Changes of chromophoric dissolved organic matter in Heterosigma akashiwo (Hada) and its effects on other microalgae
赤潮异弯藻有色可溶性有机物的变化以及对其他微藻的影响

The initiation and collapse of red tide will induce changes of chromophoric dissolved organic matter (CDOM), which may potentially affect the community structure of marine organisms. Heterosigma akashiwo (Hada) is one of common red tide species, with ichthyotoxicities, and production of CDOM. In this study, the chemical characteristics of CDOM from H. akashiwo have been analyzed along with its population growth cycle, as well as the various light source treatments. The effects of CDOM on different microalgae have been also quantified. The results showed that (1) the production of CDOM is inversely correlated with the population growth, namely, increase of microalgal density accompanied by decrease of CDOM content, vice versa. The production of CDOM is continually increased in the maintenance of high density population. (2) The light irradiation affected content and composition of CDOM significantly, resulting in large degradation of humic substances by UV. (3) CDOM affected the growth of microalgae depending on the species. Stimulating effects were observed on Karlodinium micrum and Nitzschia closterium f. minutissima, and inhibitory effects on Prorocenturm micans. Such effects will be decreased for the CDOM after UV treatment. In conclusion, H. akashiwo, especially at large population, can affect the water qualities and phytoplankton community structures through the production of extracellular chromophoric dissolved organic matter.