Flow cytometric analysis of virus-like particles and heterotrophic bacteria within coral-associated reef water

Using flow cytometry, two distinct populations of virus-like particles (VLP) and heterotrophic bacteria were defined within the 12 cm water layer immediately overlying healthy, diseased and dead acroporid corals. Bacterial abundances were similar in overlying water for all coral types, however, VLP were 30% higher above diseased corals than healthy or dead corals. Mean virus to bacteria ratios (VBR) were up to 30% higher above diseased corals than above healthy or dead coral or in distant water. Concomitant with increasing VLP concentrations within 5 cm of coral surfaces, VBR distributions were generally highest above healthy and diseased coral and depressed above dead coral. These results suggest fundamental shifts in the VLP and bacterial community in water associated with diseased corals.