Feeding behavior and morphological adaptations in two sympatric sea urchin species in central Chile

Loxechinus albus and Tetrapygu niger are 2 sympatric sea urchin species present in the rocky intertidal and subtidal zones of central Chile.In this study we test the hypothesis that the 2 species employ dfferent feeding mechanisms, and that this has resulted in distinct ecological roles for the 2 species.We also analyze structures associated with feeding.Results from field studies indicate that T niger principally consumes benthic algae (i.e.Gelidium spp.) and in doing so clears significantly more primary space than does L. albus.Laboratory experiments confirmed this observation, and demonstrated that T. niger consumes significantly more benthic algae (i.e.Gelidiurn spp.) attached to rock than floating algal pieces (i.e.Lessom'a nigrescens).Small L. albus ( < 3 cm diameter) consume significantly more benthic than floating algae pieces; the reverse is true for large (> 3 cm diameter) individuals.While oral podia in both species are modified terminally to form suckers, only L. albus possesses such modifications on aboral poda.Additionally, in T. niger the pyramids of Aristotle's lantern are roughly twice as long as those in L, albus.We discuss the possible ecological roles of each species with reference to the structure of intertidal communities.