by Liz Lam, Biological Oceanography Lab
Ballast water treatment and testing is a big focus here in the Biological Oceanography lab, and this is no exception even when it comes to class projects. Last semester, I started a project aiming to improve one of our counting techniques. I’d previously written about IMO’s restriction to 10 organisms per 1,000 liters of discharged ballast water and counting zooplankton under a microscope in order to check for these results. But when it comes to even smaller organisms, such as algae and other even tinier phytoplankton, different methods are called for.
We already have a pretty clever way of quantifying such microscopic organisms by using a few chemical and optical tricks. The first key ingredient is fluorescein diacetate, or FDA. One of the special features of this molecule is that it can only be cleaved by certain proteins in live cells. Once FDA is split, what remains is fluorescein, a compound that glows bright green when excited under blue light. We can then use an epifluorescence microscope to both shine the right wavelength of light and magnify a sample in order to count any green organisms. If it glows green, then it means it’s alive! This allows us to quantify the number of live organisms that are extremely small and difficult to see.