Effects of dead conspecifics, hunger states, and seasons on the foraging behavior of the purple urchin Heliocidaris crassispina

The top-down component of trophic cascades exerts a powerful effect between predator and prey relationships in an ecosystem. In aquatic environments, the signals associated with predators and predation are used by prey as a cue to avoid encountering predators when foraging for food. These cues are powerful enough to control prey populations and indirectly protect primary producers. We evaluated the effects of cues associated with predation on the purple urchin, Heliocidaris crassispina and also examined the how starvation and season influenced the effects. Using time-lapse photography, we conducted a series of manipulative and in situ behavior experiments to determine foraging behavior patterns which demonstrate behavior modification. The results suggest that starved urchins were less sensitive to predation cues when compared to normally fed urchins. Field experiments indicated that a proportion of fed urchins fled when exposed to a predation cue (presence of a dead urchin), whereas all starved urchins remained regardless of the cue, which complemented the results from the laboratory. Sea urchin activity and feeding rates were lower in winter-spring than in summer-autumn. We suggest that starvation has a large influence over the decision-making process of sea urchins, and their response is affected by season due to metabolic control. In general, the hunger response overrides predator avoidance behaviors and exposes prey species to higher risks of predation.