Trail following in the chiton Acanthopleura gemmata: operational and ecological problems

Abstract

The Indo-Pacific, intertidal chiton Acanthopleura gemmata (Blainville) is a central place forager which occupies definite, actively dug and defended scars, and migrates during nocturnal low tides up to 3 m away to feed on algal grounds. After each feeding excursion, most chitons home precisely to their scars. Photographic tracking, using lightemitting diodes (LED) glued to the chitons, and experiments were conducted throughout 45 d (August to September 1984) along the Nimu Peninsula (Somalia) in order to elucidate the importance of trail following in the homing and feeding of this species. LED tracking of the chitons throughout each activity phase and trail interruption experiments showed that following the personal outgoing trail is a basic homing mechanism in this species. Translocation of the chitons on a conspecific trail and homing performance analysis revealed that the trail-associated information involved in the homing is polymorphic in the population, thus minimizing the probability of following a conspecific trail despite the frequent trail crossings due to high population density. The LED tracking throughout successive activity phases showed a high coincidence between the paths traced by the same chiton night after night. In the few cases when the outgoing and return paths of the first night markedly diverge, the home-feeding ground route of the successive night overlaps the return trail of the previous night. A less pronounced inter-individual trail following also occurs during foodward excursions. These findings suggest that the trails released by A. gemmata are complex, including both quasi-individual and species-specific information. Moreover, this chiton may utilize its trail following capacity not only to home, but also for the retrieval of the feeding grounds night after night.