Worldwide, urchins are key herbivores that create macroalgae-depleted ‘barrens’ due to their grazing, yet the nutritional importance of macroalgae compared to invertebrates is unclear for the omnivore Centrostephanus rodgersii (long-spined urchin; “Centro”) across its native New South Wales (NSW) range. It is thought that large-bodied predators like the Palinurid Sagmariasus verreauxi (eastern rock lobster), Wrasse Achoerodus viridis (blue groper wrasse) and Sparid Chrysophyrus auratus (pink snapper) control Centro. If urchin grazing is the key reason for macroalgae loss we would expect macroalgae to be the primary nutritional item. Similarly, if large predators control Centro we would expect it to be prominent in the diet. To investigate, we undertook Bayesian isotope mixing models with 150 Centro collected in nearshore barrens and macroalgal forests as well as 275 lobsters, 45 gropers and 73 snappers gained from donations. Surprisingly, macroalgae was only a portion (~ 30 %) of Centro diets irrespective of habitat, with urchins eating more invertebrates (> 50%) and particulates (> 60 %). For predators, groups including Centro had low dietary importance for lobsters (~ 10 %) but were greater for groper (~ 30 %) and snapper (~ 60 %). Surprisingly, there was little effect of size for lobsters (+ 4.5 %) and gropers (+ 9.1 %) compared to snappers (+ 19.1 %). These results indicate Centro barrens models are significantly more complicated than previously considered. The fundamental biology of Centro and ecology of its predators needs to be more fully considered for best-case future management of native urchins to occur.