AN IMAGING-IN-FLOW SYSTEM FOR AUTOMATED-ANALYSIS OF MARINE MICROPLANKTON

Present automated systems for counting and measuring marine plankton i nclude flow cytometers and in situ plankton video recorders. Neither o f these approaches are optimal for the microplankton cells which range in size from 20 to 200 mu m and can be fewer than 10(4) l(-1). We des cribe here an instrument designed for rapid counting, imaging and meas uring of individual cells and particles in the microplankton size rang e from cultures and natural populations. It uses a unique optical elem ent to extend the depth of focus of the imaging lens, allowing a sampl e stream flow rate of 1 ml min(-1) The instrument stores a digital ima ge of each particle along with real time fluorescence and size measure ments. An interactive cytogram links a dot-plot of the size and fluore scence data to the stored cell images, allowing rapid characterization of populations. We have tested the system on live phytoplankton cultu res and bead standards, proving the system counting and sizing accurac y and precision. The system provides images and size distributions for cultures or natural marine samples. It has been used successfully at sea to continuously monitor particles while underway. It may prove use ful in studies of plankton community structure, ocean optics and monit oring for harmful algal species.