PARTICULATE ORGANIC MATTER I N SEA WATER
107
of food. Work by Conover (1964) on Calanus hyperboreus is useful in
evaluating this problem.
This copepod is a surface form in high latitudes and is a minor
constituent of the bathypelagic fauna of lower latitudes. It is well
adapted to the rigors of its normal habitat at the surface, where food
is abundant in summer but virtually absent during much of the year.
Conover has demonstrated that there is a high rate of accumulation of
stored fat when it is fed at an optimal level, and it can survive starvation for some months with a reduced rate of metabolism that conserves
its stored food.
Conover found that the normal daily food requirement at low
temperature is about I yo of the weight of the animal ; under starvation
conditions carbon consumption is reduced to as little as 0.4%. According to average grazing estimates presented earlier a 1 yo respiratory
requirement would be accompanied by a filtering rate of about 235 ml
of water per milligram of zooplankton carbon in a day. This filtration
rate would require a concentration of 17 pgllitre of assimiIable carbon
to supply a maintenance ration even at a reduced level approaching
starvation metabolism. Most of the values that have been reported
for deep water particulate carbon fall within the general range of 1050pgC/litre, which appears to be inadequate unless it is more completely assimilable than is indicated by experiments with enzymes
(Gordon, 1970b). As far as present information is concerned, there is
little likelihood that bathypelagic organisms can support themselves
solely by indiscriminate filter feeding.
According to Conover ( I 964) C. hyperboreus is capable of either
selective capture or filter feeding, and the present discussion points
toward a tentative conclusion that this kind of feeding habit is essential
for bathypelagic copepods with foliaceous appendages. Possible food
materials would include smaller zooplankton, living and dead, large
aggregates, and faecal pellets. Reports by divers of " marine snow "
indicate that there are organic aggregates of visible size in the deep
ocean. These presumably have a fairly rapid sinking rate, and the
number delivered into deep water may be much greater than might
be inferred from the relative scarcity of large aggregates in water
samples. Faecal pellets of visible size can sink at rates of 50-375 m/day
(Smayda, personal communication). They, too, may be a source of
particulate food that is much more important than would be suspected
on the basis of their relative abundance. These various sources can
only be mentioned in passing. Little can be said about their nutritive
value or rate of supply. Certainly the sparse nature of the bathypelagic
population is sufficient evidence that the food supply is minimal.
107
of food. Work by Conover (1964) on Calanus hyperboreus is useful in
evaluating this problem.
This copepod is a surface form in high latitudes and is a minor
constituent of the bathypelagic fauna of lower latitudes. It is well
adapted to the rigors of its normal habitat at the surface, where food
is abundant in summer but virtually absent during much of the year.
Conover has demonstrated that there is a high rate of accumulation of
stored fat when it is fed at an optimal level, and it can survive starvation for some months with a reduced rate of metabolism that conserves
its stored food.
Conover found that the normal daily food requirement at low
temperature is about I yo of the weight of the animal ; under starvation
conditions carbon consumption is reduced to as little as 0.4%. According to average grazing estimates presented earlier a 1 yo respiratory
requirement would be accompanied by a filtering rate of about 235 ml
of water per milligram of zooplankton carbon in a day. This filtration
rate would require a concentration of 17 pgllitre of assimiIable carbon
to supply a maintenance ration even at a reduced level approaching
starvation metabolism. Most of the values that have been reported
for deep water particulate carbon fall within the general range of 1050pgC/litre, which appears to be inadequate unless it is more completely assimilable than is indicated by experiments with enzymes
(Gordon, 1970b). As far as present information is concerned, there is
little likelihood that bathypelagic organisms can support themselves
solely by indiscriminate filter feeding.
According to Conover ( I 964) C. hyperboreus is capable of either
selective capture or filter feeding, and the present discussion points
toward a tentative conclusion that this kind of feeding habit is essential
for bathypelagic copepods with foliaceous appendages. Possible food
materials would include smaller zooplankton, living and dead, large
aggregates, and faecal pellets. Reports by divers of " marine snow "
indicate that there are organic aggregates of visible size in the deep
ocean. These presumably have a fairly rapid sinking rate, and the
number delivered into deep water may be much greater than might
be inferred from the relative scarcity of large aggregates in water
samples. Faecal pellets of visible size can sink at rates of 50-375 m/day
(Smayda, personal communication). They, too, may be a source of
particulate food that is much more important than would be suspected
on the basis of their relative abundance. These various sources can
only be mentioned in passing. Little can be said about their nutritive
value or rate of supply. Certainly the sparse nature of the bathypelagic
population is sufficient evidence that the food supply is minimal.