Patelloida saccharina (Linnaeus, 1758)

Zapanta, Eliza Ysabelle T., Fortaleza, Maybelle A., Elumba, Merlene E., Uy, Reena Cyndi L., Nañola, Cleto L. & Jr, 2020, Diel movement patterns of Pacific sugar limpet, Patelloida saccharina (Gastropoda: Patellogastropoda: Lottiidae) in response to semi-diurnal tides of Samal Island, Philippines, Raffles Bulletin of Zoology 68, pp. 870-879 : 877

Movement of P. saccharina in response to disturbance.

During field work in the last quarter, a low-pressure area at the eastern side of Mindanao brought heavy rains and strong winds. The strong waves detached some of the grid quadrats and removed the nail polish markings on some limpets, thus restricting the scope of observations. While fixing the detached grid quadrats underwater, it was observed that a large limpet lifted itself and moved away from its home scar to the leeward side of the rock to avoid dislodgement. Similar behaviour was observed in two large P. saccharina limpets from other grid quadrats that were reinstated. These limpets remained in their new sheltered locations during the low tide observation. Such movements observed among large P. saccharina limpets during heavy rains and strong waves validate the occasional activity pattern that may occur among intertidal animals, as described by Chelazzi et al. (1988).

Activity patterns in gastropods could be occasional, continuous, or rhythmic (Chelazzi et al., 1988). Continuous and rhythmic activities are associated with the processes occurring along the sea-land axis (i.e., diel cycles and tidal fluctuations). Hence, their movements become predictable and recurrent in response to the physical environment ( Underwood, 1979; Little et al., 1988; Santini et al., 2011). On the other hand, occasional activity refers to responses elicited during unforeseeable events. Chelazzi et al. (1988) discussed that this may occur in the sudden presence of predators or during unfavourable weather conditions. While periods of darkness and submersion in water are prerequisites to P. saccharina movement on the rocky intertidal shores of Samal Island, the strong wave action brought by heavy rains can also induce their movement, even during daytime. Such movement is important to prevent dislodgment by the strong waves ( Little, 1989) or avoid osmotic stress brought by rain water dilution ( Wolcott, 1973; Branch & Cherry, 1985). These deviations from the usual rhythmic patterns have adaptive value and are necessary for survival (Chelazzi et al., 1988; Naylor, 1988).

Overall, activity patterns are variable in response to competitive interactions ( Underwood, 1979, 1984), predation ( Bertness et al., 1981), and desiccation ( Cook, 1969), which are key evolutionary drivers to limpet behaviour ( Chelazzi & Vannini, 1988; Little, 1989). Additionally, Branch & Cherry (1985) noted that food availability, wave action, and osmotic stress can also influence these movement patterns. Given that most limpet species reported are of marine origin, Little (1989) emphasised that desiccation is more important in limiting the behavioural plasticity of limpets. However, Branch (1981) argued that if desiccation is the motivation for preference of movement while submerged, why was there no movement during daytime submergence?

The scope of the current study may not be able to determine whether P. saccharina movement is driven by competition, predation, or food availability. However, it is probable that P. saccharina limpets thriving on the horizontal surface of the high intertidal zone may experience hotter conditions and higher rates of water loss, similar to the reported habitat partitioning in the tropical Cellana grata ( Gould, 1859) population in Hong Kong ( Williams & Morritt, 1995). Moreover, the combination of nocturnal activity and homing habit appears to be a favourable response by P. saccharina limpets to persist on the tropical rocky intertidal shores of Samal Island. It should be noted that different movement patterns may be observed in other areas (e.g., Villarta et al., 2019), depending on the habitat type and corresponding environmental gradients ( Branch, 1981). Similar studies may be conducted on other limpet species in Samal Island to enrich our understanding of the dynamics of the tropical intertidal environment.