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

• Published in: Coral reefs 1999-09, Vol.18 (3), p.255-262
• Main Authors: CHARPY, L, BLANCHOT, J
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; chlorophyll; Fiji; Fundamental and applied biological sciences. Psychology; Marine; Prochlorococcus; Sea water ecosystems; Synechococcus; Synecology
• ISSN: 0722-4028; 1432-0975
• DOI: 10.1007/s003380050190

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, super(14)C-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll < 3 mu m. Consequently, the percentage contribution to chl a < 3 mu m from each picoplankton group could be calculated using regression estimated values of psi sub(i) (fg chl a per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m super(-3) with 45% of phytoplankton < 3 mu m. Primary production reached 1.3 g Cm super(-2) day super(-1) with 53% due to phytoplankton < 3 mu m. 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 a < 3 mu m, 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 > 3 mu m size fraction. In deeper water, the < 1 mu m size fraction dominated. Prochlorococcus was the most abundant picoplankton group and their contributions to the chlorophyll a < 3 mu m were close to that of the picoeukaryotes (50% each).