title: Resetting predator baselines in coral reef ecosystems.
abstract: What did coral reef ecosystems look like before human impacts became pervasive? Early efforts to reconstruct baselines resulted in the controversial suggestion that pristine coral reefs have inverted trophic pyramids, with disproportionally large top predator biomass. The validity of the coral reef inverted trophic pyramid has been questioned, but until now, was not resolved empirically. We use data from an eight-year tag-recapture program with spatially explicit, capture-recapture models to re-examine the population size and density of a key top predator at Palmyra atoll, the same location that inspired the idea of inverted trophic biomass pyramids in coral reef ecosystems. Given that animal movement is suspected to have significantly biased early biomass estimates of highly mobile top predators, we focused our reassessment on the most mobile and most abundant predator at Palmyra, the grey reef shark (Carcharhinus amblyrhynchos). We estimated a density of 21.3 (95% CI 17.8, 24.7) grey reef sharks/km2, which is an order of magnitude lower than the estimates that suggested an inverted trophic pyramid. Our results indicate that the trophic structure of an unexploited reef fish community is not inverted, and that even healthy top predator populations may be considerably smaller, and more precarious, than previously thought.
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Darcy
authors.initials: D
authors.lastname: Bradley
authors.affiliation: The Nature Conservancy, Hawai'i, 923 Nu'uanu Avenue, Honolulu, HI 96817, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Conklin
authors.affiliation: Department of Biological Sciences, Florida International University, North Miami, FL 33181, USA.
authors.forename: Yannis P
authors.initials: YP
authors.lastname: Papastamatiou
authors.affiliation: Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: McCauley
authors.affiliation: The Nature Conservancy, Hawai'i, 923 Nu'uanu Avenue, Honolulu, HI 96817, USA.
authors.forename: Kydd
authors.initials: K
authors.lastname: Pollock
authors.affiliation: U.S. Fish and Wildlife Service, 300 Ala Moana Blvd, Honolulu, HI 96850, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Pollock
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Kendall
authors.affiliation: Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Gaines
authors.affiliation: Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Caselle
mesh_terms: D000818:Animals; D057894:Coral Reefs; D017753:Ecosystem; D011156:Population Density; D012754:Sharks / Q000254:growth & development*