154
E. D. 9. CORNER AND ANTHONY 0 . DAVIES
Pond (Nova Scotia) using the methods of Strickland and Parsons
(1960) t o measure inorganic and total phosphorus. Phosphorus excretion was found to increase with temperature and salinity and to decrease when the animals were used at higher experimental densities.
A further factor, influencing the excretion of inorganic phosphorus by
Acartia tonsa, was time of day, excretion being maximal during the
early evening when the feeding rate increases in the sea as Acartia
migrate towards the surface. These animals were found to excrete
about 40% more phosphorus when fed: an even greater increase
was found in experiments with Pseudocalanus minutus and Oithona
sirnilis.
These various factors were used in predicting the quantities of
inorganic phosphorus excreted by zooplankton under conditions prevailing in the sea. For the mixed species in Bras #Or Lake the
predicted values, as pg P/mg dry weight/day, were 1.52 (nauplii),
0.93 (copepodites) and 1.27 (adults): those for Acartia in Morrison’s
Pond were 1.37 (nauplii), 1.27 (CII-CIV) and 1-02 (CV-CVI). The higher
rate of phosphorus excretion observed with the younger stages of
Acartia is similar to the finding described by Corner et al. (1965, 1967)
for nitrogen excretion by the younger stages of Calanw.
As in the study by Pomeroy et al. (1963) much of the total phosphorus excreted was ‘( organic ”, 74% being excreted in this form by
Oithona, and 67% by Acartia and Pseudocalanus. However, in many
of the excretion experiments plant food was present and the question
arises whether all the phosphorus excreted by feeding animals represents
true end-products of metabolism or includes soluble unassimilated
material released with faecal pellets (Harvey et al., 1935). Relevant
here are observations by Johannes (1964a) using the gammarid amphipod Lembos intermediw Schellenberg. He found that, compared with
animals containing food in the guts, those with the guts empty released
75% less inorganic phosphate and 53% less ‘( organic ” phosphorus.
However, as Johannes makes clear, food was superabundant in these
experiments, the animals apparently eating at a rate too high for adequate digestion, and only 16% of the phosphorus captured was
assimilated. This value is very much lower than that found by Marshall
and Orr (1955a) and Berner (1962) for zooplanktonic animals, and it is
worth noting that in a recent study the rate of phosphorus excretion by
Calanus with food in the guts was compared with that of animals with
the guts empty and no significant difference was found (Butler et al.,
1970). It is also worth noting that studies on phosphate metabolism in
certain mammals have shown that the excretion of body phosphorus
can take place across the intestinal l i i g (see Wasserman, 1967).
E. D. 9. CORNER AND ANTHONY 0 . DAVIES
Pond (Nova Scotia) using the methods of Strickland and Parsons
(1960) t o measure inorganic and total phosphorus. Phosphorus excretion was found to increase with temperature and salinity and to decrease when the animals were used at higher experimental densities.
A further factor, influencing the excretion of inorganic phosphorus by
Acartia tonsa, was time of day, excretion being maximal during the
early evening when the feeding rate increases in the sea as Acartia
migrate towards the surface. These animals were found to excrete
about 40% more phosphorus when fed: an even greater increase
was found in experiments with Pseudocalanus minutus and Oithona
sirnilis.
These various factors were used in predicting the quantities of
inorganic phosphorus excreted by zooplankton under conditions prevailing in the sea. For the mixed species in Bras #Or Lake the
predicted values, as pg P/mg dry weight/day, were 1.52 (nauplii),
0.93 (copepodites) and 1.27 (adults): those for Acartia in Morrison’s
Pond were 1.37 (nauplii), 1.27 (CII-CIV) and 1-02 (CV-CVI). The higher
rate of phosphorus excretion observed with the younger stages of
Acartia is similar to the finding described by Corner et al. (1965, 1967)
for nitrogen excretion by the younger stages of Calanw.
As in the study by Pomeroy et al. (1963) much of the total phosphorus excreted was ‘( organic ”, 74% being excreted in this form by
Oithona, and 67% by Acartia and Pseudocalanus. However, in many
of the excretion experiments plant food was present and the question
arises whether all the phosphorus excreted by feeding animals represents
true end-products of metabolism or includes soluble unassimilated
material released with faecal pellets (Harvey et al., 1935). Relevant
here are observations by Johannes (1964a) using the gammarid amphipod Lembos intermediw Schellenberg. He found that, compared with
animals containing food in the guts, those with the guts empty released
75% less inorganic phosphate and 53% less ‘( organic ” phosphorus.
However, as Johannes makes clear, food was superabundant in these
experiments, the animals apparently eating at a rate too high for adequate digestion, and only 16% of the phosphorus captured was
assimilated. This value is very much lower than that found by Marshall
and Orr (1955a) and Berner (1962) for zooplanktonic animals, and it is
worth noting that in a recent study the rate of phosphorus excretion by
Calanus with food in the guts was compared with that of animals with
the guts empty and no significant difference was found (Butler et al.,
1970). It is also worth noting that studies on phosphate metabolism in
certain mammals have shown that the excretion of body phosphorus
can take place across the intestinal l i i g (see Wasserman, 1967).