The invasive exotic zebra mussel (Dreissena polymorpha) is native to the Caspian Sea region of Asia but was accidentally brought to North America in the ballast water of an international ship in 1986. Since then, the mussels have rapidly reproduced and infested waters throughout the Great Lakes and the Mississippi, Arkansas, Ohio, Tennessee and Cumberland rivers. After several near misses, when they were observed on boats about to be launched, zebra mussels found their way into the Lake of the Ozarks in 2006.
For several years following their introduction, the invasive mussels spread rapidly in the Lake of the Ozarks. Their population became established in the Osage River below Bagnell Dam and in the Lake from the Dam to the Gravois Arm. For the last couple of years, however, zebra mussels have declined or disappeared from some areas of the Lake. MDC Fisheries Biologist Greg Stoner says that the warm water temperatures during the summer is probably a factor in the recent decline. The summer of 2011 was definitely a hot one and lake water temperatures reached into the 80s and 90s. That is enough to stress or kill a mussel that is adapted to the cooler water temperatures of the Caspian Sea. Disease and natural predators are other factors that could contribute to a decline in numbers.
A study by researchers in Texas indicated that the upper temperatures that zebra mussels can normally tolerate are in the 68- to 77-degree range. But they noted that there is a “thermally tolerant” population in one lake in Kansas that can survive higher-temperature water, up to about 87 degrees. If zebra mussels in North America are undergoing natural selection toward greater heat-tolerance, then the decline in zebra mussels in the Lake of the Ozarks may be only a temporary respite from their overall population expansion.
Despite recent declines, public awareness and preventing the spread on boats and other marine equipment are our best tools for slowing the zebra mussel invasion. See our website for recommended preventative measures.