Ronald E. Zegers, Ricardo DeLeon, and Peggy Roefer

SUMMARY:
The quagga mussel has become the most serious non-indigenous biofouling pest ever to be introduced into North American freshwater systems. It has the ability to tolerate a wide range of environmental conditions, is extremely adaptable, and has very high growth and reproductive rates. It has the potential to significantly alter the ecosystem of any body of water it invades and to degrade water delivery systems that it enters. It has been broadly stated that the invasion of the lower Colorado River is a “giant experiment” as these are the first large reservoir systems invaded by quagga mussels. Experts predict that in this system there will be an explosive growth of the quagga mussel population and depletion of the natural food resources currently being utilized by endemic zooplankton. The negative impact on the zooplankton community is predicted to cause a complete disruption of fishery resources (including endangered species) in the three reservoirs as the established food chain is altered.

The quaggas are also expected to result in the replacement of desirable forms of algae/phytoplankton by less desirable forms. Filamentous and gelatinous blue-green algae will dominate the deeper portions of the reservoirs as their growth forms are more resistant to consumption. Simultaneously, there will be an accumulation of large quantities of quagga mussel pseudofeces at the sediment surface, which can adversely affect water chemistry, create an inhospitable environment for other aquatic organisms, and threaten the quality of the reservoir as a drinking water source. Complete incrustation by mussels of the bottom of the lake, rock walls, and any other hard structures in Lake Mead (including water supply intakes and related structures) is predicted to occur in the years following invasion. These high population densities can transform the shoreline into thick rows of dead shells and will require increased and continuing maintenance of structures in and around the lake, marinas, docks, and watercraft that are in contact with the water.

The majority of research conducted on mussel infestations and their impacts has been specific to zebra mussels with much less emphasis on quagga mussels. While the two species have many similar characteristics, existing research does not provide reliable information to predict the potential impacts of the current infestation in the Colorado River system or on the water suppliers that draw from this system. What is apparent, even at this early date is that the quagga invasion is proceeding at a more rapid pace than was experienced in the eastern United States. As a result, water managers have had little advanced notice prior to experiencing serious system impacts.

The Southern Nevada Water Authority and the Metropolitan Water District of Southern California received grant funding from the Awwa Research Foundation (now the Water Research Foundation) to host a workshop to explore strategies for responding to the presence of quagga mussels in the lower Colorado River. The facilitated two-day workshop was held April 3−4, 2008 in Las Vegas, Nevada, and was attended by approximately 140 people. The objective was to involve individuals with direct experience using all of the available control methods and a diverse array of stakeholders, and to provide a forum for a focused exchange of ideas, opinions, research results, technical approaches, applications, and future perspectives to technologies and strategies for controlling quagga mussels in water conveyance systems and in source waters used for drinking water, such as rivers, lakes, or reservoirs. Workshop attendants discussed information and data gaps, research priorities, and implications for real world application of quagga mussel control. The workshop involved invited participants with expertise in current state-of-knowledge on water system protection, exploratory approaches for water system protection, protection and management of lakes and reservoirs prior to and after mussel infestation, management of large natural systems (rivers and lakes), statistical analysis and sampling strategies, ecological and population dynamics, and biology of invasive mussels.

The intended goal of the workshop was to utilize suggestions and information exchanged at the conference to develop a report that captures important issues and stakeholder concerns regarding quagga information needs. This white paper identifies research needs to address invasive mussel control in the Southwest.