The New Zealand mudsnail. Photo: Montana State University
Mudsnails next to a dime for size comparison. Image: CA Fish and Game
Locations in the Malibu Creek Watershed where the New Zealand mudsnail has been found. Image: Heal the Bay

Recent aquatic invertebrate surveys in the Malibu Creek watershed have confirmed the presence of the New Zealand mudsnail, an insidious exotic invasive species that could potentially wreak havoc on the watershed's native organisms.

Although the mudsnail has been found in numerous waters throughout California's Eastern Sierra, this is the first time it has been confirmed in the Malibu Creek watershed.

Recent surveys conducted Heal the Bay, the Santa Monica Bay Restoration Commission and UCLA graduate students have confirmed the presence of the mudsnail at 16 of 45 locations throughout the watershed. In particular, the mudsnail has been found in the following locations: Medea Creek (Stream Team Chemistry Site 7), Las Virgenes Creek (upstream of Stream Team Chemistry Site 5 and Site 12), Malibu Creek (near Stream Team Chemistry Site 1), Lindero Canyon Creek (no Stream Team sampling), and the Medea Creek outlet into Malibou Lake (Stream Team Chemistry Site 21).

In addition, samples from 4 locations in the Malibu Creek and Topanga Creek watersheds have been sent to Washington State University for DNA confirmation.

A Potentially Dangerous Invader
New Zealand mudsnail, scientifically known as Potamopyrgus atipodarum, is approximately 1/8 of an inch (5 millimeters) in length, but can be even smaller in size. mudsnails spread by attaching themselves to waders, fishing gear, shoes, equipment, animals, and boats — easily "hitchhiking" to other locations. These invaders grow in large quantities and densities up to 500,000 organisms per square yard. To make matters worse, the New Zealand mudsnail is asexual which means only one is necessary for reproduction.

The presence of the mudsnail in the Malibu Creek watershed is alarming and of grave concern. Because of their massive density and quantity, the New Zealand mudsnail can out-compete and reduce the number of native aquatic invertebrates that the watershed's fish and amphibians rely on for food. This reduction in aquatic invertebrate food supply can disrupt the entire food web with drastic consequences.

In fact, impacts of the New Zealand mudsnail's presence in the watershed are already being seen: in reviewing the aquatic invertebrate survey data, never has the Stream Team seen so few native organisms in any bug sample. More studies are needed to determine the ultimate impact that the snail will have on the wildlife in the Malibu Creek watershed.

Stream Team Water Chemistry Testing Suspended
Due to their small size and the fact that the snails can live out of the water on moist or damp equipment for as long as a month, the Heal the Bay Stream Team voluntarily suspended all monitoring activities until further notice.

Although June 2006 was the first month since November of 1998 that the Stream Team will not be testing the water in the Malibu Creek Watershed, the additional water chemistry information is not worth the risk of potentially spreading the mudsnail further throughout the watershed.

Additionally, Heal the Bay successfully called on the Santa Monica Bay Restoration Commission which held an emergency snail summit on June 20th where experts from throughout the state attended.

Initial Survey Completed - September 2006
Conducted by the Santa Monica Bay Restoration Commission and Heal the Bay, a "snail survey" team visited 44 sites during the summer of 2006 in the Santa Monica Mountains, monitoring for the presence of New Zealand Mudsnails.

The survey confirmed that while the New Zealand mudsnail has established itself in three streams within the Malibu Creek watershed, many of the watershed's streams are not yet infested.

The survey also found no evidence to indicate they have spread to other Santa Monica Mountain watersheds at the time of the report's release (Sep 2006).