Mixotrophs are important components of the bacterioplankton, phytoplankton,
microzooplankton, and (sometimes) zooplankton in coastal and oceanic
waters. Bacterivory among the phytoplankton may be important for alleviating
inorganic nutrient stress and may increase primary production in
oligotrophic waters. Mixotrophic phytoflagellates and dinoflagellates are often
dominant components of the plankton during seasonal stratification.
Many of the microzooplankton grazers, including ciliates and Rhizaria, are
mixotrophic owing to their retention of functional algal organelles or maintenance of algal endosymbionts. Phototrophy among the microzooplankton
may increase gross growth efficiency and carbon transfer through the
microzooplankton to higher trophic levels. Characteristic assemblages of
mixotrophs are associated with warm, temperate, and cold seas and with
stratification, fronts, and upwelling zones. Modeling has indicated that
mixotrophy has a profound impact on marine planktonic ecosystems and may
enhance primary production, biomass transfer to higher trophic levels, and
the functioning of the biological carbon pump.