Small shifts in collection site result in large intraspecific differences in macroalgal palatability

The role of herbivorous fishes in coral reef resilience has increased interest in the process of herbivory and has focused attention on herbivore feeding behavior, making it important to evaluate experimental methods used to assess herbivore decisions. We tested whether small-scale differences in collection site play a role in within-species palatability of macroalgae. Baseline grazing assays using algae collected on a fringing reef in Moorea, French Polynesia, revealed that herbivore preferences among three common species ranked Padina boryana > Sargassum mangarevense ≫ Amansia rhodantha. Comparing grazing preferences between individual thalli of the same species collected <15 m apart revealed that consumption of intertidal S. mangarevense was nearly six times greater than for conspecifics collected from the adjacent subtidal reef flat. The same trend occurred for P. boryana but was not significant. This demonstrated that algal palatability can vary on a very small spatial scale, presenting a potential trap for the unwary when setting up experiments; we encourage researchers to consider this potential complication in experimental studies of herbivory.