Characterizing the effect of prey on swimming and feeding efficiency of the scyphomedusa Chrysaora quinquecirrha

The scyphomedusa Chrysaora quinquecirrha (Desor, 1848) is an important pred ator in many coastal and estuarine systems of the eastern USA, but little i s known of its swimming or feeding behavior. Medusae were collected from tw o tributaries of Chesapeake Bay, USA, in August-October 1998 and videotaped in three dimensions in a 10,000 1 tank (diameter 2.4 in, depth = 2.3 in). Their swimming patterns were dependent on the presence of prey. When prey w ere present, medusae decreased their pulsation rate by 17%, and increased t heir velocity and acceleration by 87% and 78%, respectively, as compared to when prey were absent. In addition, cyclical variations in each of these c haracteristics were prey dependent. When prey were absent, medusae altered their pulsation rate and velocity cyclically every 50-100 s. By contrast, w hen prey were available, pulsation rate and velocity varied every 18 s, and acceleration varied every 37 s. Medusae often were near the surface or bot tom of the tanks regardless of the availability of prey, but swimming betwe en these two locations was more frequent when prey were available. We attri bute these prey-dependent changes in swimming to feeding behavior that mini mizes energy expended while searching for and capturing prey in habitats wh ere prey is heterogeneously distributed.