Tidal Amplitude and Activity in the Pulmonate Limpets Siphonaria normalis (Gould) and S. alternata (Say)

Cook, Susan; Cook, Clayton

The timing and extent of activity of homing limpets in different populations of Siphonaria normalis (Gould) at Enewetak Atoll and S. alternata (Say) in Bermuda were studied on tides of varying amplitude. Two distinct behavioural patterns were found. At sites where the first pattern was the rule, movement began just as limpets were exposed to air by falling tides or were wet by rising tides. These animals were less active on spring tides than on neap tides: they spent less time moving and in some cases did not move as far. On spring tides at some sites fewer animals were active. In the second pattern of behaviour, activity did not change with tidal amplitude. Limpets maintained relatively high levels of activity on spring ebbing tides by either continuing to move for relatively long periods after aerial exposure or by starting to move before they were exposed to air. The degree of environmental rigour at a site may determine what resident limpets do. Limpets with the first sort of behaviour all lived in places where water drained rapidly from rocks at low tide and/or places where the splash from waves was considerable at high tide. In contrast, limpets resident at more benign sites fell into the second behavioural category. Limpets at rapidly draining sites also tended to be more active on rising tides than on falling tides near the spring end of the tidal spectrum while limpets at other sites either divided activity equally between ebb and flood tides or were more active on ebbing tides.

Tidal Amplitude and Activity in the Pulmonate Limpets Siphonaria normalis (Gould) and S. alternata (Say)

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