A team of UC Davis scientists has discovered a way to eliminate an invasive clam species that posed a threat to the original water chemistry of Lake Tahoe.
Marion Wittmann, part of the UC Davis Tahoe Environmental Research Center, specified the clams posed a bigger threat than just altering the water quality. They have affected many dimensions of the lake.
“Asian clam have never been eradicated or removed from any freshwater system,” Wittmann said in an e-mail interview. “Asian clam are also capable of rapid reproduction, high rates of feeding, and high rates of survivability in adverse conditions.
“Because of this, it is likely that their populations will become greater than any native invertebrate in Lake Tahoe, and they will out-compete these native species for resources.”
Wittmann added that if the problem were to go unsolved, many aspects of Lake Tahoe’s ecosystem would be harmed.
“Over time, Lake Tahoe’s bottom may become a monoculture of clams,” Wittmann said. “This will impact food web dynamics, fisheries and water quality.”
Scientists recently discovered that the best way to deal with the situation and strive to eliminate the species is through a process involving “bottom barriers.” The team will lay these sheets of rubber tarp on top of clam beds to reduce the amount of oxygen available to the clams; eventually the clams will receive no oxygen and die.
“Within 24 hours they start running out of oxygen, and within four weeks we have found that we can kill almost all the clams underneath the barrier,” said Geoff Schladow, director of the Tahoe Environmental Research Center. “They are buried into the sediment about eight inches, and during that four-week period they all come to the surface as the oxygen depletes, and die,”
This process has so far been effective; however it poses an unwanted threat to the non-invasive clams.
“The native species are found to die too, but these species seem to be able to survive a little better in the absence of oxygen,” Schladow said. “We are hopeful that we can find a process to just kill the invasive clams.”
Researchers have expressed concern over the preservation of the native clams. They believe that all native species are vital to the lake’s natural habitat.
“These clams interrupt the food chain in the lake by consuming food sources native species depend on,” said Dennis Oliver, public information officer at the Tahoe Regional Planning Agency. “The clams also excrete large quantities of nutrients, resulting in concentrations high enough to encourage algal blooms.”
Oliver believes that the invasive clams were first introduced by fishers, who used the clams as bait.
Scientists have been surprised by the way the clams thrive so effectively. While the clams are currently seen in areas with a depth of three to 30 feet, some research indicates an entire patch in an area of 200 feet below.
“Asian clam feed on phytoplankton (floating algae) and algae that is found on surrounding sediments,” Wittmann said. “They are voracious feeders, and can out-compete native species for food resources.”
This feeding strategy allows the clams to have a comparative advantage, but it is also detrimental to Lake Tahoe. It lucidly destroys its appearance and alters its chemistry.
“[The clams] then excrete increased levels of nitrogen and phosphorus. This stimulates the growth of filamentous green algal species, like cladophera or zygnema, which makes the near-shore of Lake Tahoe’s water look very green,” Oliver said.
“The new method has thus far seemed effective,” he said. “With continued effort by the TRPA and UC Davis researchers the clams will be eradicated.”
SADAF MOGHIMI can be reached at campus@theaggie.org.
