152
THE BIOLOQY OF EUPHAUSIIDS
four have been shown, conclusively, to perform a diurnal vertical
migration. Lewis (1954) concluded from his data that Xtylocheiron
suhnzii and S . longicorne did not perform a marked migrat,ion but
Moore (1949) presents some evidence of vertical movement in the latter
species. Holt and Tattersall (1905~) present data which are indicative
of a vertical migration in S. suhmii. Contradictory results have been
obtained in species which definitely do, in the majority of cases,
perform such a migration ; for instance, Smith (1879), Paulsen (1909),
and Bigelow (1926) failed to demonstrate a diurnal migration in
Meganyctiphanes norvegica yet the majority of workers who have
examined the behaviour of this species in different sea areas present
conclusive evidence to the contrary. There are, of course, certain
properties both of the organisms themselves and of the environment
which modify the general pattern of the migration and these will be
discussed shortly. Nyctiphanes australis and Euphausia lucens perform
a vertical migration but Bary (1956) only counts those reaching the
surface a t night and gives no further details. Brinton (1967) examined
the vertical migration of euphausiids in the California Current. He
found that Euphausia brevis, E . hemigibba, E . pacijca, E . recurva,
E . gibboides, E. eximia, E . mutica, and Thysanopoda aequalis migrated
from a day time depth of 300-600 m to the surface while Nematoscelis
tenella, N . atlantica, and N . dijicilis migrated from the same depth
upwards to the thermocline ; Nyctiphanes simplex and Stylocheiron
carinatum migrated from about 150 m depth to the surface. He found
that the following species did not migrate vertically : Thysanoessa
gregaria, Nematobrachion boopis, N . Jlexipes, S. afine, S. suhmii, X.
elongatum, S. longicorne, S. abbreviatum, and S. maximum.
Marr (1962) examined the vertical distribution of Euphausia
superba in a most detailed manner and anyone especially interested in
this species must examine his results in detail because only a very brief
summary of them can be given here. E . superba appears to be an
exceptional species of euphausiid in one or two ways. First, it feeds,
frequently almost exclusively, on phytoplankton and we shall return
to this topic when considering the food of euphausiids in general. Since
it is so dependent on phytoplankton, it must spend a considerable time
in near-surface water layers where the diatoms are present and Marr
shows that the majority of the population of this species is in fact
present in these layers both by day and night; further there is considerable doubt about the extent of the diurnal vertical migration
undertaken by this species. The following are the conclusions drawn by
Marr from his data :
THE BIOLOQY OF EUPHAUSIIDS
four have been shown, conclusively, to perform a diurnal vertical
migration. Lewis (1954) concluded from his data that Xtylocheiron
suhnzii and S . longicorne did not perform a marked migrat,ion but
Moore (1949) presents some evidence of vertical movement in the latter
species. Holt and Tattersall (1905~) present data which are indicative
of a vertical migration in S. suhmii. Contradictory results have been
obtained in species which definitely do, in the majority of cases,
perform such a migration ; for instance, Smith (1879), Paulsen (1909),
and Bigelow (1926) failed to demonstrate a diurnal migration in
Meganyctiphanes norvegica yet the majority of workers who have
examined the behaviour of this species in different sea areas present
conclusive evidence to the contrary. There are, of course, certain
properties both of the organisms themselves and of the environment
which modify the general pattern of the migration and these will be
discussed shortly. Nyctiphanes australis and Euphausia lucens perform
a vertical migration but Bary (1956) only counts those reaching the
surface a t night and gives no further details. Brinton (1967) examined
the vertical migration of euphausiids in the California Current. He
found that Euphausia brevis, E . hemigibba, E . pacijca, E . recurva,
E . gibboides, E. eximia, E . mutica, and Thysanopoda aequalis migrated
from a day time depth of 300-600 m to the surface while Nematoscelis
tenella, N . atlantica, and N . dijicilis migrated from the same depth
upwards to the thermocline ; Nyctiphanes simplex and Stylocheiron
carinatum migrated from about 150 m depth to the surface. He found
that the following species did not migrate vertically : Thysanoessa
gregaria, Nematobrachion boopis, N . Jlexipes, S. afine, S. suhmii, X.
elongatum, S. longicorne, S. abbreviatum, and S. maximum.
Marr (1962) examined the vertical distribution of Euphausia
superba in a most detailed manner and anyone especially interested in
this species must examine his results in detail because only a very brief
summary of them can be given here. E . superba appears to be an
exceptional species of euphausiid in one or two ways. First, it feeds,
frequently almost exclusively, on phytoplankton and we shall return
to this topic when considering the food of euphausiids in general. Since
it is so dependent on phytoplankton, it must spend a considerable time
in near-surface water layers where the diatoms are present and Marr
shows that the majority of the population of this species is in fact
present in these layers both by day and night; further there is considerable doubt about the extent of the diurnal vertical migration
undertaken by this species. The following are the conclusions drawn by
Marr from his data :