Temperature Relations in Two Species of Tropical West American Littorines

The intertidal zonation and temperature relationships of two Littorina species which co—occurred over a wide range of latitudes in the West American tropics were studied. It was found that L. aspera lives higher in the intertidal zone, experiences higher tissue temperatures in the field, and has a higher upper lethal temperature than L. modesta. A positive correlation between intertidal height and heat resistance has been observed previously in temperature latitudes. A similar correlation in two high intertidal tropical snails was found in this study. There is a large difference between maximum temperature recorded in the field and thermal tolerance determined in the laboratory, providing the animals with a considerable safety factor. It is suggested that temperature is a major factor influencing the intertidal distribution of these species.