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Environmental Applications and Research Group — Publications

Zebra Mussel Monitoring Research Program at the Bureau of Reclamation: Summary of 1995 Monitoring Activities

Technical Memorandum No. 8552-96-15
Tracie Greene and Fred Nibling

Methods and Materials
Results and Discussion
Appendix I (Figures)


Zebra mussels (Dreissena polymorpha) are fresh water molluscs with the capability to rapid reproduction cycles and spread throughout a water system. Zebra mussels are unique among fresh water mussels in North America for their ability to firmly attach to a wide variety of submerged structures and objects. They are a major concern to water resource managers because they threaten catastrophic economic and ecological impacts on regional water systems. These molluscs clog intakes and distribution canals, pipelines in industrial and domestic facilities, increase corrosion potential of steel and iron pipes, taint and contaminate potable water supplies, encrust hulls of boats, decrease or eliminate recreational uses of water, displace native species and destroy or alter food chains.

These molluscs are native to the Caspian Sea region of East-Central Asia. Following the improvement of transportation systems and industrialization, they spread throughout the major water systems of Europe by the nineteenth century. In 1988, they were first observed in the waters of the Great Lakes in North America. They have subsequently spread from their point of origin near Detroit throughout the Mississippi River to 19 states and two provinces of Canada.

The zebra mussel can grow to an adult size of approximately 5 cm long, weighing less than two grams. They have a D-shaped shell that has alternating light and dark stripes, hence the name zebra mussel, The shell is thin and somewhat fragile. They prefer subdued light and flowing water. Feeding is performed by filtering microscopic phytoplankton from up to two liters of water per day. A mature female produces from 30,000 to 40,000 eggs per spawning, and they can spawn several times per year. Within eight hours of fertilization, swimming larvae often referred to as a veligers are formed. Veligers may remain suspended in the water column for several weeks until settling on a desirable substrate. The colonizing mussels produce byssal threads and attach to hard substrates such as rocks, pipes and walls of man-made structures or to each other. They usually grow in clusters and are generally found in shallow (2 - 5 meters), algaerich water. Whole colonies of the molluscs can be transported on the hulls of boats or barges and be scraped off or dumped into new habitats to start new populations. Under moist and reasonably cool conditions, zebra mussels can stay alive out of the water for up to 14 days.

Control of this new pest has been a challenge to water resource managers since its initial North American discovery, Clusters resulting from multiple generations of animals have plugged screens and trash racks, blocked pipes, and interfered with pumps at state-of-the-art electric power and water treatment facilities on the Great Lakes before maintenance and preventive measures were taken. Large populations of adult mussels have reduced flow rates in water conduits and disrupted gaging and flow-rate instrumentation networks. Maintenance costs for infested structures and intakes cost millions of dollars annually. Plant redesign and zebra mussel control for 72 nuclear and fossil fuel generating plants in the Great Lakes Basin are anticipated to cost in excess of $860 million over the next 10 years. Water system overhaul and fishery repair in the Great Lakes region will cost an estimated $4-$5 billion during the next decade. Some facilities are already spending $250,000 a year to combat the zebra mussel.

Bureau of Reclamation (Reclamation) facilities are not excluded from this threat. Reclamation is the largest water supplier in the 17 western states and has constructed numerous dams, hydroelectric plants, canals and facilities for recreation and environmental protection. If these molluscs spread without detection and control to western water systems, their impacts would likely be as dramatic as have been witnessed in the East. The likely results would include blockage and friction loss, corrosion, and environmental impacts. Blockage and friction loss of water flow are major problems for water conduits such as pipes, channels and distribution canals. Corrosion of metallic surfaces and pipes leads to an increase of plant maintenance costs. Also, when present in large numbers, zebra mussels out-compete or displace native species by removing food and nutrients from the aquatic ecosystem. They can also contaminate potable water supplies and decrease or eliminate recreational uses of water. Reclamation is currently undertaking activities involving education, early detection, and preventive maintenance to minimize zebra mussel impact on facilities.

The zebra mussel has now become established within the eastern fringe of Reclamation's geographic area of responsibility (Figure 1). It presently occurs in the navigable portion of the Arkansas River as far west as Tulsa, Oklahoma. This is within 90 miles of the nearest Reclamation facility. There are six Reclamation facilities within 250 miles of the site. Consequently, Reclamation is actively involved in a monitoring program that services several water districts in Oklahoma. Navigation and recreation seem to be the major component in the relocation of the organism. The zebra mussel has been detected in six separate incidences on the hulls of recreational boats at border check points in California. On at least two occasions live mussels were found.

Methods and Materials

Reclamation has implemented a monitoring program to provide zebra mussel detection services to affiliated water districts in Oklahoma. The goal is to detect the zebra mussel in early stages of infestation. Experience in the Great Lakes has shown that a proactive approach is the most successful and cost-effective management practice. Once the mussel is detected, water system managers will hopefully have enough lead time to begin appropriate management activities and avert major impacts. Four water districts and one navigation system are currently involved in the monitoring program. The participants are Arbuckle Master Conservancy District (Davis, OK), Central Oklahoma Master Conservancy District (Norman, OK), Foss Reservoir Master Conservancy District (Foss, OK), Lugert-Altus Irrigation District (Altus, OK), and the U.S. Army Corps of Engineers Kerr-McCellan Navigation System (Tulsa, OK). Three other Reclamation affiliated water districts did not participate in 1995, but they will again be invited to participate in the 1996 monitoring program. These are Fort Cobb Reservoir Master Conservancy, McGee Creek Authority, and Mountain Park Master Conservancy District (Figure 2).

Participants were sent sampling kits containing the following items (Figure 3):

The samplers (Figure 4) were placed by cooperating field staff in locations that were easily accessible for monthly collections. They were hung (2-3 meters deep) from concrete or metal works around outlet structures or from boat docks. The sampler or "trap" consists of a plastic mesh cage and a bridal veil substrate which simulates aquatic vegetation and is believed to be a desirable attachment site for the free swimming veligers. Monthly, the bridal veil substrate is exchanged with a fresh one, and the sample is returned to Reclamation's laboratories in Denver for analysis.

During sample processing, the netting is rinsed with water to dislodge any attached veligers (immature zebra mussels). The netting is properly disposed to prevent the possible contamination of Reclamation's laboratory water facilities. The rinse extract is stored at I O'C for analysis. A small portion (approximately IO ml) of this liquid is poured into a petri dish and then examined for veligers under a high power dissecting microscope equipped with a polarized light source (Figure 5). While a veliger (Figures 6 and 7) is detectable under a traditional microscope, polarized light causes them to appear as a "cross" making them easier to distinguish from silt residues which often contaminate the samples. Following each analysis, a letter is sent to the respective participants reporting the findings.

Results and Discussion

Table 1 shows the sites where sampling kits were deployed and the results of their analysis. No zebra mussels were found in any of the 1995 samples. Kerr Lock operated by the U.S. Army Corps of Engineers (Corps) was used as a control site to test detection methods at a site known to be infested by zebra mussels. The same sample processing methods were used for all of the sites, including Kerr Lock. No positive samples were detected in any site. Previous studies by the Corps have found veligers in Kerr Lock. It is believed that low densities of veligers and/or low sensitivity of the sampling methods may be a factor which contributed to the negative findings at the Kerr Lock site. Alternative sampling methods are being proposed and investigated.

Sample Collection
Monthly monitoring of veligers will continue using the bridal veil substrates for all sites for the duration of the reproductive season. Additionally, veliger monitoring will include the use of plankton net tows (mesh size of 63 microns) on an annual basis to coincide with predicted peak time of reproduction for all sites. Raw (untreated) water from selected sites will be pumped through a garden hose and filtered by plankton nets for analysis of veligers and plankton. Monitoring for settlement of adult mussels will be conducted annually.

Sample Processing
There is considerable colloidal clay-like contamination in some of the samples which cover veligers and limit their detection with a microscope. A necessary additional step is needed to reduce the clumped silt size in the sample. Once done, the sediments can be separated from the larger veligers by using fine mesh screens. Preliminary studies have shown that sodium hexametaphosphate breaks up sediment clusters, but its effect on veliger shells is unknown. Additional studies will be conducted on this topic.

Environmental Parameters
The most critical parameters affecting the degree of zebra mussel establishment in Oklahoma are likely to be water salinity, temperature, pH level, calcium concentration, dissolved oxygen, and turbidity. Depending on the values, these factors can either increase or decrease growth and reproduction of zebra mussels. Measurements of water quality parameters (such as dissolved oxygen, turbidity, temperature, pH, etc.) are needed to complete necessary risk assessments. A cooperative study with a regional academic institution has been initiated to determine water quality, the growth rates, reproduction rates, and the time of the year that the mussel veligers are found as well as other biological factors. The possibility of using cameras and divers to observe zebra mussel activity will be explored.

Risk Assessment
Future work includes site visits for risk assessment. Also the results of a survey conducted to determine the probability of infestation of zebra mussels will be used in the assessment of the sites. The survey will include environmental parameters, the distance to the nearest known infestation, habitat suitability, public use, and operations and maintenance.


Funding for these activities was provided by Great Plains Region, Reclamation Water Research Project (EE025) "Biological Control of Mollusks" and Reclamation's Program Analysis Office. Assistance from Dr. James Schooley and the cooperators with the Arbuckle Master Conservancy District (Davis, OK), Central Oklahoma Master Conservancy District (Norman, OK), Foss Reservoir Master Conservancy District (Foss, OK), Lugert-Altus Irrigation District (Altus, OK) is greatly appreciated.