AME prepress abstract  -  DOI: https://doi.org/10.3354/ame01873

Trichodesmium and other planktonic cyanobacteria in New Caledonian waters (South West Tropical Pacific) during an El Niño Episode

Márcio Murilo Barboza Tenório, Cécile Dupouy*, Martine Rodier, Jacques Neveux

*Email: cecile.dupouy@mio.osupytheas.fr

ABSTRACT: Contributions of filamentous and picoplanktonic cyanobacteria to the phytoplankton community structure were examined in New Caledonian waters during the 2001-2003 El Niño period at three stations. Morphometric characteristics of diazotrophic filamentous cyanobacteria are given as well as the seasonal and inter-annual variations of their surface areas and integrated abundances. Trichodesmium tenue and T. thiebautii were the dominant species followed by T. erythraeum, altogether accounting for more than 51-80% of the biomass of the free-living filamentous cyanobacteria. Katagnymene spp. accounted for a smaller percentage (<13.8% at ocean stations, <3.6% in the lagoon). R. intracellularis biomass was relatively small (<1% of total surface area and volume of Trichodesmium trichomes) with the highest concentration observed in summer (735 trichomes l-1). Colonies of unidentified cyanobacteria composed of spherical cells accounted on average for <1% of the Trichodesmium biomass, with maximum values exceeding 4000 cells l-1. Abundance of filamentous cyanobacteria varied according to environmental factors, with summer 2001-2002 characterized by low filamentous diazotroph abundance and summer 2003, occurring at the peak of the 2001-2003 El Niño, particularly rich in filamentous cyanobacteria (with a maximum Trichodesmium spp abundance of 4500 trichomes l-1 in the Loyalty Channel). A similar variability pattern was observed for large diatoms and dinoflagellates, and for all picoeukaryotic populations. Different biomass estimators are provided as cell abundances, pigment concentrations including chlorophylls and phycoerythrin, and carbon content. The filamentous communities dominated in summer in oceanic waters while Synechococcus and picoeukaryote communities dominated in lagoon waters in winter at all stations.