The Moore Underwater Microscope: An In Situ Imaging System for Marine Microorganisms

Marine microorganisms, including bacteria, protozoans and phytoplankton, constitute more than half of the biomass in the ocean and also play many important ecological roles, such as substrate conditioning and nutrient cycling. However, due to many challenges associated with their microscopic size, these organisms are studied in the laboratory setting instead of in the field. To advance the understanding of these microorganisms in the field, the Moore Underwater Microscope was created to image microbes in situ. The microscope utilizes dark-field illumination by focusing 450nm light from ten laser diodes on a small area, allowing a field of view of 1.2 mm x 1.2mm with a pixel size of 0.5µm and a system resolution of 1.0µm. The system contains two cameras; one directly captures scattered light from dark field illumination, and the other has a high-pass filter to image fluorescence. Laboratory experiments verify that the microscope can reliably detect individual large motile bacterium (1.1µm diameter) and also detect fluorescence from individual phytoplankton such as Nannochloropsissp. with 2.3µm diameter. During the summer of 2019, the system was deployed in a shallow protected lagoon nearby Coconut Island, Hawaii, and successfully captured the development of biofilm on a glass substrate over a period of 24-72 hours. The cameras reveal interactions between microorganisms on the substrate over the biofilm development, as well as the rate of autotroph colonization. This new facility can also be applied to a host of other research questions that require the system’s resolution and contrast capability.