134
E. D. 9. CORNER AND ANTHONY 0. DAVIES
Thus, with Ditylum as a diet, late naupliar and young copepodite
stages assimilated 77.8-95.9y0 of the food ; with Syracosphuera
(Criwsphuera), assimilation was consistently higher than 98% ; and
copepodite I, feeding on Skeletonema, assimilated 48.9-91.5%. Berner
(1962), studying feeding by the copepod Temora longicornis (Miiller),
also found high assimilation efficiencies, the animals assimilating
52.0-97-5% (average 77 yo) of a diet of [3aP]-labelled Skeletonema
cells.
Because carbon and phosphorus are important constituents of the
algal cell, Marshall and Om (1955a) concluded that the major part of
the organic material ingested by Calanus was assimilated. It would be
unreasonable, however, to expect every dietary constituent to be
assimilated with the same high efficiency ; and lower values have been
obtained for the assimilation of nitrogen, studied by Corner et al.
(1967) using Skeletonema as the test diet. The level of particulate
nitrogen available to the animals at the start of a feeding experiment
was determined by chemical analysis and compared with the quantity
remaining after the animals had fed on the culture for 24 h. The
difference between the two levels gave the quantity of nitrogen removed by the animals. Faecal pellets produced during the experimental
period were collected and analysed for nitrogen to obtain the quantity
unassimilated. The amount of nitrogen assimilated was estimated by
subtracting the quantity present as faecal pellets from the total amount
removed by the animals, and the value so obtained, when expressed as
a percentage of the total amount removed, gave the assimilation efficiency. The values found, with Skeletonema used at concentrations
representing 35-270 pg particulate N/1, were in the range 57-5-67.5%
and, as found by Marshall and Om (1955a) in their experiments with
32P, there was no correlation between the level of available food and
the proportion assimilated.
This method, like that of Marshall and Orr (1955a), included the
quantitative collection of faecal pellets ; and the separation of these
from uneaten plant cells and eggs is always difficult and laborious. I n
addition, Corner et al. (1967) found that in studies using Brachiomonas
submarina Bohlin and Criwsphuera as plant foods the level of particulate
nitrogen increased during the feeding experiments, in spite of grazing
by the animals (as demonstrated by the production of faecal pellets).
A possible cause of this increase may have been that soluble products
excreted by the animals encouraged cell division by the plants. However, it is difficult to understand why this should have influenced the
results obtained in experiments with Brachiomonas and Criwsphuera,
but not those found using Skeletonema.
E. D. 9. CORNER AND ANTHONY 0. DAVIES
Thus, with Ditylum as a diet, late naupliar and young copepodite
stages assimilated 77.8-95.9y0 of the food ; with Syracosphuera
(Criwsphuera), assimilation was consistently higher than 98% ; and
copepodite I, feeding on Skeletonema, assimilated 48.9-91.5%. Berner
(1962), studying feeding by the copepod Temora longicornis (Miiller),
also found high assimilation efficiencies, the animals assimilating
52.0-97-5% (average 77 yo) of a diet of [3aP]-labelled Skeletonema
cells.
Because carbon and phosphorus are important constituents of the
algal cell, Marshall and Om (1955a) concluded that the major part of
the organic material ingested by Calanus was assimilated. It would be
unreasonable, however, to expect every dietary constituent to be
assimilated with the same high efficiency ; and lower values have been
obtained for the assimilation of nitrogen, studied by Corner et al.
(1967) using Skeletonema as the test diet. The level of particulate
nitrogen available to the animals at the start of a feeding experiment
was determined by chemical analysis and compared with the quantity
remaining after the animals had fed on the culture for 24 h. The
difference between the two levels gave the quantity of nitrogen removed by the animals. Faecal pellets produced during the experimental
period were collected and analysed for nitrogen to obtain the quantity
unassimilated. The amount of nitrogen assimilated was estimated by
subtracting the quantity present as faecal pellets from the total amount
removed by the animals, and the value so obtained, when expressed as
a percentage of the total amount removed, gave the assimilation efficiency. The values found, with Skeletonema used at concentrations
representing 35-270 pg particulate N/1, were in the range 57-5-67.5%
and, as found by Marshall and Om (1955a) in their experiments with
32P, there was no correlation between the level of available food and
the proportion assimilated.
This method, like that of Marshall and Orr (1955a), included the
quantitative collection of faecal pellets ; and the separation of these
from uneaten plant cells and eggs is always difficult and laborious. I n
addition, Corner et al. (1967) found that in studies using Brachiomonas
submarina Bohlin and Criwsphuera as plant foods the level of particulate
nitrogen increased during the feeding experiments, in spite of grazing
by the animals (as demonstrated by the production of faecal pellets).
A possible cause of this increase may have been that soluble products
excreted by the animals encouraged cell division by the plants. However, it is difficult to understand why this should have influenced the
results obtained in experiments with Brachiomonas and Criwsphuera,
but not those found using Skeletonema.