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In this article we will discuss about the collection of plankton.
I. Biotic Community:
An aquatic microscopic biotic community is constituted by:
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(a) Pelagic forms suspended in water, localised mostly towards the surface, and
(b) Benthonic or bottom dwellers attached to the bottom or submerged in mud.
Collection of Plankton:
Pelagic forms:
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A. Hand net:
1. The plankton is collected from pond with a hand net (Fig. 45.1).
2. The hand net is conical and the diameter of the mouth is 20 cm. It is made of bolting silk, 120-250 mesh.
3. At the end of the net a glass jar is tied lightly.
4. Collect 50 litres of water from different zones of the pond with a bucket. Filter the samples separately through plankton net.
5. Transfer the plankton collected in the jar (collector) at the end of the plankton net to specimen tube.
B. Drag net:
Pelagic planktons are captured by dragging a plankton net made of fine mesh silk or nylon cloth through water. The planktons in the net are transferred to a container by dipping the inverted net in the water of the container and with repeated flushing of water form above.
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Benthic forms:
Planktons are collected by grabbing method. The bottom soil of a measured area up to a measured depth is scooped out by a grabber. The soil is thoroughly mixed with water and strained through sieves of different meshes and the organisms separated.
Killing:
It is difficult to separate microscopic organisms in live state. They are killed by slow addition of formaldehyde in water, and separated later. The specimens are collected in a watch glass or a petri dish containing distilled water and identified under a field microscope.
