Sea Monkeys!! (Brine Shrimp of Mono Lake)

Mono Lake, an otherworldly spot east of the Sierra Nevada in California's Great Basin desert, is such a fascinating place in so many ways, I could spend days reading and writing about it.  The geological history of the area is rich: Mono Lake, a salty inland sea with no outlet, sits in a fault basin and was formed from the melting of glaciers during the last ice age.  The glacial history written in the bordering mountains and the volcanic history seen in nearby craters, Mammoth Mountain, the Long Valley Caldera, and islands in Mono Lake itself are all worthy topics of study in their own right.  And the lake's famed tufa towers certainly deserve the spotlight in an article of their own, as do my beloved plants - in this case, those plants that have evolved to tolerate not only harsh desert conditions, but extreme salinity and alkaline soils as well!  The wonders are new every morning at Mono Lake! 

Shoreline at Mono Lake's South Tufa Area
Political struggles surrounding the lake have been quite fierce.  The lake is fed by streams flowing from the Sierra Nevada, but water was diverted from these streams and sent to water the landscapes and booming population of Los Angeles beginning in 1941.  As a result, lake levels dropped 45 vertical feet.  (That is a story for another day; suffice to say that for now, at least, while the future of the lake is not entirely secure, conditions are an improvement on what they have been.)
But today, I'm more interested in discussing the ecology of Mono Lake, focusing on one of its most famous inhabitants: the sea monkey.
Little greenish brine shrimp, each about 0.4 inches long.

Brine Shrimp (yes, they really are the very same critters sold in shops under the name "Sea Monkeys") form an integral part of Mono Lake's food web.  The lake boasts its own unique species of brine shrimp, Mono Lake Brine Shrimp (Artemia monica), an enchanting, translucent-greenish little crustacean.  The salty, alkaline lake waters absolutely teem with billions of these little guys; estimates put their numbers around 5 trillion during the summer months.  And insignificant though they may seem, the ecosystem would collapse without them.
The lake initially appears "dead" and desolate to any casual observer, and it's true that the ecosystem found here really is comparatively simple, with just a few key species.  But the lake is far from a "dead sea" and the species that do survive here are present in massive numbers, which makes all the difference. 
Brine shrimp in a shallow disc (ok, it's a Frisbee).  They're barely visible in the photo above, but you can see one where
the finger is pointing.  This gives a sense of just how tiny brine shrimp are.

The ecosystem of Mono Lake is a great teaching tool for illustrating the concept of a simple food web.  The entire ecosystem is based on three key species: algae, alkali flies, and brine shrimp.  Green algae is photosynthetic, using the sun's energy to grow and obtaining nutrients from the lake water.  Alkali flies and brine shrimp feed on the algae.  Over a million birds flock to Mono Lake every summer to feed on the flies and shrimp, including gulls, phalaropes, grebes and others.  Waste from the birds and dead organisms sink to the bottom of the lake to decompose and act like fertilizer for the algae.  And so, the cycle is complete! 
Notice that there are no fish in Mono Lake.  With a pH of 10 (on a scale where 7 is neutral), the lake's waters are far too alkaline to support other life.  The water is also 2.5 times saltier than the ocean!
Alkali flies around a puddle on the lake shore.  They may not look appealing, but they are a critical part of this ecosystem.
Also, we noticed the flies don't bother people, so don't worry about them and leave them be.
Hardy as they are, brine shrimp cannot overwinter in the cold lake as adults.  Late in the season, before they die, the shrimp produce eggs designed to overwinter as "cysts."  These tough cysts sink to the bottom of the lake where they persist in a state of suspended animation until the water warms sufficiently the following spring.  These hard, leathery cysts or eggs are what is harvested and sold as "Sea Monkeys" and fish food.
The huge abundance of aquatic life found in Mono Lake during the summer makes the lake one of the most important sites for nesting and migrating birds in the west, particularly as other western wetland habitat has been lost to development. 
Two gulls, happily foraging in Mono Lake.
Though the ecosystem of Mono Lake thrives in a combination of harsh conditions, including desert heat, winter cold and extremely high salinity and alkalinity, it is remarkably fragile.  Because it relies so heavily on just a few species, the loss of even one species, such as the brine shrimp or the alkali fly, would be catastrophic for dependent populations - especially birds.
Abundant numbers of these tiny creatures does not necessarily guarantee a stable ecosystem, safe from collapse.  Since the entire ecosystem is essentially built on just three groups of organisms (algae, brine shrimp and alkali flies), it is very susceptible to climate change and other damaging factors.  Since brine shrimp and alkali flies are ancient, primitive creatures perfectly adapted to the saline, alkaline waters of Mono Lake, a rapid change in the lake's chemistry would likely prove too much for them to handle and result in population collapse. 

Diversion of streams from Mono Lake began in the 1940's and was finally stopped 40 years later.  Between that time, the salinity of the lake doubled (as half of the lake's volume of water was lost) and the productivity of the brine shrimp and alkali flies dropped significantly.  The loss of either one of these species would mean disaster.  In particular, the failure of the brine shrimp population one year would mean starvation for thousands of birds.
As you may know by now, flipping over rocks often reveals a treasure trove of unseen life.  Underneath this piece of tufa
is the remnants of dozens of alkali fly pupae.  Birds are happy to eat alkali flies during all life stages, but the pupae were
once an especially important food source for local native people.
If you visit:  I highly recommend stopping to check out the Mono Basin Scenic Area visitor center on highway 395 and going on a docent-led walk at the South Tufa Area along the lake.  Other activities include hiking, birding, kayaking and swimming.  (We went swimming at Navy Beach and loved it!  The water is dense, making it easy to float, but all that salt makes it important to remember to keep your mouth closed!  Also, the salt forms a crust on your skin and brine shrimp may get stuck in your hair!  Still, it's a worthwhile experience.)
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