Limpet aggregation does not alter desiccation in the limpet Cellana tramoserica

Animals, particularly intertidal snails, are frequently found in groups or aggregations. The biological explanations for such patterns frequently espouse a behavioural response to physical stresses, i.e. is that limpets form groups to minimise desiccation risks. There is little or no reliable experimental evidence for this. I experimentally manipulated the surroundings of individual limpets, such that grouped limpets became solitary and solitary limpets became grouped, with appropriate controls. If grouping reduced desiccation, this should result in a changed osmotic potential of circulatory fluid; a measure of desiccation. Testing this required new information on extraction and storage of haemolymph. The methods of extraction had a small, but significant, effect on the osmolality of haemolymph, with in-situ collection probably the most desirable. I found the haemolymph may be stored for up to 4 days at 4 °C and 3 weeks at − 10 °C without any measurable changes. The prediction of a link between desiccation and aggregation in limpet was not supported. Hence the idea that limpets may gain the benefit of reduce desiccation by joining a group was refuted. These results are similar to those from studies examining the vertical distribution of limpets, that desiccation is not likely to be a causal factor in determining small spatial scale distributions of limpets. It is less likely then that limpet aggregation occurs in response to desiccation risks and it is more likely that behavioural responses to predation risk may be involved.