How nature itself could help quash the quagga mussel invasion on the Colorado River

For the past 15 years, federal agencies have tried to subdue growing populations of quagga mussels, an invasive species that interferes with water infrastructure and threatens ecosystems. Crews tried scrubbing the mollusks off equipment, power washing them off boats and deploying chlorine and UV lights to prevent them from settling in pipes.

But the tiny mussels have not only resisted all deterrents, they’ve clogged cooling equipment, reduced water flow to hydropower and even changed the water quality, making it less suitable for native species.

So far, the best solutions have been too expensive and complicated to treat large, open bodies of water. Chlorine treatments can damage the hydropower infrastructure. Pesticides can harm non-target species. And manually scraping is not feasible in those vast, open waters.

To control them in a significant way, federal managers hope nature will lend a hand and plan to try natural control methods that, like predators on a landscape, are always at work and spread naturally.

The U.S. Bureau of Reclamation is taking the lead, funding a slew of new research projects that agency officials hope will give them an edge in managing the freshwater mussel.

Reclamation staff say this technology will be essential if they are to effectively manage quagga mussels in a safe, cost-effective way. If they don’t find a self-spreading solution, open water control will be impossible. And management inside hydroelectric infrastructure will continue to cost the agency millions of dollars.

"We are doing many different research projects because this is a really tough topic," said Sherri Pucherelli, a biologist with the bureau. "And so honestly, anything that shows promise will be wonderful."

Finding replacements for bleach and chlorine

Quagga mussels are about the size of an adult human thumb, making them hard to detect early on. Researchers have documented up to 100,000 per square meter in the Great Lakes, an area the species colonized over four decades ago.

Biologists think boaters from the Great Lakes region unwittingly brought the mussels to Arizona when the tiny mollusks hitched a ride on the bottom or inner structure of a boat. The National Park Service, which manages the lakes created by Reclamation's dams, has mounted an aggressive education campaign that now requires boaters to clean and dry their boats.

But this strategy only prevents expansion. At this point, the mussels are well established in Arizona, with trillions found throughout Lake Powell, Lake Mead, Lake Mohave, Lake Havasu and Lake Pleasant. The sheer size of the population and vast areas they occupy make control difficult.

In a large body of water, pesticides and chemicals, a traditional control source, are unfeasible. They cost too much to deploy and require a lot of people to do the work, which requires time and effort.

This dilemma has led to the need to explore other treatment options. Since 2007, Reclamation has used its science and technology program to explore control methods for invasive mussels. The office is an extension of the agency's research and development office and its main purpose is to explore new and emerging technologies.

This year alone, the agency has dedicated almost $5 million to new research projects and another $3.5 million to 134 existing projects. Many of them are long-term projects that will take several years to come to fruition, if they ever do.

The transition to studying biocontrol methods signals a shift away from the more physical or chemical aspect of control to one that will allow the agency to let nature do the work. Officials hope at least some of the projects will allow them to mitigate the cost of treating quagga mussel populations while also reducing their numbers in an environmentally safe way.

To help the agency fine-tune its research, Yale Passamaneck, a biologist with the bureau, has been sequencing the genome of quagga mussels since 2015.

"I think there are a lot of different approaches that we could go after," said Pasamaneck. "The genome will just help us find what those mechanisms are, what the pathways to them are, and hopefully bring to light things that we would never have thought of before as we start to understand it."

There are several ways his research could help Reclamation keep quagga mussel populations under control. The projects span an array of potential solutions, from figuring out a way to weaken the mussels' appendages that allow them to attach to surfaces to using parasites to kill them.

Tapping into the mussel genome

Recent advances in science have reshaped how scientists study genes. CRISPR, a sequence of DNA, and Cas9, a naturally occurring protein, have allowed researchers to make breakthroughs in gene editing.

The discovery has opened new frontiers in how scientists hope to treat illnesses like cancer and hereditary diseases like sickle cell anemia. Since both compounds stem from nature, they can be applied to humans, animals and plants.

To truly take advantage of the potential for gene editing, the genome must first be sequenced, something that has not happened with the quagga mussel. But that's changing with funding from the Bureau of Reclamation.

Since joining the bureau, Passamaneck, the biologist, has led a project to uncover what lies beneath quagga DNA. As someone who studies marine invertebrates, Passamaneck is used to projects that deal with less-studied species. Before his work at the agency, one of his projects looked at a species last studied in 1956. His work with molecular biology and genomics at Reclamation could change how the agency manages mussels in the future.

"It's basically a resource that allows us to ask ... what genes does this organism have? How are they used? How might we then use those genes to help control the species itself?" said Passamaneck.

Sequencing the quagga genome would allow the agency "to better understand the general biology of this organism, which will help us understand what kind of controls would be worth pursuing and how we would implement them," he said.

Using the genome to control species are already showing promise. Last year, researchers at the University of California, Santa Barbara, studied a control method that resulted from sequencing the mosquito genome. In the project, male mosquitoes were rendered sterile, leading to infertility. The researchers continued their research to look at how females could also be neutered.

Passamaneck said researchers don't know how quagga mussels determine which become males or females, which is a problem he hopes to address with the project. Their sex could be determined by DNA inherited from their parents, or it could be temperature-related, like turtles and crocodiles.

Another tool could produce a completely novel way to control them.

"The folks who have worked on the zebra mussel genome at the University of Minnesota have been looking at using functional genes that are involved in the function of the organism. For example, the genes that are involved in the byssus, the little threads that attach it to substrates," said Passamaneck.

"Their idea is that if you go after something like that or the genes that are involved in shell formation, then you can target those things as a way to keep the animal from attaching and growing or growing a shell."

In theory, researchers could target the genes that create the appendages that allow the mussels to attach to surfaces and then weaken them by either starving them of nutrients or blocking their growth. This would then rob the mussels of their ability to settle and feed, leading to starvation.

Such solutions a long way from completion. Researchers need to collect and understand the entire genome first. At this point, they've only amassed brief snippets.

"The problem is analogous to having a book written in a foreign language but lacking a dictionary with which to translate and decipher it," said Passamaneck.

Infecting with a natural cancer

In 2018, Reclamation ran a competition that sought to find ideas with the potential to treat quagga mussel populations in large bodies of water. Steve Suhr and Marie-Claude Senut, from Lansing, Michigan, won. They heard about the contest through InnoCentive, a crowdsourcing company that allows organizations to put forward questions for researchers to answer.

For the past 20 years, Suhr and Senut have worked on various projects by studying cell biology at institutions around the county. Through this work, they've worked on a range of projects that studied everything from fruit flies to sheep to research into treatments for diseases like Alzheimer's and Huntington's diseases.

Their proposal focused on using disseminated neoplasia, a tumor that infects the hemolymph system, a type of artery system in some invertebrates, to kill large populations of quagga mussels. Biologists believe this cancer is one of the most lethal diseases among bivalve mollusks like quagga mussels.

In the last seven years, Suhr and Senut have set up a lab, called Biomilab, to conduct their work. They've tested various methods of injecting mussels with disseminated neoplasia in a culture. And they're exploring ways to deliver these cells to live mussels to act as a toxicant. Passamaneck's work has helped them identify targeted genes that would make the mussels more susceptible to the tumor.

"We're going to try to mimic the natural neoplasia that's found in marine mussels," said Suhr. “The idea is that we will engineer a defect into the same cell-cycle control genes found in marine mussel disease to produce a virtually identical type of cancer that will specifically target invasive quagga and zebra mussels.”

The challenge, say the researchers, is that to do this, the cells produced from quagga and zebra mussels have to survive and grow in culture long enough for the genetic modifications to be performed.  Thus far, the researchers have kept cells alive in a dish for weeks or even months, but they're only now seeing progress in coaxing the cells to divide.

One key to making this work, said Suhr, is finding a way to compromise the function of a specific gene called p53. This gene is considered a master regulator of the cell cycle and without it, cells are transformed and immortalized into the continually-dividing cells common to all cancers.

When the researchers are able to scale molecular hurdles involving cell cycle regulation and knock-out genes such as p53, they will be able to proceed with testing the effectiveness of the control agent in a larger setting.

"Once the neoplasia is produced and amplified in cell culture, the next step is to then test it on individual mussels and small mussel colonies in the laboratory," said Suhr.

"We can determine if it can be added directly into the water, or if we need to infect a mussel by direct injection and then introduce that mussel into a colony with other mussels. Then we simply wait and watch, Suhr said. "Does the neoplasia spread from animal to animal over time and is it toxic?”

Deploying parasites

Research into a naturally occurring parasite that could kill quagga and zebra mussels has been ongoing since at least the early 1990s, when the New York State Museum Field Research Laboratory started looking into a natural way to control zebra mussels. As in the Southwest today, the mussels posed a major problem to hydroelectric power plant pipes.

The work of Dr. Dan Molloy, a biologist at the museum, led to the discovery of Zequanox, a derivative of Pseudomonas fluorescent, which is a naturally occurring bacteria in soil. The biopesticide is the first environmentally safe molluscicide to use inside power plants.

In 2009, Marrone Bio Innovations, a pest management firm, began working with Reclamation to study the efficacy of Zequanox in its hydropower facilities. And in 2011, the Environmental Protection Agency registered Zequanox as a pesticide. Its process is simple: Quagga mussels ingest the material when it's released into the water and it kills them from the inside.

Further research suggested that compared to its safety and effectiveness in cleaning mussels out of power plant pipes (the purpose Molloy had invented the product for), the treatment was relatively ineffective and impractical in open waters, as the concentrations that were added to plots of water quickly dissipated with the current.

Continued research suggests that the large amounts that would be needed to adequately treat water bodies leave some researchers concerned that the use of Zequanox could threaten other species by changing water quality.

And to use Zequanox in cooling pipes, MBI estimated that it could cost the Reclamation up to half a million dollars to treat just the systems at Hoover Dam. With costs so high and treatment less effective than they'd hoped for, Reclamation was back at square one.

Enter Molloy: Since 2011, Molloy & Associates has operated as a consulting firm that researches environmentally safe ways to control invasive mussels worldwide. So in 2017, when Reclamation was looking to launch a project to find a naturally occurring lethal parasite, the agency reached out to him with a proposal.

"I'd say right now, as we speak, we have just incredible groundwork that we've done in terms of the capacity of this joint project with Reclamation to find a hypervirulent parasite," said Molloy. It takes an established lab to transmit an infection from one cousin species to another, he added.

In the last five years, Molloy has set up a lab with 72 aquariums across Europe and Asia, closer to the zebra and quagga mussels' native range, hoping to find and rear a parasite that might prove fatal. Mussels from Turkey, Bulgaria, and Montenegro are all being examined. His team has dissected over 5,000 mussels and identified a dozen parasites from cousin mussels. None has yet demonstrated the ability to kill quagga mussels.

However, his research team has successfully infected zebra mussels with parasites from these cousin mussels in lab and field trials, proving that the technique is possible. The challenge now is to find one that is lethal.

Reclamation recently awarded Molloy's firm a new three-year contract to continue his work. In the next few years, he hopes to identify a lethal parasite, work with regulating organizations, and conduct safety trials to ensure they don't affect non-target species, an essential requirement of their research plan.

"We're really on the launching pad to intensively examine if these cousins, the parasites of the cousins, can be so novel that the naive zebra and quagga mussels, which haven't seen these parasites in millennia, if not millions of years, are infected and either sterilized or killed," says Molloy.

Effective and environmentally safe solutions sought

While most of these research areas are far from ready to deploy, there is a consensus among Reclamation staff that natural solutions will have to come into play for control to be effective. Other potential solutions researchers and partners are looking into include injecting quagga mussel food sources with an immunotoxin and infusing carbon dioxide into water pipes and other water infrastructure.

"Zebra and quagga mussels love to eat algae, and especially microalgae," says John Higley, CEO and founder of Environmental Quality Operations, an organization that Reclamation has collaborated with. "And so if you just grow up this toxin in that microalgae, and then you kill off the microalgae, you're not adding anything alive to the system. Now you've got a really environmentally friendly way to target zebra and quagga mussels only."

The transition to biocontrol marks a new era in how the agency hopes to reduce mussel populations, but it's just the beginning. These projects still have years' worth of research to do, including ensuring that the methods only affect quagga and zebra mussels. Many native invertebrates, such as pea clams, are currently threatened, and the agency will want to remove any potential threats to their survival.

Once officials have guaranteed the methods are safe, the agency will also have to clear a series of regulatory hurdles and work with communities and industry groups that rely on the water. Biocontrol naturally raises ethical questions around population control that the agency will want to figure out.

Sherri Pucherelli, a bureau biologist, emphasizes that one of their top priorities, in addition to finding a lethal control method, is finding one that is safe. So far, everything is a potential solution.

"I would say we are doing many different research projects because this is a really tough topic. And so, honestly, anything that shows promise will be wonderful. There are different situations that we could potentially use each of these control methods in," said Pucherelli.

"Obviously, the projects that have methods that are safe for the environment are most important for us and very species-specific and cost-effective. Because right now, what is available is not effective for treating a large water body."

Lindsey Botts is an environmental reporter for The Arizona Republic/azcentral. Follow his reporting on Twitter at @lkbotts and Lkbotts on Instagram. Tell him about stories at lindsey.botts@azcentral.com

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.

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This article originally appeared on Arizona Republic: Feds try to slow quagga mussel spread using science and nature