Echinogammarus ischnus

The Ponto-Caspian amphipod Echinogammarus ischnus was discovered in the Great Lakes in 1995. It is replacing the North American amphipod Gammarus fasciatus in many areas of the lower Great Lakes and St. Lawrence River (Palmer & Ricciardi 2004, 2005).  However, Gammarus remains dominant at sites in the upper St. Lawrence where the river mixes with ion-poor waters of the Ottawa River.  Experimental evidence suggests that the outcome of antagonistic interactions between the native and invasive amphipods is mediated by water chemistry (Kestrup & Ricciardi 2009).