Could Ambient Vibrations Be Related to Cerithidea decollate Migration?

Physiological and behavioral systems exist to reduce the stress that the intertidal fauna may face during the unsuitable tidal phase. Cerithidea decollata is a common western Indian Ocean mangrove gastropod. It feeds on the ground at low tide, and climbs the trees two-three hours before the water arrival to avoid submersion. Moreover, it regularly settles on the trunk roughly 40 centimeters above the level that the water will reach, in spite of the irregular East African tidal pattern. Migration usually takes place about twice a day unless at Neap Tide, when snails may remain on the dry ground. Biological clock cannot account for water level foreseeing while direct visual cues or chemical information from the water itself or from previous migrations have already been experimentally discarded. Indirect cues could be hypothesize related to the effect of the oceanic wave reaching the coast and the barrier reef (seismic noise), or alternatively related to changes in ground resistivity (self potential) caused by the sea water moving close. To verify these hypotheses a seismic noise and self potential survey was carried out at Mida Creek (Kenya). This paper presents the first results of the seismic noise measurements. A significant correlation between the time evolution (mean value) of the low frequency seismic signal, tides, and snails movements has been identified.