Decline of Diporeia in Lake Michigan: Was Disease Associated With Invasive Species the Primary Factor?

Populations of the freshwater amphipod Diporeia spp. have steadily declined in Lake Michigan since the late 1980’s. Prior studies have provided inconclusive data on possible reasons for their decline. However, some authors suggest that food competition and/or diseases associated with aquatic invasive species (AIS), such as zebra mussels (Dreissena polymorpha), may have caused the collapse of Diporeia. In this project, the possibility of pathogens as the cause of the collapse of Diporeia has been examined. Linear regression modeling show a significant positive linear association between percent of Diporeia exhibiting a pathogenic infection and year (r=0.7202264, p<=0.0124). Chi-square testing for independence was also used to test if there was an association between year and percent infection (X2 = 50, df = 10, p<=0.0001), implying significant association between year and infection. Hence, the introduction of zebra mussels and the diseases they carry may have been the root cause for the decline of Diporeia. Future research is needed to examine other invasive species for similar pathogens, including live studies showing direct causality between zebra mussels and the decline in Diporeia.