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 irradiance, 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. KEY WORDS: Nerita · Foraging behaviour · Tropical shoreResale or republication not permitted without written consent of the publisher Aquat Biol 16: 177-188, 2012 Such lability in foraging behaviour represents important adaptive traits in organisms (Mery & Burns 2010). Climatic seasonality, for example, is a large time-scale temporal pattern that affects foraging behaviour owing to changes in physical stress, predation pressure and food availability as well as associated changes in tidal and diurnal conditions. As a result, such variation in foraging behaviour can make it difficult to define precise behavioural patterns of a species (Chapman & Underwood 1992a, Ng & Williams 2006, Santini et al. 2011.The gastropod genus Nerita Linnaeus 1758 (Neritacea) has a high abundance and diversity in tropical regions (Vermeij 1973). Most species, such as N. textilis (Chelazzi et al. 1983) and N. polita (Chelazzi 1982) are zonal shuttlers (Chelazzi et al. 1988), which forage from a refuge either up-or downshore during each tidal cycle before returning to their resting level (Chelazzi et al. 1988). Previous observations on the behaviour of Nerita have not, however, investigated longer-term variations in foraging patterns, such as monthly or seasonal variation, al though a longerterm study of N. plicata, N. textilis and N. undata in Kenya showed these species to be more active on spring than neap tides (Ruwa & Jaccarini 1988).Nerita are important herbivores in the Hong Kong rocky intertidal zone (Hill 1980). In contrast to other tropical localities where the foraging beh...