The global expansion of red tide and toxic dinoflagellates is facilitated by increasing the transportation of their cysts in the ballast water of cargo ships. Preventive measures for such expansion should be urgently developed. The potential of hydrogen peroxide as an extermina-tion agent was investigated under laboratory conditions.
Natural cysts were isolated after an ordinary cleaning procedure and were exposed to several concentrations of hydrogen peroxide solution ranging from 0 to 1, 000mg/l. Then, the cysts were rinsed and incubated individually in sterile filtered seawater to observe their mor-phological change and germination ability.
The cysts of Polykrikos schwartzii were exterminated after exposure to 100mg/l hydrogen peroxide for 24h. No germination was observed from cysts of Alexandrium catenella exposed to 30mg/l hydrogen peroxide for 48h. All cysts of A. tamarense exposed to 30mg/l hydrogen peroxide for 48h showed protoplasm contraction and decolorization. Hydrogen peroxide at a 100mg/l concentration in seawater broke down within 30 days, and showed no significant difference from seawater in corrosion ability. The present results definitely support the notion that hydrogen peroxide has high potential as an extermination agent against dinoflagellate cysts in ballast water without damaging tank materials and environmental concerns.