On the behaviour of barnacles III. Further observations on the influence of temperature and age on cirral activity

Abstract

The range of temperature over which the cirri were active, and the frequency of beating of the cirri at different temperatures were measured in a further five species of barnacles from a variety of habitats. In three of the species the temperature range and frequency of cirral beat were related to the geographical distribution of the species. The tropical and warm temperate species Balanus amphitrite was active at higher temperatures, and showed a greater frequency of beating than the northern species B. balanus; conversely, the latter was active to much lower temperatures than JB. amphitrite. The species with the widest geographical range, B. improvisus, showed cirral activity over the widest range of temperatures, although its behaviour at high temperatures was similar to that of the related species B. amphitrite. It is suggested that B. improvisus is a tropical species that has adapted itself to colder climates; its tolerance of a wide range of temperatures may be associated with its tolerance of low salinities.The stalked barnacle Lepas anatifera showed too restricted a temperature range for its supposed world-wide distribution, and it is suggested that the species may contain physiological races adapted to different climates. The extremely restricted range of temperatures over which the cirri of the deepsea barnacle Hexelasma hirsutum were active can be correlated with the almost uniform temperature conditions at great depths.In B. balanus age-groups can be clearly distinguished by growth rings on the shell, and the cirral frequency was found to be slower in the older specimens. Even slower cirral beating was found in some starved specimens.