Monthly microphytoplankton (~20 - 200 mm diameter fraction) samples were collected from Port Hacking 100m coastal station by hauling a 20 μm mesh net (245 mm diameter, 1.2 m length) with an attached 120 mL plastic jar (no flow meter) from a depth of 50 m from September 1998 to December 2009. Samples were preserved using 3% glutaraldehyde (final concentration) and stored at 4°C prior to microscopic examination. An Olympus BH2 microscope equipped with Differential Interference Contrast (DIC) and Phase Contrast (≤ 400X magnification) was used to identify and enumerate microphytoplankton taxa. In order to characterise the structure of the microphytoplankton community, species presence/absence and abundance were measured. Species presence/absence was estimated by attempting to identify all microphytoplankton taxa present in each sample to species. For some taxa, species-level identification was not possible using routine light microscopy. In such instances, individuals were identified to genus (e.g. Chaetoceros, Pseudo-nitzschia, and Thalassiosira). The length of time devoted to enumerating taxa in a sample varied from 1 hr to 2 hr, as determined using the timed-interval protocol of the Australian Rivers Assessment System (AUSRIVAS) (http://ausrivas.ewater.com.au). Abundance was estimated by counting to a minimum of 100 cells, or 10 traverses, using the Lund cell method (Hotzel and Croome 1999). Trichodesmium erythraeum filaments were converted to cell counts using a conversion factor (30 cells filament-1) that was obtained by averaging the cell counts of 40 filaments (standard deviation: 6.4 cells filament-1).
Maintenance and Update Frequency: notPlanned
Statement: Sampling was performed approximately monthly with some missing dates.
The abundance estimates obtained for this study should be viewed as semi-quantitative due to known biases associated with net sampling. Lund et al (1958) recommended counting to a minimum of 100 cells to give a 95 percent confidence interval of the estimate within +/- 20% of the mean and up to 400 cells to give a 95 confidence interval of +/- 10% of the mean (Sournia 1978).
Samples for this work were collected and paid for by the Office of Environment and Heritage and CSIRO (Contact Dr Tim Ingleton, Tim.Ingleton@environment.nsw.gov.au).
Australian Postgraduate Award (APA)
NSW Food Authority
Linnean Society of NSW
Australian Government’s Australian Biological Resource Study
Integrated Marine Observing System (IMOS)
Principal PhD supervision by Leanne Armand (now deceased)