MEPS 124:89-103 (1995)  -  doi:10.3354/meps124089

Populations of the tropical limpet Cellana grata Gould were studied on exposed shores around Cape d'Aguilar, Hong Kong. C. grata is a high shore species, the zonation pattern of which varies seasonally, shifting downwards in association with increasing summer temperatures. C. grata is a non-homing species and was active (foraging) whilst awash by the tide, moving up and down the shore with the flood and ebb tides, respectively. Limpets moved up to 1 m in the vertical plane over a tidal cycle. When not foraging limpets took refuge in habitats that reduced the effects of high temperature and desiccation stress. Temperature measurements of individuals and their physical environment showed that the quality of these refuges varied both spatially and temporally. Horizontal rock surfaces were hotter than vertical surfaces; limpet body temperatures and habitat temperatures in refuges (crevices, pool interfaces and east-facing vertical surfaces) were consistantly cooler than adjacent habitats by 3 to 8*C and limpet body temperatures were usually 2*C warmer than the rock they rested on. Experimental manipulations with specimens restrained 0.5 m above their normal resting height or on horizontal rock surfaces and prevented from returning to refuges caused desiccation, osmotic stress and, in many cases, death as a consequence of prolonged emersion in these sub-optimalhabitats. Individuals on horizontal surfaces lost water more rapidly than those on vertical surfaces and showed higher mortality. C. grata does not adopt many of the behavioural adaptions to reduce heat stress shown by other gastropod species. It does, however, exhibit 'mushrooming' behaviour, lifting its shell from the rock surface, although the exact benefits of this behaviour are unclear. Summer physical extremes may strongly select for limpet activity rhythms entrained by wave splash and the selection of refuges from high temperatures and desiccation when inactive. Variation in the quality of these refuges can lead to selective mortality during very hot periods.

Limpet . Habitat partitioning . Desiccation . Behaviour . Temperature . Tropical rocky shore