The upper temperature tolerance of prosobranch gastropods of rocky shores at Hong Kong and Dar Es Salaam, Tanzania

The upper thermal tolerance of 22 species of prosobranch gastropods collected at Hong Kong and Tanzania, determined by acute and chronic immersion methods, showed a significant rank correlation with vertical distribution on the shore. The coma point was also correlated with vertical distribution but less significantly so. The difference between coma point and lethal temperature was generally smaller in lower shore species. The acute LT 50 of species occurring at both sites were 0.5–3°C higher in Hong Kong than Tanzania, which may be explained by greater seasonal temperature fluctuation and/or differences in geomorphology and microclimate. Intraspecific differences were found between seasons and high and low shore populations, coma point showing greater adaptation than lethal temperatures. Deviations in tolerance of particular species from the general relationship with zonation could be related to differences in microhabitat, shell colour and morphology, and reported thermoregulatory capacity.