Theory predicts that bottom-heavy biomass pyramids or ‘stacks’ should predominate in real-world communities if trophic-level increases with body size (mean predator-to-prey mass ratio (PPMR) more than 1). However, recent research suggests that inverted biomass pyramids (IBPs) characterize relatively pristine reef fish communities. Here, we estimated the slope of a kelp forest fish community biomass spectrum from underwater visual surveys. The observed biomass spectrum slope is strongly positive, reflecting an IBP. This is incongruous with theory because this steep positive slope would only be expected if trophic position decreased with increasing body size (consumer-to-resource mass ratio, less than 1). We then used δ15N signatures of fish muscle tissue to quantify the relationship between trophic position and body size and instead detected strong evidence for the opposite, with PPMR ≈ 1650 (50% credible interval 280–12 000). The natural history of kelp forest reef fishes suggests that this paradox could arise from energetic subsidies in the form of movement of mobile consumers across habitats, and from seasonally pulsed production inputs at small body sizes. There were four to five times more biomass at large body sizes (1–2 kg) than would be expected in a closed steady-state community providing a measure of the magnitude of subsidies.
History
Publication title
Proceedings of the Royal Society of London: Biological Sciences
Volume
283
Issue
1833
Article number
20160816
Number
20160816
Pagination
1-9
ISSN
0962-8436
Department/School
Institute for Marine and Antarctic Studies
Publisher
Royal Soc London
Place of publication
6 Carlton House Terrace, London, England, Sw1Y 5Ag
Rights statement
Copyright 2016 The Author(s)
Repository Status
Restricted
Socio-economic Objectives
Assessment and management of terrestrial ecosystems