The best way to concentrate protists from the water column is the use of a plankton net. These are conical nets made of a mesh which end in a small receiving jar. Biggers nets with wider openings are used where the plankton is sparse. The pore diameter of the mesh can vary – down to 10 microns or so, and a pore size that suits the target organisms must be sought (that is, marine diatoms may be collected with a 100 mesh net whereas synurophytes in a freshwater pond may require a 20 mesh net).

Procedure

Can be done from shore, but this is like to lead to shoreline debris getting caught up in the same

Doing this from a jetty or boat is better

• The net must be flung into the water, typically allowed to sink so that is just below the surface (although this can be adjusted) and then must be towed for a distance / period of time. The more water that flows through the net the more will be collected. The operation may be repeated several times if for example the only way of towing the net through the water is to allow it to sink vertically and then pull it up, but in this case be careful not to get bottom debris in the net

• Remove net while spinning / twisting it so that the remaining water washes any collection from the side of the net and this will then flow into the receptacle at the bottom of the net

• You can use a squirt bottle – squirting from the outside, to release any captured material from the mesh

• This approach can be quite brutal on the specimens, and many species in the material once concentrated will not remain viable for very long. SO, if the material is not being fixed, it should be processed quickly

• Samples can be observed under a dissecting scope, or picked so that they may be observed under high power.

Notes

• Remember to hang on to your end of the piece of string

• When finished force clean water backwards through the net to clean out any pores

• Hang up to dry

• This net can be used to sample the surface of the water, simply by slowly pulling it along the top of the water, or it can be dropped to a certain depth in the water (from a pier or boat for example) and pulled vertically upward to sample the water column.

• You can use more simpler things to concentrate samples, for example coffee filters
• To transport organisms back to the lab, empty the concentrated sample from the test tube into a slightly larger jar, add water from the environment sampled, and cover. The temperature of the sample should not be allowed to change very much. Covered jars can be kept in a large bucket and covered with water from the environment to keep the temperature from changing too much.

Samples can be observed under a dissecting scope, or pipetted onto a microscope slide and observed under high power.