Marine food web complexity counters size-based constraints on pyramids of life: consequences for ecosystem structure and fisheries

Marine ecosystems are believe to be constrained to bottom-heavy trophic structure (more plants than animals). However, size-based approaches only account for bottom-up processes (resource supply), and are often limited to confined trophic level windows where energy transfer is predicted by size alone. In real food webs, energy flow is more complex and top-down processes also shape trophic structure. In this talk, we show that food web complexity allows for top-heavy or cascade-like trophic structure more often than predicted by size-based theory alone. Trophic structure inversion occurs through complex energy pathways and top-down effects on ecosystems. Our results suggest that marine ecosystems should generally be top-heavy, and observed bottom-heavy trophic structurmay be result of human defaunation of the ocean that has been more extreme than presently recognized, and comparable in effect to terrestrial defaunation. Accounting for this new view of marine ecosystems in fisheries models suggests maximum sustainable yield should be at much higher abundance levels than presently assumed.