*Jenni Szlosek 1,2 , Anja Engel 2 , Cindy Lee 1 , Robert Armstrong 1

1. Coagulation Efficiency of Phytoplankton Cells During Different Growth Stages and Its Relationship to Exopolymer Particle Properties *Jenni Szlosek1,2, Anja Engel2, Cindy Lee1, Robert Armstrong1 1Marine Sciences Research Center, Stony Brook University, Stony Brook, NY USA 2Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany *jszlosek@ic.sunysb.edu

2.  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  Introduction • 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 exopolymerparticle abundance and exopolymer chemical composition plays in enhancing phytoplankton aggregation. • 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

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

4. 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

5. Coagulation Efficiency =Q • 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 Alpha with Growth Stage alpha Exponential Growth Rate (d-1)

6. TEP Abundance E. hux TEP with Growth Stage TEP conc. (µg Xanthan Gum L-1) Exponential Growth Rate (d-1) direction of “bloom” progression Alpha with Growth Stage • Increase in TEP with decrease in growth stage • Correlation between TEP abundance and  yields an R2 of 0.85 alpha Exponential Growth Rate (d-1)

7. 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) Exponential Growth Rate (d-1)

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

9. 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 

10. Acknowledgements • Nicole Händel, AWI • Umesh Gangeshetti, AWI • Stephanie Koch, AWI