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Abstract Effective management of wild animals requires understanding how predation and harvest alter the composition of populations. These top‐down processes can alter consumer body size and behavior and thus should also have consequences for bottom‐up processes because (1) body size is a critical determinant of the amount of nutrients excreted and (2) variation in foraging behavior, which is strongly influenced by predation, can determine the amount and spatial distribution of nutrients. Changes to either are known to affect ecosystem‐scale nutrient dynamics, but the consequences of these dynamics on ecosystem processes are poorly understood. We used an individual‐based model of an artificial reef (AR) and reef fish in a subtropical seagrass bed to test how fish body size can interact with variation in foraging behavior at the population and individual levels to affect seagrass production in a nutrient‐limited system. Seagrass production dynamics can be driven by both belowground (BGPP) and aboveground primary production (AGPP); thus, we quantified ecosystem‐scale production via these different mechanistic pathways. We found that (1) populations of small fish generated greater total primary production (TLPP = BGPP + AGPP) than large fish, (2) fish that foraged more increased TLPP more than those that spent time sheltering on ARs, and (3) small fish that foraged more led to greatest increases in TLPP. The mechanism by which this occurred was primarily through increased BGPP, highlighting the importance of cryptic belowground dynamics in seagrass ecosystems. Populations of extremely bold individuals (i.e., foraged significantly more) slightly increased TLPP but strongly affected the distribution of production, whereby bold individuals increased BGPP, while populations of shy individuals increased AGPP. Taken together, these results provide a link between consumer body size, variation in consumer behavior, and primary production—which, in turn, will support secondary production for fisheries. Our study suggests that human‐induced changes—such as fishing—that alter consumer body size and behavior will fundamentally change ecosystem‐scale production dynamics. Understanding the ecosystem effects of harvest on consumer populations is critical for ecosystem‐based management, including the development of ARs for fisheries. 

Abstract Consumers mediate nutrient cycling through excretion and egestion across most ecosystems. In nutrient‐poor tropical waters such as coral reefs, nutrient cycling is critical for maintaining productivity. While the cycling of fish‐derived inorganic nutrients via excretion has been extensively investigated, the role of egestion for nutrient cycling has remained poorly explored. We sampled the fecal contents of 570 individual fishes across 40 species, representing six dominant trophic guilds of coral reef fishes in Moorea, French Polynesia. We measured fecal macro‐ (proteins, carbohydrates, lipids) and micro‐ (calcium, copper, iron, magnesium, manganese, zinc) nutrients and compared the fecal nutrient quantity and quality across trophic guilds, taxa, and body size. Macro‐ and micronutrient concentrations in fish feces varied markedly across species. Genera and trophic guild best predicted fecal nutrient concentrations. In addition, nutrient composition in feces was unique among species within both trophic guilds (herbivores and corallivores) and genera (AcanthurusandChaetodon). Particularly, certain coral reef fishes (e.g.,Thalassoma hardwicke,Chromis xanthura,Chaetodon pelewensisandAcanthurus pyroferus) harbored relatively high concentrations of micronutrients (e.g., Mn, Mg, Zn and Fe, respectively) that are known to contribute to ocean productivity and positively impact coral physiological performances. Given the nutrient‐rich profiles across reef fish feces, conserving holistic reef fish communities ensures the availability of nutritional pools on coral reefs. We therefore suggest that better integration of consumer egestion dynamics into food web models and ecosystem‐scale processes will facilitate an improved understanding of coral reef functioning.