Oysters as microbial engineers govern planktonic viral and microbial dynamics

Oysters are ecosystem engineers that restructure their environments through intense filtration and reef-building, known for their ability to remove plankton and particulates from seawater. As microbialization and eutrophication increasingly undermine coastal water quality, understanding how oyster filtration shapes viral and microbial assemblages is essential to evaluate its role in countering these degradation processes. Here, we incubated the eastern oyster, Crassostrea virginica, in natural seawater and conducted a high-resolution 24-hour time-series analysis to track changes in viral and microbial abundances. Oysters preferentially removed autotrophic microbes, skewing community composition toward heterotrophy and altering local carbon and energy fluxes. Understanding the extent to which viral and microbial components contribute to oyster nutrition could provide new insights into these shifts and their broader ecological consequences. Viral abundances displayed Lotka–Volterra-like oscillations, suggesting that phage replication was sustained through lytic cycling rather than integration into microbial genomes, even under reduced microbial availability. Elevated virus-to-microbe ratios (VMRs) in oyster-associated mucus compared to ambient seawater points to a role of bacteriophage adherence-to-mucus (BAM) in modulating host-microbiome interactions within the oyster holobiont. Together, these findings highlight oysters as ecosystem de-microbializers and holobiont viralizers, simultaneously suppressing water-column microbes and stimulating localized viral activity that reshapes microbial interactions and coastal biogeochemistry.