Evaluation of a virus-based control method to protect cultured oysters from the harmful dinoflagellate Heterocapsa circularisquama

Abstract This study evaluates a novel control method for harmful algal blooms (HABs) that uses natural sediment including associated viruses. In Japan, commercial aquaculture of bivalves such as oysters, pearl oysters and clams is severely threatened by blooms of the harmful dinoflagellate, Heterocapsa circularisquama. HcRNAV is a single-stranded RNA virus that specifically infects H. circularisquama. Given that high concentrations of HcRNAV remain in bottom sediment following a H. circularisquama bloom, dispersal of sediments containing HcRNAV was expected to provide a promising tool to mitigate blooms of this dinoflagellate. A laboratory experiment demonstrated the effectiveness of a) HcRNAV alone, and b) sediments with HcRNAV, in reducing H. circularisquama densities. For the first time, a field test was implemented in an active oyster farm on Sado Island, Japan in which sediment containing HcRNAV collected from nearby waters was dispersed into 15,000 L floating mesocosms during early stages of a H. circularisquama bloom. In the treatment spraying with sediment containing HcRNAV, the density of H. circularisquama decreased significantly until it reached only ~1% of the initial after five days, while that of HcRNAV increased significantly by Day 2 (one-way ANOVA, n = 3, P