Promoted growth with dynamic cellular stoichiometry driven by utilization of in-situ dissolved organic matter:...

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 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, and the ecological implications were then discussed. Additionally, parallel cultures revealed the phycosphere bacterioplankton community compete with the algae cell regarding the nutrient utilization. This study 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.