ABSTRACT
Comparative studies on cirral behavior, physiological adaptations, growth rates, and fecundity all provide interpretations of how some barnacles are better able to survive in specific habitats and climates than others. Microenvironments beneath barnacle attachments provide conditions suitable for rapid growth of sulfate-reducing bacteria, which play a significant role in the corrosion process. The intertidal zone is inhabited principally by marine organisms and a few terrestrial species tolerant of short periods of tidal submersion. Barnacle zonation is less striking on tropical rocky shores, perhaps because of prolonged high temperatures that must be tolerated at the upper intertidal levels. Barnacles inhabiting shores are more temperature and desiccation tolerant than subtidal ones; those extending their populations to higher shore levels are more tolerant than the lower ones. Barnacles are unique among crustacea in having taken on an exclusively sessile habit. There are three distinct easily recognizable types: goose or peduculate barnacles, asymmetric barnacles and acorn barnacles.
