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Offshore DAPI

Method

Epifluorescence microscopes was used to analyse three DAPI stained 25mm filters for possible microbes and living cells containing chlorophyll. The microscope works by firing a light with a specific wave length at the filter (UV for 4,6-Diamidino-2-phenylindole (DAPI) and green for chlorophyll), and allowing a lower energy and longer wave length light to be reflected and passed to the microscope lens. LED lights are used as they are more light specific and reduce photo-bleaching. A mercury lantern was used in our microscopy so we had to get a health and safety briefing. Sample 19 was smashed by a rouge elbow; however, another glass cover slip was placed on top of it and the sample was processed. Oil was placed on top of the coverslip to prevent heavy refraction of light from the microscope.

Results

Each sample analysed has a lower chlorophyll reading for estimated total microbial abundance than DAPI stained cells. Sample 18 that was taken at a shallower depth than sample 3 is seen to have less chlorophyll but more DAPI stained cells (Figure 1). A possible reason for this is the formation of a deep chlorophyll maximum observed by the CTD dataset, resulting in more planktonic species at a greater depth. While there could be a higher abundance of microbes at the surface due to more light availability. The lowest chlorophyll and highest DAPI stained cells observed in sample 19 could possibly be due to contamination by the desk and elbow when the slide was broken. However, sample 19 is also the deepest sample taken from a separate cast therefore, could have less light available for plankton and more space for microbes to grow.

Figure 1: Estimated total microbial abundance based off of cell count/ml. Samples 3 and 18 were taken during the same cast but at 20m and 1m depths respectively. Meanwhile sample 19 was taken from a different prior cast at 28ms.