Microbial Community Structure

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	To assist in the interpretation of the data, it can be displayed using the Hawaii Ocean Time-series Data Organization & Graphical System (HOT-DOGS©).

Analytical Method

Analysis of microbial numbers was made using an EPICS 753 flow cytometer (Coulter Electronics Corporation, Hialeah, FL, USA) which has been upgraded with a Cicero Data Acquisition System (Cytomation Inc., Boulder, Colorado). Prior to analysis by flow cytometry, samples were prepared using standard protocols (Monger & Landry 1993; Campbell et al. 1994). Enumeration efficiency was tracked using flurescent beads. Cyanobacteria of the genera Prochlorococcus and Synechococcus were separately enumerated, as well as non-pigmented bacteria/archaea and pigmented eukaryotes.

Results

Depth profiles of heterotrophic bacterial (actually non-pigmented picoplankton and archaea) and Prochlorococcus abundances for each cruise in 2006 are presented in Figure 60A & Figure 60B. A contour plot is shown in Figure 61. At the surface, heterotrophic bacterial numbers (blue) range from 3 to 7 x 10⁵ cells ml^-1. In most cases bacterial numbers decrease with depth although there are some profiles where the numbers remain fairly constant with depth throughout the euphotic zone. Prochlorococcus cells (red) are found at concentrations ranging from around 1 to 3 x 10⁵ cells ml^-1 at the surface and usually decrease with depth but with a subsurface maximum between 75 and 125 m.

Depth profiles of Synechococcus and pigmented eukaryotes are presented in Figure 62A & Figure 62B. A contour plot is shown in Figure 63. At the surface, Synechococcus numbers (blue) range from 1 to 4 x 10³ ml^-1, and decrease with depth with a subsurface maxima between 50 and 100 m. The abundances of picoeukaryotes (red) typically ranges from 0 to 2 x 10³ ml^-1, and similar to Synechococcus, the eukaryote populations generally decline with depth, occasionally exhibiting a subsurface maximum.