Pelagic Tunicata — Bary 
119 
FIG. 23- Diurnal variation of numbers of specimens 
(collected at the surface) of Oikopleura dioica, 0. 
fusiformis, and Ihlea magalhanica, as shown when the 
average catch per four-hour period is expressed as a 
percentage of the totalled average catches. 
Foveaux Strait in water of subtropical origin 
(where it occurred with Thalia democratica ) . 
Again, when occurrences are plotted against 
salinity and temperature (Fig. 21) a distinct 
preference is demonstrated for the warmest 
water, which Bary (1959^) regards as being 
influenced by water of subtropical origin. The 
temperatures given by Thompson (11.6° to 
22.25° C.) are inclusive of the range for sub- 
tropical water, given by Deacon (1937). The 
evidence from the present material, and possibly 
that from Thompson also, suggests the species 
may have subtropical, rather than cold-water 
origins. 
DIURNAL MIGRATION 
As the collections being considered are from 
the surface waters, diurnal migration can only 
be inferred from the variation of numbers be- 
tween day and night samples. Oikopleura dioica, 
0. fusiformis, and Ihlea magalhanica occur spas- 
modically, but if the average four-hour catch is 
plotted as a percentage of the totalled average 
catches (Fig. 23) some smoothing of their oc- 
currences is introduced. It is then found that 
0. dioica and I. magalhanica increase to a high 
percentage in the early evening (at 1800 to 
1900 hours in untreated data). Ihlea magal- 
hanica is present otherwise in comparatively 
small numbers, while O. dioica tends to occur 
throughout the day. Oikopleura fusiformis was 
present in markedly high numbers at 2400 
hours (2400 to 0100 hours in untreated data), 
and again, but in lower numbers, at 1600 hours 
(two peaks, one at 1500 and the other at 1700 
hours, in untreated data) . Thus there are indica- 
tions that numbers increase towards evening, or 
during darkness. However, the shoaling of salps, 
and, to judge from their irregular... appearances, 
a tendency to swarming among appendicu- 
larians, makes any other than these tentative 
conclusions unwarranted. 
In connection with vertical migration among 
tunicates, Russell and Colman (1935) showed 
that in the area of the Great Barrier Reef ap- 
pendicularians migrated to near the surface be- 
tween 2100 and 2325 hours and sank during 
daylight, when they concentrated at about 10 m. 
Mackintosh (1934: 94) and Hardy (1936: 521) 
illustrate and discuss vertical migration among 
salps, including the effects of swarming. It is 
shown that increases occur at or near the surface 
around midnight if due allowance is made for 
the existence of the swarms. It is probable, 
therefore, that the increases illustrated in Fig- 
ure 23 to some extent are the result of vertical 
migration, although further sampling will al- 
most certainly refine the patterns obtained. 
Variation of numbers at the surface is shown 
by Dolioletta valdiviae for Stations 74 to 85 (at 
these stations the net was streamed in a tidal 
stream whilst the ship was at anchor, see Bary, 
1956). The combined gonozooids, phorozooids, 
and old nurses (Fig. 24) increase in numbers to 
a peak at 2200 hours, decline to zero at 2400 
hours, and increase to a second peak at 0200 
hours. Data concerning doliolids for Station 83 
Fig. 24. Variation of numbers of the gonozooid, 
phorozooid, old nurse, and totalled specimens of 
Dolioletta valdiviae, during the course of one night 
when the ship was anchored and the net was streamed 
in a tidal stream. 
