Ontogenetic changes in the diet of the herbivorous Scartichthys viridis in a rocky intertidal zone in central Chile

Scartichthys viridis maintains a herbivorous diet following recruitment to rocky intertidal areas, where it consumes almost exclusively macroalgae. The sheet–like green macroalgae Ulva and Enteromorpha were the main items consumed by individuals <130 mm L T . The tough branching red macroalga Gelidium made the bulk of the gut contents of specimens >220 mm L T , Ulva being consumed to a much lesser extent. Further, Gelidium increased in importance in the total gut contents during ontogeny. In contrast, both small (70–120 mm L T ) and medium–sized (140–210 mm L T ) S. viridis individuals preferred Ulva in the laboratory. It is suggested that the increasing consumption of Gelidium along the ontogeny of S. viridis results from the limited availability of Ulva in the field. Large S. viridis individuals possessed longer guts relative to their body length, in comparison with small individuals.