The scyphomedusa, Chrysaora quinquecirrha, preys on a variety of estuarine organisms. A series of experiments were conducted to measure the feeding rate of adult medusae on zooplankton prey. Artemia was used as a substitute for the endemic and abundant copepod, Acartia tonsa. The feeding rates ranged from three Artemia per hour per ml of medusae volume to 107 per hour per ml in 51 trials. The consumption was also linearly related to the initial prey concentration. Certain results suggested that a toxic factor might be exuded by the medusae, affecting the observed feeding rates. The results verify the possibility that Acartia may be a major prey organism in estuarine environments.