Measuring the rates of biological processes in the open sea remains a challenging problem to experimentalists. The problems are especially acute in the central gyres of the subtropical oceans where the concentrations of plankton and nutrients take minimum values (i.e., in oligotrophic waters). Historically, this led to the use of radioisotopic tracers to measure fundamental rate processes of the plankton such as photosynthetic carbon assimilation. Such technology requires incubating samples of seawater in bottles. This has long been worrisome since enclosing the plankton for several hours may well lead to artifacts. There ought to be better ways of making the measurements; finding some is one of the PRPOOS tasks.