Zooplankton — Bary 
33 
(1924) appreciation of its distribution. Thus 
the distribution of these species as shown in 
the T-S-P diagram (Fig. 7) agrees with previ- 
ous accounts. The distribution of P. parvus is 
restricted to that recorded previously (see 
p. 17). 
The distributions of the species and the 
numbers captured relative to temperatures 
and salinities are shown in Figure 7. It is evi- 
dent that the numbers taken were often large. 
All species were strongly represented at Sta- 
tions 292, 330, 310, 79, etc., and 189, 190, 
(referred to as being in mixed waters in the 
discussion of the Southern Subantarctic 
Group), but are present only as rarities, or are 
absent from collections at other stations in 
coastal-subtropical waters. Reduced numbers 
were taken at Stations 212 and 214 in colder 
waters. As these were night stations this re- 
duction may be a reflection of the effects of 
the lower temperatures. At some other sta- 
tions in these colder waters, e.g., Stations 5, 
191 , 6, specimens were absent or rare, but 
this may be a result of the stations being 
occupied in daylight. 
Not only do the Northern Subantarctic 
species inhabit the comparatively warmer wa- 
ter of subantarctic origin, but they can pene- 
trate into warm mixed waters in larger num- 
bers than any of the Southern Group of spe- 
cies. This may be consequent on their adapta- 
tion to higher temperatures in their more us- 
ual habitat. According to John (1936), there 
is a gradual amelioration of conditions, with 
changes in the composition of the planktonic 
fauna to correspond, as one proceeds from 
colder to warmer northern waters in the sub- 
antarctic. Therefore the abrupt transition sug- 
gested by the convenient subdivision of the 
species into Northern and Southern Subant- 
arctic Groups probably over simplifies the 
faunal distribution. Further sampling at tem- 
peratures lower than 11°C. may demonstrate 
a gradual decrease in the frequency of occur- 
rences and in the number of species taken of 
the Northern Subantarctic Group — a decrease 
which would accord with John’s views. How- 
ever, such would not necessarily detract from 
either the Southern or Northern groups of 
species as indicators of the particular condi- 
tions for which they have been selected. 
Subtropical Group 
The species of the Subtropical Group have 
been selected on the basis of their previous 
distributional records. Although detailed sam- 
pling is required in those New Zealand waters 
which are beyond doubt of subtropical origin 
in order to demonstrate that the species origi- 
nated there, it is believed that they are typi- 
cally of the subtropical population. The 
species selected are Sapphirina sp., S. angusta 
Dana, S. gemma Dana, S. salt Farran, and S. 
pyrosomatis Giesbrecht (see Wilson, 1932), 
Ihlea magalhanica Apstein, Thalia democratica 
Forskal (see Thompson, 1942, 1948), and 
Hyperoche mediterranea Senna (Stephensen, 
1924 , Hurley, 1955). Of these, H. mediterranea 
did not occur at Stations 322 and 326, and 
Sapphirina spp. were taken only at these 
stations. 
The wide range of salinities (Fig. 8) over 
which these species are taken points to their 
tolerance in this regard. On the other hand, 
the species maintain a close association with 
the warmest water and only exceptionally are 
specimens taken outside of it. The group thus 
strongly contrasts with the two Subantarctic 
groups. 
The species of this group are normally as- 
sociated with subtropical water. In this survey 
they occur largely in the warmest water (Fig. 
8), and therefore it is suggested that this 
water is of, or is being influenced by, water of 
subtropical origin. Except for Stations 322 
and 326, the majority of the collections of the 
Subtropical species were from stations of 
Series 1 (see Figs. 1, 3), mostly within 
Foveaux Strait, i.e., within the area expected 
to be most strongly influenced by any east- 
ward flow of water from subtropical sources. 
The few other occurrences of the species 
usually are associated with coastwise exten- 
sions of the subtropical influence. 
