, Volume 74, Issue 2, pp 115-125

A comparative study on the movement patterns of two sympatric tropical chitons (Mollusca: Polyplacophora)

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The individual positions of 200 intertidal chitons [Acanthopleura brevispinosa (Sowerby) and A. gemmata (Blainville)] were recorded throughout 55 low tides on a Somalian shore, using a discrete sampling method. Both species feed during nocturnal low tide and rest during the day and high tide. Due to this activity rhythm, individual positions recorded during diurnal and nocturnal low tides give information on the rest habits of the chitons and on their movements, respectively. The resting and feeding fixes were analyzed with two new complementary methods. Both species show a distinct homing behaviour with periodical shift to new homes more frequent in A. brevispinosa than in A. gemmata. The latter species shows a stronger constancy to its feeding ground. The two species differ most in the orientation and length of their excursions. Due to their different movement pattern the two species minimize zonal overlapping during the night, which in turn reduces the interspecific competition for food.

Communicated by O. Kinne, Hamburg