OLI Grant: A submersible imaging-in-flow instrument to monitor nano- and microphytoplankton

Robert Olson, Heidi Sosik, and Scott Gallager, Biology

Grant Funded: 2003

Proposed Research

Abstract
Plankton account for almost all the primary productivity and a majority of the biomass in the ocean, and the structure of the microbial community determines in large part that of higher trophic levels, including the production available for human consumption. Although we are beginning to appreciate the potential effects of human activities and climate change on plankton community structure, a fundamental understanding of the complex interaction between physical and biological factors that regulate community structure requires more detailed and sustained observations. We have begun to continuously monitor the smallest phytoplankton at the MVCO using FlowCytobot (a submersible flow cytometer), and the plankton at the other end of the size spectrum (mainly zooplankton >100 µm) will soon be monitored with the Video Plankton Recorder. However, neither of these instruments will sample well the phytoplankton in the size range 10-100 µm. This represents a serious gap because phytoplankton in this size range, which includes many diatoms and dinoflagellates, can be especially important in coastal blooms.

The goal of this proposal, therefore, is to develop an in situ instrument to characterize these large phytoplankton cells. We propose to use a combination of flow cytometric and video technology to both capture images of cells for identification and measure chlorophyll fluorescence associated with each image. We also propose to utilize a recently-developed optical technique called wavefront coding to increase our imaging depth of field and hence increase the rate at which we can examine water samples. The data from this instrument, in conjunction with the other plankton-monitoring instruments and other data collected at the MVCO, will help us to better understand how coastal plankton communities are regulated.

Progress Report

Our goal is to develop an in situ instrument to characterize large phytoplankton cells and small zooplanktonic organisms, in the size range 10 to 100 mm. To do this, we are combining aspects of FlowCytobot, a submersible flow cytometer which analyzes pico- and nanophytoplankton (1-10 mm) and of the Video Plankton Recorder, a video system for analyzing larger zooplankton. We have constructed a functioning prototype of the instrument (called the Imaging FlowCytobot, IFCB), which includes a high-resolution digital video camera, a xenon strobe/fiber optic illumination system, a custom quartz flow cytometer flow cell that can accommodate sample particles as large as 180 mm, a diode laser and photomultipliers for flow cytometric measurements of particle size and chlorophyll fluorescence, electronic circuitry for digitizing the flow cytometric signals and triggering the camera system, and an internal PC104+ computer. We are now working on software for image and data acquisition and instrument control, and fabricating the instrument's pressure housing (a cylinder 12 by 30 inches). IFCB will be receive power from and transmit images and data to shore via cables. We plan to test IFCB off the WHOI dock this spring and deploy at Martha's Vineyard Coastal Observatory later this summer. The data from this instrument, in conjunction with the other plankton-monitoring instruments and other data collected at the MVCO, will help us to understand how coastal plankton communities are regulated.