Role of chemical signals in the orientation behavior of the sea star Asterias forbesi

The importance of chemical signals as foraging and orientation cues has been demonstrated for many marine organisms. It is still unclear whether sea stars use chemical signals during orientation and whether chemoreception occurs in the absence of macroscale flow, To determine whether the sea star Asterias forbesi can perceive chemical signals in the absence of flow and what role such signals play in orientation and foraging behavior, we tested the orientation behavior of sea stars to prey and nonprey items under conditions of nondirectional flow, Prey items were whole and broken clams (Mercenaria mercenaria) and mussels (Mytilus edulis): the nonprey item was squid flesh, Asterias forbesi showed the ability to successfully locate odor sources irrespective of the type of odor. Only in trials with the broken clam did the animals reveal an initial directional choice towards the odor source, There were significant changes in the movement rates and heading angles during orientation for all three stimuli. In addition? orientation paths were different for each of the chemical stimuli tested. From these results, we conclude that sea stars can detect and respond to chemicals in the absence of macroscale flow, Orientation paths appear to be more of a taxis, in which heading is directly guided by the stimulus field.