Tahoe researchers probe tiny critter population plunges

Researchers at Lake Tahoe are trying to figure out why some of the tiniest creatures and plants at the bottom of the alpine lake appear to be disappearing at an alarming rate.

Scuba divers recently completed a first-of-its kind circuit of the entire lake to assess the ecological changes that could be affecting a host of native macro invertebrates — some that exist only in Tahoe’s waters.

Sudeep Chandra, a freshwater science expert at the University of Nevada, Reno, says a variety of worms, stoneflies, bottom shrimp and water mites are crashing in population compared to levels measured in the 1960s.

He says populations of two, the blind amphipod and Tahoe flatworm, have dropped by as much as 99.9 percent.

“They are disappearing. It’s unprecedented. It’s absolutely dramatic,” Chandra said.

Chandra said the lake bottom serves as the “backbone” for chemical cycling of the lake’s waters.

“It’s the sponge of the lake, basically,” Chandra said. “Protecting Lake Tahoe and its clarity in the long run is really dependent on a functional lake bottom.”

“We basically have new habitats being created in the shallows,” Chandra said.

The animals depend to a large degree on native bottom plants such as skunkweed and moss for habitat, and those plants also appear to be vanishing, research suggests.

Part of the trend could be attributed to crayfish — not native to Tahoe — that are grazing on the plants. First introduced to the lake in the late 1800s, Tahoe’s thriving crayfish population is now estimated at 200 million to 300 million.

Another possibility is a legacy effect of Tahoe’s diminished clarity. In the late 1960s, one could see more than 100 feet from the surface into Tahoe’s depths. Today, visibility extends to only about 70 feet, a trend experts attribute to the presence of suspended sediments and algae growth associated with human activity.

While evidence suggests environmental restoration projects around the lake over the past 18 years have stopped mid-lake clarity loss, bottom plants may have already been damaged as murkier waters cut off sunlight.

“It looks like clarity is beginning to stabilize, but the bottom of the lake continues to change at a dramatic rate,” Chandra said.