Abstract

Phenotypic modifications in the structure of barnacle cirri constitute an adaptive mechanism associated with food availability in wave-exposed and wave-protected areas. Given that crowding during growth provokes density-dependent effects, access to food could also be a factor that generates morphometric and meristic changes in cirri. Length, diameter, and number of segments of the 3 rd to 6 th cirri were determined in Jehlius cirratus, the dominating species in the upper and middle intertidal zones of the Chilean coastline. Specimens collected in Metri Bay (41°36′S 72°42′W), southern Chile, were distinguished according to their growth conditions: isolated, contiguous, or aggregated. Crowding level during growth affected the structural characteristics of the cirri: the cirral appendages of crowded individuals are longer, thicker, and have more segments than those of individuals that grow in isolation. The results obtained indicate that the morphometric and meristic characteristics of morphological structures associated with filtration vary according to the grouping level at which individuals grow, with a possible threshold density level at which cirral morphology is modified. The results hence suggest that intraspecific competition for food at high densities is expressed in cirral morphology. © 2007 Brill Academic Publishers.