Influences of ontogenetic phase and resource availability on parrotfish foraging preferences in the Florida Keys, FL (USA)

ABSTRACT: Over the previous 35 yr, Caribbean coral reefs have experienced decreases in coral cover and increases in algal cover, leading to calls for increased protection of reef herbivores such as parrotfish. Previous studies have classified parrotfish into functional foraging groups based on beak morphology, gut content analyses, isotopic composition, and direct observations of foraging behaviors. However, few studies have examined how parrotfish foraging behaviors change with ontogenetic phase, substrate composition, and parrotfish biomass. In this study, we determined the foraging preferences of 10 parrotfish species and examined how these preferences varied with ontogeny, algal composition, and parrotfish biomass. We observed foraging behaviors of 3 phases (juvenile, intermediate, terminal) of 10 parrotfish species on 34 reefs in the middle Florida Keys (USA) that varied in coral and algal composition. Cluster analysis of Manly’s alpha electivity indices revealed 3 functional feeding groups that differed in their selectivity of turf, calcareous, and fleshy algal communities as preferred foraging habitats. Juvenile parrotfishes of different foraging groups had similar foraging preferences that diverged with maturation. Preferences for turf algal communities increased with increasing turf algal cover but were not influenced by parrotfish biomass. In contrast, preferences for fleshy algal communities decreased with increasing parrotfish biomass. These results suggest that parrotfish species have different foraging preferences, which may vary with ontogeny, algal abundance, and parrotfish biomass. Thus, efforts to increase parrotfish biomass may not always lead to a predictable decrease in algal abundance.