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J. E. a. RAYMONT
be noted that some of the glycollate released may be used by bacteria
to synthesize particulate matter, thus contributing to production as a
whole. The possibility also exists that algae may themselves absorb
such extra-cellular substances and use them in synthesis. A moat
interesting related observation by Smith et al. (1960) is that carbaminocarboxylic acids may be used as a carbon source by phytoplankton,
apparently even preferentially by Nitzschia. Similarly, Parsons and
Strickland (1962) have commented on the limited heterotrophy of
algae. Although in their work uptake of such dissolved organic carbon
as glucose and acetate was due to microorganisms, such as bacteria, we
know that limited uptake of carbon compounds can occur in algal
groups. Thus Lewin and Lewin (1960) and Lewin (1963) showed that
different diatom species show marked differences in their heterotrophic
abilities; some can utilize such organic carbon as glucose and lactate,
though generally their heterotrophic powers appear to be rather limited.
Among the flagellate chrysomonads, however, Pintner and Provasoli
(1963) showed that an array of organic acids as well as carbohydrates
may be used as carbon sources, though specific differences again are
evident; Coccolithus huxleyi, for example, shows very little ability to
utilize organic carbon. These same authors noted that glycero-phosphate
may be used in place of orthophosphate. As regards nitrogen, such substances as adenylic acid and a range of amino-acids may be employed
by these flagellates, though these substances appear to be inferior to
inorganic nitrate. Guillard (1963) had shown that some diatoms and
unicellular flagellates could make use of organic nitrogen (amino-acids,
urea, uric acid) in bacterial-free culture, and Provasoli and McLaughlin
( 1963) demonstrated limited utilization of dissolved organic nitrogen
by dinoflagellates.
At first sight it might seem that this limited heterotrophic ability of
phytoplankton is unimportant in the oceans, but it must be remembered
that the amount of dissolved organic matter, relatively, is very large in
sea water. Provasoli (1963) suggests that it may be some 7 to 8 times the
amount of particulate matter in the euphotic zone, where the plankton
is, of course, relatively rich; in deep waters the dissolved organic matter
may approach 1 000 times the particulate matter (cf. Duursma,, 1961).
Parsons and Strickland (1962) suggest that the average amount of
dissolved carbon in .sea water is about 1 g/m3, but in surface waters and
near land the concentration may be 5 to 10 times greater. Despite the
earlier work of Krogh (1934) which suggested a mean value of > 2.OgC/
m3 and that the amount of dissolved organic matter was relatively
stable in the oceans, there appear to be considerable variations both
horizontally and vertically. Duursma (1961) finds lower values in the
northern Atlantic; few areas exceeded 1.0 gC/mS, but the upper layers
J. E. a. RAYMONT
be noted that some of the glycollate released may be used by bacteria
to synthesize particulate matter, thus contributing to production as a
whole. The possibility also exists that algae may themselves absorb
such extra-cellular substances and use them in synthesis. A moat
interesting related observation by Smith et al. (1960) is that carbaminocarboxylic acids may be used as a carbon source by phytoplankton,
apparently even preferentially by Nitzschia. Similarly, Parsons and
Strickland (1962) have commented on the limited heterotrophy of
algae. Although in their work uptake of such dissolved organic carbon
as glucose and acetate was due to microorganisms, such as bacteria, we
know that limited uptake of carbon compounds can occur in algal
groups. Thus Lewin and Lewin (1960) and Lewin (1963) showed that
different diatom species show marked differences in their heterotrophic
abilities; some can utilize such organic carbon as glucose and lactate,
though generally their heterotrophic powers appear to be rather limited.
Among the flagellate chrysomonads, however, Pintner and Provasoli
(1963) showed that an array of organic acids as well as carbohydrates
may be used as carbon sources, though specific differences again are
evident; Coccolithus huxleyi, for example, shows very little ability to
utilize organic carbon. These same authors noted that glycero-phosphate
may be used in place of orthophosphate. As regards nitrogen, such substances as adenylic acid and a range of amino-acids may be employed
by these flagellates, though these substances appear to be inferior to
inorganic nitrate. Guillard (1963) had shown that some diatoms and
unicellular flagellates could make use of organic nitrogen (amino-acids,
urea, uric acid) in bacterial-free culture, and Provasoli and McLaughlin
( 1963) demonstrated limited utilization of dissolved organic nitrogen
by dinoflagellates.
At first sight it might seem that this limited heterotrophic ability of
phytoplankton is unimportant in the oceans, but it must be remembered
that the amount of dissolved organic matter, relatively, is very large in
sea water. Provasoli (1963) suggests that it may be some 7 to 8 times the
amount of particulate matter in the euphotic zone, where the plankton
is, of course, relatively rich; in deep waters the dissolved organic matter
may approach 1 000 times the particulate matter (cf. Duursma,, 1961).
Parsons and Strickland (1962) suggest that the average amount of
dissolved carbon in .sea water is about 1 g/m3, but in surface waters and
near land the concentration may be 5 to 10 times greater. Despite the
earlier work of Krogh (1934) which suggested a mean value of > 2.OgC/
m3 and that the amount of dissolved organic matter was relatively
stable in the oceans, there appear to be considerable variations both
horizontally and vertically. Duursma (1961) finds lower values in the
northern Atlantic; few areas exceeded 1.0 gC/mS, but the upper layers