MEPS 297:15-21 (2005)  -  doi:10.3354/meps297015

Phosphate availability controls Trichodesmium spp. biomass in the SW Pacific Ocean

Thierry Moutin1,*, Nathalie Van Den Broeck1, Beatriz Beker1, Cécile Dupouy2, Peggy Rimmelin1, Aubert Le Bouteiller2

1Laboratoire d’Océanographie et de Biogéochimie (UMR 6535), Centre d’Océanologie de Marseille, Campus de Luminy, 13288 Marseille Cedex 09, France
2Institut de Recherche pour le Développement (IRD), BP A5, 98848 Nouméa, New Caledonia

ABSTRACT: Throughout tropical and subtropical seas, Trichodesmium spp. contribute significantly to marine fixation of atmospheric di-nitrogen and influence the global carbon cycle. We suggest that dissolved inorganic phosphate (DIP) availability has a predominant role in controlling Trichodesmium spp. biomass. From experimental work carried out on cruises in the SW Pacific Ocean, and by re-analysing previous data, we have defined a critical level of DIP needed for single filaments of Trichodesmium spp. to grow. Thus, seasonal variations in DIP availability could control Trichodesmium spp. growth and decay. As this critical level is below the detection limit of classical DIP measurements obtained during oceanic cruises, we suggest a re-evaluation of the phosphate availability in the oligotrophic ocean in order to determine what ultimately controls di-nitrogen fixation in the sea.

KEY WORDS: Trichodesmium spp. · Phosphate availability · Diazotrophy · South Pacific Ocean

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