162
E. D. 5. CORNER AND ANTHONY 0. DAVIES
Ketchurn’s (1962) view. Thus, for the atomic ratio excreted nitrogen
(as ammonia) : excreted phosphorus (as inorganic phosphatc) Harris
(1959), using mixed zooplankton from Long Island Sound, obtained an
average value of 9.7 ; and an average of 9.3 can be calculated from the
data of Martin (1968) for Acartia spp. in Narragansett Bay ; furthermore, Beers (1964) obtained a value of 11-7 for the chaetognath
Sagitta hispida collected off the coast of Bermuda. Butler et al. (1969)
measured the ratio total excreted nitrogen (both inorganic and
organic) : total excreted phosphorus (both inorganic and organic)
for Calanus finmarchicus from the Clyde Sea-area and for Calanus
helgolandicw from the English Channel and obtained an average value
of 12.1. In a later study (Butler et al., 1970), using the same species,
they found a small but significant difference between the N : P ratioin
spring (1 1.0) and in winter (14.6). However, in general the N : P ratios
for the soluble excretion products of zooplankton are fairly consistent,
and lower than those found for either the animals or the plants on which
they feed.
Values for the N : P ratios in zooplankton, phytoplankton and the
soluble excretion products of the animals have been used in calculations
of feeding efficiencies ; and a more detailed treatment of this topic is
given in the following section.
XI. GROWTH OF ZOOPLANKTON IN TERMS OF
NITROGEN AND PHOSPHORUS
An important quantitative aspect of the nitrogen (or phosphorus)
cycle in the sea is the efficiency with which zooplankton convert dietary
forms of this element into animal tissue. Of the food captured by
zooplankton, only a fraction will be invested in growth or egg production, losses being incurred through incomplete assimilation as well aa
through metabolic activities associated with maintenance. We have
already seen (Section VIII) that the assimilation of nitrogen and phosphorus by zooplankton is, in general, a very efficient process : but also
(Section X) that the metabolic losses represented by the levels of nitrogen and phosphorus excreted in soluble form by the animals are often
considerable. In the present section we deal with various attempts to
estimate nitrogen and phosphorus “ budgets ” for the animals, i.e.
the proportions of captured nitrogen and phosphorus invested in
growth and used in metabolism.
A. Rate of growth
Growth rates of zooplankton, as daily increments in body nitrogen,
have so far been obtained only with Calanusfinmarchicus (Corner et d.,
E. D. 5. CORNER AND ANTHONY 0. DAVIES
Ketchurn’s (1962) view. Thus, for the atomic ratio excreted nitrogen
(as ammonia) : excreted phosphorus (as inorganic phosphatc) Harris
(1959), using mixed zooplankton from Long Island Sound, obtained an
average value of 9.7 ; and an average of 9.3 can be calculated from the
data of Martin (1968) for Acartia spp. in Narragansett Bay ; furthermore, Beers (1964) obtained a value of 11-7 for the chaetognath
Sagitta hispida collected off the coast of Bermuda. Butler et al. (1969)
measured the ratio total excreted nitrogen (both inorganic and
organic) : total excreted phosphorus (both inorganic and organic)
for Calanus finmarchicus from the Clyde Sea-area and for Calanus
helgolandicw from the English Channel and obtained an average value
of 12.1. In a later study (Butler et al., 1970), using the same species,
they found a small but significant difference between the N : P ratioin
spring (1 1.0) and in winter (14.6). However, in general the N : P ratios
for the soluble excretion products of zooplankton are fairly consistent,
and lower than those found for either the animals or the plants on which
they feed.
Values for the N : P ratios in zooplankton, phytoplankton and the
soluble excretion products of the animals have been used in calculations
of feeding efficiencies ; and a more detailed treatment of this topic is
given in the following section.
XI. GROWTH OF ZOOPLANKTON IN TERMS OF
NITROGEN AND PHOSPHORUS
An important quantitative aspect of the nitrogen (or phosphorus)
cycle in the sea is the efficiency with which zooplankton convert dietary
forms of this element into animal tissue. Of the food captured by
zooplankton, only a fraction will be invested in growth or egg production, losses being incurred through incomplete assimilation as well aa
through metabolic activities associated with maintenance. We have
already seen (Section VIII) that the assimilation of nitrogen and phosphorus by zooplankton is, in general, a very efficient process : but also
(Section X) that the metabolic losses represented by the levels of nitrogen and phosphorus excreted in soluble form by the animals are often
considerable. In the present section we deal with various attempts to
estimate nitrogen and phosphorus “ budgets ” for the animals, i.e.
the proportions of captured nitrogen and phosphorus invested in
growth and used in metabolism.
A. Rate of growth
Growth rates of zooplankton, as daily increments in body nitrogen,
have so far been obtained only with Calanusfinmarchicus (Corner et d.,