108
GORDON A . RILEY
Coming back to the earlier comments about a “rain of detritus
from the surface ”, faecal pellets derived from the surface can sink
quite rapidly and conceivably could arrive in the bathypelagic zone
before their organic content, such as it is, has been seriously depleted
by bacterial activity. Most of the other suspended matter would have
a residence time ranging from one year to many years, and there is
little likelihood that any biologically usable fraction of it could escape
consumption by one means or another during that period. The continued existence of particles containing a significant fraction of usable
substances (as indicated for example by hydrolysis experiments
quoted above) must be due to in situ processes. There are indications
that particles can form de novo. There are also indications of interchanges of simple molecules such as amino acids between the dissolved
organic pool and various kinds of particulate matter, living and dead.
The pathways are complex and probably have not all been properly
identified. Our knowledge of probable rates of exchange is very limited.
The rates are low, due to the dilute nature of the medium, and it will
be a very difficult job indeed to obtain realistic information on natural
rates of exchange.
Possibly carnivorous activity is quantitatively more important than
heterotrophic processes in energy transfer and vertical flux of materials
toward the bottom. This remains to be seen. Present information is
crude and equivocal. However, heterotrophy is more important than
was realized until recently, and by the same token there is opportunity
for complexity and diversification of food web relations to a degree
perhaps approaching that of the surface layer.
Finally we come to a consideration of deposition and utilization of
organic matter on the bottom. Analyses of the carbon content of deep
water particulate matter have indicated that it is probably of the order
of 10-30% of the dry weight, although some records of as little as 1%
have been reported. However, bottom sediments in deep ocean basins
commonly contain only a fraction of 1 % of organic carbon, so that
most of this material must be consumed on the bottom. The ocean
bottom is of course a more favorable site for organic consumption than
is the water column. Abundant surfaces are provided for bacterial
growth, and presumably dissolved materials are more highly concentrated in the interstitial water than in the free water above. Compaction of organic matter into a relatively small volume makes it readily
available to sediment feeders, and although the bottom fauna is sparse
in the deep ocean compared with shallower areas, it is more concentrated than the bathypelagic assemblage.
Estimates of biological activity of the benthic population are no
GORDON A . RILEY
Coming back to the earlier comments about a “rain of detritus
from the surface ”, faecal pellets derived from the surface can sink
quite rapidly and conceivably could arrive in the bathypelagic zone
before their organic content, such as it is, has been seriously depleted
by bacterial activity. Most of the other suspended matter would have
a residence time ranging from one year to many years, and there is
little likelihood that any biologically usable fraction of it could escape
consumption by one means or another during that period. The continued existence of particles containing a significant fraction of usable
substances (as indicated for example by hydrolysis experiments
quoted above) must be due to in situ processes. There are indications
that particles can form de novo. There are also indications of interchanges of simple molecules such as amino acids between the dissolved
organic pool and various kinds of particulate matter, living and dead.
The pathways are complex and probably have not all been properly
identified. Our knowledge of probable rates of exchange is very limited.
The rates are low, due to the dilute nature of the medium, and it will
be a very difficult job indeed to obtain realistic information on natural
rates of exchange.
Possibly carnivorous activity is quantitatively more important than
heterotrophic processes in energy transfer and vertical flux of materials
toward the bottom. This remains to be seen. Present information is
crude and equivocal. However, heterotrophy is more important than
was realized until recently, and by the same token there is opportunity
for complexity and diversification of food web relations to a degree
perhaps approaching that of the surface layer.
Finally we come to a consideration of deposition and utilization of
organic matter on the bottom. Analyses of the carbon content of deep
water particulate matter have indicated that it is probably of the order
of 10-30% of the dry weight, although some records of as little as 1%
have been reported. However, bottom sediments in deep ocean basins
commonly contain only a fraction of 1 % of organic carbon, so that
most of this material must be consumed on the bottom. The ocean
bottom is of course a more favorable site for organic consumption than
is the water column. Abundant surfaces are provided for bacterial
growth, and presumably dissolved materials are more highly concentrated in the interstitial water than in the free water above. Compaction of organic matter into a relatively small volume makes it readily
available to sediment feeders, and although the bottom fauna is sparse
in the deep ocean compared with shallower areas, it is more concentrated than the bathypelagic assemblage.
Estimates of biological activity of the benthic population are no