Lake Tahoe's Ecosystem Facing Invasive Threat

An invasive species of snail has been discovered in Lake Tahoe for the first time, sparking fears for the local ecosystem.

New Zealand mud snails are an invasive species in the U.S., having spread to 22 states including California, Nevada and Colorado and the Great Lakes since they were first discovered in Idaho in 1987.

"Divers monitoring Lake Tahoe have discovered invasive New Zealand mud snails in areas off the South Shore," the Tahoe Regional Planning Agency (TRPA) and Tahoe Resource Conservation District (Tahoe RCD) said in a statement on Friday. "This is the first time the species has been detected in the Tahoe Basin."

"Contract divers with Marine Taxonomic Services, Ltd. surveying invasive weeds on the South Shore discovered tiny snails on the bottom of the lake nearly a half mile offshore from the mouth of the Upper Truckee River. Consultation with experts and a DNA lab analysis confirmed the species is New Zealand mud snail, an aquatic invasive species (AIS) that has been detected in nearby waterways including the Lower Truckee River downstream from Lake Tahoe near Reno, Nevada. No other AIS, such as the destructive quagga and zebra mussel, have been detected, according to the agencies."

The snails are thought to have been brought to the U.S. by shipping activity or aquaculture, and they have spread throughout the country probably because of aquatic recreation and fishing gear not being properly cleaned. California saw its first New Zealand mud snail population in the Owens River in 2000, according to the Center for Invasive Species Research, University of California Riverside, with all the western states, except New Mexico, now having permanent populations of the species.

"They are considered invasive because of the capacity for them to cause ecological damage and subsequent economic harm," Emily Bovee, previously a New Zealand mud snail researcher at Oakland University and a current research associate with the Detroit Zoo, told Newsweek. "They are able to reproduce by a method called parthenogenesis, which just means they can clone themselves.

"So the introduction of a single female into a water body has the potential for a new population to grow. This allows them to have a very rapid population growth, and they can reach incredibly high population densities. At such high densities they can outcompete the native invertebrates in the ecosystem, which then leaves less resources and nutrients for species further up the food web, like fish."

The snails only grow to about 0.15 to 0.24 of an inch in length, and graze on plant and animal detritus, algae and diatoms in waterways. This is an issue because native invertebrates can't then access the food they need and are outcompeted, leading to large knock-on effects across the entire food web of the waterway.

Due to their ability to reproduce asexually, each snail can produce around 230 offspring a year, which can lead to these snails being found in densities of up to 46,500 per square foot. This makes them an especially formidable invasive species, as they rapidly proliferate and replace themselves.

"Unfortunately it is nearly impossible to remove them once established in a new water body," Bovee said. "They are resilient to a range of environmental conditions, and so there are no tried and true methods that have been found that can target NZMS without disturbing the other native species. And since they are so small it is not feasible to physically remove them. This is why it is imperative that aquatic recreationists properly clean equipment after each use, especially before traveling to a different lake or river, because they could unknowingly introduce NZMS and other aquatic invasive species into a new area."

To tackle this new invasive species in Lake Tahoe—one of the most protected waterbodies in the country—the TRPA has deployed scientists to determine how many of the snails are in the lake, and they are making plans to eradicate the snails if possible.

"Lake Tahoe has a well-established network of regional and national partnerships that are all working together to reduce the threat of AIS," TRPA Aquatic Invasive Species Program Manager and incident team co-lead Dennis Zabaglo said in the statement. "The incident team and our partners are dedicated to protecting Lake Tahoe and will be working together to evaluate options for responding to this new finding."

In the meantime, every boater, paddler, and angler on the lake is being urged to "Clean, Drain, and Dry" any equipment or boats brought into the water, and to avoid using live bait when fishing.

"Strict protocols reduce the risk posed by watercraft of spreading these species by requiring every vessel to be decontaminated that is known to have been in water associated with New Zealand mud snails or other AIS [aquatic invasive species]," the statement reads.

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