Coagulation Efficiency of Phytoplankton Cells During Different Growth Stages and Its Relationship to Exopolymer Particle Properties *Jenni Szlosek 1,2, Anja Engel 2, Cindy Lee 1, Robert Armstrong 1 1 Marine Sciences Research Center, Stony Brook University, Stony Brook, NY USA 2 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany *

Approach: Compare effect of TEP number vs. exopolymer chemical quality on  Limit variability in  due to experimental set-up Compare results for diatoms vs. coccolithophores  increases with drop in phytoplankton growth rate Increase in TEP abundance leads to increased  No indication that differences in dissolved polysaccharide composition with growth affects  Phytoplankton aggregation is an important mechanism for the export of organic carbon Exopolymer particles such as TEP may play an important role in the coagulation efficiency of cells The value of  used in aggregation calculations may not always represent the “real” value of the system. Goal: Understand the role exopolymer particle abundance and exopolymer chemical composition plays in enhancing phytoplankton aggregation. Introduction

Drapeau et al., 1994 photo of Couette flow deviceschematic of Couette flow device Coagulation Efficiency =Q=Q ln(∑C(t)) time sampled slope=Q What affects  … ? Known: G m, mean shear Constants describing physics: 7.82, π Uncertain: , volume fraction  TEP contribution Chemical quality of exopolymers as cell coatings and transparent particles # of particles unit volume C i = after Kiørboe et al., 1990:

Experimental Set Up Emiliania huxleyi grown as chemostat cultures Grown at 15˚C in enriched media: 50 µM N 3 µM P f/2 trace metals and vitamins Steady-state growth reached for turnover times of: 0.48, 0.25, 0.1, 0.05 d -1 Cell exponential growth rates equaled turnover times

Coagulation Efficiency No indication of coagulation at highest growth rate (0.48 d -1 ) The magnitude of the slope (Q) increases with decreasing exponential growth rate Alpha increases with decreasing exponential growth rate =Q=Q Alpha with Growth Stage Exponential Growth Rate (d -1 ) alpha

TEP Abundance Increase in TEP with decrease in growth stage Correlation between TEP abundance and  yields an R 2 of 0.85 E. hux TEP with Growth Stage Alpha with Growth Stage Exponential Growth Rate (d -1 ) TEP conc. (µg Xanthan Gum L -1 ) alpha direction of “bloom” progression

Dissolved Aldose Composition Decrease in Mol% Glucose with decreasing exponential growth rate Sugars found in coccoliths of E. huxleyi present in nearly constant amounts throughout growth stages Effect of changes in dissolved sugar composition on  requires further work Exponential Growth Rate (d -1 )

Diatoms vs. Coccolithophores Thalassiosira weissflogii (batch culture) Emiliania huxleyi (chemostat culture) TEP concentration (µg Xanthan Gum L -1 ) 

Conclusions Attachment probability, , increases with decreasing exponential growth rate (progression of “bloom”)  correlates with TEP abundance as expected Possible importance of DOM chemical composition on attachment probability of cells is undetermined Chemostat culturing is a useful technique to reduce the experimental variability of 

Acknowledgements Nicole Händel, AWI Umesh Gangeshetti, AWI Stephanie Koch, AWI