104
GORDON A. RILEY
particulate matter in the water column rather than from the dissolved
fraction. There is a further implication in his results that the dissolved
matter is older and has gone through more metabolic transformations
than the particulate fraction. This sort of conclusion could be valid as
a generalization without denying the concept developed above that a
small fraction of the dissolved material is new and metabolically
usable.
The problem of estimating zooplankton food requirements and
feeding rates is not an easy one. Experimental estimates vary widely,
and probably there are similar variations in nature. The problem is
particularly difficult in the present case because most of the experimental information has been obtained from surface forms. Our opinion
about what bathypelagic organisms eat is largely a matter of inference,
based upon the character of their mouth parts. The question is largely
unresolved as to whether there are local concentrations of food that
ameliorate the average picture of extreme scarcity. There is as yet no
clear answer to the question of whether food requirements and metabolic rates in the deep sea are essentially similar to those of nearsurface waters.
Attempts to investigate pressure effects have led to somewhat
equivocal results. Napora (1964) reported that pressure slightly increased the respiratory rate of Xystellaspis debilis, a prawn which is a
member of the mid-depth population that migrates to the surface at
night. He was working with animals that live in the Sargasso Sea,
where the thermocline is not particularly steep, and the effect of
decreasing temperature as the animals moved downward was approximately balanced by the pressure effect, so that the animals maintained
an essentially constant respiratory rate at all depths. Teal and Carey
(1967) found a significant pressure effect with Thysanopoda monocantha,
a euphausiid which normally lives at mid-depths and apparently does
not come to the surface at night. However, they tested several migratory euphausiids and found that pressure effects were operative only
at temperatures that were too high to be of any significance at the daytime level. Pearcy and Small (1968) examined two euphausiids and a
prawn, all migratory forms, and found no significant pressure effects.
I n short, no consistent pattern emerges among the mid-depth forms,
and the writer has failed to find any information on truly bathypelagic
animals. Provisionally the problem must be considered in terms of
what is known about surface forms although the deep sea environment
may have a significant effect on physiological rates.
Present estimates of zooplankton respiratory requirements have
been based upon measurements of oxygen consumption of surface
GORDON A. RILEY
particulate matter in the water column rather than from the dissolved
fraction. There is a further implication in his results that the dissolved
matter is older and has gone through more metabolic transformations
than the particulate fraction. This sort of conclusion could be valid as
a generalization without denying the concept developed above that a
small fraction of the dissolved material is new and metabolically
usable.
The problem of estimating zooplankton food requirements and
feeding rates is not an easy one. Experimental estimates vary widely,
and probably there are similar variations in nature. The problem is
particularly difficult in the present case because most of the experimental information has been obtained from surface forms. Our opinion
about what bathypelagic organisms eat is largely a matter of inference,
based upon the character of their mouth parts. The question is largely
unresolved as to whether there are local concentrations of food that
ameliorate the average picture of extreme scarcity. There is as yet no
clear answer to the question of whether food requirements and metabolic rates in the deep sea are essentially similar to those of nearsurface waters.
Attempts to investigate pressure effects have led to somewhat
equivocal results. Napora (1964) reported that pressure slightly increased the respiratory rate of Xystellaspis debilis, a prawn which is a
member of the mid-depth population that migrates to the surface at
night. He was working with animals that live in the Sargasso Sea,
where the thermocline is not particularly steep, and the effect of
decreasing temperature as the animals moved downward was approximately balanced by the pressure effect, so that the animals maintained
an essentially constant respiratory rate at all depths. Teal and Carey
(1967) found a significant pressure effect with Thysanopoda monocantha,
a euphausiid which normally lives at mid-depths and apparently does
not come to the surface at night. However, they tested several migratory euphausiids and found that pressure effects were operative only
at temperatures that were too high to be of any significance at the daytime level. Pearcy and Small (1968) examined two euphausiids and a
prawn, all migratory forms, and found no significant pressure effects.
I n short, no consistent pattern emerges among the mid-depth forms,
and the writer has failed to find any information on truly bathypelagic
animals. Provisionally the problem must be considered in terms of
what is known about surface forms although the deep sea environment
may have a significant effect on physiological rates.
Present estimates of zooplankton respiratory requirements have
been based upon measurements of oxygen consumption of surface