Flow cytometry data was collected in December 2008, in waters off South Australia.
The general purpose of the study is to be able to establish background knowledge on the ecosystem on the continental shelf of South Australia and the impact of upwelling/saline outflow events on microbial communities to ultimately develop a biogeochemical model of the region. Sampling was carried out during cruises conducted on board the RV Ngerin as part of the Southern Australian Integrated Marine System (SAIMOS). During each cruise, the physical, chemical and biological properties of the chlorophyll fluorescence maximum (FM) layer were investigated. Flow cytometry data has been collected for picophytoplankton (not bacteria and viruses this cruise).
Six main stations have been sampled over the course of the study, five are located on the 100 m isobath, i.e. RS (35.508S, 136.278E), B2 (35.418S, 136.148E), B3 (35.258S, 136.048E), B4 (35.168S, 135.418E) and B5 (35.008S, 135.198E), and one from an offshore station (B1; 36.188S, 136.178E) located southwest of Kangaroo Island. Note that combining the distances between stations (14–25 nautical miles), the average component of the current velocity at middepth along the shelf (0.01 m s21) and the average speed of the vessel (i.e. 9 knots) indicate that different water masses were sampled at each station. Additional samples have on occasion been collected from the National Reference Station (NRS) at Kangaroo Island (35.832S, 136.447E) and the SA Spencer Gulf Mouth Mooring (SAM8SG, 35.25S, 136.690E), where the saline outflow occurs.
Maintenance and Update Frequency: asNeeded
Statement: At each station, in vivo fluorescence profiles were used to identify the depth of the FM from where we collected seawater with Niskin bottles. These were subsequently homogenized prior to subsampling for nutrients, Chl a concentration, picophytoplankton, bacteria and virus analysis. If no FM could be identify, seawater sampling was done in the surface mixed layer at a depth of 15 m that we previously identified to avoid the effects of photoinhibition.
Seawater samples of 50 mL were filtered through
bonnet syringe filters (0.45 um porosity, Micro Analytix Pty Ltd) and stored at –20oC for nutrient analysis. Nutrient concentrations are not always available for all stations on all cruises. All other
samples were analysed according to the Lachat
Quickchem methods for phosphate (PO3-,4, detection limit; 0.03 uM), nitrate + nitrite (NO-,x, detection limit; 0.07 uM) and ammonium (NH+,4, detection limit; 0.07 uM) on a QuickChem QC8500 Automated Ion Analyser. Chl a concentrations were determined using triplicate 300 mL seawater samples filtered through fibre glass filters (Whatman GF/C, 1.7 um porosity). Filters were stored at –20oC until analysis. Chl a was extracted by placing each filter in 5 mL of methanol for 24 h in the dark at 4oC (Welschmeyer, 1994). Chl a concentrations in the extracts were determined using a Turner 450 fluorometer previously calibrated with Chl a extracted from Anacystis nidulans (Sigma Chemicals, St Louis, MO, USA).
Triplicate 1 mL seawater samples were fixed with
paraformaldehyde (2% final concentration), frozen in liquid nitrogen and stored at –80oC. Samples were processed by flow cytometry (FacsCanto Becton Dickinson) within a month following each cruise. Prior to analysis, 1 um fluorescent marker beads (Molecular Probes, Eugene, OR, USA) were added to each sample (Marie et al., 1999) and each sample was run for 5 min. For each sample, natural orange fluorescence from phycoerythrin and red fluorescence from chlorophyll, together with forward light scatter and side light scatter (SSC), were recorded. All cytograms were then analysed using the software flowJo (TreeStar) following the method described in Marie et al. (Marie et al., 1999). The three known major picophytoplankton
groups, i.e. Synechococcus, Prochlorococcus and picoeukaryotes, could be easily discriminated by their distinct autofluorescence and light scatter properties relative to the beads. Gates or regions around each observed group were drawn such that no adjustment was needed and to maximize cell counts.
Australia’s Integrated Marine Observing System (IMOS) is enabled by the National Collaborative Research Infrastructure Strategy (NCRIS). It is operated by a consortium of institutions as an unincorporated joint venture, with the University of Tasmania as Lead Agent.
South Australian Research and Development Institute (SARDI)