Activity

Actitity 1 - Sampling and Observing Plankton

Objective:

This activity shows you how to collect plankton sample including the making of a plankton net, and observe the plankton under microscope.

Materials:

- compound microscope
- plankton net
- preservative / fixative

Step 1 – Plankton Net Making

Plankton are very small organisms that can be found in all water bodies. However, they are very difficult to be observed if a plankton specimen is not concentrated. Plankton net is a device used for concentrating plankton for closer examination. The following instructions will show you how to make a simple plankton net (Fig.1) by using common household items.

Fig. 1 Plankton Net Structure

Materials:

1. Silk screen for printing (mesh size = 625 is equal to 625 holes in 1.25cm)
2. Wire coat hanger
3. Small plastic bottle with a fairly small mouth size (clean plastic bottles for drinks)
4. Scissors
5. Water proof adhesive tape
6. Rubber band
7. String
8. Key ring
9. Thread and needle

Net Assembly

1. Uncoil the coat hanger and bend it into a circle with diameter about 15 to 25cm. Use waterproof adhesive tape to fasten the loose ends together.

2. Prepare a cone shaped net by using the silk screen as shown in the figure below. Diameter of the wider end and narrower end of the plankton net is about 20cm and 4 cm respectively.

Net Assembly

3. Sew the wider end of the cone to the circle wire by using thread and needle.
Caution: Before sewing on the net to the circle, fold the edge of the net several times. This is to prevent leaking of plankton specimen from the seam of the net.

4. Use string or rubber band to attach the plastic bottle tightly to the lower end of the net.

5. Cut three pieces of string (about 20cm) and tie them to the mouth of the net in the shape of a pyramid. Tie the other end of the string to the key ring.

6. Attach a longer towing string or rope to the key ring.

Step 2 – Plankton Sampling

Warning! Sampling should be performed in an area where the water is calm and shallow, and supervised by teachers.

Sampling of Plankton

	Step 1 Lower the net vertically into the water until the bottle is filled with water.

	Step 2 Please wait until the net is fully extended.

	Step 3 Pull the net horizontally across the water. The longer time you tow the net in the water the more plankton will be concentrated.

	Step 4 Raise the plankton net from the water slowly.

	Step 5 Use filtered seawater to wash all the plankton retained on the inner surface of the net into the bottle.

Step 3 – Plankton Fixation

The collected plankton can simply be kept alive for 24 hours at room temperature. If the sample cannot be observed in time, you can preserve (up to about 1 month) and stain the plankton by adding a few drops of Lugol’s solution.

Warning! Lugol's solution is a harmful chemical mixture. Great care should be taken when preparing and using the solution. It should be prepared by qualified technician.

Preparation of Lugol’s Solution
Materials
	1. Iodine 5g 2. Potassium Iodide 10g 3. Acetic acid10ml 4. Distilled water100ml
Procedure
	Caution! The Lugol's solution must be prepared in the fumehood. Appropriate safety gears should be wore during preparation. Please read carefully the MSDS before using chemicals. 1. Add chemicals as listed above one by one into 100ml distilled water. 2. Stir the solution continuously until all the chemicals dissolve into the water. 3. The Lugol’s solution is in dark brown color and it should better be kept in an amber glass bottle and store in an appropriate area.

Fixation of Plankton

	Step 1 Add 4 - 8 drops of Lugol’s solution into the sample bottle containing the plankton sample.

	Step 2 Cover the bottle. Shake gently to mix the solution thoroughly. The sample is ready for observation under microscope.

Step 4 – Plankton Observation

Plankton are very small organisms and usually cannot be observed by naked eyes. Students should use a microscope to observe the plankton specimen. See if you can identify some of them.

Magnification = 40x

Magnification = 100x

Please use the red tide data base to help identify some of the phytoplankton species

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