Zebra mussels are small, striped mollusks that are typically seen as an invasive pest species in most waterways. They spread aggressively, often outcompeting native species and clogging up pipes and other underwater infrastructure. However, despite their destructive tendencies, zebra mussels do provide some benefits in certain contexts.
Quick Answers
Here are some quick answers to common questions about whether zebra mussels have any positive uses:
- Zebra mussels can help clean up polluted water in some cases by filtering out contaminants.
- Their shells can provide habitat for small fish and other aquatic life.
- Scientists use zebra mussels as bioindicators to monitor environmental pollutants in fresh water.
- In some contexts, they may provide food for aquatic animals and birds.
- There is research into using their byssal threads for biomedical adhesives.
- Their shells can potentially be used to make fertilizer or chicken feed supplements.
Zebra Mussels as Biofilters in Polluted Water
One of the main positives of zebra mussels is their ability to filter water. They are voracious filter feeders, sucking in plankton and particulate matter from the surrounding water. Each zebra mussel can filter around 1-4 liters of water per day. In areas with dense zebra mussel populations, they can significantly clean up suspended contaminants and pollutants in the water column.
For example, research in the Hudson River Estuary found that zebra mussels helped remove much of the organic seston pollution, which led to improved oxygen and clarity levels. Other studies in polluted areas like Lake Erie have shown similar water purification benefits from zebra mussel filtration.
However, these benefits are very context dependent. In waterways that are already relatively clean, zebra mussel filtration may have little positive impact. Additionally, their feces and pseudofeces can accumulate on the lake floor, leading to other ecological problems. But in specifically contaminated sites, strategic introduction of zebra mussels could potentially help remediate pollution.
Case Study: Zebra Mussels in the Hudson River Estuary
A multi-year study published in 2008 examined the impacts of zebra mussel filtration on water quality in the Hudson River Estuary near New York City. This area was highly polluted by sewage runoff, with high levels of organic seston pollution and low oxygen.
Researchers found that after zebra mussels became established in the estuary in the 1990s, they significantly reduced organic seston pollution during the summer months. Dissolved oxygen levels also increased and clarity improved dramatically. In this case, the zebra mussels boosted water quality by feeding on excessive organic contaminants.
However, zebra mussels also depleted the plankton, which could negatively impact food webs. And there were concerns their feces and pseudofeces could accumulate on the river floor, causing anoxic conditions. Still, researchers concluded zebra mussels provided a net benefit in filtering this heavily polluted waterway.
Providing Habitat for Fish and Aquatic Life
In addition to filtering water, the physical shells of zebra mussels can also create habitat structure for other aquatic organisms when they colonize an area. Their clusters of shells provide crevices and surfaces for small fish, aquatic invertebrates and biofilm to colonize.
For example, research in Ireland found significantly more macroinvertebrates living in zebra mussel beds compared to bare sediment in a lake basin. The mussel shells offered more complex habitat with higher surface area, increasing biodiversity. Another study in Lake Erie found fish like round gobies congregating around zebra mussel beds, likely using them for shelter, spawning and feeding.
So in locations where zebra mussels establish dense populations, they can sometimes boost biodiversity by providing novel habitat for other organisms. The crevices in their shells offer refuge and surfaces for aquatic life to attach and colonize.
Zebra Mussel Shells Offer Habitat for Aquarium Fish
Within the aquarium hobby, some fishkeepers actually utilize zebra mussel shells as decorations and habitat in freshwater aquariums. The empty shells add naturalistic surfaces for beneficial bacteria to grow as part of the nitrogen cycle.
Fish like cichlids, bettas, killifish and gouramis often enjoy grazing and picking food from the crevices of zebra mussel shells. The shells also provide shelter and surfaces for fish to spawn on. Aquarists typically use sterilized shells to avoid introducing disease.
So within aquarium contexts, zebra mussel shells can be sustainably repurposed as habitat decor. This represents one small beneficial use for their shells, as an alternative to them just going to waste or littering shorelines.
Use as Bioindicators of Freshwater Pollution
Zebra mussels are also utilized as bioindicator species by scientists researching pollution in freshwater ecosystems. Bioindicators are organisms that can be studied to monitor the health of the surrounding environment based on their physiology or community structure.
Zebra mussels are useful bioindicators for a few reasons:
- They are stationary filter feeders unable to move away from pollution.
- They bioaccumulate pollutants in their tissues.
- They are abundant in many waterways.
- Specimens are easy to collect and study.
By sampling zebra mussel tissues from an area, scientists can analyze the levels of heavy metals, PCBs, pesticides and other hazardous chemicals to assess aquatic pollution levels. Comparing contamination in different sized specimens indicates pollution trends over time.
Studies across Europe, North America and elsewhere demonstrate the efficacy of using zebra mussels for biomonitoring. While invasive, their prevalence and immobility make them ideal sentinel species to study freshwater chemical pollution and inform mitigation efforts.
Table 1. Studies Using Zebra Mussels as Bioindicators
| Study | Location | Findings |
|---|---|---|
| Saglam et al. 2013 | Istanbul Strait, Turkey | Zebra mussels showed presence of heavy metal contamination from industrial pollution. |
| Rutzke et al. 2000 | Lake Erie, USA & Canada | Zebra mussels revealed trends of declining PCB contamination after regulations. |
| Mersch et al. 1996 | Rhine River, Netherlands | Zebra mussels mirrored decreases in cadmium, lead and zinc pollution from 1980s-1990s. |
Potential Food Source
In some contexts, zebra mussels may serve as a supplemental food source for certain animals and birds. Diving ducks like scaups, coots, mergansers, and other waterfowl will eat zebra mussels in areas where they are abundant.
Freshwater drum, sturgeon, sunfish and other native fish species may also occasionally feed on zebra mussels. However, most fish have difficulty eating the mature mussels and typically only consume veligers (juvenile mussels) which are small enough to ingest.
While zebra mussels are not a major dietary component for North American wildlife, their prevalence does provide an additional food source in cases when native mussels or other mollusks are not as abundant. This supplemental food could potentially help support higher populations of some aquatic birds and fish.
However, zebra mussels may also reduce food sources in some cases. One study in Lake Huron found diving ducks shifted away from their typical sculpin diet once zebra mussels invaded and became 90% of the ducks’ food source. The ducks’ weights declined after this shift, indicating zebra mussels were a lower quality food option.
So the benefits of zebra mussels as an additional food source depends greatly on context. Their nutritional value and availability as prey needs to align with the needs of predators and fish in the ecosystem. When conditions are right, they can supplement native food sources, but zebra mussels may also displace more optimal prey if they become overly dominant.
Harvesting Zebra Mussels for Food
Given their high densities, some government agencies actually promote harvesting and eating zebra mussels as a form of biocontrol. For example, Minnesota’s DNR encourages people to harvest and consume zebra mussels to help curb their spread. When properly cooked, zebra mussel meat can be safe and palatable to humans.
Some commercial harvesting operations in the U.S. Midwest have also begun collecting and processing zebra mussels to sell their meat for human consumption. While niche, this represents one way to intentionally utilize zebra mussels for food before they die off and rot on beaches.
However, zebra mussels from polluted waters may accumulate toxins and heavy metals that make them unsafe for frequent human consumption. But in clean waters, eating zebra mussels could provide a local, abundant source of protein and minerals.
Research Into Byssal Threads for Adhesives
Scientists are also investigating potential applications for zebra mussel byssal threads – the small fibers they use to securely attach to surfaces underwater. Researchers are interested in these threads as a basis for novel marine adhesives, fillings, antifouling coatings and biosealants.
The natural zebra mussel byssal threads form strong, flexible, water-resistant bonds while remaining pliable. The threads contain unique proteins that scientists have been trying to isolate and synthesize in the lab. These proteins called byssal collagens resist degradation and provide remarkable sticking power that can adhere to rocks, metal, wood and more both in and out of water.
Early research has shown promise in using these byssal collagens to create synthetic underwater adhesives, dental composites, and other biomedical materials. While still in the early stages, tapping into zebra mussel byssal threads represents an intriguing area of natural product biotechnology research.
Potential Applications of Byssal Thread Research
- Underwater adhesives for ship hull coatings, ocean instruments
- Flexible liquid sealants for pipes, joints, or gaskets
- Antifouling marine paints that prevent biofouling attachment
- Moisture resistant coatings for reducing corrosion
- Dental composites and fillings
- Surgical adhesives, tissue glues
- Cosmetic ingredients like hair gels or skin moisturizers
The chemistry of natural zebra mussel byssal threads offers interesting models for developing synthetic polymers with similar properties like strength, flexibility, and adhesiveness. More research is needed, but their byssal fibers show promise as the basis of new bio-inspired materials.
Shell-Based Fertilizer or Feed Supplement
Another potential application takes advantage of zebra mussel shells. Researchers have explored processes to grind down zebra mussel shells into a fine powder that can then be used as a fertilizer or animal feed additive.
For example, one study found that adding zebra mussel shell powder to chicken feed as a calcium supplement significantly increased eggshell strength and thickness. The shell powder could also partially replace conventional limestone-based chicken feed supplements.
Similarly, mixing the powdered mussel shells into soil may provide a slow-release calcium source to help plants. The shell-based powder or meal contains over 30% calcium oxide along with other minerals like sodium and magnesium.
This provides a possible use for the mountains of waste zebra mussel shells that build up on Great Lakes shores each year. Rather than just leaving them to litter beaches, the shells could be collected and recycled into fertilizer or feed to reclaim some of their nutrients.
However, the shells would need to be sterilized first to kill any zebra mussel larvae. And deeper questions remain about whether broader use of zebra mussel shells is prudent given their invasive origins. But in targeted applications, shell-based soil amendments or supplements show promise.
Table 2. Nutrient analysis of zebra mussel shell powder from a Lake Erie study:
| Component | Percentage |
|---|---|
| Moisture | 2.32% |
| Calcium oxide | 30.98% |
| Phosphorus pentoxide | 0.37% |
| Magnesium oxide | 3.21% |
| Sodium oxide | 0.67% |
Conclusion
To summarize, zebra mussels do have some limited benefits worth considering:
- They can help filter polluted waterways in some specific contexts.
- Their shells provide habitat for small fish and invertebrates.
- Scientists use them as bioindicators for freshwater pollution studies.
- They offer a supplemental food source for some aquatic animals and birds.
- Research into their adhesive byssal threads may enable new biomedical materials.
- Their shells can potentially be used for fertilizer or animal feed supplements.
However, these benefits are extremely situational, and in no way outweigh the serious harm caused by zebra mussel invasions to ecosystems, infrastructure, fisheries and more. Their impacts are overwhelmingly negative and massively costly.
A limited number of isolated benefits do exist, but focusing too much on these fringe positives risks losing sight of the grave threats posed by unchecked zebra mussel spread. While interesting academically, their few benefits have minimal real-world application for mitigating zebra mussel damage.
In most cases, viewing zebra mussels comprehensively as a detrimental invasive species remains appropriate. But in specific contexts, usually with direct human oversight, certain aspects of zebra mussel biology could be cautiously utilized while still working to restrict their ecological impacts.
