Morphological responses of the exoskeleton in the intertidal barnacle Jehlius cirratus (Darwin, 1854) growing at different densities

Abstract

We evaluated density-dependent morphological variation in exoskeletal structures associated with feeding and reproduction in the intertidal cirripede Jehlius cirratus (Darwin, 1854) in Metri Bay, southern Chile. In July of 2010, we undertook artificial density reductions of J. cirratus that resulted in control and experimental quadrats of high (4 individuals/cm2), to intermediate (2.4 individuals/cm2 and 1.2 individuals/cm2), and low density levels (0.4 individuals/cm2). Sampling of specimens grown at each density was subsequently carried out 4 times at 20-day intervals. Penis length and the lengths of the third and sixth cirri were measured for every sampled specimen. Synchronous density-dependent changes in both penis and cirrus length were verified. From day 60, penis length showed a significant increase with decreasing experimental density. From day 40, the third and sixth cirri were both significantly longer in specimens grown at 4 individuals/cm2 than at lower densities, showing a decrease from day 40 possibly in response to intraspecific competition for food. These results suggest density-dependent effects on this species regarding structural plasticity of the exoskeleton when growing at high densities. No clear density range for morphological changes was observed, yet there was synchrony in changes to functionally independent organs. Given that the time lag before any response and the ability to undergo density-dependent morphological changes depend on the type of organ, and in other species have different response times to density changes.