Flow cytometry has been used over the past 5 years to begin detailed exploration of the distribution and abundance of picoplankton in the oceans. Light scattering and fluorescence measurements on individual plankton cells in seawater samples allow construction of population signatures from size and pigment characteristics. The use of "list mode" data has made these studies possible, but on-shore analysis of copious data does not permit on-site reexamination of important or unexpected observations, and overall effort is greatly handicapped by data analysis time.Here we describe the application of neural net computer technology to the analysis of flow cytometry data. Although the data used in this study are from oceanographic research, the results are general and should be directly applicable to flow cytometry data of any sort.Neural net computers are ideally suited to perform the pattern recognition required for the quantitative analysis of flow cytometry data. Rather than being programmed to perform analysis, the neural net computer is "taught" how to analyze the cell populations by presenting examples of inputs and correct results. Once the system is "trained," similar data sets can be analyzed rapidly and objectively, minimizing the need for laborious user interaction. The neural network described here offers the advantages of 1) adaptability to changing conditions and 2) potential realtime analysis. High accuracy and processing speed near that required for real-time classification have been achieved in a software simulation of the neural network on a Macintosh@ SE personal computer. In the past 5 years, the technology of flow cytometry has been assimilated into oceanography from biomedical research, and it shows great promise for contributions in phytoplankton ecology (3,211. These instruments have begun to serve as a new form of microscope in oceanographic research, one that identifies organisms not through pattern recognition of the human eye, but through multiparameter characterization and discell types over vast regions of the oceans (3,4,12,14), to characterize changes in size and fluorescence properties of cells with depth (lo), to distinguish between cell types that cannot be distinguished by any other methods (12,20), and to detect populations of cells too small to be studied microscopically (4). Flow cytometry has also been used to study plankton physiology and ecology in the laboratory. Cell cycle progression and differcrimination according to predesignated objective criteria. This technology has revolutionized the way phytoplankton and particle dynamics at sea are studied and, in turn, has changed our concepts of the processes we are trving to model and understand.

Richard 14,: Epplev has established himself as one ~f ttte most iJ!fluential biological oceanographers of this century through his contributions to the fieM of phytoplankton physiological ecology and his interdisciplinary approach to oceanographic processes. Dick's ability to generalize and conceptualize, to take separate threads of research and weave them into a cohesive fi'amework, has enabled hint to use established techniques in novel appli~'ations, to define new approaches to old oceanographic questions, and to chart new paths. The nature attd quality of his work, and particularly the breadth c~'his interest and e.wertise, places hint with H.H. Gran, G.A. Riley, J.D.H. Strickland, and others who have given the field ef biological oceanography its conceptual structure. Dick's retirement in December 1989, after thirty-m'o years ~?/ progressional service to the oceanographic community, provides an opportlmi(v to reflect on his various accomplishments. In this article, his./briner Ph.D. students and postdoctoral associates briefly (and incompletely) review his contributions to oceanographic research attd the oceanographic community. While Dick built on the work ~?f earlier researchers and matt 3' others ~ 'ere cono'ibuthlg to the same topics that Di~ "k was studyhtg, due to .wace ~'onstraints only those papers authored by Dick are cited. Because Dick always strove to place his work in historical cmztext, the papers referred to below provide a key to the groundbreaking work by othepw.