VARIABILITY IN BROODING ACTIVITY IN THE STALKED BARNACLE POLLICIPES POLYMERUS

¹ Department of Biological Sciences, University of Southern California, Los Angeles, California, U. S. A. 90007

Reproductive activity in the barnacle, Pollicipes polymerus, was studied at sites along the west coast of North America and in the laboratory. Patterns of seasonal brooding activity reveal two physiological races: a northern one with maximum brooding activity at cold seawater temperatures (14°C or less) and a southern one which broods most at warmer temperatures (20°C). The distribution of these two races corresponds, respectively, to the cold and warm temperate zones located north and south of Point Conception.

Laboratory experiments support field results that the northern physiological race broods at lower temperatures than the southern physiological race and that seasonal brooding activity is controlled more by water temperature than by food. A specific temperature level does not account for the onset of seasonal brooding activity as well as does a change in temperature toward the optimum level for each physiological race. A possible reason that food does not regulate seasonal reproductive activity in P. polymerus is that this large species has sufficient food reserves as compared with smaller barnacles found at higher intertidal levels.