RBMO 46(3): 329-338 | 2011
Article

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Ontogenetic habitat shift of an herbivorous crab: A chemically mediated defense mechanism?

Alvaro T. Palma^1*, Mauricio Soto-Gamboa² & F. Patricio Ojeda¹

¹Center for Advanced Studies in Ecology and Biodiversity, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Casilla 114-D, Santiago, Chile

²Instituto de Zoología, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile

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Many herbivores specialize on a specific type of host that can serve both as food and shelter. Such associations, however, do not necessarily last throughout the ontogeny of the herbivore. For example, in field surveys a close association between the herbivorous crab Taliepus dentatus and brown algae has been found. However, newly settled and juvenile individuals were only found on patches of the brown algae Glossophora kunthii, while older individuals of the population were most frequently found living on the common brown kelp Lessonia trabeculata. Our field and laboratory experiments showed that different size classes of this crab species may actively select these algal habitats, and that these preferences are even more conspicuous for small newly settled individuals. Bioassay experiments showed that fish specifically avoided either T. dentatus or G. kunthii, which suggests that consumption of this alga by T. dentatus could decrease their natural rates of mortality due to fish predation. These results were further corroborated through field tethering experiments, where individuals of this species exhibited high survivorship regardless of the surrounding substrate on which they were placed. In this study, we speculate that incorporation of anti-predator defenses from algae may then enhance the survivorship of juveniles, thus, deterring consumers like carnivorous fish common in these environments. Although less threatened, because they are too large to be consumed by predatory fish, older individuals might also benefit from living on L. trabeculata, which is rich in secondary metabolites. 

Key words: Secondary metabolites, Taliepus dentatus, Glossophora kunthii, Lessonia trabeculata 

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