Life cycle of the marine alga Phaeocystis: A conceptual model to summarize literature and guide research

This paper reviews literature on the life cycle of the marine algal genus Phaeocystis, and organizes existing information in the form of a qualitative conceptual model of life-cycle stages, stage transitions, ecosystem inputs and outputs, and internal and external controlling factors. Conceptualization is the first phase of modeling, typically continued in later quantitative phases by mathematical formulation, calibration of parameters, dynamic simulation, and different forms of systems analysis. Qualitative conceptualization can also promote multidisciplinary interactions and structure early stages of scientific inquiry. To exploit the qualitative benefits of conceptual modeling, the goals of this paper are to: (1) review the literature of Phaeocystis life-cycle biology and ecology; (2) from the material of this review, construct, a conceptual life-cycle model covering all Phaeocystis species; and (3) show how this model, a platform for further quantitative development, is also used as a qualitative tool to guide empirical research. The conceptual model includes known and putative life-cycle stages, colony size classes, and genetic, physiological, semiotic, and ecological information expressed or potentially expressed across the genus. It consists of 15 compartments. Seven are single-celled: Solitary Diploid Flagellates (x1), Solitary Diploid Non-flagellates (x2), Benthic Solitary Diploid Non-Flagellates (x3), Solitary Diploid Flagellated Macrozoospores (x8), Solitary Haploid Flagellated Microzoospores (x9), Solitary Haploid Microflagellates (x10), and Solitary Haploid Mesoflagellates (x11). The remaining eight compartments represent the New stage, and Small, Medium, and Large size classes of Healthy/Growing Colonies (x4-x7), and Senescent/Declining Colonies (x12-x15). Six flow types interconnect the compartments: (a) physical transport, (b) solitary cell transformations, (c) solitary cell↔colony transitions, (d) colony growth and differentiation, (e) colony senescence, and (f) syngamy of solitary haploid cells. Boundary inputs and outputs include flows associated with transport, nutrient exchange, chemical signals, and grazing and cell lysis. Factors controlling flows include genetics, cellular and organismal biology, info-chemistry, and ecology.