Limited Cross-Species Virus Transmission in a Spatially Restricted Coral Reef Fish Community

The Great Barrier Reef (GBR) – the largest coral reef ecosystem in the world – supports over 1200 fish species with some of the highest population densities and diversities seen in vertebrates, offering a high potential for virus transmission among species. As such, the GBR represents an exceptional natural ecosystem to determine the impact of host community diversity on virus evolution and emergence. In recent decades the GBR has also experienced significant threats of extinction, making it one of the most vulnerable ecosystems on the planet. However, our understanding of virus diversity and connectivity in tropical reef fishes remains poor. Here, we employed metatranscriptomic sequencing to reveal the viromes of 61 reef fish species. This identified a total of 132 viruses, 38 of which were vertebrate-associated and therefore likely infecting the fish, including a novel isolate of Santee-cooper ranavirus ( Iridoviridae ). Notably, we found little evidence for virus transmission between fish species living within a very restricted geographical space – a 100 m 2 coral reef ecosystem – suggesting that there might be important host genetic barriers to successful cross-species transmission despite regular exposure. We also identified differences in virome composition between reef fish families, such that cryptobenthic reef fishes – characterized by small body sizes and short life-spans – exhibited greater virome richness compared to large reef fishes. This study suggests that there are important barriers to cross-species transmission, and that successful emergence in a reef fish community likely requires active host adaptation, even among closely related host species.