140
E. D. S. CORNER AND ANTHONY Q. DAVIES
grazing will not start (approximately 70 pg C/1, Adanis and Steele,
1966; 50-190 pg C/1, Parsons et al., 1969).
Clearly, some of the assumptions that have been made in order to
calculate assimilation efficiences from field data are to some extent
oversimplifications. On the other hand, laboratory studies with zooplankton can also be criticized on the grounds t h a t thc animals are
used under confined and unnatural conditions (although it is worth
e~nphasizing that findings made in the laboratory havc often been used
at somc stage during calculations of secondary production in the sea).
Accordingly, one may well expect to encounter differences between
finduigs made in the laboratory and those made in the field. An example
of such a difference is the finding by Conover (196Gb) that the average
assimilation of Thalassiosira by Calanus hyperboreus feeding on a wide
range of concentrations, including values wcll above that corresponding to 390 mg C/m3, was about 70% : whereas Beklemishcv (1962)
regarded this level as the threshold at which superfluous feeding begins
in nature, so that only about one third of the captured food should be
assimilated. More recent studies, involving the use of both field and
laboratory data, have shed further light on the question of superfluous
feeding (Butler et al., 1970). The animal used was Calanus$nmarchicus
and the calculations were based on measurements of nitrogen and phosphorus excretion as well as N : P ratios in the animals, phytoplankton
and faecal pellets. It was found that even in a high concentration of
natural phytoplankton, 77% of captured phosphorus and 62.5% of
captured nitrogen was assimilated, values close to those observcd in
laboratory experiments but much higher than those suggested by
Beklemishev (1962).
IX. LEVELS OF NITROGEN AND PHOSPHORUS IN ZOOPLANKTON
Recent measurements of the nitrogen content of zooplankton have
employed the micro-Dumas method, using a Coleman Nitrogen Analyser
(Butler et al., 1969, 1970; Herman and Beers, 1969). In earlier studies,
however, both nitrogen and phosphorus contents of zooplankton have
been determined after preliminary digestion of the samples with concentrated suphuric acid, the nitrogen then bcing estimated as ammonia
after the normal micro-Kjeldahl procedure, and the phosphorus aa
inorganic phosphate by the method of Murphy and Riley (1962).
In some studies (e.g. Curl, 1962) there is reason to believe that digestion
of the samples was incomplete and the data have not becn included in
Table VI, which summarizes values found for both nitrogen and phosphorus, as percentage dry body weight, in various zooplankton from
different sea areas.
E. D. S. CORNER AND ANTHONY Q. DAVIES
grazing will not start (approximately 70 pg C/1, Adanis and Steele,
1966; 50-190 pg C/1, Parsons et al., 1969).
Clearly, some of the assumptions that have been made in order to
calculate assimilation efficiences from field data are to some extent
oversimplifications. On the other hand, laboratory studies with zooplankton can also be criticized on the grounds t h a t thc animals are
used under confined and unnatural conditions (although it is worth
e~nphasizing that findings made in the laboratory havc often been used
at somc stage during calculations of secondary production in the sea).
Accordingly, one may well expect to encounter differences between
finduigs made in the laboratory and those made in the field. An example
of such a difference is the finding by Conover (196Gb) that the average
assimilation of Thalassiosira by Calanus hyperboreus feeding on a wide
range of concentrations, including values wcll above that corresponding to 390 mg C/m3, was about 70% : whereas Beklemishcv (1962)
regarded this level as the threshold at which superfluous feeding begins
in nature, so that only about one third of the captured food should be
assimilated. More recent studies, involving the use of both field and
laboratory data, have shed further light on the question of superfluous
feeding (Butler et al., 1970). The animal used was Calanus$nmarchicus
and the calculations were based on measurements of nitrogen and phosphorus excretion as well as N : P ratios in the animals, phytoplankton
and faecal pellets. It was found that even in a high concentration of
natural phytoplankton, 77% of captured phosphorus and 62.5% of
captured nitrogen was assimilated, values close to those observcd in
laboratory experiments but much higher than those suggested by
Beklemishev (1962).
IX. LEVELS OF NITROGEN AND PHOSPHORUS IN ZOOPLANKTON
Recent measurements of the nitrogen content of zooplankton have
employed the micro-Dumas method, using a Coleman Nitrogen Analyser
(Butler et al., 1969, 1970; Herman and Beers, 1969). In earlier studies,
however, both nitrogen and phosphorus contents of zooplankton have
been determined after preliminary digestion of the samples with concentrated suphuric acid, the nitrogen then bcing estimated as ammonia
after the normal micro-Kjeldahl procedure, and the phosphorus aa
inorganic phosphate by the method of Murphy and Riley (1962).
In some studies (e.g. Curl, 1962) there is reason to believe that digestion
of the samples was incomplete and the data have not becn included in
Table VI, which summarizes values found for both nitrogen and phosphorus, as percentage dry body weight, in various zooplankton from
different sea areas.