Значение и использование

3.1 The advantages of using conical tow nets are as follows:

3.1.1 They are relatively inexpensive and highly versatile in a variety of inland, estuarine, coastal, and marine waters.

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

3.1.3 They can be used to collect qualitative samples and semiquantitative samples when fitted with a flowmeter and even better samples when fitted with a companion meter on the outside of the hoop to monitor filtering efficiency.

3.2 The disadvantages of conical tow nets are as follows:

3.2.1 When equipped with a flowmeter they require frequent maintenance including calibration and, in some types, lubrication.

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

3.2.3 They are not suitable for collecting in very shallow water.

3.2.4 They are clogged by grass beds, coelenterates, and filamentous algae.

3.2.5 When used with a flowmeter, they collect only qualitative samples, or semiquantitative samples.

3.2.6 When sampling discrete depths using a horizontal tow, the sample can be contaminated from other depths during the deployment and retrieval of the samples if opening and closing devices are not used.

3.3 There are several special considerations that shall be observed when using conical tow nets. They are:

3.3.1 Conical tow net samplers are designed to be towed at speeds less than three knots; however, greater speeds have been used for the larger nets with a concomitant increase in capture.²

3.3.2 A conical tow net 0.5 m in diameter or larger shall be used to reduce avoidance by organisms.²

3.3.3 The nets shall be washed frequently and inspected for pin-size holes, tears, net deterioration, and other anomalies.

3.3.4 Nets should be allowed to dry while suspended full length in air and in subdued light prior to storage.

3.3.5 Lower catches per sample may result when collections are made during the day. These are particularly noted in the larger zooplanktons.

TABLE 1 Size of Common Zooplankton^A

Species  

Fresh

Marine

Habitat  

Size Range 

Habitat  

Size Range  

Protozoans (single cells)

 

6 to 1,000 μ

 

−2.0 mm

Ciliophora (ciliated single cells)

few fresh

22 to 600 μ

 

 

Coelenterata

few fresh (Hydras)

<20 mm

 

 

Ctenophora

 

 

 

10 to 121 mm

Platyhelminthes (flatworms)

 

1 to 30 mm

inland waters

0.5 to 40 mm

Nemertea (Proboscus worms)

 

<20 mm

great variation

5 mm to 6.5 m

Nematoda (Round worms)

 

<2.3 mm

 

7 mm

Nematomorpha (horsehair
 worms)

pools, slow brooks

10 to 70 cm

 

 

Gastrotricha

most fresh (shallow)

70 μ–615 μ

 

 

Rotifera

90 percent fresh

80 μ–1,500 μ

 

 

Bryozoa (moss animals)

some fresh;

 

most species encrusting

 

 

statoblasts

0.4 to >1.0 mm

statoblasts

 

Chaetognatha (arrowworms)

 

 

high salinity

up to 40 mm

Annelida (segmented worms)

 

 

 

 

 Oligochaeta

most fresh

0.5 to 5 mm

very few

 

 Polychaeta

few fresh

 

most spp. small except Nereis

up to 50 cm

 Hirundinea

most fresh (standing

adults 5 mm to 45.7 cm

few marine

 

 

 waters)

 

 

 

Arthropoda

 

 

 

 

 Crustacea

 

 

 

 

  Branchlopoda

most fresh

3 mm to 30 mm

some marine

10 mm

  Cladocerans

most fresh
(lenthic waters)

up to 3 mm; 0.2 to 18.0 mm
0.6, 0.3, 0.4 mm; 1.7, 1.0, 0.9 mm

few marine
most estuarine/marine
in top of
bottom sediment

 

 Ostracoda

 

 

 

 

 Copepoda

 

 

 

 

  Calenoida

 

nauplius—<4.0 mm

 

0.5 to 10.0 mm

  Cyclopoida

 

nauplius—<3.0 mm

 

<0.5 to 1.0 mm

  Harpacticoid

 

nauplius—1.0 mm

 

<0.5 to 1.0 m

 Ectoparasites

some fresh

5 to 25 mm

some estuarine

5.5 to 25 mm

 Cirripedia

 

 

estuarine/marine:nauplii

 

 Mysidacea

few in cold lakes

8 to 30 mm

 

 

 Amphipoda

some fresh

5 to 25 mm

 

5 to 30 mm

 Decapoda

some associated with debris

15 to 200 mm

 

2.0 mm to 20 to 40 cm

Insecta (aquatic)

most fresh

 

 

 

Mollusca

 

 

 

 

 Gastropoda

 

 

 

 

 

 

adults <2 to 70 mm

 

8 to 80 mm trochophore

 Pelecypoda

some fresh

adults 2 to 250 mm

most have free
swimming larvae

 

 Echinodermata

 

 

 

 

 Fish eggs/larvae

eggs 0.75 to 3 mm

400 μ to 505 μ

 

 

 

larvae 1.5 mm

 

 

 

^A Sage, L. E., “Zooplankton ,” In: Methods for the Assessment and Prediction of Mineral Mining Impacts on Aquatic Communities: A Review and Analysis, Fish Wildlife Service/Office of Biological Services, Vol 78/No. 30, April 1978, pp 55–65. Область применения

1.1 This practice covers the procedure for obtaining qualitative samples of a zooplankton community by use of conical tow nets. Nets will collect most zooplankton, but some forms will avoid nets.

1.2 This standard does not purport to address all of the safety problems, 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.