This incredible abundance allows brine shrimp to play major ecological roles despite individual tiny sizes. Pretty impressive for a creature you can barely see!
Ecological Significance
Don’t be fooled by their miniature proportions. Here are some of the vital ecological functions performed by abundant brine shrimp populations:
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Food source: Fish, birds, and crustaceans feed off huge numbers of brine shrimp. Especially important for migratory birds.
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Nutrient cycling: As filter feeders, brine shrimp transfer nutrients like carbon and phosphorus between trophic levels.
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Bioindicators: Their presence indicates healthy, well-oxygenated brine pool conditions. Declines signal ecosystem issues.
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Genetic diversity: Their cysts remain viable for years, maintaining high genetic diversity. Improves adaptation.
So tiny individual size does not prevent brine shrimp from having an oversized ecological impact in the unique environments they inhabit.
Economic Importance
In addition to ecological roles, brine shrimp have substantial economic value:
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Aquaculture feed: Brine shrimp are harvested and sold as feed for commercial fish and shellfish farming.
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Pet food: Dried brine shrimp marketed as “sea monkeys” are popular first food for aquarium fish.
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Bird food: Brine shrimp sold as food supplement for captive waterfowl and shorebirds.
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Nutritional supplement: Dried brine shrimp contain omega-3s and protein. Marketed as human health supplement.
The brine shrimp industry brings in $50-100 million annually to communities around key salt lakes like Great Salt Lake.
Tiny Creatures, Big Impacts
Brine shrimp are truly tiny creatures, reaching a maximum of only 0.4 inches in length as adults. But their small stature hides incredible ecological and economic importance.
These diminutive crustaceans nourish birds, fish, and shellfish, cycle nutrients, and generate millions in commercial harvest revenue. Never underestimate the power of small packages, as exemplified by the mighty brine shrimp!
Economic Importance for Humans: Positive
Since brine shrimp reproduce quickly and their environment is easy to copy, they can be used to test for toxicity and teach. They teach students the right way to observe live animals and how to set up experiments to find out things like behavior, how to get food, and the best place for reproduction and growth.
Because they are cheap and easy to use, both the eggs and the adults are fed to coral, young fish, and other crustaceans. They sell for about $7 a pound and are most popular from May to July, but they can be made in a lab at any time of the year. (Grzimek, 1972).
- Positive Impacts
- pet trade
- research and education
Artemia salina Facebook Twitter
This type of shrimp lives in salt water bodies inside of states, like the Great Salt Lake in northern Utah. It can also be found on the rocky coast south of San Francisco and in the Caspian Sea. They can also be found in many other salty bodies of water, such as the intermountain desert in the western US, salt swamps near any coast, and many man-made saltpans around the world. (Grzimek, 1972; Pennak, 1989).
- Biogeographic Regions
- nearctic
- native
- palearctic
- native
The artemia salina are very hardy and can live in a lot of different salinity levels of water. All contain some salt content ranging from seawater (2. 9-3. 5 percent) to the Great Salt Lake (25 to 35 percent), and they can handle up to a 2050 percent salt concentration, which is almost full. Some live in salt swamps near the dunes, but never in the ocean itself because there are too many animals that eat them. They also inhabit man-made evaporation ponds, used to obtain salt from the ocean. They can handle the high salt level because their gills help them take in and get rid of ions as needed, and their maxillary glands make concentrated urine. The water temperature also varies a lot, from about 6 deg C to 37 deg C. The best temperature for reproduction is around 25 deg C, which is room temperature. They don’t have many predators because they live in a salty area, which is good, but it means they can only eat certain things. (Banister, 1985).
- Habitat Regions
- saltwater or marine
- Aquatic Biomes
- lakes and ponds
- temporary pools
- brackish water
A full-grown Artemia salina is usually between 8 and 10 mm long, but it can grow up to 15 mm if it needs to. Its long body is made up of at least 20 segments, and about 10 sets of flat, leaf-like appendages called phyllopodia are attached to its trunk and 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.
The shrimp Artemia salina is in the order Anostroca, which means “no shell.” This puts it in the same group as other species that don’t have a carapace, which is a hard, bony shell. It belongs to the subclass Brachiopoda, which means “gill foot” because the gills are on the outside of the bases of the limbs. (Banister, 1985; Najarian, 1976).
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
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- Range length
- 8 to 15 mm
- 0.31 to 0.59 in
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- Average length
- 8-10 mm
- in
There are a lot of males in the Great Salt Lake, as shown by studies. They reproduce by grabbing a female with their big second antennae and fertilizing her eggs, making 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. It needs to be about 30 degrees Celsius, there should be a lot of water, and the salt level shouldn’t be too high. If these conditions aren’t met, fertilized eggs are laid as cysts and stay dry and surrounded by a thick shell until they are ready to hatch, which could take up to 50 years. The cyst may need to be submerged in water more than once before it hatches, and some need to stay wet for at least 36 hours to make sure that the population doesn’t die off when it doesn’t rain enough. A brine shrimp grows from a nauplii larva to an adult in about a week. It then lives for a few months and can make up to 300 new nauplii every four days. (Banister, 1985; Captains Universe, 1996; Najarian, 1976).
- Key Reproductive Features
- parthenogenic
- sexual
- fertilization
- internal
- oviparous
- Parental Investment
- no parental involvement
The oddest behavior of A. salina is that they swim up-side down as compared to the majority of aquatic animals. This happens because of positive phototaxis, which means the brine shrimp is drawn to light. In the wild, it lives with its legs facing upwards because the sun is a natural light source. If you put a specimen on a dissecting scope with a base light source, it would flip over and swim “normally.” Also, brine shrimp rise to the surface during the day and sink again at night because they are drawn to light. High intensities of light, however, create a negative phototaxis response and drive the shrimp away. Newborn A. Because of gravity, salina show positive geotaxis, which can be seen when the nauplii sink to the bottom after hatching.
The way brine shrimp move is through the same rhythmic movement of their phyllopodia that moves their food forward. They swam through the water by beating their bodies to get to the food, not caring much about the rest of the environment. (Grzimek, 1972; Pennak, 1989).
- Key Behaviors
- motile
- aestivation
Artemia salina live on photosynthetic green algae, one type is Dunaliella. They get food by swimming and filtering small particles through fine, slender spines on their legs, or by grazing on bottom mud and quickly scraping algae off rocks with their limbs. Once the algae is caught, a feeding current moves it forward to the mouth through a central median food groove. This is done by using the regular rhythm of the phyllopodia, which are appendages that look like leaves. (Banister, 1985; Pennak, 1989).
- Primary Diet
- planktivore
- Plant Foods
- algae
- phytoplankton
- Foraging Behavior
- filter-feeding
Adult Brine Shrimp
What does a brine shrimp look like?
Brine shrimp measure up to 15 mm (0.6 inch) in length and have a discrete head with a nauplius (larval) eye and stalked compound eyes, a thorax bearing a series of leaflike limbs, and a slender abdomen without appendages. The body normally swims in an upside-down position by rhythmically beating their legs.
What is the life cycle of brine shrimp?
The life cycle of brine shrimps begins with a cyst. These tiny, hard-shelled eggs can survive for years in a dormant state until the right conditions trigger them to hatch. When the cysts are exposed to water, they absorb it and begin to swell. After several hours, the cysts burst open, and the nauplii emerge.
What are the parts of a brine shrimp?
As with other fairy shrimp, the brine shrimp’s body is distinctly separated into head, thorax, and abdomen. The head consists of two sections—the first one with the antennae and eyes, and the second one bearing the jaws (mandibles and maxillae).
What do brine shrimp consume?
Brine shrimp, any of several small crustaceans of the order Anostraca, inhabit brine pools and other highly saline inland waters worldwide. They feed primarily on green algae. Brine shrimp normally swim in an upside-down position by rhythmically beating their legs and are consumed by birds and fishes.