Scientists: Tiny Tahoe bottom-dwelling species in decline | SierraSun.com

Scientists: Tiny Tahoe bottom-dwelling species in decline

Margaret Moran
mmoran@sierrasun.com

The number of small critters living on the bottom of Lake Tahoe is declining at dramatic rates, and scientists say that could have ripple effects for its future health.

A recent survey of the lake has revealed the population of most bottom-dwellers the size of a thumbnail or smaller have decreased between 99.9 percent and 34 percent since the 1960s.

"The invertebrates in the bottom of lakes in general may act like worms in a garden; they are very important to the cycling of organic matter," said Sudeep Chandra, associate professor of limnology with the University of Nevada, Reno. "In addition, these bottom invertebrates could be important food sources for fishes."

Some declining species include the Tahoe flatworm and blind amphipod at 99.9 percent, Tahoe deepwater stonefly (94 percent), Tahoe seed shrimp (83 percent), segmented worms (57 percent) and non-bitting midges (34 percent).

NATIVE VS. NONNATIVE

While the reason for their decline is unknown, it's believed one contributing factor may be the introduction or increased populations of nonnative species since the 1960s.

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Invasive species such as the signal crayfish ­— whose numbers have doubled since the '60s — are like "little cattle in the landscape feeding on plants and invertebrates," as they migrate, Chandra said.

Another possibility is impact to their preferred habitats (plants for most species) as a result of a decrease in Lake Tahoe's clarity.

Loss of invertebrates could cause changes to the lake's ecosystem, impacting clarity as a result, Chandra said, although more study and funding are needed.

While most lake research over the years has focused on understanding clarity changes, Chandra said open water where clarity is measured and Lake Tahoe's bottom are linked.

"For example, much of the material that comes from the watershed is processed at the bottom of the lake by these animals," he said. "This prevents the material from being resuspended in the water column when the lake is remixed."