Predation efficiency in visual and tactile zooplanktivores

Abstract

Gelatinous zooplanktivores (medusae, siphonophores, and ctenophores) and visual zooplanktivores (fish) interact through competition, predation, and commensalism. In the search for key factors governing the outcome of competition, we examined the instantaneous predation efficiency and its light dependency. The visual predator Gobiusculus flavescens and the tactile predator Bolinopsis infundibulum were used as experimental models for the two predation modes. The predation rate of G. flavescens was adequately described by Holling's curvilinear disc equation, and that of B. infundibulum was proportional to prey density. However, because of superfluous feeding, the feeding rate of B. infundibulum differed from the predation rate and approached the asymptotic limitation at high prey levels. The predation rate was reduced for G. flavescens at irradiances <5–10 µmol photons m−2 s−1, whereas light had no significant impact on the feeding pattern of B. infundibulum. Provided sufficient light, the predation rate of G. flavescens was several orders of magnitude higher than that of B. infundibulum. These results are consistent with the results of other studies, which suggests that the maximum clearance rate (Cmax) of visual and tactile predators is described by the power functions Cmax = 3.42 × 10−7 L2.94 and Cmax = 6.02 × 10−8 L1.77, respectively, where L is the length of the organisms in centimeters. We conclude that visual predation is most efficient at high visibility and low prey densities. As visibility decreases and prey density increases, the competitive efficiency of tactile predators increases.