Three distinct groups of picoplankton were identified in the Patagonian Shelf region: Prochlorococcus, Synechococcus, and picoeukaryotes. Prochlorococcus populations were detected at four stations within the Brazil Current but did not extend further south than 40°S. Cyanobacterial abundance, primarily Synechococcus, was greatest in warmer, more oligotrophic conditions corresponding to regions outside the shelf break. Picoeukaryotes dominated at most other stations. Heterotrophic bacteria abundances were two orders of magnitude higher than autotrophs, indicating rapid nutrient recycling. Cyanobacterial abundance correlated positively with temperature and negatively with nutrients, influenced by hydrographic features and seasonal blooms in the

1. Picoplankton distribution and abundance patterns across the
Patagonian Shelf break region during Austral Summer
Conclusions
Materials and Methods
Picophytoplankton and heterotrophic bacteria populations were
quantified using a flow cytometer at the University of Southern
Maine. Three distinct groups of picoplankton were delineated
based on their auto-fluorescence and light-scattering properties.
Heterotrophic bacteria (not shown) were quantified using a
nucleic acid staining method (Marie, et al. 1997).
Literature cited
Garcia et al, 2008. Environmental factors controlling the phytoplankton blooms at the
Patagonia shelf-break in spring. Deep-Sea Research I 55: 1150-1116.
Marie, et al., 1997. Enumeration and Cell Cycle Analysis of Natural Populations of
Marine Picoplankton by Flow Cytometry Using the Nucleic Acid Stain SYBR Green I.
Applied and Environ. Microbiol. 63: 1. 186-193.
Painter, S. 2010. Unpublished, personal communication.
Partensky, F., W.R.Hess, D. Vaulot. 1999 Prochlorococcus, a marine photosynthetic
prokaryote of global significance. Microbiol. Mol. Biol. Rev. 63:1: 106-127.
Schlitzer, Reiner. Ocean Data View. http://odv.awi.de
Heather A. Wright, Lisa R. Moore, Department of Biology Graduate Program, University of Southern Maine
Introduction
Marine phytoplankton are widely distributed throughout the
global oceans and play an important role in carbon cycling and
primary productivity. The smallest of the microbial community,
the picoplankton, ranging in size from 0.1 – 2.0µm are the most
abundant. Marine cyanobacteria comprise the dominant
photosynthetic organisms in this size class and are found in high
abundances up to 106 cells ml-1.
Two genera, Prochlorococcus and Synechococcus, have been
found co-occuring within subtropical, oligotrophic regions of the
world, with Prochlorococcus having a global distribution between
40 N and ~40 S (Partensky, et al. 1999).
To further investigate the biogeography of these microbes, our
research addressed spatial distribution patterns of picoplankton in
the Patagonia shelf break region of the Southern Atlantic Ocean
with the following motivation:
• What are the dominant picophytoplankton populations?
• What are the distribution and abundance patterns of these
populations?
• What is the latitudinal extent of Prochlorocccus and are there
correlations between the physico-chemical features and
picoplankton populations?
Prochlorococcus 0.7µm Synechococcus 0.9µm
TEM image of marine cyanobacteria from image archives Station
Biologique de Roscoff (Vaulot).
Figure 1. Flow Cytometric signatures showing distinct Synechococcus
population in fuschia, Prochlorococcus population in blue and bulk
picoeukaryote signature in green. Multiple populations were present
but were not distinguished based on flow cytometric analysis.
Acknowledgements
Gratitude is extended towards the captain, crew and shipboard technical
support of Scripps Institute of Oceanography, RV Roger Revelle, chief
scientist of COPAS08, Dr. William Balch and his lab members. Dr. Lisa
Moore for funding and collaboration on this project.
Special thanks to K.E. Callnan for her assistance with sample collection,
K.R-Johnson for technical support and training on flow cytometry, and all
members of the Moore laboratory for their insightful feedback.
Additional thanks to M. Esty for assistance with SEADAS data files.
NSF funding awarded to L.R.Moore grants # 0847890 and #0851288.
The Patagonian Large Marine Ecosystem
The PLME is located in the Southwest Atlantic Ocean and is one of the largest
continental shelf regions in the world. These waters sustain high levels of
productivity and are important fishing grounds . Seasonal blooms of
phytoplankton dominated by calcite-containing coccolithophores can be
observed using satellite remote sensing (Garcia, et al. 2008) and seen in Fig.2.
This region is characterized by distinct hydrographic features (see Fig.3).
As part of a larger study to investigate a seasonally occurring bloom, our
laboratory collected samples for picoplankton abundance during the
COPAS08 cruise.
2
5
1
3
4
Malvinas-Falkland
Brazil
SubAntarctic
High salinity
Low salinity
Figure 3. COPAS08 cruise track hydrographic regions
of the PLME. As defined by their T/S (temperature
and salinity) ranges. Credit: Painter, S. NOCS Univ. of
Southampton (personal, communication)
Figure 2.
NASA MODIS satellite image of chlorophyll a averaged
between December 2009 and January 2010 . Scale is not
shown but regions of high chlorophyll (mg/m3) are
indicated by yellow to red coloration and lower
chlorophyll regions are in turquoise to green. During this
time period the COPAS08 cruise was conducted and
confirmed the presence of the phytoplankton bloom.
NASA Ocean Color : http://oceancolor.gsfc.nasa.gov/
Prochlorococcus populations were measured at four stations
within the Brazil Current hydrographic feature but did not
extend further southwards than 40 S. Their abundance
contributed to overall higher cyanobacterial populations at
stations outside the shelf break .
Cyanobacterial abundance (primarily Synechococcus) was
greatest in regions corresponding well with higher
temperatures and oligotrophic conditions. Picoeukaryotes
were the dominant photosynthetic organisms throughout the
majority of other stations. Heterotrophic bacteria was two
orders of magnitude higher than autotrophic abundance. The
high ratio of heterotrophic bacteria to autotrophic
picoplankton suggests there is rapid recycling of nutrients as a
result of primary production.
There was a strong, positive relationship between
cyanobacteria abundance and temperature (Fig.5), whereas
nutrients confirm a negative correlation, most likely due to the
fact that the flow cytometrically determined picoeukaryotic
populations do not reflect a single genus (Fig.1).
Our results show that picoplankton distribution
patterns within the PLME are associated with bloom
formations, continental shelf topography and
hydrographic fronts and that physico-chemical
features are influencing the distribution and
abundance of cyanobacterial populations on a
seasonal scale.
Chlorophyll a fluorescence profiles
Picoplankton population patterns Figure 4.
Stations sampled during the
COPAS08 Coccolithophores
of the Patagonian Shelf
Cruise. The right hand scale
bar indicates bathymetry
using the global ocean
database from Ocean Data
View (Schlitzer, R.). The
shelf break occurs along the
200-1500m isobath.
cyanobacteria
Heterotrophic bacteria
picoeukaryotes
Figure 5. Depth integrated cell abundance of
picoplankton across latitude depicted in 2D spatial
plots in left-hand column. 5a. Shows relationship
between cell abundance (log cells m-3 ) and
temperature shown in scatter plots.
Cyanobacteria are correlated with higher
temperatures of the Brazil current 5b.
Cyanobacteria (circles) are negatively correlated
with TDN r2=0.4776 but picoeukaryotes (squares)
have no relationship r2=0.0831.
email: heather.wright@maine.edu, lmoore@usm.maine.eduUniversity of Southern Maine, Portland, ME, USA
5b. Picoplankton vs Total dissolved nitrogen
5a. cyanobacteria vs. temperature
Figure 6. Depth profiles for station 20 located within the
bloom feature. Measured cell abundance (cells/ml) of each
picoplankton population at depth (left) and corresponding
cell autofluorescence (right) and total chlorophyll. Although
cell abundance of cyanobacteria was higher than
picoeukaryotes, the chlorophyll fluorescence at this station
confirms the presence of larger nanoplankton within the
bloom formation.