Artificial reefs alter viral communities and functional traits in coastal waters

Artificial reefs (ARs) are widely deployed as engineered coastal structures to enhance habitat complexity and support marine resource management, yet their impacts on marine viral ecology remain poorly understood. Viruses regulate microbial communities and biogeochemical processes, and their functional traits are sensitive to environmental change. Here, we investigated how artificial reefs influence viral community composition, functional gene profiles, and virus-environment interactions across paired reef and non-reef sites in coastal shelf systems. Using an integrated viromic and metagenomic approach, we compared viral assemblages in both seawater and sediments under artificial reef influence. ARs significantly modified seawater physicochemical conditions, including pH, sulfate concentration, dissolved oxygen, and salinity, whereas sediment properties remained largely unchanged. These environmental differences coincided with distinct virus-environment association patterns across habitats. Notably, artificial reefs were associated with viral functional profiles characterized by a reduced genomic representation of lysis-related genes and an increased representation of genes involved in DNA replication and nucleotide metabolism. Network analyses further showed differences in the balance of positive and negative virus-host correlations between AR and non-AR sites. Together, these results indicate that engineered coastal structures are linked to habitat-specific patterns in viral functional traits and virus-host associations. Our findings highlight viruses as sensitive indicators of anthropogenic habitat modification and underscore the importance of incorporating viral dynamics into assessments of microbial and biogeochemical responses in engineered coastal ecosystems.