A MOTOGRAPHIC ANALYSIS OF FORAGING BEHAVIOR IN INTERTIDAL CHITONS (ACANTHOPLEURA-SPP)

The behaviour of two intertidal chitons (Mollusca: Polyplacophora) from the western Indian Ocean (Acanthopleura gemmata and A. brevispinosa) and one from the Caribbean Sea (A. granulata) were analyzed in order to assess the spatial and temporal organization of their foraging activity. Individual paths were recorded in the field using a motographic method based on LED-tracking and the speed variation during each excursion used to reveal the places where the animals slowed down or stopped for the purpose of grazing. Foraging segments of each trajectory were selected according to a threshold speed which was individually calibrated. The three species of Acanthopleura exhibited graded foraging strategies of different spatial complexity. Acanthopleura gemmata focused its foraging on a few large feeding sites well separated from its permanent home. Acanthopleura brevispinosa exploited more subdivided feeding grounds not distinctly separated from its rest area. Acanthopleura granulata spreads its grazing activity over many small segments, throughout each excursion. Due to different tidal and diel constraints on their activity the three species allocated different absolute time to foraging, but the fraction of time spent foraging relative to the total excursion was similar in each.