Evidence for benthic primary production support of an apex predator–dominated coral reef food web

Abstract

Five hundred and ninety-nine primary producers and consumers in the Papahānaumokuākea Marine National Monument (PMNM) (22°N–30°N, 160°W–180°W) were sampled for carbon and nitrogen stable isotope composition to elucidate trophic relationships in a relatively unimpacted, apex predator–dominated coral reef ecosystem. A one-isotope (δ13C), two-source (phytoplankton and benthic primary production) mixing model provided evidence for an average minimum benthic primary production contribution of 65 % to consumer production. Primary producer δ15N values ranged from −1.6 to 8.0 ‰ with an average (2.1 ‰) consistent with a prevalence of N2 fixation. Consumer group δ15N means ranged from 6.6 ‰ (herbivore) to 12.1 ‰ (Galeocerdo cuvier), and differences between consumer group δ15N values suggest an average trophic enrichment factor of 1.8 ‰ Δ15N. Based on relative δ15N values, the larger G. cuvier may feed at a trophic position above other apex predators. The results provide baseline data for investigating the trophic ecology of healthy coral reef ecosystems.