While detrital material has been recognized as an important food source on coral reefs, its role in reef food webs remains unclear. We quantified detritus standing stock and flux rates to the detrital resource pool in two different habitats (exposed forereef and protected backreef) of Palmyra Atoll National Wildlife Refuge, while also measuring the trophic structure of the overlying fish assemblage. While the standing stock of detritus was 1.6 times higher on the protected backreef than the exposed forereef, input rates were 1.7 to 2.9 times higher on the forereef. These differences can be attributed to both variation in water motion and differential rates of biomass contributions to and removals from this resource pool. We found through stable isotope analyses of delta13C and delta15 N that benthic reef detrital composition is a combination of organic material from pelagic and benthic origins.

However, detrital composition varied among reef habitats as would be predicted by spatial differences in the overlying reef fish assemblage. Planktivores were the most numerically abundant guild in the forereef habitat, and stable isotope signatures of detritus reflected a greater input from pelagic sources (i.e., depleted in 13C). In contrast, herbivores and detritivores numerically dominated the backreef habitat, and detrital stable isotope signatures appeared to be predominately of benthic origin (i.e., enriched in 13C). Through total organic carbon and nitrogen analyses we found that benthic detritus may represent a significant nutritional source to benthic communities. Converting total nitrogen into maximum protein estimates, we found high deposition of protein (104-124 mg m-2) and organic carbon (184-190 mg m-2 ) to the benthos, but very low standing stock amounts of these materials.

While high water flow rates may explain low standing stocks of detritus in exposed forereef habitats, the lower flow rates in protected backreef habitats suggest that removal of this material is via consumption by abundant roving detritivorous fishes. Our results provide support for the hypothesis that reef fish detritivory represents a significant consumer-mediated energy pathway, promoting nutrient recycling by linking many elements of a complex food web.