PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
155
Accordingly, even phosphorus released in soluble form from the gut of
an animal may not necessarily represent material that has not been
assimilated. Further light might be shed on this matter if determinations were made of both oxygen consumption (as an independent
measure of metabolic rate) and phosphorus excretion by feeding and
starving animals. So far, however, these experiments seem not to have
been done. True, Satomi and Pomeroy (1965) have established a
positive correlation between respiration rate and phosphorus excretion
by zooplankton, but their findings do not include separate data for
feeding and starving animals.
According to Redfield et al. (1963) the complete oxidation of organic
material with composition similarto that of plankton requires 276 atoms
of oxygen per atom of phosphorus. Satomi and Pomeroy (1965) found
an average value of only 72. One interpretation of this low value is
that the estimations of excreted phosphorus probably included
material that had not been amimilated (Corner and Cowey, 1968).
Some recent evidence, however, supports the possibility, suggested by
Satomi and Pomeroy (1965), that the animals excrete large quantities
of phosphorus in an “ organic ” form which has not been completely
oxidized. Thus, during short-term excretion experiments in which
freshly-caught animals were given no food and the excreted phosphorus
contained no undigested material, Butler et al. (1969) found that
Calanus helgolandicus from the English Channel excreted small and
variable amounts of “ organic ” phosphorus. These experiments were
made in summer, however, and when identical experiments were
carried out with CalanusJinmarchicus in the Clyde during the spring
diatom flowering, “ organic ” phosphorus accounted for a much higher
fraction of the total, the proportion varying (maximum 72%) with the
amount of plant food that had been available to the animals in the sea
immediately before the experiment (Butler et al., 1970).
Phosphorus excretion by carnivorous zooplankton has so far
received little study, the only data presently available being those of
Beers (1964) for the excretion of inorganic phosphate by the chaetognath Sagitta hispida. These measurements, like those of ammonia
excretion, were made with animals kept previously in the laboratory
without food for 24 h and Beers regards the value found, 2-39 pg P/mg
dry body weightlday, as a ‘‘ basal ” rate of phosphorus excretion.
Even so, the value appears to be high in terms of total body phosphorus.
Thus, Beers (1966) found that phosphorus accounted for 0.63% of the
dry body weight of chaetognaths from the same sea area. It therefore
seems probable that the Sagitta excreted some 40% of their body
phosphorus daily.
155
Accordingly, even phosphorus released in soluble form from the gut of
an animal may not necessarily represent material that has not been
assimilated. Further light might be shed on this matter if determinations were made of both oxygen consumption (as an independent
measure of metabolic rate) and phosphorus excretion by feeding and
starving animals. So far, however, these experiments seem not to have
been done. True, Satomi and Pomeroy (1965) have established a
positive correlation between respiration rate and phosphorus excretion
by zooplankton, but their findings do not include separate data for
feeding and starving animals.
According to Redfield et al. (1963) the complete oxidation of organic
material with composition similarto that of plankton requires 276 atoms
of oxygen per atom of phosphorus. Satomi and Pomeroy (1965) found
an average value of only 72. One interpretation of this low value is
that the estimations of excreted phosphorus probably included
material that had not been amimilated (Corner and Cowey, 1968).
Some recent evidence, however, supports the possibility, suggested by
Satomi and Pomeroy (1965), that the animals excrete large quantities
of phosphorus in an “ organic ” form which has not been completely
oxidized. Thus, during short-term excretion experiments in which
freshly-caught animals were given no food and the excreted phosphorus
contained no undigested material, Butler et al. (1969) found that
Calanus helgolandicus from the English Channel excreted small and
variable amounts of “ organic ” phosphorus. These experiments were
made in summer, however, and when identical experiments were
carried out with CalanusJinmarchicus in the Clyde during the spring
diatom flowering, “ organic ” phosphorus accounted for a much higher
fraction of the total, the proportion varying (maximum 72%) with the
amount of plant food that had been available to the animals in the sea
immediately before the experiment (Butler et al., 1970).
Phosphorus excretion by carnivorous zooplankton has so far
received little study, the only data presently available being those of
Beers (1964) for the excretion of inorganic phosphate by the chaetognath Sagitta hispida. These measurements, like those of ammonia
excretion, were made with animals kept previously in the laboratory
without food for 24 h and Beers regards the value found, 2-39 pg P/mg
dry body weightlday, as a ‘‘ basal ” rate of phosphorus excretion.
Even so, the value appears to be high in terms of total body phosphorus.
Thus, Beers (1966) found that phosphorus accounted for 0.63% of the
dry body weight of chaetognaths from the same sea area. It therefore
seems probable that the Sagitta excreted some 40% of their body
phosphorus daily.