PLANKTON IN NITROGEN AND PHOSPIIORUS CYCLES
165
k values for the later stages of growth were similar to those found in
experiments with Thalassiosira : but during naupliar development
the k value was markedly greater (0.64 compared with 0.15).
B. Egg production
A further important aspect of zooplankton growth is the amount of
nitrogen and phosphorus invested in egg production by adult femalcs.
The number of eggs produced is known to be affected by factors such
as the quantity and quality of food (Marshall and Orr, 1952 ; Edmondson et al., 1962) but so far the only estimate of the quantity of nitrogen
involved in egg production is that of Corner et al. (1967) for Calanus
finmarchicus, and no data have been obtained for egg production in
terms of phosphorus. Earlier work by Marshall and Orr (1952) indicated
that the average total of eggs produced by a female Calanusfinmarchicus
was 250, over a period of 35 days: from which Corner et al. (1967)
estimated the daily quantity of nitrogen involved to be 0.25 pg (approximately 10% of the body nitrogen). However, Mullin and Brooks (1967)
found a higher rate of egg production by the related species Calanus
helgolandicus, mean values being 613 and 691 eggs per female over a
period of 9 weeks. Even higher values have been found by Paffenhbfer (1969) using females feeding on phytoplankton cultures containing 25-400 pg particulate C/L, a range of concentrations similar to that
found in ocean waters off La Jolla. The number of eggs Iaid was 1991
per female, a value close to that of 2 267 claimed for animals in “the
wild ”. Paffenhbfer quotes no value for the nitrogen content of the
eggs, but using the figure of 0.0345 pg N per egg found by Corner et al.
(1967) for Calanus finmarchicus, about 70 pg nitrogen would have been
released as eggs by each female. Assuming a dry weight of 250 pg, of
which about 10% would be nitrogen, this means that roughly three
times the nitrogen content of the female would have been used to form
eggs. These figures therefore indicate that egg production by zooplankton is of considerable importance in the turnover of nitrogen (and
presumably phosphorus) in the sea.
C. Net and gross growth eficiencies
Two important factors in zooplankton growth are the fractions of
captured food (K,) and assimilated food (K,) converted into new tissue,
K , being defined as gross growth efficiency and K , as net growth
efficiency (vide Conover, 1968).
Values for these coeficients have been obtained for many species of
marine zooplankton, but so far the data have been expressed only in
165
k values for the later stages of growth were similar to those found in
experiments with Thalassiosira : but during naupliar development
the k value was markedly greater (0.64 compared with 0.15).
B. Egg production
A further important aspect of zooplankton growth is the amount of
nitrogen and phosphorus invested in egg production by adult femalcs.
The number of eggs produced is known to be affected by factors such
as the quantity and quality of food (Marshall and Orr, 1952 ; Edmondson et al., 1962) but so far the only estimate of the quantity of nitrogen
involved in egg production is that of Corner et al. (1967) for Calanus
finmarchicus, and no data have been obtained for egg production in
terms of phosphorus. Earlier work by Marshall and Orr (1952) indicated
that the average total of eggs produced by a female Calanusfinmarchicus
was 250, over a period of 35 days: from which Corner et al. (1967)
estimated the daily quantity of nitrogen involved to be 0.25 pg (approximately 10% of the body nitrogen). However, Mullin and Brooks (1967)
found a higher rate of egg production by the related species Calanus
helgolandicus, mean values being 613 and 691 eggs per female over a
period of 9 weeks. Even higher values have been found by Paffenhbfer (1969) using females feeding on phytoplankton cultures containing 25-400 pg particulate C/L, a range of concentrations similar to that
found in ocean waters off La Jolla. The number of eggs Iaid was 1991
per female, a value close to that of 2 267 claimed for animals in “the
wild ”. Paffenhbfer quotes no value for the nitrogen content of the
eggs, but using the figure of 0.0345 pg N per egg found by Corner et al.
(1967) for Calanus finmarchicus, about 70 pg nitrogen would have been
released as eggs by each female. Assuming a dry weight of 250 pg, of
which about 10% would be nitrogen, this means that roughly three
times the nitrogen content of the female would have been used to form
eggs. These figures therefore indicate that egg production by zooplankton is of considerable importance in the turnover of nitrogen (and
presumably phosphorus) in the sea.
C. Net and gross growth eficiencies
Two important factors in zooplankton growth are the fractions of
captured food (K,) and assimilated food (K,) converted into new tissue,
K , being defined as gross growth efficiency and K , as net growth
efficiency (vide Conover, 1968).
Values for these coeficients have been obtained for many species of
marine zooplankton, but so far the data have been expressed only in