Fig. 7: Principle component analysis associates bloom phases with distinct physiological states and extracellular signatures.

(Top row) PCA showing interrelationships among measured intra- and extracellular properties for phytoplankton populations across bloom seasons combined with clade relative abundance determined by either a Pigment-based community composition⁶² or b 16S rRNA-based community composition⁶¹. Symbols are shaped and colored by station. Small symbols represent individual sampling events during each bloom phase; large symbols represent the average value for each respective bloom phase. Percent variability in each dimension is the amount of variance explained in the dataset. Ellipses represent the 95% concentration estimate. W.Tran = Winter Transition; Acc = Accumulation; Clim = Climax; Decl = Decline. (Bottom row) PCA scores and vectors for measured intra- and extracellular properties with respect to c Pigment-based community composition and d 16S rRNA-based community composition. Longer arrows represent a stronger correlation with each respective dimension. Phytoplankton cells L⁻¹ = phytoplankton cell concentration; ROS = reactive oxygen species in phytoplankton (log₁₀ fold change in fluorescence from unstained); Comp. membrane = % of phytoplankton population with compromised membranes; TEP cell⁻¹ = transparent exopolymer particle concentration (µg XG eq. L⁻¹) normalized to bacteria and phytoplankton concentration; Virus cell⁻¹ = virus concentration normalized to bacteria and phytoplankton concentrations; OxPC PC⁻¹ = oxidized phosphatidylcholine (peak area) normalized to total phosphatidylcholine; TAG ChlA⁻¹ = triacylglycerol (pM) normalized to ChlA (peak area/L); Caspase activity = caspase activity (µmol caspase substrate cleaved h⁻¹ µg protein⁻¹); Metacaspase activity = metacaspase activity (µmol metacaspase substrate cleaved h⁻¹ µg protein⁻¹); DOC_SA = seasonally accumulated dissolved organic carbon; Phytoplankton biovolume L⁻¹ = phytoplankton µl L⁻¹; Stratification = stratification of the upper 300 m, expressed as buoyancy frequency (s⁻¹). Biomarkers are plotted according to their co-variability with phytoplankton groups defined by pigments (i.e., Green Algae, Cyanobacteria, Diatoms, Dinoflagellates, Haptophytes) or 16S (i.e., Cyanobacteria, Chrysophyceae, Dictyochophyceae, Prymnesiophyceae, Rappemonad, Bolidophyceae, ASV357, Bacillariophyceae, Cryptophyceaea, Micromonas, Bathycoccus, Ostreococcus).