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Anti-predator responses of the intertidal crab Heterozius rotundifrons (Brachyura: Belliidae) in air and water

The intertidal crab Heterozius rotundifrons responds to tactile input, as occurs during a predation attempt, by hyper-extending all of its limbs and remaining in that posture for a variable length of time. We compared the duration of this anti-predator response: (1) in the day versus night (2) in two fluid media (air versus water) (3) after exposure to additional predator cues in one medium (air or water) and testing in the other medium (4) for crabs from different parts of the tidal range and (5) for females with and without eggs on their pleopods. Crabs showed the posture at night as well as during the day. They also executed the posture when tested in air and extended the duration of the posture in air when they detected an additional predation-risk cue, shadows passing overhead. When crabs experienced input in one medium there was no effect on the duration of behavior shown in the other medium. Crabs from the lower portion of the intertidal showed a markedly longer duration of the limb-extended posture compared to crabs from the higher end of the tidal range of this crab. Berried females responded the same as females without eggs in both air and in water. Thus, crabs show this anti-predator behavior under a wide variety of conditions, but do not appear to transfer information received in one medium to behavior shown in the other media.