Abstract

We analyse the effects of crowding ('hummocking') on the growth, reproduction and mortality of the chthamaloid barnacle Jehlius cirratus (Darwin, 1854) on the coast of Chile. Recruitment intensity, ranging from solitary individuals to dense groups, generates different growth conditions. Density-dependent effects are reflected in the shape, growth parameters, fecundity, sexual maturity and mortality of solitary and crowded specimens. The skewing of size distribution during growth was not significant at the beginning of the growth period, irrespective of initial density. Nevertheless, skewness in size increased with time, both at high and low densities, indicating that the dominance and suppression exerted by larger specimens over smaller ones generate a density-dependent effect on size during growth. Mortality was greatest when high-density recruitment occurred immediately before the period when water temperature and food quantity are highest (spring), when it is assumed that growth is greatest; this seasonal effect was not detected at lower levels of recruitment density. Similarly, no differences in mortality were detected between recruitment densities during the period when temperatures are lowest (autumn) and growth is probably slower. In the middle-high intertidal zone, where J. cirratus co-exists with Notochthamalus scabrosus (Darwin, 1854), the proportion of dead J. cirratus specimens was directly related both to the relative abundance of N. scabrosus and the total barnacle density. Although the mortality of J. cirratus was density dependent, the increase in the number of N. scabrosus towards the lower section of the middle intertidal zone could have a greater effect on J. cirratus mortality than intra-specific competition.