MEPS 180:37-49 (1999)  -  doi:10.3354/meps180037

DMSP synthesis and exudation in phytoplankton: a modeling approach

D. Laroche1,2, A. F. Vézina1,*, M. Levasseur1, M. Gosselin2, J. Stefels3, M. D. Keller4, P. A. Matrai4, R. L. J. Kwint3

1Institut Maurice-Lamontagne, Ministère des Pêches et des Océans, CP 1000, 850 route de la Mer, Mont-Joli, Québec G5H 3Z4, Canada
2Département d'océanographie, Université du Québec à Rimouski, 310, allée des Ursulines, Rimouski, Québec G5L 3A1, Canada
3Department of Marine Biology, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands
4Bigelow Laboratory for Ocean Sciences, 180 McKown Point, W. Boothbay Harbor, Maine 04575-475, USA
*Addressee for correspondence. E-mail:

ABSTRACT: In the marine environment, phytoplankton are the fundamental producers of dimethylsulfoniopropionate (DMSP), the precursor of the climatically active gas dimethylsulfide (DMS). DMSP is released by exudation, cell autolysis, and zooplankton grazing during phytoplankton blooms. In this study, we developed a model of phytoplankton DMSP and DMS production allowing quantification of the exudation rates of these compounds during different growth phases. The model was tested on published data from axenic cultures of Prorocentrum minimum and Phaeocystis sp.; DMSP exudation rates vary considerably between the 2 species. Model results show that P. minimum exudes around 1% d-1 of its DMSP quota during the latent, exponential and senescent phases. This is comparable to the average exudation rate estimated from previous laboratory experiments. However, Phaeocystis sp. exudes from 3 to 11% d-1 of its DMSP quota. For this species, DMSP exudation rates apparently show an inverse relationship with the population growth rate. The maximum DMSP exudation rate in Phaeocystis sp. is 10 times higher than previously reported DMSP or DMS exudation rates. Our results suggest that exudation may be as important as cell autolysis in the release of DMSP during Phaeocystis sp. blooms. We conclude that exudation should be incorporated in models of DMS cycling in the marine environment. Moreover, our results for Phaeocystis sp. suggest that a low and constant exudation rate, as sometimes used in models, is not suitable for all conditions.

KEY WORDS: DMS · DMSP · Exudation · Synthesis · Phaeocystis · Model

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