Resetting predator baselines in coral reef ecosystems

Area of Science:

• Marine Ecology
• Coral Reef Ecosystems
• Trophic Dynamics

Background:

• Early studies suggested pristine coral reefs had inverted trophic pyramids with high top predator biomass.
• The validity of these inverted trophic pyramid hypotheses remained empirically unresolved.

Purpose of the Study:

• To empirically test the inverted trophic pyramid hypothesis in coral reef ecosystems.
• To reassess the population size and density of grey reef sharks (Carcharhinus amblyrhynchos) at Palmyra Atoll.

Main Methods:

• Utilized an eight-year tag-recapture program.
• Employed spatially explicit, capture-recapture models to estimate predator density.
• Focused on the grey reef shark, a highly mobile top predator.

Main Results:

• Estimated grey reef shark density at 21.3 sharks/km².
• This density is an order of magnitude lower than previous estimates.
• Found that the trophic structure of the unexploited reef fish community is not inverted.

Conclusions:

• The inverted trophic pyramid hypothesis for coral reefs is not supported by empirical data.
• Top predator populations in healthy reef ecosystems may be smaller and more vulnerable than previously believed.
• Accurate assessment of mobile species' populations is crucial for understanding ecosystem structure.