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Aquatic Microbial Ecology

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AME 34:93-104 (2004)  -  doi:10.3354/ame034093

Transparent exopolymer particles and dissolved organic carbon production by Emiliania huxleyi exposed to different CO2 concentrations: a mesocosm experiment

Anja Engel1,*, Bruno Delille2, Stéphan Jacquet3, Ulf Riebesell1, Emma Rochelle-Newall4, Anja Terbrüggen1, Ingrid Zondervan1

1Alfred Wegener Institute for Polar- and Marine Research, 27515 Bremerhaven, Germany
2Unité d¹Océanographie Chimique, Université de Liège, 4000 Liège, Belgium
3UMR CARRTEL, Station INRA d¹Hydrobiologie Lacustre, 74203 Thonon-les-Bains cedex, France
4Laboratoire d¹Océanographie de Villefranche-sur-Mer, 06234 Villefranche-sur-Mer, France

ABSTRACT: The role of transparent exopolymer particles (TEP) and dissolved organic carbon (DOC) for organic carbon partitioning under different CO2 conditions was examined during a mesocosm experiment with the coccolithophorid Emiliania huxleyi. We designed 9 outdoor enclosures (~11 m3) to simulate CO2 concentrations of estimated ŒYear 2100¹ (~710 ppm CO2), Œpresent¹ (~410 ppm CO2) and Œglacial¹ (~190 ppm CO2) environments, and fertilized these with nitrate and phosphate to favor bloom development. Our results showed fundamentally different TEP and DOC dynamics during the bloom. In all mesocosms, TEP concentration increased after nutrient exhaustion and accumulated steadily until the end of the study. TEP concentration was closely related to the abundance of E. huxleyi and accounted for an increase in POC concentration of 35 ± 2% after the onset of nutrient limitation. The production of TEP normalized to the cell abundance of E. huxleyi was highest in the Year 2100 treatment. In contrast, DOC concentration exhibited considerable short-term fluctuations throughout the study. In all mesocosms, DOC was neither related to the abundance of E. huxleyi nor to TEP concentration. A statistically significant effect of the CO2 treatment on DOC concentration was not determined. However, during the course of the bloom, DOC concentration increased in 2 of the 3 Year 2100 mesocosms and in 1 of the present mesocosms, but in none of the glacial mesocosms. It is suggested that the observed differences between TEP and DOC were determined by their different bioavailability and that a rapid response of the microbial food web may have obscured CO2 effects on DOC production by autotrophic cells.

KEY WORDS: Emiliana huxleyi · Transparent exopolymer particles · TEP · Dissolved organic carbon · DOC · Carbon overconsumption · CO2 · Redfield ratios · Mesocosms

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