PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
133
Calanus, dead animals lost 32P at a much faster rate and they regarded
the repeated handling of the animals during the excretion experiments
as probably leading to an over-estimate of the amount of 32P lost.
In addition, they doubted that 32P newly acquired from the labelled
plant food was in equilibrium throughout the bodies of the animals and
thought that it might be preferentially excreted. Accordingly, they
regarded the excretion of 32P as probably rather low and did not include
it as part of the total quantity originally ingested by the animals. As a
consequence, this led to a slight underestimate of assimilation efficiency.
The actual values found were much higher than expected. Thus,
of four species of diatom tested, the percentage assimilation was always
over 50% and usually over 80%. Moreover, this percentage did not
sensibly change with the concentration of food organism. Nine species
of flagellate were also used, and again assimilation efficiencies were
generally high. For example, in a series of experiments involving a
range of concentrations of Cricosphaera elongata (Droop) Braarud (as
Syracosphaera ebngata Droop) assimilation efficiency was always
greater than 90%. Similar results were obtained with six species of
dinoflagellate. A particularly striking observation was that Calanus
feeding on rich cultures of Chaetoceros decipiens Cleve produced a
faecal pellet every 5-7 min, yet even in these circumstances 86% of
the food was assimilated.
By rough dissection of the Calanus after feeding with labelled
cultures it was possible t o see the approximate distribution of the
absorbed 32P throughout the body. It is interesting to note that a large
quantity was found in the fat in the pre-adult stage V and in males,
whereas in females-which normally do not contain a fat-reserve-it
was present largely in the reproductive system.
One criticism that might be made of these findings, and one fully
recognized by the authors, is that they refer only t o the phosphoruscontaining part of the food and may not apply to other dietary constituents. However, the results of other experiments by Marshall and
Orr (1955b), using cultures labelled with 14C instead of 32P, generally
confirmed those obtained in the earlier study. Thus, in experiments
with the flagellate Cryptomonas sp., assimilation efficiency ranged from
53-78%, compared with 51439% in cultures labelled with 32P. Similarly, the values obtained in experiments with the diatom Skeletonema
eostatum were 60-75%, compared with those of 54~5437.0% found in
the earlier study.
Marshall and Orr (1956) obtained data for phosphorus assimilation
using the younger stages of CalanusJinmarchicus. They found, as in
the case of adults, that the animals showed high assimilation efficiencies.
133
Calanus, dead animals lost 32P at a much faster rate and they regarded
the repeated handling of the animals during the excretion experiments
as probably leading to an over-estimate of the amount of 32P lost.
In addition, they doubted that 32P newly acquired from the labelled
plant food was in equilibrium throughout the bodies of the animals and
thought that it might be preferentially excreted. Accordingly, they
regarded the excretion of 32P as probably rather low and did not include
it as part of the total quantity originally ingested by the animals. As a
consequence, this led to a slight underestimate of assimilation efficiency.
The actual values found were much higher than expected. Thus,
of four species of diatom tested, the percentage assimilation was always
over 50% and usually over 80%. Moreover, this percentage did not
sensibly change with the concentration of food organism. Nine species
of flagellate were also used, and again assimilation efficiencies were
generally high. For example, in a series of experiments involving a
range of concentrations of Cricosphaera elongata (Droop) Braarud (as
Syracosphaera ebngata Droop) assimilation efficiency was always
greater than 90%. Similar results were obtained with six species of
dinoflagellate. A particularly striking observation was that Calanus
feeding on rich cultures of Chaetoceros decipiens Cleve produced a
faecal pellet every 5-7 min, yet even in these circumstances 86% of
the food was assimilated.
By rough dissection of the Calanus after feeding with labelled
cultures it was possible t o see the approximate distribution of the
absorbed 32P throughout the body. It is interesting to note that a large
quantity was found in the fat in the pre-adult stage V and in males,
whereas in females-which normally do not contain a fat-reserve-it
was present largely in the reproductive system.
One criticism that might be made of these findings, and one fully
recognized by the authors, is that they refer only t o the phosphoruscontaining part of the food and may not apply to other dietary constituents. However, the results of other experiments by Marshall and
Orr (1955b), using cultures labelled with 14C instead of 32P, generally
confirmed those obtained in the earlier study. Thus, in experiments
with the flagellate Cryptomonas sp., assimilation efficiency ranged from
53-78%, compared with 51439% in cultures labelled with 32P. Similarly, the values obtained in experiments with the diatom Skeletonema
eostatum were 60-75%, compared with those of 54~5437.0% found in
the earlier study.
Marshall and Orr (1956) obtained data for phosphorus assimilation
using the younger stages of CalanusJinmarchicus. They found, as in
the case of adults, that the animals showed high assimilation efficiencies.