Standard Practice for
Sampling Phytoplankton with Conical Tow Nets1

This standard is issued under the fixed designation D 4132; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This practice covers the procedures for obtaining qualitative samples of a phytoplankton community by use of conical
tow nets. Nets will not retain all phytoplankton taxa; for
example, nannoplankton and ultraplankton generally will pass
through a net.

1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Summary of Practice

2.1 The net is attached to a tow line and towed at the surface
or at a greater depth using a cable depressor. After a specified
distance or period of time, the net is retrieved and the captured
phytoplankton are removed from the net. The phytoplankton
may be preserved as dictated by the objective of the study.

3. Significance and Use

3.1 The advantages of conical tow nets are as follows:

3.1.1 They are relatively inexpensive, easy to construct, and
highly versatile in a variety of surface waters.

3.1.2 They can be used from a small powered boat with a
minimum of auxiliary equipment.

3.1.3 They provide a simple means by which to collect
qualitative samples of macro- and micro-plankton.

3.1.4 They can be adapted with a flowmeter to collect
semiquantitative samples of macro- and micro-plankton.

3.2 The disadvantages of conical tow nets are as follows:

3.2.1 They are effective only where drawn through a stratum
of water having considerable thickness. They are not suitable
for collecting samples from a small or restricted region.

3.2.2 They are not suitable for collections in very shallow
water.

3.2.3 They collect only qualitative samples, or semiquantitative samples when used with a flowmeter.

3.2.4 Clogging of the net by extraneous materials, such as
floating vascular plants or debris can cause erroneous results.

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