Question

You are provided a seawater sample with some marine phytoplankton. You are asked to design a test to tell if the marine phytoplankton in the seawater sample is limited by a specific nutrient. How would you do that and which nutrient(s) would you include?

Answer 1

It is quite normal to relate certain nutrients to plankton as limiting nutrients in their growth, in this case, the experiment would measure biomass growth in different treatments where each kind of nuetrient is being limited. To begin with we have to make our list of suspected nutrients that may be the limiting nutrients, let's take phosphorus, nitrogen, carbon and iron. One treatment will have a limited source of phosphorous, while having a constant non ending source of other nutrients; the second treatment will have a limited source of nitrogen, while having a constant non ending source of other nutrients; and don't forget to make a control groups in which all the nuetrients won't be limited. We will start to grow separated populations in each treatment, we will measure their growth and will plot all the data. We will compare the resulting graphs, a stationary behavior around depletion of a certain nutrient and the later decreasing phase will indicate us that this is a limiting nutrient.