Epibenthic Predators and Marine Meiofauna: Separating Predation, Disturbance, and Hydrodynamic Effects

In many marine soft—bottom systems, natant predators disturb the bottom while foraging for infaunal prey. This study was designed to determine if the predatory fish Leiostomus xanthurus exerts its effect on meiofaunal prey primarily via predation (consumption) or via disturbance and if flow modifies this effect. Experiments were conducted in a laboratory flume that allowed for both the addition and removal of fish and the mimicking of predator—induced disturbance, while controlling flow. Prey species differed with respect to the relative effects of predation and predator—induced disturbance. Disturbance accounted for 30—55% of the predator—associated decreases in copepods and foraminiferans, while disturbance accounted for virtually all of the nematode mortality. The latter was significant only when flow was absent. For other prey taxa, mortality was not influenced by flow; however, predator—induced drift (down—stream transport) of all meiofauna was significantly increased when flow was present. If experimental sites are not in equilibrium between upstream and downstream transport, then ignoring this drift could result in an overestimation of fish consumption on meiofauna by as much as 50%. Thus, the mechanisms by which fish predators influence meiofauna prey included direct consumption, disturbance—induced mortality, and enhanced water—column transport.