Functional diversity in herbivorous fishes on Caribbean reefs: The role of macroalgal traits in driving interspecific differences in feeding behavior

Abstract

Understanding how functional traits drive plant-herbivore interactions often illuminates the mechanisms driving niche partitioning and functional diversity in this important guild of consumers. On coral reefs, a diverse suite of herbivorous fishes is key for controlling algal abundance and impacting benthic community dynamics. Here, we focus on how algal traits shape complementarity in feeding for a diverse suite of large herbivorous fishes on a coral reef in the wider Caribbean. We used feeding assays in the field to document feeding patterns of the different herbivorous fishes across 50 species of macroalgae. Then, we used a suite of macroalgal traits such as dry mass, nutrient content, calcification, and chemical defenses to assess how these traits influenced patterns of consumption. Algal defenses were the major traits determining the overall vulnerability of algae to herbivores, with uncalcified algae from undefended genera being consumed 40% more rapidly than algae that were either calcified or chemically defended. Nutrient content of algae explained little in patterns of overall herbivory. We found significant niche diversification in feeding both among and within genera with the three major genera having unique feeding patterns on different suites of algae (Acanthurus spp. - red macroalgae, Sparisoma spp. - brown and green macroalgae, and Scarus spp. - benthic filamentous algae). With respect to how algal traits influenced patterns of feeding in individual species, we found that: (1) some herbivore species were almost exclusively influenced by avoiding algal defenses, (2) some species showed strong interactions between algal defenses and nutrient content that determined their feeding, and (3) some species (Kyphosus spp., Pomacanthus arcuatus) targeted chemically-defended algae with high nutrient content. Our work highlights the role that algal traits play in influencing patterns in the diversity and redundancy of feeding in herbivorous fishes on coral reefs.