Application of a Cooled CCD Imaging System to the Study of Microorganisms and Non-Living Particles in the Picoplankton Size Range

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Sub-Micrometer particles in marine plankton systems may play important roles in the basic chemistry and biology of the system, in population and food web dynamics and in biogeochemical cycling. Particles in the picoplankton size range include living microorganisms, viruses and non-living detrital particles. The abundance, size spectra and fluorescent nature of these various particles can be measured using image analyzed epifluorescence microscopy. With funding from the "Long-Lead Time Development Program" of the US Joint Global Ocean Flux Study, a sensitive, accurate image analysis system, has been developed, based on a cooled CCD camera, to automate these measurements of natural samples. This award which constitutes a renewal of the past award is to upgrade the spatial resolution of the system to increase the precision of the size measurements of these particles. The instrument will than be used for the characterization of small particles in terms of population abundances, size spectra, and fluorochrome staining. The system will be calibrated using known virus concentrates to determine if they can be distinguished from small bacteria based on their size and fluorescence characteristics. The instrument will be used to characterize particle populations at the JGOFS Bermuda Time Series station and in local estuarine waters. Samples will also be analyzed by electron microscopy as well as for carbon and nitrogen composition, particularly some of the size-fractionated samples. This variety of measurements should lead to a better understanding of the nature of these particles and their potential roles in marine biogeochemical cycles.