Recommendations for Advancing Mixoplankton Research through Empirical-Model Integration Provisionally Accepted

Nicole Millette^1* Suzana Leles² Matthew D. Johnson³ Ashley E. Maloney⁴ Emily F. Brownlee⁵ Natalie Cohen⁶ Solange Duhamel⁷ Nicole J. Poulton⁸ Sarah D. Princiotta⁹ Karen Stamieszkin⁸ Susanne Wilken¹⁰ Holly V. Moeller¹¹

• ¹William & Mary's Virginia Institute of Marine Science, College of William & Mary, United States
• ²University of Southern California, United States
• ³Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, United States
• ⁴Princeton University, United States
• ⁵St. Mary's College of Maryland, United States
• ⁶Skidaway Institute of Oceanography, Odum School of Ecology, University of Georgia, United States
• ⁷University of Arizona, United States
• ⁸Bigelow Laboratory For Ocean Sciences, United States
• ⁹Penn State Schuylkill, United States
• ¹⁰University of Amsterdam, Netherlands
• ¹¹University of California, Santa Barbara, United States

Protist plankton can be divided into three main groups: phytoplankton, zooplankton, and mixoplankton. In situ methods for studying phytoplankton and zooplankton are relatively straightforward since they generally target chlorophyll/photosynthesis or grazing activity, while the integration of both processes within a single cell makes mixoplankton inherently challenging to study. As a result, we understand less about mixoplankton physiology and their role in food webs, biogeochemical cycling, and ecosystems compared to phytoplankton and zooplankton. In this paper, we posit that by merging conventional techniques, such as microscopy and physiological data, with innovative methods like in situ single-cell sorting and omics datasets, in conjunction with a diverse array of modeling approaches ranging from single-cell modeling to comprehensive Earth system models, we can propel mixoplankton research into the forefront of aquatic ecology. We present eight crucial research questions pertaining to mixoplankton and mixotrophy, and briefly outline a combination of existing methods and models that can be used to address each question. Our intent is to encourage more interdisciplinary research on mixoplankton, thereby expanding the scope of data acquisition and knowledge accumulation for this understudied yet critical component of aquatic ecosystems.