2010 Poster presentation
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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
2010 Poster presentation
- 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 Unpublished, personal communication.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.