Calculation of Intensity and Efficiency of Nutrition
113
bodies (Ra) during 14C feeding experiments (see below, Sect. 3.4.2). Such a
procedure equalized the counting efficiencies by estimating Cr and R a , thus
avoiding time-consuming requirements in the endless quench corrections
during radioassay.
Returning to the practical procedure of determining the r values, a suspension of labeled algae or bacteria or a solution of dissolved organic matter,
both of which have very high specific radioactivity, should first be diluted 50
to 100 times with water. Then 0.3-0.5 ml portions of this dilution are added to
scintillation vials by automatic pipette, followed by a standard portion of unlabeled material of the consumers' bodies, treated in the same way as counting
samples for radioassay of the consumers, as given above. The radioactivity of
labeled phytoplankton or bacterioplankton in natural water is estimated after
the filtration of 5-10-ml subsamples through membrane filters: 0.45-l1m pore
size for algae and 0.2-l1m for bacteria, The filters with algae are then treated
as for primary production estimation (see Sect. 2.3.2.5). The filters with bacteria are washed free of the remains of labeled organic matter by subsequent
filtration of 5 ml of prefiltered natural water and 2 ml of also prefiltered yeast
extract. The filters are placed into scintillation vials and dissolved with 1 ml
ethylene glycol. The unlabeled animal material in this case should be added
to the vials and appropriately treated before placing the filters with algae or
bacteria into them.
To measure r in the food animals, it is necessary to place a definite number,
previously washed free of labeled food, into a scintillation vial. If they are
the ciliates, their number in 1 ml of culture, in which they have been labeled,
is first estimated by their viable count in a special chamber (see Fig. 6.6). Some
3-5 ml of this culture is then placed into a short test tube and fixed with 0.3%
gutaraldehyde solution (final concentration). The ciliates are then settled by
centrifugation at ~500rpm for several minutes. The supernatant liquid,
together with the remaining nongrazed labeled bacteria or small algae, is
removed with a syringe. The test tube is then placed into the scintillation vial
and the sediment treated in the same way as described above for algae. The
radioactivity thus measured is calculated per 10 3 of ciliate individuals.
Radioactivity in small rotifers can be measured as in ciliates. Larger
rotifers can be prepared for radio assay after fixation with a weak, slightly
yellow Lugol solution. When fixed in a beaker, they settle on the bottom. Then
the water over them is discharged out and they are resuspended and resettled
again to remove the remains of labeled food. Then the water over them is
again removed, having a 0.5-1 ml to transfer into a watch glass. The latter is
placed under the stereomicroscope and the total amount of rotifers is counted.
They are then transferred into a small test tube together with water. When
they settle, the liquid is carefully removed with a fine pipet with hooked end,
attached to the syringe. The water taken out is checked for the presence of
rotifers to be sure that their number does not change after transfer. The test
tube with the rotifers is placed into a scintillation vial and treated as described
above. Radioactivity thus measured is calculated per 10 3 sp. of rotifers. The
113
bodies (Ra) during 14C feeding experiments (see below, Sect. 3.4.2). Such a
procedure equalized the counting efficiencies by estimating Cr and R a , thus
avoiding time-consuming requirements in the endless quench corrections
during radioassay.
Returning to the practical procedure of determining the r values, a suspension of labeled algae or bacteria or a solution of dissolved organic matter,
both of which have very high specific radioactivity, should first be diluted 50
to 100 times with water. Then 0.3-0.5 ml portions of this dilution are added to
scintillation vials by automatic pipette, followed by a standard portion of unlabeled material of the consumers' bodies, treated in the same way as counting
samples for radioassay of the consumers, as given above. The radioactivity of
labeled phytoplankton or bacterioplankton in natural water is estimated after
the filtration of 5-10-ml subsamples through membrane filters: 0.45-l1m pore
size for algae and 0.2-l1m for bacteria, The filters with algae are then treated
as for primary production estimation (see Sect. 2.3.2.5). The filters with bacteria are washed free of the remains of labeled organic matter by subsequent
filtration of 5 ml of prefiltered natural water and 2 ml of also prefiltered yeast
extract. The filters are placed into scintillation vials and dissolved with 1 ml
ethylene glycol. The unlabeled animal material in this case should be added
to the vials and appropriately treated before placing the filters with algae or
bacteria into them.
To measure r in the food animals, it is necessary to place a definite number,
previously washed free of labeled food, into a scintillation vial. If they are
the ciliates, their number in 1 ml of culture, in which they have been labeled,
is first estimated by their viable count in a special chamber (see Fig. 6.6). Some
3-5 ml of this culture is then placed into a short test tube and fixed with 0.3%
gutaraldehyde solution (final concentration). The ciliates are then settled by
centrifugation at ~500rpm for several minutes. The supernatant liquid,
together with the remaining nongrazed labeled bacteria or small algae, is
removed with a syringe. The test tube is then placed into the scintillation vial
and the sediment treated in the same way as described above for algae. The
radioactivity thus measured is calculated per 10 3 of ciliate individuals.
Radioactivity in small rotifers can be measured as in ciliates. Larger
rotifers can be prepared for radio assay after fixation with a weak, slightly
yellow Lugol solution. When fixed in a beaker, they settle on the bottom. Then
the water over them is discharged out and they are resuspended and resettled
again to remove the remains of labeled food. Then the water over them is
again removed, having a 0.5-1 ml to transfer into a watch glass. The latter is
placed under the stereomicroscope and the total amount of rotifers is counted.
They are then transferred into a small test tube together with water. When
they settle, the liquid is carefully removed with a fine pipet with hooked end,
attached to the syringe. The water taken out is checked for the presence of
rotifers to be sure that their number does not change after transfer. The test
tube with the rotifers is placed into a scintillation vial and treated as described
above. Radioactivity thus measured is calculated per 10 3 sp. of rotifers. The