RESEARCH ARTICLE Human, Oceanographic and Habitat Drivers of Central and Western Pacific Coral Reef Fish Assemblages

Coral reefs around US- and US-affiliated Pacific islands and atolls span wide oceano-graphic gradients and levels of human impact. Here we examine the relative influence of these factors on coral reef fish biomass, using data from a consistent large-scale ecosys-tem monitoring program conducted by scientific divers over the course of>2,000 hours of underwater observation at 1,934 sites, across ~40 islands and atolls. Consistent with pre-vious smaller-scale studies, our results show sharp declines in reef fish biomass at rela-tively low human population density, followed by more gradual declines as human population density increased further. Adjusting for other factors, the highest levels of oce-anic productivity among our study locations were associated with more than double the biomass of reef fishes (including ~4 times the biomass of planktivores and piscivores) compared to islands with lowest oceanic productivity. Our results emphasize that coral reef areas do not all have equal ability to sustain large reef fish stocks, and that what is natural varies significantly amongst locations. Comparisons of biomass estimates derived from visual surveys with predicted biomass in the absence of humans indicated that tota