Seasonal grazing rates and food processing by tropical herbivorous fishes

Abstract

Seasonal variability in grazing rates and food‐processing characters were assessed for three abundant fishes in a tropical rocky shore: the damselfish Stegastes fuscus, the parrotfish Sparisoma atomarium, and the surgeonfish Acanthurus bahianus. Significant differences were found in grazing rates among hour of day and seasons, and in food‐processing characters among seasons for the three fishes. Grazing rates for S. atomarium and A. bahianus peaked at 1300 and 1400 hours for S. fuscus. Three main periods of different intensity in bite rates, low, intermediate and intense, were identified for all fishes. As expected, total bite rates, ingestion rates and gut fullness were highest in A. bahianus, the largest species studied, followed by S. atomarium and S. fuscus. S. atomarium with fused jaw teeth, holds the highest bite size and S. fuscus the lowest one. Gut turnover was high for S. fuscus and similar for S. atomarium and A. bahianus. Grazing rates and food‐processing characters seem to vary between seasons not only due to changes in temperature, but also affected by other factors. Fishes employ different food‐processing mechanisms and bear some differences in food‐processing characters to achieve optimal energetic supplies from a poor nutrient food resource.