USE OF A THERMAL AND LIGHT REFUGIUM BY DAPHNIA AND ITS EFFECTS ON FORAGING PUMPKINSEEDS

The effects of thermal stratification and light gradients on the feedi ng behavior of pumpkinseeds, Lepomis gibbosus, were tested in vertical aquarium columns. Successful captures, unsuccessful captures and unsu ccessful searches by foraging sunfish on Daphnia pulex were recorded. Clearance and feeding rates of the sunfish were lowest when prey densi ties remained high, indicating that the Daphnia were occupying an area that could not be searched by the sunfish. Thermal stratification lim ited the searching volume and prey availability of the sunfish, while creating a refuge for the Daphnia. Light intensities 14.2 x 10(-3) W m (-2) decreased the searching and capture abilities of the sunfish unde r isothermal conditions. Thermal stratification had more of an effect than the light gradients, creating a refuge for the Daphnia causing th em to be unavailable and less vulnerable to predation by the sunfish.