RECRUITMENT REGULATES DEMOGRAPHIC VARIATION IN A TROPICAL INTERTIDAL BARNACLE

Chthamalus fissus was studied on the central Pacific coast of Costa Rica. Mortality after settlement (=after day 1) was density independent for at least 90 d, so recruitment reflected settlement. Abundance appeared limited by sparse recruitment since considerable bare space was available at most sites during much of the study. Intraspecific competition (preemptive and adult-adult) was weak, except after occasional peaks of dense recruitment. Interspecific interactions were also weak, except for localized, intense predation by the thaidid gastropod Acanthina brevidentata near cracks and crevices, and sporadic competition with the small mussel Brachidontes semilaevis. In large part, demography of C. fissus was regulated by events in the water column affecting settlement and subsequent recruitment. Recruitment of Chthamalus spp. is very sparse in the Bay of Panama, sparse with occasional peaks in C Costa Rica, and consistently dense in the N Gulf of California. Post-settlement processes involving Chthamalus spp. (competition and predation) appear strong and pervasive only in the N Gulf of California. -from Author