Dr. Kevin Strychar


Populations of the freshwater amphipod Diporeia spp. in the Great Lakes have steadily declined since the late 1980’s. Prior studies have provided inconclusive data on possible reasons for their decline, but suggest that factors such as food competition, predation, toxic excretions, and potential diseases associated with aquatic invasive species (AIS), in particular zebra mussels (Dreissena polymorpha), may have caused the collapse of Diporeia throughout the Great Lakes. In this project, I examined the possibility of pathogens as the root cause of Diporeia’s collapse. Linear regression modeling showed a significant positive linear association between percent of Diporeia exhibiting a pathogenic infection and year (r=0.7202264, p-value≤0.0124). Chi-square testing for independence was also used to test if there was an association between year and percent infection. Values obtained were X2 = 50, df = 10, p-value≤0.0001, implying significant association between year and infection. As such, the data indicates that zebra mussels and possibly other AIS (e.g. Quagga mussels; Dreissena rostriformis) may have acted as the vector for pathogen(s) that infected Diporeia and be the cause of their decline. Future research is needed to examine zebra and quagga mussel tissues for similar pathogens, including live studies of potential infection.