DIRECT OBSERVATION OF PHYTOPLANKTON, TEP AND AGGREGATES ON POLYCARBONATE FILTERS USING BRIGHTFIELD MICROSCOPY

There has been little use of standard (i.e. non-inverted) microscopes for observing and counting phytoplankton in filtered water samples usi ng brightfield white light illumination due to light interference from the filters. If filters are placed on newly designed frosted slides ( Cyto-clear, Poretics Corp.), however, phytoplankton can be viewed dire ctly on the surfaces of polycarbonate filters under brightfield illumi nation. Lake and seawater samples were used to show that samples stain ed with alcian blue (to identify the presence of particulate polysacch arides) and analyzed with white light can also be simultaneously stain ed with fluorochromes (i.e. DAPI and acridine orange) for additional e xamination of the sample using fluorescent techniques. Black filters, which are necessary for epifluorescent techniques, did not interfere w ith brightfield viewing. Using double staining techniques, we found th at transparent exopolymer particles (TEP) recently discovered in marin e systems are also present in lakes. Not all aggregates in the fresh a nd seawater systems absorbed the alcian blue stain, however, indicatin g that not all amorphous particles in these systems are rich in negati vely charged polysaccharides.