Make Your Own Plankton Sieves
A Tool for Studying Plankton
This guide provides step-by-step instructions on making a series of sieves or strainers
that can be used to separate marine plankton into different size class. Each sieve is constructed using a fine netting material with a particular mesh size. When a plankton sample is poured through a series of
sieves, organisms in the sample can be separated based on their overall length or size. This technique is called size fractionation and it provides a starting point for a variety of further studies and activities for students of all grade levels.
Why size fractionate?
When a plankton sample is separated by size, the specific size categories can provide useful information about the organisms and can be a good starting point for further studies. Size categories can help narrow down species identification or they can be used to investigate the different trophic levels (i.e., producers, herbivores and carnivores) of the marine food web. Plankton samples obtained from offshore tows will collect a diversity of species including a variety of phytoplankton as well as zooplankton. Phytoplankton are typically microscopic in size and are the primary producers in the marine ecosystem. Zooplankton are often macroscopic in size and are considered consumers since they feed on phytoplankton or other types of zooplankton.
Materials Needed:
- 2” PVC pipes - each sieve is 4” in length
- 2” PVC couplings - 1 coupling per sieve
- Nitex mesh cloth of various sizes
can be order from www.wildco.com, www.sterlingnets.com, or www.sefar.com - Small tube of silicone
- Scissors
- Marker
- Hacksaw or pipe cutters
Alternative materials:
- You can make plankton sieves out of plastic beakers or even plastic cubs instead of PVC piping.
- You can also hot glue the Nitex mesh cloth to the PVC pipe edge instead of using silicone. However, hot glue tends to breaks down and degrades more quickly than silicone.
- Although PVC piping is more challenging to cut, the snug fit of the inside pipe against the inner lip of the coupling creates a more effective and durable straining device.
Instructions:
- Cut the PVC piping into pieces that are approximately 4 inches in length. Make sure that the cut edges are smooth and as straight as possible. If using plastic beakers or cups, cut off the bottom making sure that the cut edges are as straight as possible.
- Trace a circle onto the mesh netting using one of the 4” PVC pipes as a template. When you cut out the mesh circle, leave a margin about one finger thick around the outside edge of the circle.
- Dab a small amount of silicone on the cut end of the 4” PVC pipe. Place the mesh circle on top of the silicon and pull the netting tight over the end of the pipe.
- Press firmly around the edges until the silicone squeezes through the holes of the mesh. Smooth the silicone with your finger and then allow it to dry for about 30 minutes.
- Insert the 4” PVC pipe into the PVC coupling making sure that the mesh covered end is orientated down.
Force the 2 pieces together until the bottom of the 4” PVC pipe fits snugly against the inner lip of the coupling. To make sure that the PVC pipes are securely connected, place both hands on the upper pipe and lean down hard with your body. Or carefully bang the sieve on a hard surface a few times. - For sieves made from PVC piping, examine the mesh to make sure that it’s connection with the inner lip of the outer couplings is complete and secure.
Your fractionate sieve is now ready to use!
If you make several sieves with various mesh sizes, you can stack them one on top of the other to select for specific size categories. The number of categories and their respective sizes will depend upon the number of sieves used as well as the specific mesh sizes of each sieve.
Stack the sieves making sure that the smallest mesh size is on the bottom and the largest mesh size is at the top. Place the stack of sieves in a plastic pan or tray to catch the filtrate. Slowly pour the sample through the top sieve.
Organisms of specific sizes or lengths are now caught on the inside of each sieve. To get them off the mesh, you will need to backwash each sieve into a separate container.
Stack the sieves making sure that the smallest mesh size is on the bottom and the largest mesh size is at the top. Place the stack of sieves in a plastic pan or tray to catch the filtrate. Slowly pour the sample through the top sieve.
Congratulations! You have now separated your plankton sample into size classes based on your selection of plankton sieves.
Organisms of specific sizes or lengths are now caught on the inside of each sieve. To get them off the mesh, you will need to backwash each sieve into a separate container.
First separate the different sieves in the stack. Then for each sieve, turn the sieve upside down over a clean container and squirt the water on the mesh netting. This will wash the plankton off the mesh netting and into the container below.
What you might find in various plankton size classes
- 1 mm and above: jelly plankton and fish larvae
- 200 microns – 1 mm: large zooplankton
- 64 - 200 microns: small zooplankton
- 20 - 64 microns: phytoplankton
- less than 64 microns: smaller phytoplankton, microbes, viruses
