title: Human Disruption of Coral Reef Trophic Structure.
abstract: The distribution of biomass among trophic levels provides a theoretical basis for understanding energy flow and the hierarchical structure of animal communities. In the absence of energy subsidies [1], bottom-heavy trophic pyramids are expected to predominate, based on energy transfer efficiency [2] and empirical evidence from multiple ecosystems [3]. However, the predicted pyramid of biomass distribution among trophic levels may be disrupted through trophic replacement by alternative organisms in the ecosystem, trophic cascades, and humans preferentially impacting specific trophic levels [4-6]. Using empirical data spanning >250 coral reefs, we show how trophic pyramid shape varies given human-mediated gradients along two orders of magnitude in reef fish biomass. Mean trophic level of the assemblage increased modestly with decreasing biomass, contrary to predictions of fishing down the food web [7]. The mean trophic level pattern is explained by trophic replacement of herbivorous fish by sea urchins at low biomass and the accumulation of slow-growing, large-bodied, herbivorous fish at high biomass. Further, at high biomass, particularly where fishers are not selectively removing higher trophic level individuals, a concave trophic distribution emerges. The concave trophic distribution implies a more direct link between lower and upper trophic levels, which may confer greater energy efficiency. This trophic distribution emerges when community biomass exceeds ∼650 kg/ha, suggesting that fisheries for upper trophic level species will only be supported under lightly fished scenarios.
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK; Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia. Electronic address: nick.graham@lancaster.ac.uk.
authors.forename: Nicholas A J
authors.initials: NA
authors.lastname: Graham
authors.affiliation: Wildlife Conservation Society, Marine Programs, Bronx, NY 10460, USA.
authors.forename: Tim R
authors.initials: TR
authors.lastname: McClanahan
authors.affiliation: Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia; Australian Institute of Marine Science, PMB 3 Townsville MC, Townsville, QLD 4810, Australia; Department of Mathematics and Statistics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
authors.forename: M Aaron
authors.initials: MA
authors.lastname: MacNeil
authors.affiliation: Department of Parks and Wildlife, Kensington, Perth, WA 6151, Australia; School of Plant Biology, Oceans Institute, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Shaun K
authors.initials: SK
authors.lastname: Wilson
authors.affiliation: Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia.
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Cinner
authors.affiliation: Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia.
authors.forename: Cindy
authors.initials: C
authors.lastname: Huchery
authors.affiliation: Department of Parks and Wildlife, Kensington, Perth, WA 6151, Australia; School of Plant Biology, Oceans Institute, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Holmes
mesh_terms: D000818:Animals; D018533:Biomass; D003247:Conservation of Natural Resources; D057894:Coral Reefs; D017753:Ecosystem; D005398:Fisheries; D006801:Humans; D012617:Sea Urchins / Q000502:physiology
keywords: coral reef ecology; coral reef fishes; energetics; fisheries management; trophic cascades; trophic pyramids; trophic replacement; wilderness