188
J . E . a. RAYMONT
oceans appears from the recent investigations of Baylor and SutcliBe
(1963). They observed that particulate organic matter may be formed
in sea water when active foaming occurs from the dissolved organic
matter. Riley (1963b) also discusses the adsorption of dissolved organic
matter onto the surface of bubbles to form particles. Such particles
consist not only of organic aggregates, but have interstices which may
then trap bacteria and even plankton and inorganic material. Bacteria
and protozoans may use this substrate and in turn these particles may
serve as food for zooplankton. Riley has shown that this organic aggregate material may be an important accessory food source in inshore
waters. How far such material may be formed in deeper water, where
presumably bubbles are absent, is uncertain. Whatever particulate
material is present could presumably serve as a surface for the adsorption of dissolved organic material. Thus the detritus may not be only
relatively non-assimilable matter.
F. ZOOPLANKTON - QUANTITATIVE FOOD REQULREMENTS
There are several suggested routes, by which the reservoir of dissolved organic matter in the oceans might be transformed into particulate material, but there is little possibility yet of any quantitative
assessment. Indeed, even the quantitative particulate food requirements of individual species of zooplankton are but poorly known. Few
species have been accurately studied, and most investigations have
centred round assessing filtration rates in filter feeders, or in measuring
respiration rates to estimate metabolic requirements (cf. Raymont,
1963). An indication of the quantitative dietary needs of zooplankton
arises from work on copepods, chiefly Calanus.
Despite considerable variations in filtration rate recorded by investigators, a mean rate of 70 cm3/Calanus/day appears to be generally
acceptable. Experiments by Marshall and Orr (1955) using phytoplankton food labelled with 32P and W, however, have suggested rather lower
values. With rates of the order of 70 cm3/day, the average phytoplankton crop in temperate waters should be sufficient to cover maintenance
requirements. But at times of the year phytoplankton is scarce and it
seems unlikely that all the herbivorous plankton will find enough food,
not only for maintenance, but for growth and reproduction. However,
we may be misled by thinking of herbivores as automatic filterers.
Several workers have suggested that food may be actively sought, and
Cushing (1959a) has proposed from his “encounter feeding theory” that
considerably greater quantities of food may be secured. Gauld (1964)
points out that some copepods (Acartia, Centropages, Temora, Pseudocalanus and perhaps Calanus) can feed by a sweeping movement of the
maxillae (“scoop net feeding”) as well as by the usual filtration method.
J . E . a. RAYMONT
oceans appears from the recent investigations of Baylor and SutcliBe
(1963). They observed that particulate organic matter may be formed
in sea water when active foaming occurs from the dissolved organic
matter. Riley (1963b) also discusses the adsorption of dissolved organic
matter onto the surface of bubbles to form particles. Such particles
consist not only of organic aggregates, but have interstices which may
then trap bacteria and even plankton and inorganic material. Bacteria
and protozoans may use this substrate and in turn these particles may
serve as food for zooplankton. Riley has shown that this organic aggregate material may be an important accessory food source in inshore
waters. How far such material may be formed in deeper water, where
presumably bubbles are absent, is uncertain. Whatever particulate
material is present could presumably serve as a surface for the adsorption of dissolved organic material. Thus the detritus may not be only
relatively non-assimilable matter.
F. ZOOPLANKTON - QUANTITATIVE FOOD REQULREMENTS
There are several suggested routes, by which the reservoir of dissolved organic matter in the oceans might be transformed into particulate material, but there is little possibility yet of any quantitative
assessment. Indeed, even the quantitative particulate food requirements of individual species of zooplankton are but poorly known. Few
species have been accurately studied, and most investigations have
centred round assessing filtration rates in filter feeders, or in measuring
respiration rates to estimate metabolic requirements (cf. Raymont,
1963). An indication of the quantitative dietary needs of zooplankton
arises from work on copepods, chiefly Calanus.
Despite considerable variations in filtration rate recorded by investigators, a mean rate of 70 cm3/Calanus/day appears to be generally
acceptable. Experiments by Marshall and Orr (1955) using phytoplankton food labelled with 32P and W, however, have suggested rather lower
values. With rates of the order of 70 cm3/day, the average phytoplankton crop in temperate waters should be sufficient to cover maintenance
requirements. But at times of the year phytoplankton is scarce and it
seems unlikely that all the herbivorous plankton will find enough food,
not only for maintenance, but for growth and reproduction. However,
we may be misled by thinking of herbivores as automatic filterers.
Several workers have suggested that food may be actively sought, and
Cushing (1959a) has proposed from his “encounter feeding theory” that
considerably greater quantities of food may be secured. Gauld (1964)
points out that some copepods (Acartia, Centropages, Temora, Pseudocalanus and perhaps Calanus) can feed by a sweeping movement of the
maxillae (“scoop net feeding”) as well as by the usual filtration method.