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 1,200 fish species with some of the highest population densities and diversities observed 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. Despite the global importance of the GBR, our understanding of virus diversity and connectivity in tropical reef fishes remains poor. Here, we employed metatranscriptomic sequencing to reveal the viromes of sixty-one reef fish species. This identified transcripts representing 132 putative viral sequences, 38 of which exhibited strong phylogenetic relationships with known vertebrate-associated viral genera, including a novel Santee-Cooper ranavirus (Iridoviridae). We found little evidence for virus transmission between fish species living within a very restricted geographical space-a 100-m² coral reef ecosystem-suggesting that there might be important host barriers to successful cross-species transmission despite regular exposure. We also identified differences in virome composition among 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 virus transmission and that successful emergence in a reef fish community likely requires active host adaptation, even among closely related host species.