Use of Polarized Microscope Gets 'Glowing' Report

From July 28, 1992 (update #14)

GREEN BAY - The use of a binocular microscope with two polarizing filters, as described in ZMU#13, has greatly facilitated water sample analysis by Wisconsin Zebra Mussel Watch personnel. "Many of our water samples are taken from highly productive waters, such as southern Green Bay, which makes finding veligers like looking for a needle in a haystack - in this case a haystack made up of filamentous blue-green algae," said watch coordinator Clifford Kraft. "Polarizing filters cause zebra mussel veligers to glow brightly against a dark background, allowing lab personnel to quickly scan samples for brightly glowing objects amongst a tangle of algae and other plankton." Other labs analyzing water samples for zebra mussel veligers have shared similar glowing reports regarding this technique. The only other organisms that show similar characteristics as zebra mussel veligers under cross- polarized light are small ostracods, Kraft said, but it's relatively easy to distinguish between these two types of organisms rather than try to sort through an undifferentiated mass of plankton. Cross-polarization is accomplished by using a microscope with two polarizing filters both above and below the sample. Microscopes can be "jury- rigged" by purchasing polarizing plastic or lenses, he said. A plastic polarizing filter can be cut to fit and attached with hot-melt glue to the bottom of a microscope objective, and a second polarizing filter can be attached to the glass at the bottom of a microscope stage. Scientific supply dealers also sell microscopes and polarizing lenses equipped for this purpose. Further exploration of the use of polarized light to detect veligers is being undertaken by the UW-Green Bay Sea Grant Zebra Mussel Watch office (phone 414/465-2795), Ladd Johnson of Williams College (313/668-2571) and Ellen Marsden of the Illinois Natural History Survey (708/872-8676).

ID: 19920728-5.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.