PLANKTON IN NITROQEN AND PHOSPHORUS CYCLES
147
water occupied by the animals. Failure to detect these substances in
measureable amounts may therefore be taken to imply that neither of
these processes occurred to any notable extent.
Johannes and Webb (1965) and Webb and Johannes (1967) found
that considerable quantities of amino acids were released by mixed
zooplankton collected in sea areas off Georgia and the Carolinas. These
observations seemed inconsistent with the findings of Corner et al.
(1965) and led Corner and Newell (1967) t o examine this question
further, using Calanus helgolandicus. It was found by differential
chemical analysis that these animals, whether fed or starved, excreted
nitrogen mainly as ammonia, but that small and variable amounts of
other nitrogcnous substances were also excreted. Corner and Newell
(1967) concluded that one of these substances might be urea; and
Jawed (1969) has recently found that small amounts of this substance
are also excreted by Euphausia pacijim. Corner and Newell (1967)
could not detect measureable quantities of amino acids, however,
unless the test animals were used in unnaturally high density ; and they
considered the use of very high concentrations of mixed zooplankton
to be mainly responsible for the relatively high levels of amino acids
observed in the studies made by Johannes and Webb (see Corner and
Cowey, 1968). The experiments made by Corner and Newell (1967)
have recently been criticized by Webb and Johannes (1969) who claim
that bacteria attached t o the animals and their faecal pellets can
remove amino acids (as well as ammonia) during excretion experiments
carried out over long periods. Butler et al. (1969), in a study mainly
concerned with nitrogen and phosphorus excretion by Calanus jinmarchicus at different seasons, examined the forms of nitrogen excreted
over a short period by animals treated with a mixture of antibiotics
and found that the amount excreted as ammonia still accounted
for 78.3% of the total, a value close t o the average of 74.7% reported
by Corner and Newell (1967). However, no estimations of amino
acids as such were made and so the possibility remains that the
animals may have excreted small quantities of these substances
under bacteria-free conditions. Perhaps the true level of aminoacid excretion by zooplankton falls between the apparently high
values found by Johannes and Webb (1965) (caused by overcrowding of the test animals) and the insignificant amounts found by
Corner and Newell (1967) (because of bacterial contamination). Certainly the work of Jawed (1969), who has recently measured the rates
of excretion of ammonia, amino acids and urea by Neomysis rayii
Murdoch and Euphuusia pacijim would seem to support this view. Thus,
Jawed found that of the total nitrogen excreted by Neomysis rayii a t
A.M.B.-O
6
147
water occupied by the animals. Failure to detect these substances in
measureable amounts may therefore be taken to imply that neither of
these processes occurred to any notable extent.
Johannes and Webb (1965) and Webb and Johannes (1967) found
that considerable quantities of amino acids were released by mixed
zooplankton collected in sea areas off Georgia and the Carolinas. These
observations seemed inconsistent with the findings of Corner et al.
(1965) and led Corner and Newell (1967) t o examine this question
further, using Calanus helgolandicus. It was found by differential
chemical analysis that these animals, whether fed or starved, excreted
nitrogen mainly as ammonia, but that small and variable amounts of
other nitrogcnous substances were also excreted. Corner and Newell
(1967) concluded that one of these substances might be urea; and
Jawed (1969) has recently found that small amounts of this substance
are also excreted by Euphausia pacijim. Corner and Newell (1967)
could not detect measureable quantities of amino acids, however,
unless the test animals were used in unnaturally high density ; and they
considered the use of very high concentrations of mixed zooplankton
to be mainly responsible for the relatively high levels of amino acids
observed in the studies made by Johannes and Webb (see Corner and
Cowey, 1968). The experiments made by Corner and Newell (1967)
have recently been criticized by Webb and Johannes (1969) who claim
that bacteria attached t o the animals and their faecal pellets can
remove amino acids (as well as ammonia) during excretion experiments
carried out over long periods. Butler et al. (1969), in a study mainly
concerned with nitrogen and phosphorus excretion by Calanus jinmarchicus at different seasons, examined the forms of nitrogen excreted
over a short period by animals treated with a mixture of antibiotics
and found that the amount excreted as ammonia still accounted
for 78.3% of the total, a value close t o the average of 74.7% reported
by Corner and Newell (1967). However, no estimations of amino
acids as such were made and so the possibility remains that the
animals may have excreted small quantities of these substances
under bacteria-free conditions. Perhaps the true level of aminoacid excretion by zooplankton falls between the apparently high
values found by Johannes and Webb (1965) (caused by overcrowding of the test animals) and the insignificant amounts found by
Corner and Newell (1967) (because of bacterial contamination). Certainly the work of Jawed (1969), who has recently measured the rates
of excretion of ammonia, amino acids and urea by Neomysis rayii
Murdoch and Euphuusia pacijim would seem to support this view. Thus,
Jawed found that of the total nitrogen excreted by Neomysis rayii a t
A.M.B.-O
6