The mangrove snail Cerithidea decollata feeds on the ground at low water, and about two hours before high water climbs Avicennia marina trunks settling 20-40 cm above the level that the incoming tide will reach. The moment that C. decollata must start to measure the vertical distance it has to creep up the trunk to avoid submersion corresponds to the point at which creeping switches from a horizontal to vertical movement (the "0" point). Two vertical movements interrupted by a short horizontal movement were added together; however, if the horizontal interruption was wider than 10 cm a new "0" point was set, and snails climbed higher than control snails, according to the level of the horizontal interruption, without adding the two vertical segments. Through forcing snails to both climb and descend, we observed that they do not appear to be capable of subtraction.

The gastropod Cerithidea decollata typically feeds on mud at the mangrove soil surface at low tide and rests on Avicennia marina trunks throughout high tide. Tens of individuals can be observed climbing the trunks and clustering, 2-3 hr before the incoming high tide, approximately 40 cm higher than the level that the tide will reach. As soon as the water disappears, snails descend and disperse on the ground again. Signals able to tell the snails the height of the incoming tide are still unknown but we wanted to investigate whether or not some information may be transferred from resident snails to snails translocated from areas undergoing a different tidal regime. Snails from sites where tides never exceed 5 cm above ground level (translocated) were transported to sites flooded by higher tides (up to 80 cm above the ground), and their behaviour was compared with local snails (residents). At the beginning of the experiment, sea water occasionally made contact with translocated snails as they ascended the trunks later than resident snails and clustered closer to the water. After several tides, translocated snails started to behave similarly to resident snails and, by the 10th tide, the behaviour of the two groups was indistinguishable. However, the behaviour of translocated C. decollata was not affected by being in contact or not with resident snails; thus, it appears that no information was transferred from resident to translocated snails.