The influence of structural complexity on fish-zooplankton interactions: Astudy using artificial submerged macrophytes

Aquatic macrophytes produce considerable structural variation within the li ttoral zone and as a result the vegetation provides refuge to prey communit ies by hindering predator foraging activities. The behavior of planktivorou s fish Pseudorasbora parva (Cyprinidae) and their zooplankton prey Daphnia pulex were quantified in a series of laboratory experiments with artificial vegetation at densities of 0, 350, 700, 1400, 2100 and 2800 stems m(-2). S wimming speeds and foraging rates of the fish were recorded at different pr ey densities for all stem densities. The foraging efficiency of P. parva de creased significantly with increasing habitat complexity. This decline in f eeding efficiency was related to two factors: submerged vegetation impeded swimming behavior and obstructed sight while foraging. This study separated the effects of swimming speed variation and of visual impairment, both due to stems, that led to reduced prey-predator encounters and examined how th e reduction of the visual field volume may be predicted using a random enco unter model.