LIFE HISTORY AND ENVIRONMENT IN TWO SPECIES OF INTERTIDAL BARNACLES

¹ Department of Biology, San Diego State University, San Diego, California, 92182

The reproductive ecology of Chthamalus anisopoma and Tetraclita stalactifera is compared in order to understand how their life histories function in the context of their present environment, and what selective forces might have shaped their life histories. C. anisopoma is common in the lower intertidal of the Gulf of California. It initiates breeding six weeks after settlement; brooding and recruitment is year-round. Growth after settlement is rapid for two months, then slows markedly. Survivorship is fairly constant at all ages. Observations indicate that most mortality results from predatory gastropods, and from intraspecific crowding. T. stalactifera is generally confined to the upper intertidal. It failed to brood during the study period. The ovarian cycle indicates that brooding would otherwise take place during the summer. The age of first reproduction is estimated at two years. Recruitment of cyprids is strongly seasonal, peaking during August. The growth rate is relatively constant. Survivorship is initially very poor, apparently due to desiccation stress, but improves substantially after four months.

An examination of the intertidal positions and life histories of Tetraclita and Chthamalus congeners from different coastlines of the world reveals a relative conservatism of life histories, regardless of position in the intertidal. This conservatism is discussed as a general phenomena in Chthamalus and Tetraclita, and is contrasted with the relative diversity exhibited in another genus of barnacles, Balanus.