Trade-off between safety and feeding in the sea anemone Anthopleura aureoradiata

After a physical disturbance, such as a predatory stimulus, several marine organisms withdraw into a refuge to ensure survival. Consequently, they cannot engage in other essential activities. Re-emergence reflects a trade-off between avoidance of disturbance and lost feeding opportunities. The New Zealand sea anemone (Anthopleura aureoradiata) avoids predators by withdrawing its tentacles into its upper body. In a field experiment, responses of 480 A. aureoradiata to a physical disturbance were studied at three locations to assess the influence of the following factors on hiding time: physical contact with a neighbour; density of nearby conspecifics; total density per pool; and body size. Withdrawal times were significantly shorter for anemones in contact with a conspecific, occurring in high-density patches or of larger size. These patterns are consistent with rapid re-emergence being stimulated by competition for food from immediate neighbours and/or a lower risk of predation when in groups (i.e. a dilution effect), with larger size also potentially reducing vulnerability to predation.