Mixotrophic basis of Atlantic oligotrophic ecosystems

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 15; pp. 5756 - 5760
• Main Authors: Hartmann, Manuela, Grob, Carolina, Tarran, Glen A, Martin, Adrian P, Burkill, Peter H, Scanlan, David J, Zubkov, Mikhail V
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 10-04-2012; National Acad Sciences
• Subjects: Algae; Atlantic Ocean; Bacterioplankton; Biological Sciences; Biomass; carbon dioxide; Cells; Cruises; Cyanobacteria; Cyanobacteria - metabolism; Ecosystem; Ecosystems; Flow Cytometry; Food chains; food webs; Gyres; Marine ecology; Marine ecosystems; nutrients; Oceans; Plankton - cytology; Plankton - metabolism; Plant cells; Plastids; Plastids - metabolism; Sea water; Seawater - microbiology; Temperate regions; temperate zones; Tropical Climate; Atlantic Ocean
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1118179109

Oligotrophic subtropical gyres are the largest oceanic ecosystems, covering >40% of the Earth's surface. Unicellular cyanobacteria and the smallest algae (plastidic protists) dominate CO2 fixation in these ecosystems, competing for dissolved inorganic nutrients. Here we present direct evidence from the surface mixed layer of the subtropical gyres and adjacent equatorial and temperate regions of the Atlantic Ocean, collected on three Atlantic Meridional Transect cruises on consecutive years, that bacterioplankton are fed on by plastidic and aplastidic protists at comparable rates. Rates of bacterivory were similar in the light and dark. Furthermore, because of their higher abundance, it is the plastidic protists, rather than the aplastidic forms, that control bacterivory in these waters. These findings change our basic understanding of food web function in the open ocean, because plastidic protists should now be considered as the main bacterivores as well as the main CO2 fixers in the oligotrophic gyres.