Chlorophyll a concentration is widely used as a proxy to describe trends in phytoplankton biomass over spatial and temporal scales. The concentration of chlorophyll a in Storm Bay showed surprisingly little variation across the seasons. There was a gradient in concentration from site 1 to site 3, where chlorophyll a decreased slightly. It was highest and most variable at the inshore sites 1 and 9, and lowest at site 3, furthest out in the bay. There was no clear annually recurrent seasonal bloom, although data suggests higher values in spring and autumn (see later time series).
An integrated water column sample (12 m) using a weighted hose was collected for chlorophyll a analysis from February 2010. Prior to this, samples were collected from 1 m below the surface. Following the decision to include the integrated sampler, the sampling regime was revised in the following way. The contents of four sampling tube collections were mixed together and sub-sampled: 2 L samples for chlorophyll a were kept cold and dark until processing in the laboratory on return to shore. Water samples were also collected, using a 6 L or 8 L Niskin bottle, from 0.5 – 1 m below the surface, at 10 m depth, and within 5 m of the seabed. At site 3 an intermediate sample from 50 m was also collected. Chlorophyll a concentrations were determined after extraction of photosynthetic pigments using acetone 90:10 water (vol/vol), sonification and centrifuging to remove filter paper. Absorbances were measured using a Varian CBE cintra 10E spectrometer, and standard equations were applied to determine chlorophyll concentrations.