My long-term goal is to understand the mechanisms responsible for the variability in phytoplankton biomass, primary production, and species composition. I started my oceanographic career by studying the role of phosphate availability in controlling phytoplankton biomass and production in the subtropical Central North Pacific. Although I retain my interest in nutrient dynamics, my focus shifted to the interaction of phytoplankton and light in the ocean. I started this phase of my career with a study of the photoadaptive changes in the absorption cross section of photosystem I in marine phytoplankton. My present research interests include primary production (at the level of the single cell and as well as the entire phytoplankton assemblage); photosynthetic physiology as well as phytoplankton physiology in general; biological optics; and ocean observations using in-situ optics and remote sensing. I have participated in a number of cruises in both the north Atlantic and Pacific oceans. Specific research projects have included the behavior of the photosynthetic quantum yield to different environmental conditions; the use of flow cytometry to study phytoplankton photoadaptive states and vertical mixing; the development of immunological methods to determine the presence of specific bacterial and phytoplanktonic species in field samples; the development of immunological methods to determine concentrations of photosynthetic components; and a variety of direct and inverse methods to determine the phytoplankton absorption coefficient from total absorption coefficients.