History
Zebra mussels are freshwater molluscs native to Eastern Europe and Western Asia. They were probably transferred to North America in the freshwater ballast of ships sailing from European ports. Discovered in June 1988 (Lake St. Clair), the mussels have now spread throughout the Great Lakes Basin, the major river systems and many inland lakes.

First discovered in Oklahoma in the Arkansas River, January 1993 (R.S. Kerr lock), zebra mussels have now spread upstream to Lock 18 west of Inola. From fall 1994 to fall 1998, the population density at the Kerr lock has expanded from 21 to 3000 individuals per square meter (18 to 2521per square yard).

Biology
Zebra mussels are small, yellow to brown, "D" shaped clams with alternating light and dark bands or stripes. They can grow up to 5 cm (2 inches) in length but most are less than 2.5 cm. After zebra mussels invaded, phytoplankton populations decreased 80 - 90% and zooplankton by 70%. Production of juvenile fishes, native mussels and other filter feeding organisms may decline due to reduction in food supply.

Adult females can produce approximately one million eggs per year in resource rich, warm water (12 - 28EC). Fertilized eggs hatch (1-3 days) into free swimming, microscopic larvae called veligers. After approximately two to three weeks, veligers settle and attach to any stable preferred substrate, including each other. Zebra mussels are the only freshwater molluscs capable of firmly attaching themselves to submerged objects and structures. In large water intake mains, colonies up to 30 cm (12 inches) thick have formed and smaller diameter pipes have been completely closed. Attachment is accomplished by secreting durable, gluelike, elastic byssal threads.

Eggs and veligers are easily transported in water currents. Attached individuals may be carried by turtles, crayfish and birds. However, distribution by human activities is largely responsible for their rapid expansion. Transportation of larvae from infested to un-infested water is a very important concern. Examples are, commercial barge and ship ballasts, bait buckets, live wells, commercial bait and hatchery transport, and aquaria releases. Adults attached to the hulls of recreational boats, barges, dredges, construction equipment (pipe, cables, chains, etc), or to vegetation fouling these devices are also vector mechanisms.

Industries which depend on large volumes of raw surface water (power generating, water treatment plants, etc.) have been impacted most by the zebra mussel invasion. As the zebra mussel range has expanded, annual expenditures to alleviate their damage has increased from $234,140 in 1989 to $17,751,000 in 1995.

Concerns for Oklahoma Water Resources and Aquaculture
Zebra mussels thrive in a diverse array of freshwater environmental conditions. Many of Oklahoma’s streams and reservoirs may be favorable zebra mussel environments (see Table 1). Thus, municipal water reservoirs and their associated water treatment systems, and, power plant cooling systems are vulnerable.

Table 1.
Environmental Tolerances of Zebra Mussels

Temperature

0-33EC
(32-91EF)
survival
13-25EC
(55-77EF)
preferred

Calcium

5 - 6 mg/L survival
10 - 12 mg/L reproduction
35 mg/L preferred

Alkalinity

15 mg/L survival
35 mg/L preferred

Hardness

22 mg/L survival
42 mg/L preferred

pH

6.9 survival
7.5 preferred

Dissolved Oxygen

2 mg/L survival
90 % saturation preferred

Salinity

short term tolerance, 10 - 12 ppt
0 - 1 ppt preferred

Water Velocity

0.1 - 1.0 m/sec preferred

Turbidity

40 - 200 cm (Secchi disk)

Presently, most of Oklahoma’s aquaculture industry is completely dependent on surface water. Despite the obvious invasion vulnerability, caused by reliance on surface water sources, zebra mussels are more likely to invade your facility from infested hauling water or equipment contaminated from use in infested water.

Prevention is the Best Plan!
Prevention is proactive, more complete and cost effective than reactive measures. Educate your employees and associates about the zebra mussel problem and how these precautions can protect your facility and our water resources. Develop some basic safety measures and implement them. Include the following measures in developing your plan.

Fish Hauling - Using well water or other zebra mussel free water sources is best. Avoid using surface water from infested areas, it may contain zebra mussel larvae. Releasing hauling water into ponds, creeks, or any other water system is an invitation to unwanted disease, fish and possibly zebra mussels. The salt solutions used to reduce stress while transporting fish may be of some benefit in reducing mussel transport. A 1% salt (NaCl) solution (10 g/l) will kill all veligers and 98 % of settled mussels in 24 hours. However, Catfish are unable to tolerate exposure to this concentration. The precautions you take to protect your facility should be extended to your business associates also.

Cleaning Aquaculture Equipment - Wash (soak) your equipment (seines, nets, hauling boxes, etc.) with hot water (140EF or 78EC for 23 min.) or use a high pressure washer (2000 - 3000 psi). Disinfect equipment by soaking in a 100% vinegar solution for 20 minutes or benzalkonium chloride (100 mg/L for three hours or 250 mg/L for 15 min.). Benzalkonium chloride is extremely toxic to most fish and is available as RoccalTM. After cleaning, nets and other equipment used in infested water should be dried from one to two weeks.

Cleaning Sports Equipment - Anything that has been in contact with zebra mussel infested water is a potential carrier. These include plants and animals, scuba gear, fishing gear, and, boats and trailers. Clean your boat, including the engine, live well, and trailer with hot water (1400F, 780C). If hot water is not available, use chlorinated tap water and then air dry for 3-5 days. Be especially careful with your bait; do not re-use bait if it has been exposed to infested water. Fish caught in infested waters should not be released in zebra mussel free water without insuring that the holding water is zebra mussel free. When boats, water, bait buckets and tackle are used in infested water and reused in zebra mussel free water before cleaning and drying, the zebra mussel range could expand.

Public Education - Anyone whose recreational or occupational activities use public waters is a potential vector for zebra mussels. The 100th Meridian Initiative is a voluntary effort by federal and state agencies, and, volunteers to prevent zebra mussel invasion west of the 100th meridian. The 100th meridian (longitude) is the Oklahoma Eastern Texas panhandle border excluding the Oklahoma panhandle. Because humans and their activities are primarily responsible for the advance of this exotic mussel, public awareness and education are the most effective tools for slowing the advance. Tell your friends and neighbors about the zebra mussel invasion and the potential for damage to Oklahoma’s natural resources.

For more information, call or write: George Luker

Sources

Kelch, David O. 1994. Slow the Spread of Zebra Mussels and Protect Your Boat and Motor. OHSU-FS-054.

Laney, Everett. Personal Communication

O’Neill, Charles R. ,Jr. 1996.The Zebra Mussel, Impacts and Control. Cornell Cooperative Extension Bulletin 238. 62 pp.

Rice, James. Zebra Mussels and Aquaculture: What You Should Know. North Carolina Sea Grant, Fact sheet.

Zebra Mussel Alert. Nebraska Game and Fish. Website.