Description:
<jats:title>Abstract</jats:title><jats:p>Slightly acidic electrolyzed water (SAEW) is a highly safe sterilizing water that consists of an aqueous solution of hypochlorous acid (HOCl). It exhibits high sterilizing power even at low concentrations of HOCl. In this study, we evaluated the effect of SAEW on marine plankton to understand its impact on marine environments and consider its possible application on ballast water treatment or aquaculture. Experiments conducted on plankton communities obtained from Tokyo Bay showed an approximately 65% reduction in the S‐size plankton population (≥10 and <50 μm) at an available chlorine concentration of 0.5 mg/L, whereas an approximately 50% reduction of the L‐size plankton population (≥50 μm) was observed at an available chlorine concentration of 2 mg/L. We also verified the sterilization effect of SAEW against two types of single‐species plankton: <jats:italic>Chaetoceros densum</jats:italic> as S‐size plankton and <jats:italic>Tigriopus japonicus</jats:italic> as L‐size plankton. Results showed 100% population decrease for <jats:italic>C. densum</jats:italic> and <jats:italic>T. japonicus</jats:italic> at available chlorine concentrations of 3.5 and 11 mg/L, respectively.</jats:p>