First observations of tumor-like abnormalities (exophytic lesions) on LakeMichigan zooplankton

Tumor-like abnormalities (exophytic lesions) were found on a variety of pla nktonic calanoid copepods and cladocerans (Diaptomus spp., Epischura lacust ris, Limnocalanus macrurus, Polyphemus pediculus, Diaphanosoma sp., and Dap hnia galeata mendotae) collected from inshore (3-m depth contour) and offsh ore (100- to 110-m depth contours) stations of eastern Lake Michigan. The a bnormalities, which were quite large relative to animal size and variable i n shape, are documented in photographs. Abnormality incidences among specie s ranged between 0 and 72%. Predatory species of calanoids and cladocerans had higher incidences of tumors than herbivorous species. The abnormalities on some copepods were very similar to cysts described for calanoid copepod s in Lago Maggiore, Italy, which like Lake Michigan is undergoing oligotrop hication. The recent appearance of the lesions in Europe and North America may indicate an emerging global phenomenon that has a common cause.