SOME PHYSICAL FACTORS INFLUENCING THE FEEDING BEHAVIOR OF DAPHNIA MAGNA STRAUS

Abstract

The feeding behavior of Daphnia magna was studied in relation to the effect of animal size, water temperature, and light intensity. D. magna were fed on pure cultures of Chlorella vulgaris and Saccharomyces cerevisiae labelled with radioactive phosphorus.As size of D. magna increased over the range 1.25 mm to 3.54 mm, both maximum filtering rate and maximum feeding rate increased. The relation between the increase of filtering rate and the increase of maximum feeding rate is such that the "incipient limiting level" (the external level above which there is no limiting effect of food supply) also increases as size of Daphnia increases. The feeding rate of D. magna was studied over the temperature range 5 °C to 35 °C. The temperature optimum for feeding was approximately 24 °C.Feeding rate was also studied under conditions of total darkness and at light intensities of 100, 300, 500, 1,000, 3,000, and 10,000 ft-c. Illumination from total darkness to 1000 ft-c did not appear to affect the feeding rate of D. magna.The results of this investigation are discussed in relation to previous studies of filtering rates of other Crustacea.