Phytoplankton growth and microzooplankton grazing in the subarctic Pacific Ocean and the Bering Sea during summer 1999 |
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| Institution: | 1. Department of Gastroenterology and Hepatology, University Hospital Essen, Faculty of Medicine, University Duisburg-Essen, Essen, Germany;2. Department of General-, Visceral and Transplantation Surgery, University Hospital Essen, Faculty of Medicine, University Duisburg-Essen, Essen, Germany;3. Institute of Virology, University Hospital Düsseldorf, Faculty of Medicine, University Düsseldorf, Düsseldorf, Germany;4. German Cancer Research Center (DKFZ), Division of Cellular Senescence, Aging and DNA Damage, Heidelberg, Germany;5. Department of Anatomy, University Hospital Essen, Faculty of Medicine, University Duisburg-Essen, Essen, Germany;1. SLRC-Sea Lice Research Center, Institute of Marine Research, 5817 Bergen, Norway;2. SLRC-Sea Lice Research Center, Department of Biology, University of Bergen, Thormøhlensgt. 55, 5008 Bergen, Norway;1. Ludwig Boltzmann Institute for Rare and Undiagnosed Diseases, Vienna, Austria;2. CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria;3. INSERM, UMR1043, Centre de Physiopathologie de Toulouse Purpan, Toulouse, France;4. Université Toulouse III Paul-Sabatier, Toulouse, France;5. Division of Pediatric Hematology-Oncology, Department of Pediatrics and Adolescent Medicine, Research Unit for Pediatric Hematology and Immunology, Medical University of Graz, Graz, Austria;6. Centro Nacional de Biotecnología, Madrid, Spain;7. Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Madrid, Spain;8. Department of Pediatrics and Adolescent Medicine, Medical University of Vienna, Vienna, Austria;9. St. Anna Kinderspital and Children''s Cancer Research Institute, Department of Pediatrics, Medical University of Vienna, Vienna, Austria |
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| Abstract: | Phytoplankton growth and microzooplankton grazing rates were measured by the dilution technique in the subarctic North Pacific Ocean along a west–east transect during summer 1999. Average phytoplankton growth rates without added nutrients (μ0) were 0.33, 0.41, 0.20 and 0.49 d?1 for the four regions sampled: the Western Gyre, the Bering Sea, the Gulf of Alaska gyre and stations along the Aleutian Trench. Average grazing mortality rates (m) were 0.34, 0.27, 0.20 and 0.49 d?1. Limitation of phytoplankton growth by macronutrients, such as NO3 and SiO2, was identified only at a few stations, with overall μ0/μn (μn is nutrient-enhanced growth rate) averaging 0.9. Phytoplankton growth and microzooplankton grazing were approximately balanced, as indicated by high m/μ0 ratio, except in the Bering Sea, where the m/μ0 ratio was 0.65, indicating the relative importance of the diatom-macrozooplankton grazing food chain and possible higher export flux to the deep layer. Flow cytometric analysis revealed that the growth rates of picoplankton (Synechococcus and picoeukaryotes) were usually much lower than the total phytoplankton community growth rates estimated from chlorophyll a, except for stations in the Gulf of Alaska Gyre, where the growth rates for different populations were about the same. Lower than community-average growth rate for picoplankton indicates larger phytoplankters, presumably diatoms, were growing at a much faster rate. Suppressed phytoplankton growth in the Gulf of Alaska was probably a result of iron limitation. |
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