Behavioral and Morphological Influences on Predatory Interactions among Marine Copepods

Relationships among predation rates, selection patterns, swimming speed and orientation, and morphology of prey sensory and capture appendages were examined for seven species of marine copepods—Calanus pacificus, Corycaeus anglicus, Euchaeta elongata, Labidocera trispinosa, Neocalanus cristatus, Oithona spinirostris, and Tortanus discaudatus. Among these species, the ratio of preferred prey size to predator size ranges over four orders of magnitude while length-scaled, maximum clearance rates vary 1,000-fold. Different degrees of adaptation to carnivory are evident from the morphologies of prey capture appendages. However, predatory superiority inferred from these adaptations is not necessarily reflected in predator-prey size relationships or clearance rates relative to more omnivorous species. Except for Neocalanus, optimal prey size is strongly correlated with size of the prey capture appendage. Similarly, major differences in the size, structure, and distribution of sensory hairs on the first antennae of these species suggest marked differences in their abilities to detect and respond to motile prey. However, most of the variability in maximum clearance rates is explained by differences in mean swimming speeds.