An otherworldly ecosystem
Mono Lake is a terminal lake in a closed basin, meaning water flows in but does not flow out, except through evaporation. This process, occurring over at least 760,000 years, has concentrated salts and minerals, making the lake 2.5 times saltier than the ocean. Its water is a chloride-carbonate-sulfate mix with an alkalinity of pH 10, similar to household glass cleaner. The lake's features are the tufa towers, which are spires of calcium carbonate (limestone). These structures form entirely underwater when calcium-rich freshwater springs seep up from the lakebed and react with the carbonate-rich lake water. The resulting precipitate builds up around the spring's opening, growing over centuries into towers that can exceed 30 feet in height. The towers only became visible when water diversions to Los Angeles, beginning in 1941, caused the lake level to drop dramatically.
This extreme environment is inhospitable to fish, but it supports a simple, productive ecosystem. The food web is based on microscopic algae which bloom in the hypersaline water. This algae feeds trillions of endemic brine shrimp (Artemia monica) and alkali flies (Ephydra hians). These two invertebrates are the primary food source for millions of migratory birds. Annually, the lake hosts between 1 and 2 million birds, including up to 80,000 Wilson's Phalaropes and 1.8 million Eared Grebes. For the grebes, this is a large portion of the entire North American population. The lake is an important stopover on the Pacific Flyway where birds feast on the shrimp and flies to fuel their long migrations.
The science of survival
The creatures of Mono Lake have adaptations. The alkali fly, Ephydra hians, can crawl underwater to feed on algae and lay eggs, remaining submerged for up to 15 minutes. It achieves this by trapping a bubble of air around its body using a dense mat of waxy, water-repellent hairs. This "scuba suit" allows it to breathe and protects it from the caustic water. The native people of the Mono Basin, the Kootzaduka'a, historically harvested the alkali fly pupae as a primary food source rich in protein and fat. The name Kootzaduka'a translates to "fly eaters."
In 2010, the lake's sediments yielded another scientific curiosity: a bacterium strain named GFAJ-1. Initial research, published in the journal Science, suggested that this extremophile could substitute arsenic for phosphorus in its DNA and other important biomolecules. This claim suggested a form of life different from all others known, as phosphorus was considered one of the six essential elements for all life. The discovery generated immense excitement about the possibility of "weird life" on Earth and other planets. However, subsequent independent studies in 2012 refuted the original findings, showing that GFAJ-1 is an arsenic-resistant, but still phosphate-dependent, organism. While the arsenic-DNA claim was disproven, the bacterium shows life's ability to endure in chemically extreme environments.