Reef fish biodiversity guarantees productivity

Biodiversity loss on coral reefs may threaten their functioning and services to humanity. However, the impacts of biodiversity change on reef fish productivity, a key function that sustains millions of humans, are not well understood. Here, we compiled a global dataset of coral reef fish surveys to examine whether assemblage biodiversity promotes productivity, in both space and time. Diversity acts as an insurance policy for productivity: although high levels of reef fish productivity can occur at any level of local species richness, we found no diverse assemblages with low productivity. This triangular relationship reconciles the apparent contradiction of productive monocultures identified in previous studies. Importantly, productivity strongly mirrors species richness trends regardless of initial richness. Implications for conservation and management are clear: reefs that are naturally less diverse can still be productive. Yet human-driven biodiversity declines are likely to translate to productivity declines, impacting ecological productivity and coastal populations.