Looks like the 100th Meridian Initiative, whose main goal is to keep zebra mussels (Dreissena polymorpha) from spreading into the western USA, might need to rename themselves to, say, the "120th Meridian Initiative." An NAS Alert came out this week reporting that
zebra Quagga mussels have been found in Lake Mead, Nevada. Even worse, those specimens turned out to be just a few of thousands living in the lake, meaning that they came from an established population. All the more depressing considering this report (.pdf) prepared for the Initiative back in 2004, which concluded that the risk of zebra mussel establishment was low because 1) so many boaters clean their equipment and 2) few boaters come to Lake Mead from areas where zebra mussels are already found. The mussels have already been intercepted several times over the past few years on boats that were on their way to Lake Mead.
This raises some interesting questions about the root of the invasion. Were
zebra Quagga mussels already in Lake Mead when that report came out? Are existing methods to clean boats not sufficient to prevent the introduction of adult zebra and Quagga mussels and their veligers? Could other vectors besides boaters be responsible (the risk assessment does not mention divers, for example)? The 100th Meridian Initiative has put up a web page where they've been actively posting updates on the story - if any new information becomes available I will update this post.
Update 01/12/2007:Turns out the mussels in question were misidentified - a lab investigation has classified them as the related Quagga mussel (Dreissena rostriformis bugensis). Perhaps more of a surprise since the known distribution of Quaggas in North America is much smaller than that of their congeners. The updated NAS Alert is here.
Update 1/26/07: More Quaggas found nearby in California and Arizona.