Missing planktivore functions drive global variation in reef fish productivity

The functioning of high-diversity ecosystems, such as coral reefs, is intrinsically tied to the integrity and efficiency of the trophic pathways within these systems. Coral reef productivity depends, in part, on the input of external nutrients, primarily zooplankton, that is assimilated by extraordinarily diverse fish communities. The plankton-planktivore trophic pathway is thus crucial for sustaining the productivity that exemplifies coral reef ecosystems; however, it remains poorly understood at large spatial scales. Here we explore global patterns in reef fish community structure, revealing a major discrepancy between the Indo-Pacific and Caribbean in the productivity and fisheries potential of planktivorous reef fishes. Indo-Pacific reefs support 6.6 times more planktivorous fish biomass and 3.4 times greater productivity than the Caribbean, a difference largely due to the marked contribution of species that feed on gelatinous plankton in the Indo-Pacific. Although species that feed on gelatinous plankton constitute only 4% of the planktivorous fish abundance in the Indo-Pacific, they account for one-third of the biomass and one-quarter of the productivity. This divergence reflects the contrasting biogeographic histories of the two realms, with Indo-Pacific oceanography fostering diversification, while repeated extinction events and trophic erosion may have constrained planktivory in the Caribbean. Ultimately, these differences in energy flow translate into fundamental differences in coral reef functioning and, potentially, their capacity to support ecosystem services, including fisheries.