Small-scale temporal and spatial variability in foraging behaviour of the mid-shore gastropod Nerita yoldii on seasonal, tropical, rocky shores

摘要

Describing temporal variation in the foraging behaviour of intertidal gastropods is important to gain an understanding of the environmental conditions that constrain their activity patterns. Foraging behaviour in the tropical gastropod Nerita yoldi was mainly determined by the tidal cycle: individuals foraged when they were awash, or emersed when the rock was wet, migrating downshore to forage and upshore when they returned to refuges. Apart from tidal influences, foraging in N. yoldii also varied with season and tidal state. Individuals were generally more active in summer than in winter and on neap than spring tides; although small-scale daily variation existed. Such temporal variation may be caused by several interacting environmental variables,especially air temperature, pressure and irradi-ance, which influence physical conditions as well as individuals' metabolism. Individual foraging patterns were also highly labile between seasons: most individuals would stop and remain stationary on the open rock surface in winter, but returned to refuges after foraging in summer, a pattern probably driven by physical stress. The foraging behaviour of N. yoldii, therefore, is predictable on a coarse scale, in terms of when they are active, but highly labile in duration and foraging range, which indicates the importance of local, daily variation in environmental factors controlling foraging on shores that have strong temporal changes in abiotic conditions.