Feces consumption by nominally herbivorous fishes in the Caribbean: an underappreciated source of nutrients?

Abstract

AbstractParrotfishes and surgeonfishes are major Caribbean herbivores that primarily graze reef algae and thereby play an important functional role in indirectly promoting coral recruitment and growth. Yet, an emerging body of research suggests that these nominal herbivores graze on a diverse array of other food sources and researchers have questioned whether they may target more nutrient-dense foods growing within or upon algae, such as cyanobacteria. In this study, we investigated the species-specific foraging rates of parrotfishes and surgeonfishes on Brown Chromis (Chromis multilineata) fecal pellets compared to other major dietary items. We found that almost 85% of observed fecal pellets were ingested by fishes and that over 90% of ingested fecal pellets were consumed by parrotfishes and surgeonfishes alone. While there were species-specific differences in the levels of feces consumption (coprophagy), we found that all three surgeonfishes (Acanthurus chirurgus, A. coeruleus, and A. tractus) and six of the nine of parrotfish species surveyed (Scarus coeruleus, S. iseri, S. taeniopterus, S. vetula, Sparisoma aurofrenatum, and S. viride) consumed C. multilineata feces. To better understand the nutritional value of this behavior, we analyzed the composition of proteins, lipids, carbohydrates, total calories, and micronutrients in C. multilineata fecal pellets and compared these to published values for other food sources targeted by these fishes. Our findings suggest that these fecal pellets may have higher values of proteins, carbohydrates, total calories, and important micronutrients, such as phosphorus, compared to various macroalgae and the epilithic algae matrix, though comparable or lower values compared to cyanobacteria. To our knowledge, this is the first study to document coprophagy by tropical herbivorous fishes in the Caribbean region. This research advances our understanding of the foraging ecology of nominally herbivorous fishes and highlights the importance of fish feces as a nutritional resource on coral reefs. Graphical abstract