Beware of Zebra Mussels! Really? A small bivalve? What are these clam-like creatures going to do, crawl out from the bottom of a river and slime us while we’re sleeping?
No, but they are indeed a threat to our environment and the Division of Wildlife Resources has declared them to be an invasive species to be concerned about.
Here’s what DWR has to say:
Zebra mussels are freshwater bivalves (relatives of clams) and are appropriately named for the alternating wavy dark and light bands on their shells, which vary or can be absent. Adults are D-shaped and generally thumbnail-sized but can reach a maximum size of about two inches. While these bivalves are relatively short-lived (typically 2–3 years), they are extremely prolific breeders, which contributes to their ability to spread rapidly and abundantly. An adult female zebra mussel can produce about 30,000–40,000 eggs each reproductive cycle and upwards of 1 million each year. Free-swimming microscopic larvae, called veligers, will drift in the water for several weeks and then settle onto any hard surface they can find. Zebra mussels also can tolerate a wide range of environmental conditions and adults can even survive out of water for about 7 days. Unlike other freshwater bivalves, zebra mussels are able to attach to surfaces using their byssal threads (see photo) and form large clusters similar to oyster beds. It is not uncommon to find populations with densities of over 100,000 individuals per square meter, with some reaching up to 1 million per square meter.
Why be concerned?
Zebra mussel invasions have caused tremendous economic and ecological damage. Many water treatment and power facilities must now treat their systems to keep them free of zebra mussels, beaches must be periodically cleaned of decaying masses of dead zebra mussels, and bottom-dwelling organisms and fisheries have been negatively impacted. In the United States, Congressional researchers estimated that zebra mussels cost the power industry alone $3.1 billion in the 1993–1999 period, with their impact on industries, businesses, and communities over $5 billion.
Zebra mussels also represent a significant threat to the Commonwealth’s native ecology and wildlife communities. Zebra mussels are extremely efficient filter feeders. One adult can filter about a quart of water per day. While water clarity is improved as they filter out microscopic organisms, zebra mussels effectively remove the food base upon which many of our native fish and freshwater invertebrates are dependent. Because of their ability to rapidly colonize any hard surface, zebra mussels also pose a significant risk to many bottom-dwelling species, including our rare and endangered freshwater mussel populations. Zebra mussels can attach themselves to the native mussel shells, making it impossible for these animals to open or close, burrow in the stream bottom, or feed. Zebra mussels also can damage boat hulls and engines.
Therefore, it is up to each of us to take extra precautions to stop the spread of zebra mussels at Virginia’s borders! The following actions should be taken with any equipment used in potentially infested waters:
- All equipment (e.g., dive gear, boats, trailers, motors, etc.) should be visually and tactically inspected for the presence of zebra mussels prior to and after use in any water body. Additionally, any vegetation attached to this equipment must be removed and left at the site of origin.
- Remove all sediment and gritty organic materials; these could actually be zebra mussel veligers (juveniles).
- Clean and scrub boat hulls, motors, anchors and trailers, then hose equipment with hot (140°F) and/or high-pressure water, keeping in mind appropriate water conservation requirements. Bilges, live wells, and any other compartments that could hold water should be drained at the site of origin, and, if possible, flushed with disinfectant or hot water. All boat equipment should be allowed to remain completely dry for at least 24 hours before being used again.
- Thoroughly clean all diving equipment in a saltwater bath (0.5 cup per gallon) or with warm tap water (104ºF). Ensure that all equipment remains completely dry for at least 24 hours before being used again. Pay special attention to those areas and equipment that can hold water.
- Take similar precautions with waders, bait buckets, and other equipment that can hold water, or encounters water.
If you believe you have seen or found a zebra mussel, please contact DWR immediately at 804-367-6913. Your assistance is greatly appreciated!