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Marine Ecology Progress Series

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MEPS 354:3-19 (2008)  -  DOI:

Effects of phytoplankton physiology on export flux

L. Alex Kahl1,2,*, Assaf Vardi2, Oscar Schofield1,2

1Coastal Ocean Observation Laboratory, and 2Environmental Biophysics and Molecular Ecology Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road, New Brunswick, New Jersey 08901, USA

ABSTRACT: Estimates of phytoplankton sticking efficiency (α) were made in the laboratory within a 1500 l annular flume mesocosm over the initiation, maintenance and senescence phases of a bloom of the diatom Thalassiosira pseudonana. The spatially weighted mean turbulence kinetic energy dissipation rate in the annular flume was comparable to values found at the ocean’s surface on a calm day. The α of T. pseudonana varied as a result of physiological state, and ranged from 0 ± 0.08 during the bloom initiation to 0.26 and 0.73 ± 0.16, respectively, during bloom maintenance and senescence phases. During the periods of high α, physiological changes included (1) diminished phytoplankton photosynthetic quantum efficiency, (2) an increase in super-oxide dismutase protein expression, reflecting oxidative stress, and (3) the induction of a biochemical cascade initiating autocatalytic programmed cell death. Additionally, during the period of high physiological stress on the diatoms, there was an increase in the presence of transparent exopolymer particles and bacteria. Applying a variable α to a 1-dimensional export flux model shows that carbon export can be increased by at least 2-fold compared to simulations assuming a typically modeled value of α = 1 (100% sticking efficiency). The model using a physiologically dependent α had a low initial sticking efficiency that allowed a significant increase in the critical concentration of algal cells. Such an increase in the number of cells during bloom initiation followed by an increase in α during the maintenance and senescence phases resulted in enhanced export fluxes during the latter, ‘stickier’, stages of the bloom.

KEY WORDS: Phytoplankton · Export flux · Sticking efficiency · Transparent exopolymer particles · Photosynthetic efficiency · Oxidative stress · Programmed cell death · Mesocosm

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Cite this article as: Kahl LA, Vardi A, Schofield O (2008) Effects of phytoplankton physiology on export flux. Mar Ecol Prog Ser 354:3-19.

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