In some ways, Mono Lake belongs in Trip 1, where we experienced different kinds of extreme environments. In Yellowstone, many of the hot springs were acidic, which is one type of extreme environment. Mono lake provides an extreme environment that is the opposite of acidic on the pH scale. It is an alkaline lake, with a pH of about 10. Remember, a pH of 7 is neutral. Lower than 7 is acidic, higher than 7 is alkaline, with each full number representing a ten-fold increase either way. Since Mono Lake's pH is 10, 3 full numbers above neutral, it is 1,000 times more alkaline than neutral. Most freshwater lakes range from 6-8 on the pH scale, and the pH of the oceans is around 8, so Mono Lake is at least 100 times more alkaline than most aquatic environments. It is also about 3 times more salty than the ocean. While not as salty as the Great Salt Lake, this trait adds a second significant environment to which organisms need to adapt. The focus here then is on how organisms have adapted to the conditions of this environment.
The first thing to know is that no fish species have adapted to this environment. Because of that, the lake has been called a dead sea. But there are some organisms that have adapted and tend to thrive because there is little competition from other organisms. As you might expect after Trip 1, there are bacterial and archael extremophiles in the lake. There are also eukaryotic algae that exist and create the foundation for the food chain of the lake. Bacteria, like the filamentous blue-green algae Oscillatoria, along with the green algae Ctenocladus circinnatus, and diatoms, like Nitzschia frustulum, harness the sun's light to grow. These and a few protozoa provide an abundant food source for Alkaline Flies (Ephydra hydropyrus), which allows these insects to thrive.
Brine Shrimp (Artemia monica), which feed on different, single-celled algae, are also found in high numbers in the lake. There are other species of brine shrimp, like the ones found at the Great Salt Lake, but Artemia monica is only found in Mono Lake. Because the kind of algae the shrimp feed on is different than the kind the flies feed on, they are both able to thrive.
The flies and the shrimp, in turn, provide abundant food for the birds that inhabit the lake. California Gulls (Larus californicus), Eared Grebes (Podiceps nigricollis), Wilson's and Red-Necked Phalaropes (Phalaropus spp.), and Snowy Plovers (Charadrius nivosus) are some of the common birds at the lake. Thirty percent of America's Eared Grebe population stops at the lake during migration, and the second largest California Gull population in the world can be found at the lake. With all these birds around, their predators include birds of prey like eagles, owls and hawks and mammals like coyotes, bobcats and raccoons.
Because of the relative simplicity of the situation at the lake, it is a good location for learning about the concept of a food chain.
Another unique feature of the lake is geological in nature. An interaction of the fresh water with calcium flowing into the lake from underground mixing with the carbonate-rich water in the lake itself has created towers of rock, called "tufa towers". These actually play a role in the life cycle of the alkaline flies and are a sight to behold.