Collection, Enumeration, and Biomass of Zooplankton
173
2. Mix the organisms thoroughly within the graduated cylinder (vortex mixer or
magnetic stirrer) and immediately obtain a subsample. Work rapidly to minimize
the effect of settling of the organisms.
3. Obtain a subs ample of 1 ml with an automatic, volumetric pipet (use a wide-mouth
pipet so as not to restrict uptake of large zooplankton) or a Hansen-Stempel pipet
(Fig. 11.6).
4. Add this subs ample to a Sedgwick-Rafter cell and cover with a cover glass. The
Sedgwick-Rafter cell holds exactly 1 ml (see Exericse 10). Place the cell on a white
background with grid lines under a dissecting microscope.
5. Count all of the organisms in five subsamples. Use the grid lines for reference and
use hand tallies to facilitate the counting procedure of different organisms. Record
these data for each species and for the total zooplankton (see Table 11.2).
Table 11.3. Approximate volume and dry weight of some
zooplankton genera. a
Volume
Dry weight b
(/lm 3 )
(/lg)
Protozoa
small ciliates
2500
nd e
large ciliates
5 x 10 5
nd
Dileptus
3 x 10 6
nd
Bursaria
3 x 10 7
nd
Trichodina
5000
nd
Rotifers
Brachionus
6 x 10 5
nd
Keratella
0.5-1.0 x 10 5
0.05-0.1
Kellicottia
1 x 10 5
0.07-0.1
Trichocerca
1.0-1.5 x 10 5
nd
Gastropus
5.5 x 10 5
nd
Ascomorpha
3 x 10 5
nd
Asplanchna
3.0 x 10 7 -loB
0.2
Synchaeta
1-2 x 10 6
nd
Polyarthra
5-6 x 10 5
0.06
Conochilus
4-6 x 10 5
0.08
Cladocera
Daphnia
10 7 -10 9
2-35
Ceriodaphnia
5 x 10 7
2-4
Bosmina
4-7 x 10 7
1-3
Chydorus
1 x 10 7
2
Leptodora
1 x 10 10
nd
Copepods
small nauplii
5 x 10 4
nd
large nauplii
1.5 x 10 6
nd
Cyclops
107_lOB
9-22
Diaptomus
10 7 -10B
5-7
Mesocyclops
3 x 10 7
1-3
Tropocyclops
nd
1-3
"After Nauwerck (1963), Makarewicz (1974), and Hall et a!. (1970).
bDry weights might be approximated by multiplying the volume by a
specific gravity value of 1.025 (Hall et a!., 1970).
end = not determined.