Bacterial and viral dynamics during a mass spawning period on the Great barrier Reef

Bacterial and virus-like particle (VLP) abundances and physical and chemical parameters were measured in reef water and sediments over a 10 d period, coinciding with mass coral spawning at Heron Island, Great Barrier Reef. Bacterial abundances in reef water increased 2-fold after spawning and remained elevated for 3 d, before declining to below pre-spawning values. Reef water VLP abundances were also elevated 2 d after spawning; however, VLP abundances exhibited a general decline over the study. Dissolved oxygen (DO) and total nitrogen (TN) concentrations appeared to be dominant factors driving reef water bacterial and VLP dynamics. Sediment bacterial and VLP abundances exceeded those in the water column by up to 3 orders of magnitude and exhibited strong positive correlations for all investigated sediment depths. While short-lived peaks in bacterial and VLP abundances within sediments lagged behind water column trends by 2 d, reef water total phosphorus (TP) concentrations were strongly correlated with sediment bacterial and VLP abundances. Shifts in bacterial and VLP abundances in reef water and sediments during the study corresponded with 2 distinct periods: one prior to, and one after the first night of intense spawning. Scavenging by sedimenting coral spawn material is proposed as a direct mechanism contributing to these shifts, by removing bacteria and VLPs from the water column. The input of organic matter and associated nutrients from mass coral spawning, and the immediate and strongly correlated responses of bacteria and VLPs, indicate that viruses are important players in nutrient cycling processes in coral reefs.