THE PRODUCTION O F MARINE PLANKTON
185
a more detailed study of the food requirements of different species of
barnacles. Ohlorella and Dunaliella were valueless apparently for all
species. Balanus balanoides was successfully reared on diatoms (Skeletonema, Ditylum, Asterionella), but not on flagellate diet. On the other
hand, Chthamalus could be reared on severd flagellate species, but
diatoms were not utilized.
Most fish larvae, though they may take a small amount of phytoplankton food in early stages, feed mainly on zooplankton. Cod larvae
feed on euphausids, decapod larvae, and other crustaceans; occasionally
they take the larvae of other fishes (Wiborg, 1948a and b, 1949). Most
investigators have emphasized the importance of copepods as food for
larvae of fishes, and both Marak (1960) and Wiborg emphasize the
question of size selection. However, there may be a greater degree of
selectivity. Shelbourne (1963, 1957, 1962) showed that while small copepod nauplii were taken by larval plaice, the appendicularian Oikopleura was the most important constituent in the diet. Ryland (1964)
has recently confirmed the overwhelming importance of both Oikopleura and Pritillaria as food for larval plaice. Except for fish larvae, our
knowledge of the food habits of carnivorous zooplankton is particularly I
fragmentary. Pelagic heteropods are known to feed on copepods but to
a large extent on chaetognaths. Medusae and ctenophores are known to
feed on copepods, on sagittae and on fish 1arva)e. The ctenophore Beroe
feeds on Pleurobrachia; apparently in Russian waters it feeds exclusively
on Bolinopsis. The siphonophores are an exclusively carnivorous group
feeding on such zooplankton as copepods and other crustaceans, but
recently, in Florida waters, Bayer (1963) ha:3 observed that Velella,
Porpita, and even Physalia are themselves eaten by the snail Janthina.
Although our knowledge is limited, the complexity of the zooplankton ,
food net is quite extraordinary. Our knowledge of the diet of bathypelagic plankton is far less. Most deep-sea plankton has been regarded
as filtering out detritus particles, or being carnivorous on other plankton. Vinogradov (1962b) has pointed out that small particles will decompose fairly rapidly during their descent into the deep layers and ,
probably only the resistant non-assimilable fraction remains.
The problem of how far bacteria might add to the food of zooplankton
has been investigated to some extent, mainly with surface plankton
animals, chiefly copepods and bivalve larvae. I11 general, bacteria seem
to be unimportant. In any event, in really deep water most microbiologists suggest that the bacterial population is very much reduced;
there is doubt whether it could add significantlj to the diet of the larger
zooplankton. It is possible that bathypelagi c plankton (copepods,
mysids, and decapods) could filter off Radiolaria and Foraminifera
occurring in the deeper water layers (cf. Vinogrsdov, 1962b). We do not
185
a more detailed study of the food requirements of different species of
barnacles. Ohlorella and Dunaliella were valueless apparently for all
species. Balanus balanoides was successfully reared on diatoms (Skeletonema, Ditylum, Asterionella), but not on flagellate diet. On the other
hand, Chthamalus could be reared on severd flagellate species, but
diatoms were not utilized.
Most fish larvae, though they may take a small amount of phytoplankton food in early stages, feed mainly on zooplankton. Cod larvae
feed on euphausids, decapod larvae, and other crustaceans; occasionally
they take the larvae of other fishes (Wiborg, 1948a and b, 1949). Most
investigators have emphasized the importance of copepods as food for
larvae of fishes, and both Marak (1960) and Wiborg emphasize the
question of size selection. However, there may be a greater degree of
selectivity. Shelbourne (1963, 1957, 1962) showed that while small copepod nauplii were taken by larval plaice, the appendicularian Oikopleura was the most important constituent in the diet. Ryland (1964)
has recently confirmed the overwhelming importance of both Oikopleura and Pritillaria as food for larval plaice. Except for fish larvae, our
knowledge of the food habits of carnivorous zooplankton is particularly I
fragmentary. Pelagic heteropods are known to feed on copepods but to
a large extent on chaetognaths. Medusae and ctenophores are known to
feed on copepods, on sagittae and on fish 1arva)e. The ctenophore Beroe
feeds on Pleurobrachia; apparently in Russian waters it feeds exclusively
on Bolinopsis. The siphonophores are an exclusively carnivorous group
feeding on such zooplankton as copepods and other crustaceans, but
recently, in Florida waters, Bayer (1963) ha:3 observed that Velella,
Porpita, and even Physalia are themselves eaten by the snail Janthina.
Although our knowledge is limited, the complexity of the zooplankton ,
food net is quite extraordinary. Our knowledge of the diet of bathypelagic plankton is far less. Most deep-sea plankton has been regarded
as filtering out detritus particles, or being carnivorous on other plankton. Vinogradov (1962b) has pointed out that small particles will decompose fairly rapidly during their descent into the deep layers and ,
probably only the resistant non-assimilable fraction remains.
The problem of how far bacteria might add to the food of zooplankton
has been investigated to some extent, mainly with surface plankton
animals, chiefly copepods and bivalve larvae. I11 general, bacteria seem
to be unimportant. In any event, in really deep water most microbiologists suggest that the bacterial population is very much reduced;
there is doubt whether it could add significantlj to the diet of the larger
zooplankton. It is possible that bathypelagi c plankton (copepods,
mysids, and decapods) could filter off Radiolaria and Foraminifera
occurring in the deeper water layers (cf. Vinogrsdov, 1962b). We do not