Fig. 1: Phytoplankton size distributions and modeled equilibrium solutions for plankton biomass.

a Examples of measured phytoplankton size distributions for (blue symbols) stable mesotrophic conditions (chlorophyll concentration ~ 0.1 mg m⁻³) and (green symbols) seasonally productive regions (chlorophyll concentration ~ 1 mg m⁻³). (blue line) SDS = −4. (green line) SDS = −3.4. Data from (circles) Marañón²⁴ and (squares) unpublished data from the NAAMES program.⁹⁷ b Phytoplankton size distributions (dashed black line) predicted from metabolic theory (SDS = −2.25), (dashed green line) for uniform biomass in all size classes (SDS = −3), and (heavy blue line) predicted for a competition-neutral resource environment with proportional grazing size ranges (SDS = −4). Light blue shading indicates SDS range for stable environments when phytoplankton division rates (µ) and herbivore ingestion efficiency (c₂) and predatory loss (c₃) rates are assumed to be size dependent [Supplementary Information] (gray lines). Examples of measured phytoplankton size distributions in stable, nutrient-limited regions [from ²³]. All size distributions are normalized to 10⁴ cells ml⁻¹ at the 0.5 µm size bin. c Modeled (Eqs. 1 and 2) equilibrium phytoplankton and herbivore biomass as a function of phytoplankton division rate [from ²⁹].