Feeding in extreme flows: behavior compensates for mechanical constraints in barnacle cirri

Abstract

Plastic morphological changes in response to environmental cues can allow organisms to adapt to their local environment. Barnacle feeding legs (cirri) exhibit substantial plasticity in size and shape along wave exposure gradients on rocky shores, but only up to a certain limit in maximum water velocities. Above the limit, the morphology of the cirri becomes invariant. Behavioral observa- tions of barnacles feeding at a wave-exposed shore indicate that the fast response time for feeding motions allows barnacles to avoid potentially damaging flows associated with breaking waves, while still allowing feeding between wave impacts. The ability of barnacles to avoid individual waves indi- cates that the apparent limit in morphological plasticity may not be a result of physiological limits in cirral form, but rather a result of the barnacles reacting to some measure of the environment besides extreme flow speeds.