Epizoic Protozoa of Planktonic Copepoda and Cladocera from a Small Eutrophic Lake, and Their Possible Use as Indicators of Organic Water Pollution

The epizoic protozoa of planktonic copepoda and cladocera from a eutrophic lake (Ashmore Lake, Coles County, Illinois) were studied over a 13-week period in the summer and fall of 1975. All organisms were collected with a 125 micron mesh plankton net. Epizoans (all peritrichs and suctorians) were hosted by three of four species of copepods and four of the ten species of cladocerans. The percentage of total organisms hosting epizoans varied significantly (0.001 alpha level) by month, but averaged 11.6 percent. This high occurrence of epizoans was thought to be related to the highly-eutrophic conditions existing in the lake. If the occurrence of epizoans is related to the degree of organic enrichment of a body of water then the percentage of planktonic organisms hosting them could be a useful index of water quality. Several interesting symbiotic associations were found. Tokophrya cyclopum was always found on the anterior ends of its cyclopoid copepod hosts, and Vorticella microstoma occurred exclusively on the cladoceran Scapholeberis kingi. These associations were thought to result in feeding and defense advantages for the protozoa, but may have harmed the host organisms. Evidence from other studies was presented in support of these hypotheses.