250
THE BIOLOGY OF EUPHAUSIIDS
case, be a I ‘ capture rate ” and that some degree of hunting or seeking
of prey may take place so that nauplii are not simply found by random
swimming and filtering of the water. This adds support to the results of
Ponomareva (1955), which are discussed in Chapter 6 ; she found that
the euphausiids tended to have remains of luminescent copepods present
among their stomach contents more frequently than those of nonluminescent copepods and, of course, this presupposes some selection of
prey. On the other hand, Mauchline (1960) and David and Conover
(1 961) found no evidence suggesting that Meganyctiphanes norvegica
stalked or hunted its prey.
The rates a t which euphausiids pass water through their mouthparts
while filter feeding have been estimated on two occasions (Raymont and
Conover, 1961 ; Lasker, 1966). The results of these experiments are
shown in Table XXVII. The highest filtering rates, other than those
previously quoted in the case of Artemia nauplii, are those for
Platymonas su~cordi~ormis (= Tetraselmis subcordiformis (Wille)
Butcher) and Gonyaulax polyedra Stein, with Dunaliella tertiolecta
Butcher coming third. Lasker found notably lower filtering rates when
Thalassiosira Jluviatilis Hustedt was used as the food organism and
suggests that this species may be partially rejected as food. It is interesting to note that Raymont and Conover also obtained lower filtering
rates when using this organism instead of Skeletonerna costatum although
the results when using the latter organism were also low when compared
to Lasker’s estimates. Consequently, there may be some rejection of
S. costatum as well. As Lasker points out, laboratory estimates of
filtering rates may be misleading because frequently the densities of
food organisms used to determine them are not the same as occur, on
average, in the environment. Nevertheless, they give an estimate of
what the animals are capable of and Lasker concluded from environmental data that “ the total amount of particulate carbon available
in the sea is adequate to maintain Euphausia pacifica a t the filtering
rates determined in the laboratory. Phytoplankton cells alone would
not suffice (Bainbridge, 1957). It is more likely, however, that E. pacijica
depends in large part on its ability to exploit aggregations of copepods
than on its marginal ability to filter enough carbon from a dilute
suspension ”. Detritus, however, has been noted as a food of E. pacijca
(Table VIII) and this is probably an important source of nutrition in
this species as in many other species of euphausiids. Purther, the
amount of detritus obtained from the sea bed is not entirely dependent
on the potential rates of filter-feeding of the euphausiids because it
can be collected by a
These experiments of Lasker, although requiring further support
shovelling ” technique (Fig. 64).
THE BIOLOGY OF EUPHAUSIIDS
case, be a I ‘ capture rate ” and that some degree of hunting or seeking
of prey may take place so that nauplii are not simply found by random
swimming and filtering of the water. This adds support to the results of
Ponomareva (1955), which are discussed in Chapter 6 ; she found that
the euphausiids tended to have remains of luminescent copepods present
among their stomach contents more frequently than those of nonluminescent copepods and, of course, this presupposes some selection of
prey. On the other hand, Mauchline (1960) and David and Conover
(1 961) found no evidence suggesting that Meganyctiphanes norvegica
stalked or hunted its prey.
The rates a t which euphausiids pass water through their mouthparts
while filter feeding have been estimated on two occasions (Raymont and
Conover, 1961 ; Lasker, 1966). The results of these experiments are
shown in Table XXVII. The highest filtering rates, other than those
previously quoted in the case of Artemia nauplii, are those for
Platymonas su~cordi~ormis (= Tetraselmis subcordiformis (Wille)
Butcher) and Gonyaulax polyedra Stein, with Dunaliella tertiolecta
Butcher coming third. Lasker found notably lower filtering rates when
Thalassiosira Jluviatilis Hustedt was used as the food organism and
suggests that this species may be partially rejected as food. It is interesting to note that Raymont and Conover also obtained lower filtering
rates when using this organism instead of Skeletonerna costatum although
the results when using the latter organism were also low when compared
to Lasker’s estimates. Consequently, there may be some rejection of
S. costatum as well. As Lasker points out, laboratory estimates of
filtering rates may be misleading because frequently the densities of
food organisms used to determine them are not the same as occur, on
average, in the environment. Nevertheless, they give an estimate of
what the animals are capable of and Lasker concluded from environmental data that “ the total amount of particulate carbon available
in the sea is adequate to maintain Euphausia pacifica a t the filtering
rates determined in the laboratory. Phytoplankton cells alone would
not suffice (Bainbridge, 1957). It is more likely, however, that E. pacijica
depends in large part on its ability to exploit aggregations of copepods
than on its marginal ability to filter enough carbon from a dilute
suspension ”. Detritus, however, has been noted as a food of E. pacijca
(Table VIII) and this is probably an important source of nutrition in
this species as in many other species of euphausiids. Purther, the
amount of detritus obtained from the sea bed is not entirely dependent
on the potential rates of filter-feeding of the euphausiids because it
can be collected by a
These experiments of Lasker, although requiring further support
shovelling ” technique (Fig. 64).