136
E. D. 8. CORNER AND ANTHONY 0. DAVIES
material as the food were usually comparable to laboratory measurements with unialgal diets.
Direct experimental verification of the basic assumption that
inorganic material is not assimilated (or, at least, assimilated in amounts
too small to affect the issue) has not yet been obtained. Moreover, there
is the further question of whether both inorganic and organic substances
unassimilated by zooplankton may be released from the gut in soluble
form and not only as faecal material (Harvey et al., 1935 ; Harris 1959 :
see p. 154). Nevertheless, in the course of further experiments (Conover,
1966a) in which the nature and number of faecal pellets produced were
such as to allow quantitative collection t o be made, direct measurements
of assimilation were possible and gave results that compared closely
with those obtained by the “ ratio ” method.
All detailed studies of assimilation efficiency have so far been
concerned with bulk constituents of the diet (carbon, nitrogen, phosphorus), not specific dietary fractions (sugars, proteins, fats). However,
Cowey and Corner (1966), in the course of an investigation of the amino
acids in various algal diets and the faecal pellets produced by C.
finmarchicus when feeding on them, noted that amino acids accounted
for a higher percentage of the dry weight of the faecal pellets when the
animal fed on a high concentration of Skeletonem (s 162 pg N/1)
than when it fed on a low (E 14.2 pg N/l). These results indicated that
the extent of assimilation of amino acids (protein) was related to the
concentration of food available. The quantity of test material was so
amall, however, that repeated amino acid analyses essential for an
adequate statistical treatment of the data could not be made: the
question therefore needs more detailed study. Nevertheless, these
observations suggest that conclusions based on assimilation efficiencies
measured in terms of a bulk constituent of the diet, such as nitrogen,
may not necessarily apply in the case of a particular fraction of the diet,
such as amino acids.
So far, we have dealt only with measurements of assimilation
efficiency made in laboratory experiments. In contrast, certain studies
carried out in the field have led to the conclusion that when plant food
is plentiful the percentage of ingested material assimilated by ZOOplankton is by no means as high as that found in the laboratory. This
phenomenon of so-called “superfluous feeding ” in the sea will now be
considered.
E. Superfluous feeding
Beklemishev (1962) holds that superfluous feeding occurs because
animals stop increasing the quantity of food they assimilate when
E. D. 8. CORNER AND ANTHONY 0. DAVIES
material as the food were usually comparable to laboratory measurements with unialgal diets.
Direct experimental verification of the basic assumption that
inorganic material is not assimilated (or, at least, assimilated in amounts
too small to affect the issue) has not yet been obtained. Moreover, there
is the further question of whether both inorganic and organic substances
unassimilated by zooplankton may be released from the gut in soluble
form and not only as faecal material (Harvey et al., 1935 ; Harris 1959 :
see p. 154). Nevertheless, in the course of further experiments (Conover,
1966a) in which the nature and number of faecal pellets produced were
such as to allow quantitative collection t o be made, direct measurements
of assimilation were possible and gave results that compared closely
with those obtained by the “ ratio ” method.
All detailed studies of assimilation efficiency have so far been
concerned with bulk constituents of the diet (carbon, nitrogen, phosphorus), not specific dietary fractions (sugars, proteins, fats). However,
Cowey and Corner (1966), in the course of an investigation of the amino
acids in various algal diets and the faecal pellets produced by C.
finmarchicus when feeding on them, noted that amino acids accounted
for a higher percentage of the dry weight of the faecal pellets when the
animal fed on a high concentration of Skeletonem (s 162 pg N/1)
than when it fed on a low (E 14.2 pg N/l). These results indicated that
the extent of assimilation of amino acids (protein) was related to the
concentration of food available. The quantity of test material was so
amall, however, that repeated amino acid analyses essential for an
adequate statistical treatment of the data could not be made: the
question therefore needs more detailed study. Nevertheless, these
observations suggest that conclusions based on assimilation efficiencies
measured in terms of a bulk constituent of the diet, such as nitrogen,
may not necessarily apply in the case of a particular fraction of the diet,
such as amino acids.
So far, we have dealt only with measurements of assimilation
efficiency made in laboratory experiments. In contrast, certain studies
carried out in the field have led to the conclusion that when plant food
is plentiful the percentage of ingested material assimilated by ZOOplankton is by no means as high as that found in the laboratory. This
phenomenon of so-called “superfluous feeding ” in the sea will now be
considered.
E. Superfluous feeding
Beklemishev (1962) holds that superfluous feeding occurs because
animals stop increasing the quantity of food they assimilate when