AB 11:91-98 (2010)  -  DOI: https://doi.org/10.3354/ab00294

ABSTRACT: Variation in the distribution of animals across the landscape, within and between habitats, can occur at a variety of scales. At the smallest scale, individuals can either be positioned randomly or can be orientated in regard to variables. Differences in orientation can, for many animals, directly affect their reproductive success and/or survivorship, and these effects may have downstream ecological consequences. Organisms may orientate themselves in a specific way in response to varying environmental conditions or habitat properties; alternatively they may consistently orientate in a specific direction. The present study investigated patterns of orientation during low tide in the intertidal marine limpet Cellana tramoserica on steeply sloped rocky surfaces (>60° to the vertical). We also examined whether individual limpets consistently orientated in the same direction or if orientation was dependent upon their orientation during the previous low tide. There was a downward bias in orientation. Mensurative and manipulative experiments measuring limpet orientation over different days showed that individual limpets did not consistently orientate in the same direction and that their orientation was independent of their orientation during the previous low tide. Thus, whilst limpets on slopes often orientate with their heads downwards, there is much inherent individual variation in the orientation patterns exhibited by resting limpets.  Simple mechanistic explanations such as responses to desiccation are unlikely to be sufficient to explain why limpets choose different orientations at the end of foraging excursions. These findings have implications for understanding limpet distributions on rocky shores and downstream ecological consequences.

KEY WORDS: Cellana tramoserica · Direction · Consistency of orientation · Behaviour · Circular statistics · Intertidal habitat · Australia