4. THE LARVAE
141
Marr concludes that the furciliae of Euphausia superba are restricted
to the surface layers of the Antarctic but by this he means the upper
250 m and that any diurnal vertical movements which they make are
confined within this layer. The main participants in this migration are
the calyptopes and smaller furciliae but the larger furciliae, stages
IV-VI, of E. superba also tend to live in the topmost 50 m of the water
column and are present there throughout the day and night. This is
contrary to other species where these larvae tend to live at deeper
levels in the same depths as the adults and Marr in fact caught at least
three times as many of these larvae in the upper 50 m at night as he
did during the day ; this suggests that they are probably aggregating in
the upper 50 m at night more than during the day but more conclusive
data on the origins of this night population are required.
A re-examination of the data presented in Fig. 52 for species other
than Meganyctiphanes norvegica, Thysanobsa raschii, and Euphausia
superba is now called for in the light of the above discussions. A
pronounced vertical migration of the calyptopes of Pseudeuphausia
latifrons is demonstrated by Wickstead (1961) in a population occurring
in a shallow area, 82 m total depth. The daytime layer of maximum
occurrence of larvae is close to the bottom but this changes to a depth
of about 25 m at night. Baker (1959) also demonstrates a strong
upward movement of calyptopes of Euphausia triacantha to the surface
layers during the night. The migrations of the calyptopes of the other
five species were examined by Lewis (1954) in the coastal area of the
Florida Straits in depths of 700-800 m. Calyptopes of Euphausia brevis,
E. tenera, Thysanopoda tricuspidata and Nematoscelis microps occur
throughout a wide range of depth but there is a tendency for their layers
of maximum abundance to be close to the surface. The layer of maximum abundance of the corresponding larvae of Stylocheiron carinatum
occurs between 200 and 100 m from the surface, that is lower than those
of the others; this was the commonest species in Lewis’s hauls. No
diurnal vertical migration of the calyptopes of any of these species is
evident, except possibly in the case of Euphausia brevis where a surface
aggregation appears to take place at night.
A diurnal vertical migration of the furciliae clearly takes place in
E. triacantha, Thysanopoda tricuspidata, and Stybcheiron carinatum and
there are indications of such a movement in larvae of Euphausia tenera
and Nematoscelis microps. Lewis did not have enough samples of
furciliae of Euphausia brevis to provide a conclusive ,result and the
same applies to Wickstead (1961) for Pseudeuphausia latifrons. Hardy
and Gunther (1935) present data which indicate a diurnal vertical
migration of furciliae of Euphausia frigida and possibly also of the
141
Marr concludes that the furciliae of Euphausia superba are restricted
to the surface layers of the Antarctic but by this he means the upper
250 m and that any diurnal vertical movements which they make are
confined within this layer. The main participants in this migration are
the calyptopes and smaller furciliae but the larger furciliae, stages
IV-VI, of E. superba also tend to live in the topmost 50 m of the water
column and are present there throughout the day and night. This is
contrary to other species where these larvae tend to live at deeper
levels in the same depths as the adults and Marr in fact caught at least
three times as many of these larvae in the upper 50 m at night as he
did during the day ; this suggests that they are probably aggregating in
the upper 50 m at night more than during the day but more conclusive
data on the origins of this night population are required.
A re-examination of the data presented in Fig. 52 for species other
than Meganyctiphanes norvegica, Thysanobsa raschii, and Euphausia
superba is now called for in the light of the above discussions. A
pronounced vertical migration of the calyptopes of Pseudeuphausia
latifrons is demonstrated by Wickstead (1961) in a population occurring
in a shallow area, 82 m total depth. The daytime layer of maximum
occurrence of larvae is close to the bottom but this changes to a depth
of about 25 m at night. Baker (1959) also demonstrates a strong
upward movement of calyptopes of Euphausia triacantha to the surface
layers during the night. The migrations of the calyptopes of the other
five species were examined by Lewis (1954) in the coastal area of the
Florida Straits in depths of 700-800 m. Calyptopes of Euphausia brevis,
E. tenera, Thysanopoda tricuspidata and Nematoscelis microps occur
throughout a wide range of depth but there is a tendency for their layers
of maximum abundance to be close to the surface. The layer of maximum abundance of the corresponding larvae of Stylocheiron carinatum
occurs between 200 and 100 m from the surface, that is lower than those
of the others; this was the commonest species in Lewis’s hauls. No
diurnal vertical migration of the calyptopes of any of these species is
evident, except possibly in the case of Euphausia brevis where a surface
aggregation appears to take place at night.
A diurnal vertical migration of the furciliae clearly takes place in
E. triacantha, Thysanopoda tricuspidata, and Stybcheiron carinatum and
there are indications of such a movement in larvae of Euphausia tenera
and Nematoscelis microps. Lewis did not have enough samples of
furciliae of Euphausia brevis to provide a conclusive ,result and the
same applies to Wickstead (1961) for Pseudeuphausia latifrons. Hardy
and Gunther (1935) present data which indicate a diurnal vertical
migration of furciliae of Euphausia frigida and possibly also of the