Microphytoplankton abundance and composition data collected from the Port Hacking 100m station 1998-2009

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).