The zebra mussel, a notorious invasive species, has been silently infesting the rocky bottom of the Hudson River since it arrived there in 1991. But researchers from the Cary Institute for Ecosystem Studies, who have closely monitored the river before, during, and after the invasion, are noticing a promising new pattern. In this video, learn how the Cary team takes the pulse of this complex freshwater ecosystem to stay abreast of the invasion. Extensive digital classroom resources for educators are also available on AMNH's River Ecology Web site.