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Protist. 2016 Apr;167(2):106-20. doi: 10.1016/j.protis.2016.01.003. Epub 2016 Feb 3.

Defining Planktonic Protist Functional Groups on Mechanisms for Energy and Nutrient Acquisition: Incorporation of Diverse Mixotrophic Strategies.

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College of Science, Swansea University, Swansea SA2 8PP, United Kingdom. Electronic address:
College of Science, Swansea University, Swansea SA2 8PP, United Kingdom.
Alfred Wegener Institute, Am Handelshafen 12, D-27570 Bremerhaven, Germany.
Division of Plant Sciences, University of Dundee at the James Hutton Institute, Invergowrie, Dundee DD2 5DA, United Kingdom (permanent address) and Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Ultimo, NSW 2007, Australia.
Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089-0371.
University of Maryland Center for Environmental Science, Horn Point Laboratory, P.O. Box 775, Cambridge MD 21613, USA.
Sorbonne Universités, Université Pierre et Marie Curie - Paris 06, UMR 7144, Station Biologique de Roscoff, CS90074, 29688 Roscoff Cedex, France and also CNRS, UMR 7144, Laboratoire Adaptation et Diversité en Milieu Marin, Place Georges Teissier, CS90074, 29688 Roscoff cedex, France.
Centre for Ocean Life, Marine Biological Section, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark.
Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia.
Department of Biology, Temple University, Philadelphia PA 19122 USA.
Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, USA.
Marine Sciences, University of Connecticut, 1080 Shennecossett Rd, Groton CT USA 06340.
Biology Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543 USA.
Institute of Oceanography, Hellenic Centre for Marine Research, P.O. Box 2214, 71003 Heraklion, Crete, Greece.
Department of Biology and Hjort Centre for Marine Ecosystem Dynamics, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway.
Institut de Ciències del Mar, CSIC, Ps. Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain.
School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea.
Center for Applied Aquatic Ecology, North Carolina State University, Raleigh, NC 27606 USA.
Aquatic Ecology, Biology Institute, Lund University, Box 118, 22100 Lund, Sweden, and also at Florida Gulf Coast University, Kapnick Center, Naples, Florida 34112 USA.
Department of Biology and Environmental Sciences, Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, SE-39231 Kalmar, Sweden.


Arranging organisms into functional groups aids ecological research by grouping organisms (irrespective of phylogenetic origin) that interact with environmental factors in similar ways. Planktonic protists traditionally have been split between photoautotrophic "phytoplankton" and phagotrophic "microzooplankton". However, there is a growing recognition of the importance of mixotrophy in euphotic aquatic systems, where many protists often combine photoautotrophic and phagotrophic modes of nutrition. Such organisms do not align with the traditional dichotomy of phytoplankton and microzooplankton. To reflect this understanding, we propose a new functional grouping of planktonic protists in an eco-physiological context: (i) phagoheterotrophs lacking phototrophic capacity, (ii) photoautotrophs lacking phagotrophic capacity, (iii) constitutive mixotrophs (CMs) as phagotrophs with an inherent capacity for phototrophy, and (iv) non-constitutive mixotrophs (NCMs) that acquire their phototrophic capacity by ingesting specific (SNCM) or general non-specific (GNCM) prey. For the first time, we incorporate these functional groups within a foodweb structure and show, using model outputs, that there is scope for significant changes in trophic dynamics depending on the protist functional type description. Accordingly, to better reflect the role of mixotrophy, we recommend that as important tools for explanatory and predictive research, aquatic food-web and biogeochemical models need to redefine the protist groups within their frameworks.


Plankton functional types (PFTs); microzooplankton.; mixotroph; phagotroph; phototroph; phytoplankton

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