128
E. D. 9. CORNER AND ANTHONY a. DAVIES
actively growing populations. For example, Antia et al. (1963) found
that 35% of the carbon fixed in a large-scale culture of coastal phytoplankton, growing under near natural conditions, reappeared in the
sea water. Some of this released material undoubtedly consists of
compounds of nitrogen and phosphorus: thus, on several occasions it
has been observed that the levels of the organic forms of these
elements increase as a result of phytoplankton growth under natural
conditions (Strickland and Austin, 1960 ; Ketchum and Corwin, 1965),
as well as in large-scale cultures of natural populations (McAllister
et ul., 1961 ; Antia et al., 1963) and of single species (Strickland et al.,
1969).
Dissolved organic nitrogen appears to be released mainly in the form
of proteins and amino acids (Hellebust, 1965) and the release of amino
acids by nitrogen-fixing blue-green algae may be of significance in the
marine nitrogen cycle (Stewart, 1963). The nature of the organic
phosphorus released has not yet been elucidated; but it is likely to
contain monophosphate esters (Kuenzler, 1970). Kuenzler has recently
shown that the dissolved organic phosphorus (DOP) in cultures of
marine phytoplankton reaches a maximum level just when the cultures
are entering the stationary phase ; and corresponds to between 12 and
26% of the total phosphorus present. In the case of Cyclotella cryptica
Reimann, Lewin and Guiilard, the DOP thus formed is reassimilated
during the stationary phase; but with other species, such as Thulassiosiru juviatilis Hustedt and Dunuliella tertiolecta, the level of DOP
increased with the age of the culture. The assimilation by phytoplankton of the DOP produced by different species was also demonstrated,
and the fraction taken up was found to vary with species. Thus,
Dunaliella tertiolecta and Synechococcus sp. took up the smallest
amounts, probably because these species do not themselves produce
external phosphatases. Kuenzler makes the interesting point that DOP
released by phytoplankton in the euphotic zone may be as important
as that excreted by zooplankton ; and that relative abilities to utilize
this organic phosphate could provide some species with a competitive
advantage over others.
VIII. THE ASSIMILATION OF NITROGEN AND PHOSPHORUS
BY ZOOPLANKTON
This section is the first of several dealing with the part played by
zooplankton in the turnover of nitrogen and phosphorus in the sea ; and
begins with a brief account of the possible dietary sources of nitrogen
and phosphorus available t o the animals.
E. D. 9. CORNER AND ANTHONY a. DAVIES
actively growing populations. For example, Antia et al. (1963) found
that 35% of the carbon fixed in a large-scale culture of coastal phytoplankton, growing under near natural conditions, reappeared in the
sea water. Some of this released material undoubtedly consists of
compounds of nitrogen and phosphorus: thus, on several occasions it
has been observed that the levels of the organic forms of these
elements increase as a result of phytoplankton growth under natural
conditions (Strickland and Austin, 1960 ; Ketchum and Corwin, 1965),
as well as in large-scale cultures of natural populations (McAllister
et ul., 1961 ; Antia et al., 1963) and of single species (Strickland et al.,
1969).
Dissolved organic nitrogen appears to be released mainly in the form
of proteins and amino acids (Hellebust, 1965) and the release of amino
acids by nitrogen-fixing blue-green algae may be of significance in the
marine nitrogen cycle (Stewart, 1963). The nature of the organic
phosphorus released has not yet been elucidated; but it is likely to
contain monophosphate esters (Kuenzler, 1970). Kuenzler has recently
shown that the dissolved organic phosphorus (DOP) in cultures of
marine phytoplankton reaches a maximum level just when the cultures
are entering the stationary phase ; and corresponds to between 12 and
26% of the total phosphorus present. In the case of Cyclotella cryptica
Reimann, Lewin and Guiilard, the DOP thus formed is reassimilated
during the stationary phase; but with other species, such as Thulassiosiru juviatilis Hustedt and Dunuliella tertiolecta, the level of DOP
increased with the age of the culture. The assimilation by phytoplankton of the DOP produced by different species was also demonstrated,
and the fraction taken up was found to vary with species. Thus,
Dunaliella tertiolecta and Synechococcus sp. took up the smallest
amounts, probably because these species do not themselves produce
external phosphatases. Kuenzler makes the interesting point that DOP
released by phytoplankton in the euphotic zone may be as important
as that excreted by zooplankton ; and that relative abilities to utilize
this organic phosphate could provide some species with a competitive
advantage over others.
VIII. THE ASSIMILATION OF NITROGEN AND PHOSPHORUS
BY ZOOPLANKTON
This section is the first of several dealing with the part played by
zooplankton in the turnover of nitrogen and phosphorus in the sea ; and
begins with a brief account of the possible dietary sources of nitrogen
and phosphorus available t o the animals.