Specialized Snapper Reveal Reef Food Web Fragility
Tropical reef food webs are more delicate than scientists once assumed, with specific species relying on narrow energy pathways.
What does this new research suggest about the health of coral reefs? A study led by Associate Professor Kelton McMahon at the University of Rhode Island’s Graduate School of Oceanography found that many reef creatures depend on surprisingly specialized food sources, challenging the idea of a highly interconnected ecosystem.
The research used compound-specific stable isotope analysis of amino acids (CSIA-AA), a cutting-edge technique that traces nutrient pathways through ecosystems. The team examined three common reef-dwelling snapper species: Lutjanus kasmira, L. ehrenbergii, and L. fulviflamma. These fish, previously thought to be opportunistic feeders, turned out to be remarkably specialized.
- Lutjanus kasmira fed almost exclusively on food webs originating from water column phytoplankton.
- L. ehrenbergii was tied to a food web based on macroalgae on the seafloor.
- L. fulviflamma primarily consumed resources from a coral-based food web.
McMahon reflected on his initial dives in the Red Sea, noting the synchronized schooling of these snapper species. “We would never have guessed that each had carved out its own unique niche within these complex, biodiverse reef food webs,” he said. These fish, as abundant predators high on the food chain, were long assumed to be generalists, feeding broadly on available prey.
However, the findings paint a different picture: the flow of energy from primary producers like coral, macroalgae, and phytoplankton to predators is highly compartmentalized. Each species, it appears, relies on a distinct “silo” of production, forming self-contained food chains within specific microhabitats. “It’s fundamentally reshaping how we think about biodiversity of coral reefs,” McMahon stated. Seeing entire food chains tightly linked to a single primary producer, like macroalgae, even when other options like coral are nearby, is a significant revelation.
Implications for Reef Resilience and Biodiversity
This specialization offers a new perspective on how high species diversity is maintained in nutrient-poor reef environments. Normally, stable ecosystems exhibit overlap in energy sources, aiding recovery from disturbances. However, these “vertical silos” mean that if a single primary producer is impacted by climate change, overfishing, or bleaching, an entire food chain could be jeopardized.
This structure makes coral reef food webs more organized and more vulnerable to rapid environmental shifts than previously understood.
Novel Methods: CSIA-AA
McMahon’s research lab utilizes stable isotopes to reconstruct animal life histories based on diet. The team employed CSIA-AA to trace carbon and nitrogen movement through reef food webs. Unlike stomach content analysis, which provides only a brief snapshot, CSIA-AA offers a more precise, long-term view of energy flow.
“I’ve spent my career developing knowledge and tools to isolate and analyze all individual compounds within complex organisms, unlocking a metabolic history of organisms in a way we have never done before,” McMahon explained about the CSIA-AA methodology. This allows scientists to track diverse energy sources and reveal previously unseen food web patterns.
Patience is Key
Samples collected for this study in the Red Sea were archived for over a decade before analytical advancements made this research possible. McMahon collected these samples 15 years ago as a postdoc. “The data were there, but I didn’t yet have the tools or perspective to make sense of it,” he shared. The findings underscore the importance of allowing scientific ideas and methods to mature.
Future work will expand this research to other reef systems, kelp forests, and deep-sea ecosystems. The team also plans to integrate DNA metabarcoding to more accurately identify prey species within these specialized energy channels.
“In my lab, we don’t specialize on a system or species; we’ve worked in Antarctica with penguins, on ancient human diet in MesoAmerica, and locally with the burgeoning jonah crab fishery,” McMahon added. “Our goal is to develop tools that solve vexing ecological problems, and make sure diverse people and approaches are effectively brought together.”
Citation: McMahon KW, Thorrold SR, Langan JA, Pi J, Berumen ML, 2025. Highly siloed nutrient pathways fuel meso-predator fishes on coral reefs, Current Biology (2025)
