PARTICULATE ORGANIC MATTER I N SEA WATER
93
of 0.01-0.18 pg C/litre in an hour, and four samples from 100 m ranged
from 0.001-0.062 pg, with three of the four toward the lower end of the
range.
These results were on the whole somewhat higher than the ones
obtained by Parsons and Strickland, and clearly more data are needed
in order to give us a clear idea of natural ranges of variations and their
reasons. Also these tracer methods, though elegant and provocative,
do not yet provide a generalized picture of heterotrophic absorption of
the complex array of carbon sources existing in sea water. Parsons and
Strickland found that the rates of uptake of glucose and acetate were
quite different, and a few experimental results cannot be extrapolated
to generalities. However, if as much as l-lOyo of the total dissolved
organic matter is biologically usable and is as readily available as
glucose, this would provide a substrate concentration of 10-8-10- M.
Thus it is not entirely unreasonable to suppose that the dissolved
fraction might supply most or all of the necessary substrates for
heterotrophs, and also, again quoting Parsons and Strickland, " the
mediation of an adsorptive concentration onto particulate matter '' is
a distinct possibility, particularly since that is where most of the
bacteria are living.
Hamilton et al. (1968) dealt with some of these problems and quoted
unpublished references to experiments on heterotrophic uptake by deep
water organisms. One of these experiments was credited to J. D. H.
Strickland (ref. Antia et al., 1962) who showed that the rate of uptake
from 500 pgllitre of radiocarbon-labelled glucose, acetate, succinate
and citrate at in situ temperatures was less than 0.001 pg C/litre/hr at
depths greater than 1 0 0 0 m. Similar results were also obtained by
Hamilton, using 20 pg/litre of radiocarbon-labelled glucose, proline
and glycine. These experiments were mentioned in passing without
further details and presumably will be described more extensively in
a later publication.
Hamilton et al. had reported that the biomass of deep water heterotrophs in terms of organic carbon was of the order of 0.3-0.5 pgllitre.
Thus if the uptake is less than 0.001 pg C/hr, the daily consumption
will be less than 10% of the weight of the organisms. This is a remarkably low rate of turnover for small organisms ; however, in an environment that is obviously marginal for the support of heterotrophs one
would expect a low metabolic rate, and these results may be realistic.
Some algae are much less eficient in heterotrophic uptake than
bacteria. For example Wright and Hobbie (1965) found that some
freshwater algae they were studying required substrate concentrations
several orders of magnitude larger than those required by bacteria.
93
of 0.01-0.18 pg C/litre in an hour, and four samples from 100 m ranged
from 0.001-0.062 pg, with three of the four toward the lower end of the
range.
These results were on the whole somewhat higher than the ones
obtained by Parsons and Strickland, and clearly more data are needed
in order to give us a clear idea of natural ranges of variations and their
reasons. Also these tracer methods, though elegant and provocative,
do not yet provide a generalized picture of heterotrophic absorption of
the complex array of carbon sources existing in sea water. Parsons and
Strickland found that the rates of uptake of glucose and acetate were
quite different, and a few experimental results cannot be extrapolated
to generalities. However, if as much as l-lOyo of the total dissolved
organic matter is biologically usable and is as readily available as
glucose, this would provide a substrate concentration of 10-8-10- M.
Thus it is not entirely unreasonable to suppose that the dissolved
fraction might supply most or all of the necessary substrates for
heterotrophs, and also, again quoting Parsons and Strickland, " the
mediation of an adsorptive concentration onto particulate matter '' is
a distinct possibility, particularly since that is where most of the
bacteria are living.
Hamilton et al. (1968) dealt with some of these problems and quoted
unpublished references to experiments on heterotrophic uptake by deep
water organisms. One of these experiments was credited to J. D. H.
Strickland (ref. Antia et al., 1962) who showed that the rate of uptake
from 500 pgllitre of radiocarbon-labelled glucose, acetate, succinate
and citrate at in situ temperatures was less than 0.001 pg C/litre/hr at
depths greater than 1 0 0 0 m. Similar results were also obtained by
Hamilton, using 20 pg/litre of radiocarbon-labelled glucose, proline
and glycine. These experiments were mentioned in passing without
further details and presumably will be described more extensively in
a later publication.
Hamilton et al. had reported that the biomass of deep water heterotrophs in terms of organic carbon was of the order of 0.3-0.5 pgllitre.
Thus if the uptake is less than 0.001 pg C/hr, the daily consumption
will be less than 10% of the weight of the organisms. This is a remarkably low rate of turnover for small organisms ; however, in an environment that is obviously marginal for the support of heterotrophs one
would expect a low metabolic rate, and these results may be realistic.
Some algae are much less eficient in heterotrophic uptake than
bacteria. For example Wright and Hobbie (1965) found that some
freshwater algae they were studying required substrate concentrations
several orders of magnitude larger than those required by bacteria.