Mixotrophic dinoflagellates frequently cause harmful algal blooms (HABs) in eutrophic waters that contain diverse dissolved organic matter (DOM), especially intensive mariculture areas. Compared to the extensive investigation of phagotrophy and single organic molecule uptake by causative species, we have limited knowledge about the capability of mixotrophic dinoflagellates to utilize in-situ DOM in mariculture waters and its contribution to HABs. Here we use filtered in-situ mariculture water from multiple mariculture areas and types as the sole medium to examine the physiological response of Prorocentrum donghaiense to the natural mariculture DOM. Our results showed an 87.2% increase in the cell growth rate, as well as photosynthesis (16.8%-29.2%) and cellular chlorophyll a (32.4% - 70.7%) when cultured with DOM compared to those grown in the inorganic medium. Meanwhile, cellular stoichiometry varied greatly among the groups supplied with mariculture DOM of different seasons. Additionally, parallel cultures revealed different functions of the bacterioplankton between the free-living community (helper) and the phycosphere community (competitor). This study preliminarily quantifies the efficient utilization of in-situ mariculture DOM by P.donghaiense and indicates its vital role in sustaining HAB events and great effects on the biogeochemical cycle.
 

HABs, dissolved organic matter, mixotrophic dinoflagellate, Prorocentrum donghaiense, cellular stoichiometry