Backyard Biology

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plankton net

Plankton Net

Friday, August 5, 2011

There is a whole world of natural history that most people never see. It is a world of creatures so bizarre that if these creatures were of a size, they could be the subject of many an alien horror movie. As it is, they are microscopic and go totally unnoticed by most people without a microscope.
Plankton is a general term for drifting organisms - organisms that go where the currents take them. Most of them are small - a microscope is needed to see them - while others get to be quite large - like some jellyfish that stretch out over 50 feet. The plankton is made up of organisms of all types. They include plants, animals and other organisms that don’t fit into either category. They may live in fresh water or salt. Some of them are planktonic their whole lives while others spend only their young larval lives as plankton, very often growing much larger as they age.

Most any body of water has it’s assemblage of plankton. With a good microscope, one can spend hours exploring the life in any local body of water. Much of the plankton you find is big enough to see with a low-powered dissecting microscope at magnifications of 7-45, while others need the higher power of a compound microscope at magnifications of 200 or more. If you wish to purchase a microscope to oberve the plankton in your neighborhood, I recommend a low-powered dissecting microscope. With this type of microscope, you will not only be able to observe many types of plankton, you can also use it for observing many other types of organisms - from flowers to ferns, bugs to slugs, butterflies to buttercups. I can think of no better way to excite a child about the natural world than to give them a good low-powered microscope.

So how does one go about looking at plankton? If you take a bowl and scoop up some water - pond water or ocean water - and look at it under the microscope, you will probably see little more than water. Pretty disappointing. You expect a bowlfull of fascinating plankton, but the bowl is pretty void of life. In order to have a lot of plankton to observe, you need to concentrate it by using a plankton net. As the plankton net is pulled through the water, the water enters the opening of the net and leaves through the mesh of the sides. Because the mesh of the net is smaller than the plankton, they become trapped in the net. In this way, the plankton from a lot of water can be concentrated into a volume of water small enough to look at under the microscope.
Nets of different size mesh can capture different size plankton. Smaller meshed nets will capture smaller plakton as well as larger plankton. Nets with a larger mesh will only collect the larger plankton - the smaller plankton escaping through the mesh. For your first net, I would suggest a larger meshed net. The larger plankton will be easier to see, especially if you are using a low powered dissecting microscope.

Using a plankton net is easy. The trick is to drag the net through the water slowly. If you drag the net too fast, the water entering the net will not have time to exit through the mesh - no water going out means no more water coming in. No more water coming in means no more plankton.
There are four ways to drag the net through the water. The first is to tie the net to the stern of a boat and drag the net behind. The trick here is to move the boat slow enough so the water enters the net.
The second method is to tie a weight to the net and lower the net deep into the water. Then slowly draw the net up through the water column. This technique works well if you are collecting plankton from a bridge that spans deep water.
The third method involves tying the net to a long rope. While standing on the shore or a dock, swing the net back and forth, then let go, pitching the net out into the water. Once it lands, slowly draw the net back to shore.
The fourth method is to attach the net to a long pole. The extendable poles that window washers use are ideal. These can be purchased at home improvement stores. Hold the end of the polewith the attached net in the water and walk along the beach or dock, dragging the net through the water.

Whichever method you choose, the longer you drag the net through the water, the more plankton you will collect.

Materials:

  • sleeve of an old shirt or jacket It doesn’t matter too much what material the net is but you want to make sure that water wil pass through the material. A nylon sleeve makes an ideal net because it is durable, but some nylon has been treated with waterproofing material. Water will not pass through these sleeves.
    If you don’t have a suitable sleeve to use, you can buy nylon material and sew it into a cone.

  • wooden embroidery hoop

    net materials
  • small bottle with a cap

  • string

  • rubber band

 

 

Instructions:

  1. Clamp the embroidery hoop around the wide end of the sleeve. net rim













  2. Drill 4 holes through the embroidery hoop. The holes should be spaced equidistant from each other with two sets of holes opposite each other.

  3. Cut two pieces of string about 30 inches each.

  4. Tinet with stringe the ends of one string in two holes opposite each other. Tie the ends of the other string in the other two opposite holes.








  5. Gather the middle of both strings and tie in a loop.net knot

  6. Poke a good sized hole in the top of the bottle cap.
    net bottle cap
  7. Secure the bottle cap to the inside of the small end of the sleeve with a rubber band. Attach the bottle to the cap.net bottle










    plankton net