Chemical Defenses, Protein Content, and Susceptibility to Herbivory of Diploid vs. Haploid Stages of the Isomorphic Brown Alga Dictyota ciliolata (Phaeophyta)

Seaweeds with free-living diploid and haploid stages might express recessive traits during haploid stages, or exhibit other differences, that would allow those stages to differ in fitness under different environmental conditions. Heteromorphic seaweeds are well known to have variable ecological traits associated with their morphological differences, but ecological differences among isomorphic stages have rarely been investigated. The chemically defended brown alga Diclyola ciliolala has a life history with isomorphic alternation of generations, allowing us to assess how chemical traits and susceptibility to herbivory differ among stages. Herbivorous amphipods and sea urchins consumed similar amounts of diploid sporophytes and haploid female and male gametophytes. Concomitant with similar palatability, the different life stages had similar concentrations of soluble protein and levels of chemical defenses. Thus, in addition to morphological similari-ties, the life stages of D. cilio/(/ta appear to share these ecological similarities.