Zonal orientation based on local visual cues in Nerita plicata L. (mollusca: Gastropoda) at Aldabra Atoll

Nerita plicata L. from Aldabra Atoll oriented coastwards when released in front of all coasts irrespective of their compass bearing. Correct coastward orientation was achieved within a small circular arena placed in front of the coast but orientation was at random when the arena was placed on top of a coastal dune where all landscape cues were eliminated. Tests with the sun in opposite azimuth (early morning and late afternoon) revealed a negative phototaxis which barely altered orientation towards the local coast. None of the tests indicated the presence of a chronometric correction of solar azimuth variation. N. plicata thus employs local information, activating either a contour-related orientation or one based on the evaluation of differences in low lying illumination between sea and land hemicycles.