Ciliates as a Food Source for Marine Planktonic Copepods

Copepods of the genus Eurytemora, isolated from the Patuxent River, a tributary of Chesapeake Bay, were fed suspensions of the ciliate Uronema isolated from the Rhode River, a subestuary of Chesapeake Bay. Grazing by copepods was determined by the decrease in numbers of ciliates, which were monitored by both direct counting and particle size analysis. Results from both methods of analysis showed significant reduction in the numbers of Uronema in the suspension when Eurytemora was present. Survival of copepods with ciliates added as food source was significantly longer than without ciliates. Analysis of field samples collected in the fall showed that ciliates comprised approximately 20% of the total plankton biomass at selected sampling sites. The results of the laboratory and field studies indicate that copepods can feed on ciliates and suggest that, in nature, ciliates may comprise an important source of food for copepods.