Physiological and photosynthetic responses of Karenia mikimotoi to the modified clay mitigation method

Modified clay (MC) removed harmful algae Karenia mikimotoi effectively, and significantly inhibited residual algae growth. Hydrogen peroxides (H2O2) and malondialdehyde (MDA) contents of K. mikimotoi increased significantly after treatment, indicating that MC induced oxidative stress. Moreover, H2O2 content was significantly correlated with cell density, indicating that increased reactive oxygen species (ROS) were likely responsible for the growth inhibition. Further investigation showed that MC caused damage to photosynthesis of residual algae, indicated by decreased maximal photochemical efficiency (Fv/Fm) and performance index (PIABS). The density of reaction center (RC) decreased, indicating that MC induced partially inactivated RCs, then caused residual activated RCs to be over-excited. The electron transport chain was also blocked, indicated by increased WK and VJ, and decreased Sm. These effects of photosystem II (PSII) were supposed to be the main contributors to ROS over-accumulation during photosynthesis. Overall, treatment with MC is an appropriate method for controlling K. mikimotoi blooms.