Are oil spills enhancing outbreaks of red tides in the Chinese coastal waters from 1973 to 2017?

Between 1973 and 2017, evidences of red tide outbreaks and oil spill accidents in the Chinese coastal waters were collected. Statistical analysis and multiple regression models were used to determine the relationship between the red tide and the oil spill. Major findings reveal that (1) the frequency of red tides positively correlates to the number of oil spills and the volume of oil spilled as well; (2) the higher percentage of small spills (< 7 tonnes) are more likely to enhance the outbreaks of red tides; (3) both EI Niño and storm events do not show any relationship with red tides; and (4) more severe oil spill with penalty recorded implies a higher possibility to trigger the red tide afterwards. Therefore, oil spill contingency management focusing on small oil spills and mitigating their spill effect by physical measures could be of benefit to decrease the frequency of red tides significantly. For example, it is suggested to carry out physical combat instead of chemical dispersants to remove the spilled small oil in the shallow coastal areas for reducing the outbreak risk of red tides after the oil spill.