T H E P R O D U C T I O N O F M A R I N I : P L A N K T O N
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substance which is the essence of primary production. For example,
respiration has already been noted as reducing growth. But there may
be excretion of some material in soluble forin which would not appear
in 14C measurements. The amount of such “lost” material is usually
believed to be small, but Fogg (1963) suggests that the quantity may
at times be considerable (vide infra). Other discrepancies between
photosynthetic and growth rate may arise. For instance, many nutrients
are required for the further synthesis of algal cell substance; the
concentration of these nutrients may influence the amount of phytoplankton substance produced, though this is clearly closely related to
photosynthetic activity. Ideally, we should measure the actual amount
of phytoplankton material synthesized in a given volume of sea water
over a period of time, but this again requires rapid and accurate methods
for the determination of organic carbon or dry organic matter, and these
are at present not available.
Apart from the difficulty of estimating standing crop, the 14C method
may be used to measure primary productio I throughout the euphotic
zone in the sea, but the precise technique i3 important (cf. Steemann
Nielsen, 1964a). Undoubtedly the best determinations are made employing the in situ method by which a seiies of bottles is placed at
different depths in the ocean and the light intensity throughout the
euphotic zone is also measured. A reasonable method where the timeconsuming and difficult in situ method cannot be employed is to place
sealed bottles of sea water from each depth on board the research ship,
the whole being surrounded by a jacket of ;sea water, and illuminated
by fluorescent light sources of known intensity. It is essential, however,
to employ glass filters of known spectral transmission; these must be
placed above the plankton samples according to the light which they
would encounter at their normal depth distribution.
Recently investigations comparing the production of phytoplankton
by different techniques have been made. McAllister et al. (1961) enclosed a natural population of coastal phytoplankton in a large plastic
sphere sunk just beneath the sea surface. Primary production rates
were estimated by oxygen bottle and 14C methods, and showed rather
wide differences. Some of the discrepanciea were reduced, if the 14C
method was assumed to measure net photosynthesis, and if in the
oxygen experiments the photosynthetic quotient was high (1 -3). Net
production of organic particulate carbon was also estimated over three
weeks by five methods; 0,-production, 14C, #changes in CO, as revealed
by pH, cell counts, oxidizable particulate carbon produced. There was a
reasonable measure of agreement, especially witb three of the techniques (cf. Fig. 1). In a later study by Antia et al. (1963) using the same
plastic sphere, the 14C method gave good agreement with an estimate of
t ?
125
substance which is the essence of primary production. For example,
respiration has already been noted as reducing growth. But there may
be excretion of some material in soluble forin which would not appear
in 14C measurements. The amount of such “lost” material is usually
believed to be small, but Fogg (1963) suggests that the quantity may
at times be considerable (vide infra). Other discrepancies between
photosynthetic and growth rate may arise. For instance, many nutrients
are required for the further synthesis of algal cell substance; the
concentration of these nutrients may influence the amount of phytoplankton substance produced, though this is clearly closely related to
photosynthetic activity. Ideally, we should measure the actual amount
of phytoplankton material synthesized in a given volume of sea water
over a period of time, but this again requires rapid and accurate methods
for the determination of organic carbon or dry organic matter, and these
are at present not available.
Apart from the difficulty of estimating standing crop, the 14C method
may be used to measure primary productio I throughout the euphotic
zone in the sea, but the precise technique i3 important (cf. Steemann
Nielsen, 1964a). Undoubtedly the best determinations are made employing the in situ method by which a seiies of bottles is placed at
different depths in the ocean and the light intensity throughout the
euphotic zone is also measured. A reasonable method where the timeconsuming and difficult in situ method cannot be employed is to place
sealed bottles of sea water from each depth on board the research ship,
the whole being surrounded by a jacket of ;sea water, and illuminated
by fluorescent light sources of known intensity. It is essential, however,
to employ glass filters of known spectral transmission; these must be
placed above the plankton samples according to the light which they
would encounter at their normal depth distribution.
Recently investigations comparing the production of phytoplankton
by different techniques have been made. McAllister et al. (1961) enclosed a natural population of coastal phytoplankton in a large plastic
sphere sunk just beneath the sea surface. Primary production rates
were estimated by oxygen bottle and 14C methods, and showed rather
wide differences. Some of the discrepanciea were reduced, if the 14C
method was assumed to measure net photosynthesis, and if in the
oxygen experiments the photosynthetic quotient was high (1 -3). Net
production of organic particulate carbon was also estimated over three
weeks by five methods; 0,-production, 14C, #changes in CO, as revealed
by pH, cell counts, oxidizable particulate carbon produced. There was a
reasonable measure of agreement, especially witb three of the techniques (cf. Fig. 1). In a later study by Antia et al. (1963) using the same
plastic sphere, the 14C method gave good agreement with an estimate of
t ?