Picoplankton community structure in the subarctic Pacific Ocean and the Bering Sea during summer 1999

Abstract

We studied picoplankton community structures in the subarctic Pacific Ocean and the Bering Sea during summer 1999 using flow cytometric analysis. The picoplankton community in the studied area was comprised of Synechococcus spp., eukaryotic ultraplankton and heterotrophic bacteria. Prochlorococcus spp. were not detected at any station. Abundances of Synechococcus and eukaryotic ultraplankton were at approximately the same level of 10 3 to 10 4 cells ml -1 within the upper euphotic layer in the subarctic gyres. An abundance of Synechococcus spp. higher than 5 × 10 4 cells ml -1 was found at the surface to 40 m depth in the northern Gulf of Alaska, whereas low Synechococcus spp. abundance (about 500 cells ml -1 ) was found in the upper euphotic layer in the Bering Sea. Abundances of heterotrophic bacteria were about 2 orders of magnitude higher than those of Synechococcus spp. and eukaryotic ultraplankton, with higher abundance generally occurring in the area of high autotrophic biomass. Although Synechococcus spp. and eukaryotic ultraplankton occurred at comparable abundance, the latter contributed significantly more to photosynthetic carbon biomass, except in the northern Gulf of Alaska, where the biomass of Synechococcus spp. and eukaryotic ultraplankton were approximately equal. Cellular red fluorescence for Synechococcus spp. and eukaryotic ultraplankton increased by an average 4-and 2-fold, respectively, from the surface to the bottom of the euphotic layer, with the smallest increase occurring in the Bering Sea. Both the red fluorescence and forward light scatter (FSC, related mainly to cell size) per cell varied more than 2-fold spatially, with the highest value occurring in the Bering Sea. These variations were probably caused by differences in physiological conditions and species compositions. Overall, picophytoplankton was the dominant contributor to total autotrophic biomass in the subarctic North Pacific, but contributed only a small fraction to total autotrophic biomass in the Bering Sea. The Western Gyre (WG) and the Alaskan Gyre (AG) possess both similarities and differences in biogeochemical processes and microbial food-web dynamics. The slightly higher phytoplankton biomass, photosynthetic efficiencies and growth rates in WG than AG suggests less severe iron limitation in the WG.

Seasonal dynamics of picoplankton in shelf waters of the southern Bay of Biscay

“…Photosynthetic bacteria clearly outnumbered picoeukaryotes under stratification, in accordance with previous reports showing high cyanobacterial abundance in summer (Modigh et al 1996, Agawin et al 1998, DuRand et al 2001, Liu et al 2002. A strong relationship between temperature and Synechococcus growth rate was suggested by Agawin et al (1998) as the origin of this seasonality in the Mediterranean Sea.…”

Ecological Genomics of Marine Picocyanobacteria

“…In fact, the Prochlorococcus genus is confined to a latitudinal belt of the world's oceans bounded roughly by the latitudes 45°N to 40°S, and cell concentrations are often much lower in coastal than in offshore areas (26,128,153,205,219,258). This contrasts with the much more ubiquitous oceanic distribution of the marine Synechococcus genus, which can be found in any ecosystem type up to the polar circle (102,154). Besides daily and seasonal patterns in the solar light environment, there may be concomitant changes in water column structure, e.g., stratified versus well-mixed water columns, which also magnify or alter the in situ light and nutrient gradients.…”

The influence of episodic flooding on a pelagic ecosystem in the East China Sea

“…They were then immediately frozen in liquid nitrogen and kept at −80 • C prior to analysis. The heterotrophic bacteria were stained with the nucleic acid dye SYBR ® Green I (emission = 530 ± 30 nm) at a 10 4 -fold diluted commercial solution (Molecular Probes, Eugene, OR, USA; Liu et al, 2002). They were then identified and enumerated using a flow cytometer (FACSAria; BD Biosciences, Franklin Lakes, NJ, USA).…”