In the summertime, Mono Lake, a natural salt lake east of Yosemite National Park, hosts thousands of migrating birds. They visit the area to feast on tiny brine flies that swarm along the shore.
Biologist David Herbst from UC Santa Barbara’s Sierra Nevada Aquatic Research Lab says the flies’ health tells us a lot about the lake’s health.
“The brine fly is a little bit smaller than a house fly. They are insects that occur in or next to saltwater environments, mostly inland salt lakes,” he said.
He said natural salt lakes are also known as terminal lakes because there’s no outlet for the water except evaporation.
“They are lakes that are at the end of the road for a freshwater stream coming out of the mountains in closed basins. So, the minerals that are dissolved in the streams and rivers accumulate gradually in those inland lake bodies,” Herbst said.
His interest in brine flies, also called alkali flies, stems from their unusual aquatic habitat, and their huge importance to birds feeding at salt lakes.
Brine flies lay eggs and develop in their early stages under water. Herbst said they feed on algae, and once mature, they blanket the lake’s shore and become easy prey for thousands of hungry birds.
“Gulls, for example, will feed on the flies by running along the shore and kind of just snapping up mouthfuls of flies,” he said.
But Herbst said decades of diverting water away from the lake, compounded by drought, has caused the lake’s surface area to shrink and salinity to rise to unhealthy levels.
His research, recently published in the journal Frontiers in Ecology and Evolution, found brine flies are in decline – both in size and quantity.
“As the lake becomes more and more salty, that’s more and more energy they have to spend on the process of getting rid of the salts, which means there’s less and less energy available to grow,” he said.
Nora Livingston is the Lead Naturalist Guide for the non-profit Mono Lake Committee. She said brine flies provide much-needed nourishment for shorebirds as they migrate between North and South America.
“It’s really important for saline lakes like Mono Lake and the Great Salt Lake to exist for these mostly migrating shorebirds and water birds. It’s like a gas station for them on long migrations,” she said.
Livingston said, starting in the 1940s, streams that naturally flowed to Mono Lake were diverted to supply water to Los Angeles. Over time, lake levels continued to drop resulting in grassroots efforts and lawsuits to save Mono Lake. In 1994, the state placed some limits on the amount of water that can be diverted to LA. But with years of drought, she said the goals for the lake have not been reached.
Livingston said this winter’s snow melt will definitely raise the water level, but it’s likely not enough.
“The lake has risen about a foot and a half since January, and our forecasting expects the lake to rise about four more feet by the end of the run-off season,” she said.
A single wet winter, she said, can’t reverse years of diversions and drought, and there’s a critical need for a long-term solution – one that accounts for climate change and potentially more drought.
“Even the gains that we see in a big winter like we’ve just had could evaporate, quite literally, in just a few years,” she said.
And it’s not just the birds and the flies that are threatened by low water levels. Livingston said the dust, or alkali sediment, exposed by dry lake beds can be toxic on windy days.
“The particles of that dust are so small and so fine that they actually stay in your lungs and create problems like lung infections, asthma, and lung cancer. When the lake is higher, it covers up those alkali flats and is no longer a problem,” she said.
Livingston said the lake can naturally restore its ecosystem with more water – but this requires the Los Angeles Department of Water and Power (DWP) to reduce stream diversions and find new options. She said the Mono Lake Committee is awaiting a hearing with DWP and will continue to push for a solution to protect Mono Lake, and its remarkable ecosystem.
“The algae is photosynthesizing from the sunlight, and the shrimp and the flies are foraging on that algae and the birds are foraging on the shrimp and the flies, and this cycle is so dialed, this lake has been here for so many thousands of years,” she said.
UCSB researcher Herbst said studying the tiny brine fly helps us understand the larger cycle of life at Mono Lake. He knows there are many challenges, but his goal is for all of the agencies to come together and agree on how to keep the lake in a healthy condition – one that protects the aquatic life and shorebirds well into the future.
