Invasion of the Upper Mississippi River system by saltwater amphipods

Zoobenthic surveys of the large rivers of the Upper Mississippi River basin (Missouri, Upper Mississippi, and Ohio Rivers) in 2004-2006 revealed new invasions by euryhaline amphipods. The gammarid amphipods Echinogammarus ischnus and Gammarus tigrinus were discovered in the Ohio Upper Mississippi Rivers in 2004. The corophiid amphipod Apocorophium lacustre was first found in the Ohio River in 1996, and first detected in the Upper Mississippi River in 2005. None of these invaders was collected in the Missouri River. The presence of breeding adults of all three species suggests they are permanently established on the Ohio and Upper Mississippi. The range and occurence of all three species increased in the basin from 2004 through 2006. The contribution of the three invaders to total amphipod catch in the Upper Mississippi River increased from <1 % in 2004, to 5.4 % in 2005, and 15.2% in 2006, and in the Ohio River increased from 4.8% in 2004, to > 23 % in 2005 and 2006. The establishment of nonindigenous amphipods will likely contribute to alterations of food webs and native faunal diversity in the invaded rivers.