Monterey Bay National Marine Sanctuary
Plankton monitoring
Samples of phytoplankton and zooplankton are obtained using 20 um and 80 um mesh nets respectively, lowered from the Santa Cruz wharf. Often this is done with Cabrillo College students as part of the Pacific Plankton Program. Once collected, we look under a microscope to analyze the catch. Regular sampling shows seasonal changes in diatom and dinoflagellate populations. Data are entered in the national Phytoplankton Monitoring Network. Blooms of these species may be toxic and enter the food chain causing problems for wildlife and the fisheries. However, phytoplankton are at the bottom of the food chain and essential for the existence of the larger fauna we see in the Monterey Bay. On a global scale, phytoplankton in the oceans contribute as least as much as forests on land to carbon sequestration. We are also interested in monitoring microplastic contamination in the plankton samples.
Light Microscopy
Magnifications of 30x to 100x are normally sufficient to ID micro-plankton. My current set-up comprises an AmScope 120 compound microscope, with a Swift trinocular head attached to a JVC camcorder via an Eagle Optics digiscope eyepiece. I also use a simple (lenless) USB camera for direct monitoring on a computer screen and projection for live video sessions. Simple stereo and compound microscopes for the hobbyist can be extended to view plankton with Dark Field, Polarized illumination and Fluorescence excitation with little cost, as shown in YouTube videos and the articles below. Chlorophyll fluorescence can be detected by shining a 405 nm (violet-blue) laser pointer at the sample. Nile Red fluorescent stain helps identify microplastic contamination in plankton samples and can be viewed using illumination from a 450 nm blue LED flashlight in combination with a yellow filter in the emission pathway (see picture gallery below and MBNMS microplastics page for some examples).
Some of these microscope hacks are described on the San Francisco Microscopical Society website "Clive's Corner"
Condenser properties condensed (introduction to brightfield condenser settings)
Taking a walk on the dark-field side (darkfield and oblique illumination)
Setting the stage (darkfield for stereo microscopes)
Magic wands (phase telescopes and more)
Living in a polarized world (adding polarizers to a basic microscope)
Let there be light (adding a battery supply to a microscope)
A net gain (making a small plankton net)
An exciting challenge (fluorescence)
A demonstration microscope (practical tutorial on optics)
Phytoplankton photo gallery
Low power view
Protoperidinium
Polykrikos
Ceratium
Corethron
3 images at different foci
Image stacking to improve depth of field
Coscinodiscus
Bright field
Coscinodiscus
Dark field
Coscinodiscus
Dark field + fluorescence
Coscinodiscus
Fluorescence from chloroplasts
Ceratium and other plankton viewed by dark-field illumination
Erythropsidinium, with its retractable piston and eyespot, complete with lens, is unique amongst the dinoflagellates.
Pluteus (sea urchin larvae) viewed under polarized light, showing internal calcareous skeleton.
Use of a NEMA17 stepper motor on an Amscope 120 microscope to take pictures at different focal planes. As an example multiple images of the phytoplankton, Isthmia were stacked using the program "CombineZP"