Southwest Environment

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Invasive quaggas ‘musseling’ in on Arizona territory

By Colleen Svancara
sign posted about mussel laws

Photo by Colleen Svancara
A sign posted at Arizona’s Lake Pleasant reminds boaters about the laws regarding mussels.

On a wintery morning in January of 2007, a group of locals were diving in Lake Mead on the border of Arizona and Nevada.  They found small seashell-like organisms blanketing the bottom of the lake. When biologists with the Arizona Game and Fish Department followed up, they recognized them as quagga mussels – a species that had never before been seen in the Southwest. 

Unfortunately, the species, Dreissena bugensis, is invasive and potentially damaging. Mussels can interfere with local wildlife, fishermen, recreational boaters and even canal pumps.

Quagga mussels are a type of soft-bodied mollusk originally from the Black and Caspian seas of Europe.  Researchers believe the mussels reached the U.S. in the 1980s, when they were discovered in the Great Lakes.  Most likely the quagga mussel, and its cousin the zebra mussel, crossed the Atlantic in the ballast water of a cargo ship.  Officials can only speculate as to how the mussels made the jump to the Southwest. See related story.

Now the mussels are causing serious problems for the Southwest’s network of canals, rivers and lakes, explained Tom McMahon, invasive species coordinator for the Arizona Game and Fish Department.  He said large populations are already established in several lakes – Pleasant, Mead, Mohave, and Havasu – and are creating problems for local wildlife and fishing resources.  In addition, mussels have become a nuisance to boaters because they cling to watercraft, reproduce, and colonize on top of one another in concentrations up to 5 inches thick.

Ironically, some of the problems stem from their incessant cleaning of the water. Because they are filter feeders, the mussels make the water significantly clearer simply by feeding.  While clearing up the water sounds positive, “most of the things they’re taking out are nutrients, phytoplankton and zooplankton,” McMahon said, noting that the latter two form the base of the local food chain. 

As the mussels change the clarity of water, more sunlight can penetrate down to bottom-dwelling plant life.  The bottoms of these Arizona lakes are ending up with plush forests of aquatic vegetation, such as the kelp-like algae Cladophora.  This increased plant growth results in more plant death.  As the algae die, they float to the surface in long clumps of weeds.  This decaying biotic material becomes a breeding ground for bacteria, fungi and possible disease that can climb up the food chain and affect fish and birds.

In April of 2009, Game and Fish issued an advisory that cautioned against the consumption of large amounts of channel catfish and largemouth bass and in Lake Pleasant and Lake Roosevelt.  The concentration of contaminants in an organism increases as it gets passed up the food chain. When quagga mussels feed, they filter the water column, a process that allows toxins to “bioaccumulate” in their soft bodies.  Lakes Pleasant and Roosevelt had high levels of mercury, which was bioaccumulating in top predators, such as the catfish and bass.  Game and Fish therefore recommended against heavy consumption of these fish because of high mercury levels in their flesh.  quagga nd zebra mussels

Photo courtesy of U.S. Geological Survey
Quagga mussels (bottom) tend to be slightly larger than zebra mussels (top).

So far, the mussels have only impacted sport fishermen and recreational boaters to the extent of cautioned fish consumption and mandated boat maintenance.

Large yellow signs on the shore of Lake Pleasant remind boaters of the protocols they are now required by law to follow.  McMahon, as well as other Game and Fish representatives, urges recreational boaters to follow these three steps – “clean, drain, and dry” their boats. Beyond being good for boat maintenance, the procedure is meant to prevent the spread of the mussels.

“These guys aren’t just walking out of the lakes and crawling over to Bartlett” and other neighboring lakes, McMahon said. “People are moving them.” 

The species likely “hitchhiked” to the Southwest as early as 2004. Most likely they were attached inside or fixed to the side of a boat being moved from the Great Lakes area to Lake Mead, McMahon said.

To prevent further spreading, officials are asking people who use Arizona lakes to let their boats dry for five days before dropping them into another lake. Mussels can survive out of water for several days. The public has been receptive to these procedures, McMahon said.

In addition to affecting boaters, the shells of the mussels can damage public and private machinery, and pipes that transport water across Arizona.

The Central Arizona Project has faced challenges posed by the quaggas.  The CAP pumps about 489 billion gallons of water a year from reservoirs holding Colorado River water.  It delivers water to city-dwellers in the Phoenix area and Tucson, as well as farmers and tribal lands.

The CAP has been closely monitoring the quagga mussels since they were discovered in 2007. Officials observed this population surviving in significantly higher water temperatures than the quagga mussels in the chilly Great Lakes.  Albert Graves, senior maintenance engineer of civil works for CAP, noted they seem be adapting to the hotter Southwest.

“Since they reproduce so fast and they have multiple generations in a year, they can evolve fairly quickly,” added Graves.  One mussel can lay up to 1 million eggs a year, explained Renata Claudi, a mussel expert who is doing research on them for the CAP.   “We just do not know how they are going to [further] evolve,” Graves said.

To date, only one pump out of the total 14 included in the CAP network has had serious problems due to high populations of mussels.  The Mark Wilmer Pumping Plant at Lake Havasu has had to shut down a few times in summer when weeds made abundant by quagga presence clogged up intake canals,  Graves said. He added that the public’s water delivery has yet to be affected.  bulldozer dredges algae from Lake Havasu

Photo courtesy of Albert Graves
A bulldozer dredges the kelp-like algae Cladophora out of Lake Havasu. The algae expand once mussels clear the water.

In the next couple years, he said, a more serious problem will be blue-green algae that have appeared. Graves worries that the Southwest is destined for similar disease outbreak among native fish and bird species as the Great Lakes, but at much a faster rate. (See related article by Colleen Svancara.)

Graves said he expects to see an accelerated development of the situation because of the multiple spawning seasons of the mussel in the warmer Southwest.

The CAP, Arizona Game and Fish Department, and the U.S Bureau of Reclamation are all working to find the best solution to address the quagga invasion.  McMahon noted that the quantity of human labor and destructive chemicals needed to completely eradicate the population would be unacceptable. What’s more, hundreds of thousands of empty shells would be left to litter the lake bottoms.

“If we were able to eat these things, or make biofuel out of them, then we wouldn’t have a problem,” McMahon added.

Graves commented that the Bureau of Reclamation is currently funding Marrone Bio Innovations to create “Zequanox” bacteria that could wipe out any quagga mussel populations that affect pumps.  The bureau is testing to see if the inert bacteria could exterminate the mussels by ingestion, without being harmful to people.  The bacteria have been tested in closed waters, and bureau scientists hope to begin open-water testing in the near future.  

“What we saw [transpire] since 2007, is probably what the Great Lakes saw in 10 years,” Graves said, “We are on the path the Great Lakes took.  We just don’t know how quickly that’s going to happen and we don’t how that may change with a different environment.”

Colleen Svancara is a sophomore planning to major in conservation biology. She was born and raised in Tucson, Arizona.


Arizona Game and Fish Department on aquatic invasive species

U.S. Fish and Wildlife site on mussels

U.S. Geological Survey Nonindigenous Aquatic Species

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