180
J . E . a. RAYMONT
Figure 12a shows the rate of change of a population of zooplankton
obtained by Riley using the various coefficients calculated. An approximate integration of the curve may be obtained by employing mean
value for the factors in the equation over short time intervals. This
theoretical curve has been fitted to the field data for Georges Bank -
there is a considerable measure of agreement between the actual and
theoretical curves (cf. Fig. 12b).
Cushing (1959a) used a mathematical model to assess the production
of Calanus and other small copepods as the herbivore plankton in the
North Sea over a period of six months. He deduced the rate of increase
of the algae from the light energy available at various depths during the
six months (cf. p. 167), and estimated the grazing rate from the minimal
food requirements necessary for maintenance, reckoning also the rate
of increase of the herbivorous copepods. His analysis of this rate of increase is especially interesting as he obtained his data from the egg production of Calanus in relation to food concentration. Marshall and Om
had already shown that egg production appears to be a function of food
concentration. Cushing estimated the percentage mortality for juvenile
stages of Calanus and the mortality of the adults for various weekly
periods between January and June. The production of Cabnus and of
other herbivores over the six-month period is shown in Fig. 13. Cushing’s results suggested that the copepods were undernourished during
the first months of the year, but they fed excessively over t,he main
period of phytoplankton production. This apparent “wastefulness” of
production in boreal waters has already been noted.
Details of the rates of production of zooplankton must, however,
depend on a far wider and more accurate knowledge of the biology and
especially of the physiology of plankton animals. Even our knowledge
of breeding cycles of zooplankton is limited; we know fairly accurately
the breeding cycles of a few species of copepods, of a few euphausids,
some amphipods and sagittae. Most of these are boreal species; knowledge of the breeding of tropical plankton is especially lacking, and deepsea plankton is virtually unknown as regards its breeding habits.
Since zooplankton is so difficult to keep in the laboratory the effect of
various environmental factors on reproductive rate, especially the effect
of food supply, is almost unknown. The work of many investigators,
notably Marshall and Orr’ (1956), dealt with the stimulating effect of
food on reproduction in Calanus. Marshall (1949) also suggested that
abundant diatoms increased the production of other copepods. Barnes
(1957) indicated a stimulating influence of phytoplankton production
on the liberation of cirripede nauplii. Edmondson (1962) demonstrated
that the density of phytoplankton was related to successful reproduction of copepods and other animals. Work on bivalve larvae, summarized
J . E . a. RAYMONT
Figure 12a shows the rate of change of a population of zooplankton
obtained by Riley using the various coefficients calculated. An approximate integration of the curve may be obtained by employing mean
value for the factors in the equation over short time intervals. This
theoretical curve has been fitted to the field data for Georges Bank -
there is a considerable measure of agreement between the actual and
theoretical curves (cf. Fig. 12b).
Cushing (1959a) used a mathematical model to assess the production
of Calanus and other small copepods as the herbivore plankton in the
North Sea over a period of six months. He deduced the rate of increase
of the algae from the light energy available at various depths during the
six months (cf. p. 167), and estimated the grazing rate from the minimal
food requirements necessary for maintenance, reckoning also the rate
of increase of the herbivorous copepods. His analysis of this rate of increase is especially interesting as he obtained his data from the egg production of Calanus in relation to food concentration. Marshall and Om
had already shown that egg production appears to be a function of food
concentration. Cushing estimated the percentage mortality for juvenile
stages of Calanus and the mortality of the adults for various weekly
periods between January and June. The production of Cabnus and of
other herbivores over the six-month period is shown in Fig. 13. Cushing’s results suggested that the copepods were undernourished during
the first months of the year, but they fed excessively over t,he main
period of phytoplankton production. This apparent “wastefulness” of
production in boreal waters has already been noted.
Details of the rates of production of zooplankton must, however,
depend on a far wider and more accurate knowledge of the biology and
especially of the physiology of plankton animals. Even our knowledge
of breeding cycles of zooplankton is limited; we know fairly accurately
the breeding cycles of a few species of copepods, of a few euphausids,
some amphipods and sagittae. Most of these are boreal species; knowledge of the breeding of tropical plankton is especially lacking, and deepsea plankton is virtually unknown as regards its breeding habits.
Since zooplankton is so difficult to keep in the laboratory the effect of
various environmental factors on reproductive rate, especially the effect
of food supply, is almost unknown. The work of many investigators,
notably Marshall and Orr’ (1956), dealt with the stimulating effect of
food on reproduction in Calanus. Marshall (1949) also suggested that
abundant diatoms increased the production of other copepods. Barnes
(1957) indicated a stimulating influence of phytoplankton production
on the liberation of cirripede nauplii. Edmondson (1962) demonstrated
that the density of phytoplankton was related to successful reproduction of copepods and other animals. Work on bivalve larvae, summarized