| Holopedium gibberum is one of the few cladocerans to create a gelatinous sheath. For this reason it can clog drinking water filtration facilities. In order to better understand the population dynamics of Holopedium in a reservoir in the Cascade foothills, in-situ single variable treatments were used to investigate the effects of temperature, food, and turbidity. The fatty acid composition of Holopedium, Daphnia and the seston was tested to examine likely food sources and the possibility of direct competition. It was found that temperature limits the Holopedium population during the spring phytoplankton bloom and low food quality limits the population during the late summer. Competitive exploitation between Holopedium and Daphnia is possible. The composition of several fatty acids in the cladocerans was correlated, indicating shared resources. Daphnia followed the seasonal trends in the seston fatty acid composition more closely than Holopedium, indicating that the overlap in resources was not complete. Holopedium appears to be using the food resources most commonly found above the thermocline and may be able to out-compete Daphnia under conditions when chrysophytes or allochthonous fatty acid sources dominate in the seston, however, Daphnia appears to utilize a wider range of food resources. |
