Swimming behavior of Daphnia: its role in determining predation risk

Individual swimming behavior of zooplankton can play an important role in determining how planktivorous fishselect their prey. Although several studies have documented the effect of prey size, contrast or degree of pigmentation, escape ability, encounter rate and abundance in determining predation risk, the importance of individual behavior has received relatively little attention by aquatic ecologists. Recent advances in the technology of video recording and computer analysis of motion have allowed us to collect digitized three-dimensional videorecords of free-swimming zooplankton such as Daphnia. We found that Daphnia clones, including those within a single species, exhibit a wide range of swimming behaviors as measured by swimming speed. The individual behavior of a species cannot be adequately described by looking at one clone. We alsoshow that different behavior observed in live Daphnia can play an important role in determining attractiveness to visual predators. Given a choice between two clones of equal size and visibility contrast, fish selected indi viduals from the faster swimming clone. Our results suggest that current models of prey selection would be improved by the incorporation of individual swimming behavior because it is an important factor determining overall prey visibility.