Celia Symons on a research trip in the John Muir Wilderness. (Image: Provided)

It probably isn’t a stretch to say when it comes to animals in the Sierra most people are interested in those on the land. Not so for Celia Symons.

She is enthralled by the millions or billions of creatures living in alpine lakes.

Symons, an associate professor at UC Irvine, recently gave at talk hosted by Tahoe Environmental Research Center titled What Tiny Lake Organisms Reveal About a Changing Environment. She has been studying Sierra lakes since 2013.

She studies zooplankton with the Sierra Nevada Aquatic Research Laboratory in Mammoth Lakes. Research is from 25 lakes that vary in elevation as well as whether they have fish.

Symons explained the general definition of plankton is: living things that float in water and can’t overcome currents. They are in oceans, lakes and puddles—and “even in your home at the bottom of your plants.” Phytoplankton is plants. Zooplankton is animals.

“They are really important. About half of the air we are breathing right now is produced by these plants, by these phytoplankton,” Symons said. “They are also responsible for the great oxygenation event that allowed organisms to come onto land.”

She explained they do “all sorts of things for the climate” like releasing chemicals in the ocean that seed cloud formation.

Her talk focused on copepods and cladocerans. “(Copepods) are the most dominant group of animals in the world by biomass,” Symons said. They are 1-3 mm long.

Cladocerans range in size from a half millimeter to about 4 mm. Daphnia, which can be found in Tahoe, is on the larger end of that range. It eats phytoplankton.

“You can just think of them as cows of the lake, just grazing on everything,” she said. They are credited with helping with Lake Tahoe’s clarity.

Symons and other scientists are taking core sediments from lake bottoms to study changes through the years. One centimeter of sediment roughly equals one decade. So, 30 cm is like looking back 300 years.

While air temperatures in the study area have increased 2 degrees Celsius in the last 25 years, that same rise has not occurred in the water.

“Snowpack is the really important variable in how lakes function,” Symons said, adding that the dramatic swings in drought vs. super wet years is a big factor.

What type of zooplankton is in a lake is dependent on the lake’s health—things like pH, nutrient concentration, salinity, dust from the Central Valley—are all factors. Anything on the land can affect the lake as well, like changes in vegetation, nutrient cycling, as well as contaminated air from wildfires.

Researchers are looking into daphnia’s response to fish stocking—an introduced predator that feeds on zooplankton. The zooplankton create defensible physical traits to enlarge their bodies so they don’t fit in a fish’s mouth.

Ninety-nine percent of Sierra lakes above 5,900 feet were fishless until stocking began in the 1800s. Symons said fish have had a “detrimental” impact to the ecosystem.

“They eat the larvae of a lot of the emerging insects. (When) there’s fewer emerging insects, there’s a reduction in birds and bats,” she said. “And because there are fewer amphibians emerging from the lakes there’s also a reduction in snake populations. So it really kind of rewires the entire web.”

Symons said fish introduced at higher elevations have a greater impact compared to lower elevation lakes in the Sierra.

By taking water from the various lakes scientists can run experiments to see the changes in zooplankton populations, and what happens when fish are removed from lakes—which is happening in some locations.

“Zooplankton play a really pivotal role in aquatic food webs. They are moving a lot of nutrients from algae to fish, but they are also really important in nutrient cycling and carbon sedimentation,” Symons said.

Note: A version of this story first appeared in the Tahoe Mountain News.