Measuring the Natural Fluorescence of Phytoplankton Cultures

Abstract

A laboratory instrument, the Natural Fluorescence Chemostat, was developed to measure the natural fluorescence of phytoplankton cultures. With this instrument, the physical and chemical environment of a culture can be manipulated with respect to temperature, pH, nutrient delivery rate, and light intensity, while the natural fluorescence and a weak stimulated fluorescence are continuously recorded with high temporal resolution. The geometry and spectral distribution of the artificial light field minimize the contribution of scattering to the natural fluorescence signal. Preliminary investigations with the marine diatom T. weissflogii (Bacillariophyceae) indicate that the instrument can detect natural fluorescence signals in broadband artificial light fields as bright as 1250 ?mol quanta m?2 s?1. Since the influence of environmental factors on natural fluorescence is not well understood, laboratory experiments are essential for investigating how ocean physics and chemistry influence this signal. This instrument provides a quantitative means to examine how the magnitude and kinetics of phytoplankton natural fluorescence vary in response to changes in the physical and chemical environment.