138
E. D. S. CORNER AND ANTHONY 0 . DAVIES
evidence of diatom sinkage and concluded that all the plant crop had
been grazed by the zooplankton. Accordingly, some 40% of the
herbivores own weight was on average eaten daily. Harvey el a1.
concluded that this was a maximal estimate: but as the animals
probably returned phosphate to the sea as a soluble excretion product
(see p. 152) the value for total plant production based on changes in
the phosphate level in the sea could well have been an underestimate.
Thus, the above value of 40%, as deduced from these data, was
probably minimal. The green appearance of the faecal pellets produced
by thc animals and the fact that the number of faecal pellets was
closely related to the level of the phytoplankton population led to the
conclusion that the quantity of cells eaten depended on the amount of
food available instead of the dietary needs of the animals. Such needs
wcrc lat8er calculated by Harvey (1950) from data showing that 4% of
the body weight was respired daily, and that 7-10% of the body weight
was added daily as growth. These calculations, apparently based on
values found with C. jinmarchicus and a mixed community of crustacean
plankton, therefore indicated that 11-14% of the body weight was
needed daily to replace respiratory losses and ensure growth. Thus,
the finding by Harvey et al. that zooplankton grazed 40% of their body
weight as plant food daily, and the further calculation by Harvey that
only 11-14% was needed by the animals, led Beklemishev (1962) to
propose that about two-thirds of the captured food was unassimilated.
Suporting evidence for this view was provided by the field observations of Riley (1946, 1947) in a study of zooplankton production
on Georges Bank (Cape Cod, Mass.). From measurements of
respiration rate, Marshall et al. (1935) had shown that the food
requirements of C. $finmarchicus during winter were equivalent to 1.33.6% of the body carbon daily: in summer, the corresponding value
was 1.7-7-6%. Riley (1946) used these data to show that a population
of mixed zooplankton representing 1 g C/m2, would obtain its food
requirements by capturing 0.75% of the phytoplankton (as g C/m2)
daily. Riley (1947) therefore multiplied the daily values of the phytoplankton stock by a factor of 0.0075 in order to prepare a curve showing
the consumption of the phytoplankton by the animals. This curve
demonstrated that during the peak of the phytoplankton bloom (late
April) the quantity of phytoplankton carbon consumed was nearly
30% of the body carbon in the animals. It was observed by Riley that
the zooplankton assimilated nearly 8% of their body carbon daily during
late March, the period when the rate of zooplankton growth reached a
maximum. He concluded that this value of 8% represented the upper
limit of digestion by the animals and that any food consumed in excess
E. D. S. CORNER AND ANTHONY 0 . DAVIES
evidence of diatom sinkage and concluded that all the plant crop had
been grazed by the zooplankton. Accordingly, some 40% of the
herbivores own weight was on average eaten daily. Harvey el a1.
concluded that this was a maximal estimate: but as the animals
probably returned phosphate to the sea as a soluble excretion product
(see p. 152) the value for total plant production based on changes in
the phosphate level in the sea could well have been an underestimate.
Thus, the above value of 40%, as deduced from these data, was
probably minimal. The green appearance of the faecal pellets produced
by thc animals and the fact that the number of faecal pellets was
closely related to the level of the phytoplankton population led to the
conclusion that the quantity of cells eaten depended on the amount of
food available instead of the dietary needs of the animals. Such needs
wcrc lat8er calculated by Harvey (1950) from data showing that 4% of
the body weight was respired daily, and that 7-10% of the body weight
was added daily as growth. These calculations, apparently based on
values found with C. jinmarchicus and a mixed community of crustacean
plankton, therefore indicated that 11-14% of the body weight was
needed daily to replace respiratory losses and ensure growth. Thus,
the finding by Harvey et al. that zooplankton grazed 40% of their body
weight as plant food daily, and the further calculation by Harvey that
only 11-14% was needed by the animals, led Beklemishev (1962) to
propose that about two-thirds of the captured food was unassimilated.
Suporting evidence for this view was provided by the field observations of Riley (1946, 1947) in a study of zooplankton production
on Georges Bank (Cape Cod, Mass.). From measurements of
respiration rate, Marshall et al. (1935) had shown that the food
requirements of C. $finmarchicus during winter were equivalent to 1.33.6% of the body carbon daily: in summer, the corresponding value
was 1.7-7-6%. Riley (1946) used these data to show that a population
of mixed zooplankton representing 1 g C/m2, would obtain its food
requirements by capturing 0.75% of the phytoplankton (as g C/m2)
daily. Riley (1947) therefore multiplied the daily values of the phytoplankton stock by a factor of 0.0075 in order to prepare a curve showing
the consumption of the phytoplankton by the animals. This curve
demonstrated that during the peak of the phytoplankton bloom (late
April) the quantity of phytoplankton carbon consumed was nearly
30% of the body carbon in the animals. It was observed by Riley that
the zooplankton assimilated nearly 8% of their body carbon daily during
late March, the period when the rate of zooplankton growth reached a
maximum. He concluded that this value of 8% represented the upper
limit of digestion by the animals and that any food consumed in excess