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
Highlights
Herbivorous fishes play an important role in coral reef ecosystems by grazing algae that can otherwise outcompete corals, thereby indirectly promoting the recruitment, growth, and survivorship of reef-building corals (Hughes et al 2007; Bonaldo et al 2014; Adam et al 2015)
Of the 114 fecal pellets consumed by fishes, 91.2% were consumed by parrotfishes or surgeonfishes alone, while 8.8% were consumed by other fishes (Abudefduf saxatilis, Pomacanthus paru, Stegastes partitus, S. planifrons, and other Stegastes spp.)
The parrotfish S. taeniopterus and surgeonfish A. coeruleus were more frequent coprophages, where of the total 114 observed instances of coprophagy of C. multilineata fecal pellets, 44.7% were by S. taeniopterus and 26.3% were by A. coeruleus
Summary
Herbivorous fishes play an important role in coral reef ecosystems by grazing algae that can otherwise outcompete corals, thereby indirectly promoting the recruitment, growth, and survivorship of reef-building corals (Hughes et al 2007; Bonaldo et al 2014; Adam et al 2015). Parrotfishes and surgeonfishes can vary in their grazing behavior interspecifically, ontogenetically, and based on context-dependent factors, such as food and nutrient availability (Burkepile and Hay 2011; Bonaldo et al 2014; Smith et al 2018; Duran et al 2019; Ruttenberg et al 2019). Nominally herbivorous parrotfishes graze on a diverse array of other food sources such as cyanobacteria, sponges, and corals (Bruggemann et al 1994a; Burkepile et al 2019; Nicholson and Clements 2020; Rempel et al 2020). Surgeonfishes have been documented grazing on benthic cyanobacterial mats and invertebrates, such as sponges (Cissell et al 2019; Duran et al 2019)
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