28 - Inverted trophic pyramids

Summary

Trophic representations of coral reef fish assemblages are used frequently to depict the structure and functioning of reef communities. While the trophic structure of many coral reef fish assemblages reveals prey species outweighing their predators, recent observations from little-exploited reefs suggest the opposite – inverted biomass pyramids with the mass of piscivorous predators exceeding that of their prey. Such observations are paralleled by historical accounts of predator-dominated coral reefs and suggest that when fishing is light or absent, large-bodied, long-lived piscivores can quantitatively overwhelm their prey. Inverted biomass pyramids are a well-known phenomenon within the ecological literature; however, biomass-based depictions of little-exploited coral reef fish assemblages appear to provide the first empirical evidence of inverted trophic structure among vertebrates. Inverted biomass pyramids can only be maintained if the patterns of productivity (i.e. energy flux) are bottom-heavy, suggesting that predators on coral reefs are quite slow-growing per capita, or per unit biomass, relative to their fast-growing prey. Detailed investigations are needed to distinguish among competing hypotheses for how inverted biomass pyramids might arise, with the findings likely to be of great value to the improved management of reef communities.

TROPHIC PATTERNS AMONG CORAL REEF FISHES

Historical accounts suggest that tropical nearshore ecosystems were classically home to abundant populations of large organisms, with a prominent representation of predatory fishes [1225,1226,2259]. Reconstructions of Caribbean coral reef ecosystems from early explorers suggest that sharks and other large predators were common and numerous for the first centuries following European contact [1225,2610]. However, the growth of coastal human populations coupled with active nearshore fisheries led to reductions in fish populations from coral reefs globally, including dramatic reductions in the populations of predatory reef fishes [1226,1910].

Only in the past few decades, largely since the incorporation of SCUBA diving into the study of reef fishes, have we been able to gain a clearer picture of the structure of reef fish assemblages and the ecological role played by predatory fishes.