Selective grazing in the heterotrophic dinoflagellate <i>Oxyrrhis marina</i> : Effects of prey type, size, temperature, and nutrient limitation

Protists are the main consumers of phytoplankton in the marine environment, playing pivotal roles in the carbon cycle and nutrient regeneration. Heterotrophic dinoflagellates, which have been extensively studied, are the linking hubs for microbial food loops and classical food chains. In particular, Oxyrrhis marina has been used as a model predator in laboratory studies. Designed experiments were conducted to explore the effects of biological factors (prey type, particle size) and abiotic factors (temperature, nutrient limitation) on its growth and ingestion. Oxyrrhis marina had the ability to consume various algae, including Chromalveolata, Haptophyta, Chlorophyta, Bacillariophyta, and Ochrophyta. When prey had diameters ranging from 7.4 to 13 μm, O. marina exhibited the highest ingestion rates, growth rates, and cell volume. With increases in temperature, the ingestion rate, growth rate, and productivity of O. marina increased significantly, but the cell volume decreased dramatically. Compared to ingesting phosphorus-restricted prey, ingesting nitrogen-restricted prey significantly increased the ingestion rate, growth rate, and cell volume of O. marina. Nitrogen-restricted (phosphorus-restricted) O. marina preferred to select prey that contained more nitrogen (phosphorus) elements to regulate nutritional imbalance. The purpose of this study is to provide a theoretical foundation for understanding the selective ingestion of the heterotrophic dinoflagellate O. marina and its impact on the community structure of plankton.