How coral reefs survive as oases of life in low-productivity oceans has puzzled scientists for centuries. The answer may lie in internal nutrient cycling and/or input from the pelagic zone. Integrating meta-analysis, field data, and population modelling, we show that the ocean’s smallest vertebrates, cryptobenthic reef fishes, promote internal reef-fish biomass production through exceptional larval supply from the pelagic environment. Specifically, cryptobenthics account for two-thirds of reef-fish larvae in the near-reef pelagic zone, despite limited adult reproductive outputs. This overwhelming abundance of cryptobenthic larvae fuels reef trophodynamics via rapid growth and extreme mortality, producing almost 60% of consumed reef fish biomass. While cryptobenthics are commonly overlooked, their unique demographic dynamics may make them a cornerstone of ecosystem functioning on modern coral reefs.

Supplementary Raw Data and Code for Brandl et al. 2019