Picophytoplankton dynamics in the equatorial Pacific: diel cycling from flow-cytometer observations |
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| Institution: | 1. Orstom, Centre de Nouméa, BP A6, 98848, Nouméa cedex, Nouvelle Calédonie, France;2. Observatoire océanologique de Banyuls (Ura 2071), BP 44, 66651 Banyuls-sur-Mer cedex, France;1. Environmental Toxicology Laboratory, Faculty of Chemistry-Pharmacobiology, Benemérita y Centenaria Universidad Michoacana de San Nicolás de Hidalgo, 403 Santiago Tapia St., 58000, Morelia, Michoacán, Mexico;2. Environmental Toxicology Laboratory, Department of Pharmacology and Toxicology, Faculty of Veterinary, Universidad Complutense de Madrid, Av. Puerta de Hierro s/n, 28040, Madrid, Spain;3. Molecular Design Laboratory, Chemical-Biological Sciences Institute, Benemérita y Centenaria Universidad Michoacana de San Nicolás de Hidalgo, 403 Santiago Tapia St., 58000, Morelia, Michoacán, Mexico;4. Faculty of Civil Engineering, Benemérita y Centenaria Universidad Michoacana de San Nicolás de Hidalgo, 403 Santiago Tapia St., 58000, Morelia, Michoacán, Mexico;1. School of Earth and Environmental Sciences & Research Institute of Oceanography, Seoul National University, Seoul, Republic of Korea;2. Department of Ocean Environmental Sciences, Chungnam National University, Daejeon, Republic of Korea;3. Department of Marine Biotechnology, Anyang University, Ganghwagun, Incheon, Republic of Korea;4. Korea Research Institute of Ships and Ocean Engineering (KRISO), Daejeon, Republic of Korea;1. Postgraduate Program in Biological Oceanography, Institute of Oceanography, Federal University of Rio Grande, Av. Italia, km 8, Rio Grande, RS, 96203-900, Brazil;2. Laboratory of Cyanobacteria and Phycotoxin, Institute of Oceanography, Federal University of Rio Grande, Av. Italia, km 8, Rio Grande, RS, 96203-900, Brazil;3. Postgraduate Program in Physical, Chemical and Geological Oceanography, Institute of Oceanography, Federal University of Rio Grande, Av. Italia, km 8, Rio Grande, RS, 96203-900, Brazil |
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| Abstract: | The French JGOFS cruise FLUPAC was conducted in October–November 1994 in the western and central equatorial Pacific Ocean. During a 7-day time series at 150 °W, in addition to conventional sampling (four times per day from discrete depths between 0 and 150 m), a high frequency (hourly) experiment was performed by continuously pumping water at 5 m below the surface over 24 h. Flow cytometric measurements allowed us to recognise and to follow separately the two major components of equatorial picophytoplankton, the Prochlorococcus and the picoeukaryotes. The hourly surface experiment confirmed the synchrony of Prochlorococcus cell division and showed that picoeukaryotes exhibited a similar behaviour. The main consequence is that the maximum potential growth rate of picophytoplankton is one doubling per day for both cell groups. The vertical profiles indicated that the diel cycling extends throughout the surface layer for both algal groups. The cells were observed to divide daily from late afternoon to the middle of the night, and then to disappear, probably as a result of grazing. In the surface layer, variations of abundance allowed us to estimate a growth rate of about 0.6 day1. Mean cell light scattering parFS as measured by the cytometer indicated a decrease in cell size concurrent with cell division and an increase during the photosynthetic growth phase. |
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