92
GORDON A. RILEY
remains an enigma and more work is needed to establish their identity
and assess their importance, if any, in the bathypelagic food web ”.
Holm-Hansen ( I 968) found a distinct decrease in ATP with depth
in the deep ocean, suggesting a corresponding decrease in the biomass
of heterotrophs. Possibly it is too early to generalize on these results,
but there are indications that although total organic carbon does not
decrease systematically with depth, its capabilities for the support of
living organisms may decline as it sinks toward the bottom.
Nevertheless, one must conclude from this brief summary of recent
literature that the quantity of heterotrophs in deep water is much
larger than has been supposed in the past. Most of these organisms
have not been identified, and there is still little information available
on the kinds of substrates that they depend upon. Some information
is, however, now being obtained about possible rates of uptake of
organic substances and minimum concentrations required to support
growth.
Parsons and Strickland (1962b) undertook an investigation of
heterotrophic processes by measuring the uptake of C14 labelled glucose
and acetate, Sophisticated biochemical and microbiological concepts
were involved, which will not be elaborated here. It suffices to say
that they established beyond reasonable doubt that natural substrates
of 10-7 moles or less of glucose or acetate were adequate for heterotrophic growth. Their experiments were performed with natural sea
water taken off the coast of British Columbia (49”12’N, 123”58’W).
Most of the samples were taken from depths of 5-35 m, and the rate
of uptake varied from 0.004-0-3 pg C/litre in an hour, averaging 0.015.
Two samples from a depth of 175 m had values of 0.003 and 0.007.
I n discussing their results the authors concluded: “ Values for a
Michaelis-Menton type constant of less than 10- M have been reported
but are uncommon. Yet it should be reasoned that marine microorganisms must have evolved so as to utilize substrates a t the concentrations occurring in nature, with possibly the mediation of an adsorptive concentration onto particulate matter. More work with a wider
variety of samples and substrates is required to decide . . . but the
method looks promising.”
Further work along these lines was reported by Vaccaro and
Jannasch (1966). They used both pure cultures and natural populations in studies of glucose assimilation and obtained results similar
to the earlier ones in that natural substrate levels appeared t o be of
the order of 10-7 M or even as little as l o - * . They were also able t o
estimate the in situ rate of substrate removal. At five stations in the
tropical North Atlantic, samples collected in the upper 50 m gave values
GORDON A. RILEY
remains an enigma and more work is needed to establish their identity
and assess their importance, if any, in the bathypelagic food web ”.
Holm-Hansen ( I 968) found a distinct decrease in ATP with depth
in the deep ocean, suggesting a corresponding decrease in the biomass
of heterotrophs. Possibly it is too early to generalize on these results,
but there are indications that although total organic carbon does not
decrease systematically with depth, its capabilities for the support of
living organisms may decline as it sinks toward the bottom.
Nevertheless, one must conclude from this brief summary of recent
literature that the quantity of heterotrophs in deep water is much
larger than has been supposed in the past. Most of these organisms
have not been identified, and there is still little information available
on the kinds of substrates that they depend upon. Some information
is, however, now being obtained about possible rates of uptake of
organic substances and minimum concentrations required to support
growth.
Parsons and Strickland (1962b) undertook an investigation of
heterotrophic processes by measuring the uptake of C14 labelled glucose
and acetate, Sophisticated biochemical and microbiological concepts
were involved, which will not be elaborated here. It suffices to say
that they established beyond reasonable doubt that natural substrates
of 10-7 moles or less of glucose or acetate were adequate for heterotrophic growth. Their experiments were performed with natural sea
water taken off the coast of British Columbia (49”12’N, 123”58’W).
Most of the samples were taken from depths of 5-35 m, and the rate
of uptake varied from 0.004-0-3 pg C/litre in an hour, averaging 0.015.
Two samples from a depth of 175 m had values of 0.003 and 0.007.
I n discussing their results the authors concluded: “ Values for a
Michaelis-Menton type constant of less than 10- M have been reported
but are uncommon. Yet it should be reasoned that marine microorganisms must have evolved so as to utilize substrates a t the concentrations occurring in nature, with possibly the mediation of an adsorptive concentration onto particulate matter. More work with a wider
variety of samples and substrates is required to decide . . . but the
method looks promising.”
Further work along these lines was reported by Vaccaro and
Jannasch (1966). They used both pure cultures and natural populations in studies of glucose assimilation and obtained results similar
to the earlier ones in that natural substrate levels appeared t o be of
the order of 10-7 M or even as little as l o - * . They were also able t o
estimate the in situ rate of substrate removal. At five stations in the
tropical North Atlantic, samples collected in the upper 50 m gave values