152
E. D. 5. CORNER AND ANTHONY 4 3 . DAVIES
ture, salinity, season and body-size, and as only ammonia-nitrogen waa
measured in some studies (e.g. Harris, 1959; Martin, 1968) but total
nitrogen in others (e.g. Butler et al., 1969 ; Jawed, 1969), such differences
are only to be expected.
Generally speaking, the rates of nitrogen excretion by zooplankton
are high compared with values obtained using other marine inverfebrates. For example, Dresel and Moyle (1950) give a value for amphipods
of approximately 1.8 pg N/g dry weight/day; and Needham (1957)
has shown that the crab Carcinides nu;cenas (Pennant), when fasting,
excretes 44 pg N/g body weight/day. Small zooplankton of large
surface : volume ratio occupying an aquatic habitat can probably
dispose easily of the ammonia produced by protein breakdown ; and
there are certain observations consistent with the view that some
species make use of protein aa an energy source when starved (Cowey
and Corner, 1963b ; Linford, 1965). Relevant to this are certain measurements of the atomic ratio (oxygen consumed : nitrogen excreted). Thus,
the average chemical composition of particulate material in the sea
(Redfield et al., 1963) is such that one atom of nitrogen should be
excreted for 17 oxygen atoms respired. However, at a time when
phytoplankton was scarce and zooplankton abundant in Long Island
Sound, Harris (1959) obtained an 0 : N ratio of only 7.7, implying that
protein was mainly being used as an energy source.
Apart from evidence for the presence of “ peptidases ” in
Calanus spp. (Manwell et al., 1967) and a-keto-glutarate transaminases in Neomy~is integer (Raymont el al., 1968) nothing is
known about the various enzymes involved in the digestion and
metabolism of nitrogen by the animals. Possibly this field of
study will receive greater attention now that several species of
zooplankton can be cultured in the laboratory.
B. Phosphorus excretion
Cooper (1935) and Gardiner (1 937) first showed that zooplankton
rapidly increase the phosphorus content of sea water and Harris (1959)
found striking evidence of this during his study of the nitrogen cycle
in Long Island Sound. Thus, the data he obtained from experiments
in which the zooplankton were mainly Acurtia clausi show that these
animals excreted 11.0 pg P/mg dry weightlday. As Harris and Riley
(1956) had previously found that phosphorus accounted for 0.82% of
the dry weight, this excretion rate represented 130% of the body
phosphorus daily. Harris’s excretion experiments were carried out
over a short period (4 h) with animals used in natural sea water con-
E. D. 5. CORNER AND ANTHONY 4 3 . DAVIES
ture, salinity, season and body-size, and as only ammonia-nitrogen waa
measured in some studies (e.g. Harris, 1959; Martin, 1968) but total
nitrogen in others (e.g. Butler et al., 1969 ; Jawed, 1969), such differences
are only to be expected.
Generally speaking, the rates of nitrogen excretion by zooplankton
are high compared with values obtained using other marine inverfebrates. For example, Dresel and Moyle (1950) give a value for amphipods
of approximately 1.8 pg N/g dry weight/day; and Needham (1957)
has shown that the crab Carcinides nu;cenas (Pennant), when fasting,
excretes 44 pg N/g body weight/day. Small zooplankton of large
surface : volume ratio occupying an aquatic habitat can probably
dispose easily of the ammonia produced by protein breakdown ; and
there are certain observations consistent with the view that some
species make use of protein aa an energy source when starved (Cowey
and Corner, 1963b ; Linford, 1965). Relevant to this are certain measurements of the atomic ratio (oxygen consumed : nitrogen excreted). Thus,
the average chemical composition of particulate material in the sea
(Redfield et al., 1963) is such that one atom of nitrogen should be
excreted for 17 oxygen atoms respired. However, at a time when
phytoplankton was scarce and zooplankton abundant in Long Island
Sound, Harris (1959) obtained an 0 : N ratio of only 7.7, implying that
protein was mainly being used as an energy source.
Apart from evidence for the presence of “ peptidases ” in
Calanus spp. (Manwell et al., 1967) and a-keto-glutarate transaminases in Neomy~is integer (Raymont el al., 1968) nothing is
known about the various enzymes involved in the digestion and
metabolism of nitrogen by the animals. Possibly this field of
study will receive greater attention now that several species of
zooplankton can be cultured in the laboratory.
B. Phosphorus excretion
Cooper (1935) and Gardiner (1 937) first showed that zooplankton
rapidly increase the phosphorus content of sea water and Harris (1959)
found striking evidence of this during his study of the nitrogen cycle
in Long Island Sound. Thus, the data he obtained from experiments
in which the zooplankton were mainly Acurtia clausi show that these
animals excreted 11.0 pg P/mg dry weightlday. As Harris and Riley
(1956) had previously found that phosphorus accounted for 0.82% of
the dry weight, this excretion rate represented 130% of the body
phosphorus daily. Harris’s excretion experiments were carried out
over a short period (4 h) with animals used in natural sea water con-