Standing up for the little guys – Phytoplankton and Southern Ocean Ecology Laura Bretherton, January 24, 2013
If you’ ve been keeping up with the blog, you’ ll by now be well acquainted with marine plankton. These little guys are the topic of my PhD, though more specifically, I look at the phytoplankton – the photosynthetic microalgae – and how they might be affected by ocean acidification. That means I’ ve been particularly focussed on the bioassay experiments we’ ve been conducting at sea, and today marked the end of our second one. With that comes an early start and many water samples to process …
My role on this cruise is to look at the physiology of phytoplankton populations, and how that changes over the course of the bioassays. I use an instrument called a fast-rate repetition fluorometer( or FRRF for short), which monitors photosynthesis by detecting fluorescence given off by the chlorophyll inside the microalgae. Because we understand how changes in this chlorophyll fluorescence are linked to photosynthesis, the fluorometer can tell us things like how efficiently the phytoplankton are photosynthesising, or if they’ re changing the structures within their cells that catch sunlight.
The FRRF( top left), water bath( middle right) and my dark sample bottles( bottom). @ Laura Bretherton
My sample bottles are made of opaque dark plastic to keep the phytoplankton out of the light for a period of time, in preparation for being put in the FRRF. This process is called dark-acclimation, and sort of“ resets” the algae’ s photosynthetic apparatus to ensure all the models the FRRF uses fit correctly. Once they’ ve been dark-acclimated, a small volume of sample gets put in the FRRF, surrounded by cold water supplied from a water bath that’ s pumped into the instrument to keep the phytoplankton at a constant and appropriate temperature. Finally, I use a laptop to tell the FRRF to start a sequence of flashes of light, and about 20 seconds later, I get some data. The results are available instantaneously( a bit of a luxury on a cruise!), and as phytoplankton
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