Picophytoplankton biomass, community structure and productivity in the Great Astrolabe lagoon, Fiji

Phytoplankton biomass, community structure and productivity of the Great Astrolabe lagoon and surrounding ocean were studied using measurements of chlorophyll concentration and carbon uptake. The contribution of picophytoplankton to biomass, productivity and community structure was estimated by size fractionation, C14-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll is less than 3 micrometers. Consequently, the percentage contribution to chl alpha is less than 3 micrometers from each picoplankton group could be calculated using regression estimated values of psi(i) (fg chl alpha per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m(exp -3) with 45% of phytoplankton is less than 3 micrometers. Primary production reached 1.3 gC m(exp -2)/day with 53% due to phytoplankton is less than 3 micrometers. #Synechococcus$ was the most abundant group at all stations, followed by #Prochlorococcus$ and picoeukaryotes. At all stations, #Prochlorococcus$ represented less than 4 of the chl alpha is less than 3 micrometers, #Synechococcus$ between 85 and 95%, and picoeukaryotes between 5 and 10%. In the upper 40 m of surrounding oceanic waters, phytoplankton biomass was dominated by the less than 3 micrometer size fraction. In deeper water, the less than 1 micrometer size fraction dominated. #Prochlorococcus$ was the most abundant picoplankton group and their contributions to the chlorophyll alpha is less than 3 micrometers were close to that of the picoeukaryotes (50% each). (Résumé d'auteur