Brine shrimp eggs surviving 30 years of drought in salt crusts. When rain fills the lake, billions hatch simultaneously, feeding waterbirds that arrive from nowhere.
Hans Hillewaert, CC BY-SA 4.0, via Wikimedia Commons
A survival mechanism
Lake Tyrrell, Victoria's largest salt lake, spends most of its time as a dry, salt-crusted depression covering approximately 20,860 hectares. For much of the year, it appears lifeless. Beneath the surface, however, millions of embryos of the Australian brine shrimp, Parartemia zietziana, wait in a state of suspended animation. These dormant eggs, called cysts, are in a deep state of metabolic arrest known as cryptobiosis. They can endure extreme desiccation, temperature fluctuations, and high salinity within the lake's salt crust, which can be up to 7 centimeters thick.
The cysts are produced when environmental conditions become harsh, such as when the lake dries up and salinity skyrockets. A female brine shrimp can produce up to 300 cysts every four days. Each cyst contains a gastrula-stage embryo protected by a tough outer layer called a chorion. This shell protects the embryo from physical damage and UV radiation. Internally, the embryo's cells are protected by sugars that prevent damage from dehydration. In this state, the cysts can remain viable for many years, waiting for the precise conditions to trigger hatching.
An ecosystem reborn by rain
When significant rainfall eventually fills the shallow lake basin, sometimes to a depth of only 50 centimeters, the environmental triggers for hatching are activated. The influx of fresh water dramatically lowers the lake's salinity from levels that can exceed 330 grams per liter to a more habitable range. This change in salt concentration is the primary signal for the dormant embryos to resume development.
Within hours of rehydration, the cysts absorb water and the embryos re-start their metabolism. The hatching is synchronized, resulting in a massive, simultaneous emergence of billions of brine shrimp larvae, called nauplii. These nauplii are tiny, less than 0.4 mm long, and begin feeding on algae and bacteria in the water. Their life cycle is rapid; they molt multiple times and can reach adulthood in as little as eight days, an adaptation for life in an ephemeral body of water.
This growth of life is a food source for tens of thousands of migratory birds. Species like the banded stilt and red-necked avocet congregate at the lake to feast on the shrimp bloom. This ephemeral ecosystem, dormant for years, springs back to life, all driven by the biology of the brine shrimp cyst.
💡Fun Facts
The name "Tyrrell" comes from the local Wergaia word for "sky," a nod to the Boorong people's detailed astronomical traditions.
The pink and orange hues of Lake Tyrrell when it holds water are caused by the pigments in salt-loving micro-algae (*Dunaliella salina*) and halobacteria.
*Parartemia zietziana* is one of 18 endemic species of brine shrimp found only in Australia.
Brine shrimp cysts have been studied in space by NASA to understand the effects of radiation on development.
Accessible 24/7, though viewing is best during daylight hours or on clear nights for stargazing.
Admission
Free
Accessibility
A viewing platform, boardwalk, and all-access amenities are available. The lake bed itself can be soft and muddy. All-terrain wheelchairs may be available through Parks Victoria.
