How plankton copepods avoid fish predation: From individual responses to variations of the life cycle

Analysis of original and published data on predator avoidance by marine and freshwater plankton copepods, a major diet of many young fishes, suggests that individual defense mechanisms play a minor role in copepod anti-predator behavior. Capture success by planktivorous fish depends largely on prey visibility and the ability of the prey to escape. Copepods have almost no chance to avoid relatively large fish when encountered, but they can be ranked according to their ability to escape from larvae and fries. In contrast to small pelagic fish, which are also under heavy predation pressure, copepods rely more on prevention of the threat of predation than on active attempts to escape. Seeking a refuge in habitats non-accessible to predators would be more effective for these small and rather slow animals. Retreat into such refuges is accomplished by vertical and horizontal migrations, either diel, seasonal or ontogenetic. A decrease in activity (feeding, metabolism, reproduction, movement), resulting in diapause in deep water layers in its most pronounced version, is the ultimate attempt by copepods to separate from their predators, both in time and in space.