Fig. 3: Phytoplankton community composition and succession mandalas.

a Margalef’s Mandala redrawn from the original publication⁵¹ where the two determinant axes are turbulence and nutrient concentration [either nitrogen (N) or phosphorous (P)]. With respect to the successional sequence proposed, Margalef also noted characteristics of phytoplankton cell shape, community chlorophyll concentration, and K versus r life strategy.¹ b Proposed mandala where the determinant axes are the duration and magnitude of change in limiting resources and the trajectory of growth conditions. (blue shaded area) ‘Stable Solution’ where total phytoplankton biomass varies with nutrient load but the SDS is constrained to approximately −4. (blue and black arrows) Successional sequence under variable growth conditions resulting from accelerations and decelerations in phytoplankton division rate that impact the balance between division and loss rates and cause a positive tipping of the SDS. (rightward pointing black arrows) Succession of bloom-forming species where large cells ultimately dominate bloom biomass if the amplitude of change in growth conditions is sufficiently large to allow the full successional series, which may then be followed by a rise in mixotrophic species. (leftward pointing blue and black arrows) Variations on the return pathway to the ‘Stable Solution’ associated with different nutrient stoichiometries and cell sizes. The rightmost blue path is associated with Si limitation of diatoms and a shift in feeding tendencies of omnivores (red dashed arrows). (green arrows) An alternative succession scenario where blooming in a favorable high-nutrient but stable environment favors species that chemically suppress grazing (e.g., toxic algal blooms of ‘red tide’ dinoflagellates).