Invasive zebra mussels found in aquarium moss products (some in Kalamazoo) prompt national response

Attractive little balls of moss that have long been popular additions to home aquariums are the subject of a nationwide search-and-destroy response due to the danger they pose to U.S. waterways, including those in Michigan.

Some Morimo moss balls have been found to be harboring a scourge of lakes and streams — invasive zebra mussels.

If you keep one that does, you’ll be violating the state’s invasive species law, and subject to a hefty fine.

Moss: An invasive zebra mussel in a moss ball.Getting rid of it by carelessly dumping the moss or water from its tank? That could be a felony, authorities warn.

“Until we know the extent of the moss ball contamination problem, we are recommending that recently purchased moss balls be destroyed, the water decontaminated, and tanks disinfected,” says Lucas R. Nathan, aquatic invasive species coordinator with the Michigan Department of Natural Resources Fisheries Division. “We are also encouraging suspected zebra mussel contamination be reported so that we can improve our understanding of this issue.”

Nationwide alarm sounded

Marimo moss is a form of algae from Northern Europe and Asia, and the balls are a popular aquarium plant used to generate oxygen and remove nitrates from tanks, often those housing betta fish.

Authorities say they were targeted as troublemakers after a concerning report made to the Nonindigenous Aquatic Species hotline.

An alert Petco employee in Seattle had discovered some moss balls — from an imported shipment marked “certified pest-free” — actually were infested with the mussels.

Within 24 hours, aquatic invasive species program staff from several states confirmed finding zebra mussels in supplies of moss balls distributed as Mini Marimo Moss Balls (SKU 5292944) and Marimo Moss Balls (SKU 5164031) at local Petco and PetSmart stores.

Two days later, March 5, the Michigan Department of Natural Resources notified more than 3,000 aquatic pet and plant suppliers and hobbyists of the potential infestation and required them to dispose of any infested stock. 

While the corporate stores were working to quarantine stock in compliance with an order from Petco headquarters, inspectors began finding contaminated stock on the shelves of independent stores and in-store aquarium systems. The Michigan Department of Natural Resources Law Enforcement Division confirmed that infested moss balls have been found in several stores throughout the state.

Now conservation officers are visiting retailers to help identify and dispose of contaminated materials. Suppliers and hobbyists are also getting the word out on their websites and to social media groups.

A tiny, very big deal

Why so much fuss over a glob of moss the size of a large jawbreaker?

The zebra mussels (Dreissena polymorpha) potentially hitchhiking inside might not cause a problem in a homeowner’s fishbowl, but their kind has already had a devastating impact on Michigan’s inland lakes and the Great Lakes as well.
In the 35 years since their first discovery in Lake St. Clair, invasions of the tiny mussels have exploded.

Their clusters clog water intake structures of water treatment and power plants and cost millions of dollars annually to remedy. Masses of mussels on boat hulls interfere with steering and motors.

By out-competing native species for food, or killing them outright, invasive mussels are creating food deserts for fisheries in the open water of Lake Michigan.

They've been cited for contributing to avian botulism outbreaks due to increased Cladophora growth in Sleeping Bear Dunes and for playing a role in the harmful algal blooms in Lake Erie. 
‘If they invade new waters, it’s just a matter of time until that ecosystem is changed forever.’ — Tony Gibson, Allegan 
And ask any swimmer or angler — beaches encrusted with mussel shells are misery on bare feet.

Val Gent, senior communications specialist for Entergy Corporation’s Palisades Power Plant near South Haven, would not disclose the cost of zebra mussels to Palisades, calling the information “business-sensitive information.”

Gent would confirm that for about 20 years, the plant has  “conducted routine, annual treatments of its plant piping to eliminate zebra mussels.”

Multiply that headache by the dozens of other mussel-related costs, and it’s easy to see why going to great lengths to keep them out of new waters is important.
“We’ve had (zebra mussels) here for about four decades, so that horse is out of the barn, so to speak,” says Cpl. Nick Torsky of the MDNR Law Enforcement Division

Great Lakes Enforcement Unit. “But we do have many inland water bodies that are still dreissenid-free, and we’re working to maintain those. 

“In addition, there are many regions of the country where authorities are fighting desperately to keep invasive mussels out —  and we’re doing our best to support those efforts,” Torsky says.

Vincent Denef, associate professor in the University of Michigan’s Department of Ecology and Evolutionary Biology agrees that “any potential way that zebra mussels can spread further should be controlled as much as we can. 

Tony Gibson describes his tank: Planted 20g aquascape tank is a no filter, no aerator, no fertilizer, no nothing tank, going on 18 weeks of no maintenance, water is super clear, parameters are always awesome, and everything in the tank is thriving. “Mussels seem innocuous when you hold a single one of them in your hands,” Denef says, “but once you take a look underwater, and see the bottom of Lake Michigan covered by mussels, you start realizing they may be a problem.”

Waterways, not aquariums, are the worry

How, though, do infested moss in an aquarium come to threaten lakes or streams miles away?

“You never know where fish bowls and aquariums can end up or how these things move around,” Torsky says.

Discoveries of goldfish and other aquarium species in Michigan waters indicate that aquarium dumping – disposing of unwanted pets and plants into natural waterways – is still occurring in the state, authorities say.

“If allowed to grow up in an aquarium, the mussels could potentially reproduce, which produces microscopic larvae that float in the water,” says Ashley K. Elgin, Ph.D., a research ecologist at the National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory field station in Muskegon. “These tiny larvae, called veligers, are one of the reasons why zebra mussels are so effective at dispersing to new locations.”

Her colleague, Rochelle Sturtevant, Ph.D., program manager for the GLANSIS project, Michigan Sea Grant, Michigan State University, says the potential for the presence of microscopic mussel larvae means that all water coming from a tank containing a contaminated Marimo ball is a potential source of a new invasion.

“Every time an owner keeping a potentially contaminated Marimo ball changes water or cleans a tank, the water from that tank needs to be decontaminated (boiled or bleached) before being dumped,”  Sturtevant says. “Materials used to clean the tank (sponges, scrub brushes, etc.) can also be contaminated with microscopic larvae and would need to be decontaminated before cleaning another tank.”

Sturtevant has an additional concern.

“Close examination of these Marimo balls is revealing other small hitchhikers as well — oligochaetes and ostracods of as yet unidentified species have also been found,” she says. “The risk these additional species pose is not yet known, but as they are coming from environments that support zebra mussels, the chance that they could also invade this region is potentially high.  

“I'm more concerned, actually, about those other things that go with them. That, to me, is the scarier part, when you start hitting those kinds of unknowns.”

Elgin says the most important message about invasive species “is that our best line of defense is prevention. This is why it is critical that people be as cautious and proactive as possible with the moss balls so that there is no room for actions that could result in a new introduction.

“Given the impacts that zebra mussels have once introduced to a water body,” she says, “the best thing we can do is prevent any new introductions from happening.”

What’s being done

Michigan Department of Natural Resources Law Enforcement Division confirmed that infested moss balls have been found in several pet stores throughout the state, and a customer service representative at the Petco Hotline says the latest update is that the chain’s entire stock has been quarantined, the sale of moss balls has been postponed, and there are not yet any plans to resume sales.

“The response for Petco/PetSmart and their employees has been great – very cooperative,” Torsky says. “I am unaware of mussels having been found at any retailers outside of Petco, PetSmart, and Meijer,” Torsky says. “I can confirm that they have been found in Kalamazoo, Traverse City, Marquette, Sault Ste. Marie, Gaylord, and the Bay City area.”

Depending on the retailer, a full refund may be available. For instance, PetCo is offering a free refund for any moss balls purchased in the last 30 days.
As the effort to track down infested stock continues nationally, reports indicate that other brands, including Betta Buddies and Shrimp Buddies products, also may contain the invasive mussels, authorities say, and potentially infested products have been sold online as well.

What should consumers do?

Tony Gibson of Allegan is an individual happy to do his part to prevent the spread of zebra mussels.

“I have scars up and down my legs and both feet from stepping on them fly fishing as a kid, before waders were a thing,” says Gibson, who runs an aquatic animal and plant rescue, rehabilitation, and rehoming service.

He maintains many tanks in various set-ups with koi as big as two feet, lots and lots of goldfish, some native Michigan sunfish, guppies, snails, plecos, shrimps — you name it.

But no moss balls. 

That’s by design. 

Gibson says he typically avoids plants and decor that are dense and thick enough to harbor invasives. “I quarantine any plants that I do grow for weeks before introduction to my tanks,” he says. 

Zebra mussels are especially nasty hitchhikers.

“They proliferate extremely quickly,” Gibson says. “They can tolerate a plethora of water conditions, and have very few natural predators. I have not personally came across this issue, yet, but if I did, I would 'nuke' the whole quarantine tank, and everything in it. I want ZERO possibility of spreading anything.” 

That is exactly what authorities advise:

• If zebra mussels are found on any moss balls in containers or in aquariums, infested moss balls and packaging should be frozen for 24 hours, boiled for one full minute, or submerged in bleach or vinegar for 20 minutes before double-bagging, sealing and disposing of them in the trash.

• The DNR recommends that tank water from aquariums holding infested moss balls be decontaminated by removing plants and pets, adding 1/10 cup bleach to every gallon of water, and allowing at least 10 minutes of contact time before draining.

• All discoveries of zebra mussels in moss balls must be reported to the state. 
Reports should be made to Lucas Nathan, DNR aquatic invasive species coordinator, at 

Doing nothing is not a legal option

Zebra mussels are listed as restricted under Michigan's Natural Resources Environmental Protection Act (Part 413 of Act 451). This means that it is unlawful to possess, introduce, import, sell or offer that species for sale as a live organism, except under certain circumstances, Torsky says. They should be destroyed if found, and it’s important that any disposal of aquatic species is done in a manner that will not cause accidental or unwanted introductions of these or any other species.

Penalties for possession of a prohibited or restricted species begin with a civil fine of up to $5,000. Knowingly or intentionally releasing a species that can be harmful can reach felony status, he says.

“We are still gathering information on the nationwide scope of this issue, so it’s unknown if this contamination is limited to certain 'batches' or 'lots,'” Torsky says. “We are not, at this point, recommending that all moss balls be discarded.  Aquarium owners should always be vigilant of potential unwanted pests and invasive hitchhikers making their way into tanks by any means. Since certain life stages can be difficult to detect with the naked eye, periodic inspections are recommended.”

Although zebra mussel contamination in moss balls is relatively new, the sale of live organisms is a well-known pathway for invasive species introductions. 

“For this reason, we work closely with state and regional partners, retail shop owners, and distributors to minimize the risk of invasive species being transported and sold,” Nathan says. “As of 2019, sellers of non-native aquatic species in Michigan are required to register and report their sales on an annual basis. We use that information to track species that have the potential to negatively impact Michigan’s aquatic resources.”

To learn more 

— The USGS invasive species database keeps track of observations of zebra and quagga mussels lakes across the country here.  

— Michigan’s Reduce Invasive Pet and Plant Escapes (RIPPLE) program provides guidance for sellers and consumers on preventing aquatic invasive species introduction and spread here.

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Read more articles by Rosemary Parker.

Rosemary Parker has worked as a writer and editor for more than 40 years, most of that time in Southwest Michigan.