324 
PACIFIC SCIENCE, Vol. XIII, October, 1959 
subantarctic water, and again the mixture of 
species results. At these stations there is a 
slightly stronger influence of coastal water 
than in the previous examples, as shown by 
higher salinities (Fig. 1). The absence of any 
subtropical species at 187 and 189 suggests 
little influence from water of this source. 
The isotherms for January (Series 5, Fig. 
Ga, b) indicate that water of subantarctic 
origin extends at least to Cook Strait. One or 
both of the subantarctic species Parathemisto 
gaudkhaudii and Cyllopus magellanicus are pres- 
ent at four of the six stations. They are absent 
from Stations 3 and 4. This, together with 
salinities which are a little higher than in 
neighbouring subantarctic water (Fig. 1), in- 
dicates that those stations are being influenced 
by coastal water, probably from south of 
Banks Peninsula. Although this water does 
not exclude subantarctic species, it supplies a 
reason as to why Parathemisto gracilipes occurs 
at Station 3 (and also why other species of the 
Coastal Group were present at both Stations 3 
and 4). In Figure Gd, e, the subtropical con- 
vergence transects the series. Subantarctic 
species are present at Stations 337 and 330; 
P. gracilipes is also present at Station 330, and 
both P. gracilipes and P. australis at 322. Sta- 
tion 322, north of the convergence, is in 
mixed subtropical-coastal waters (Figs. 1, 2) 
and the occurrence there of a coastal species 
is consistent. Species from all groups are to 
be expected at Station 330. It is shown by the 
mixture of zooplankton to be situated in 
mixing waters in the T-S-P diagram (Fig. 2), 
and this is borne out by its geographical lo- 
cation near or within the mixing area between 
waters originating in the subtropical and sub- 
antarctic masses (Fig. Gd, e). 
Perhaps the most important feature illus- 
trated by Figure 6 is that the two subantarctic 
species, few in individuals though they are, 
are present only in water believed to have 
originated in the subantarctic. They act as 
indicators and demonstrate the northward ex- 
tent of subantarctic water, as well as demarcate 
the approximate position of the subtropical 
convergence in March, 1951. 
It perhaps should be emphasised at this 
point that in the southeast coastal area of 
New Zealand, where mixed waters of diverse 
origins predominate, it would be most diffi- 
cult to disentangle the sources of the waters 
and the species from charts of distributions 
alone. Interpretations would be largely de- 
ductive and subjective. The T-S-P diagram 
demonstrates in a clear and effective manner, 
the source of both the waters and the species 
in the area. At the same time it provides a 
means of utilising occurrences of species to 
follow the trends of water movements. Thus 
the occurrences of species of plankton at cer- 
tain localities, and of the means by which 
they arrived at their point of capture, can be 
explained with a fair degree of certainty. 
Rare species are symbolised in Figures 2,5, 
and 6 by their initial letters. Occurrences of 
one or a few species, on one or two occasions, 
are often insignificant in distributional stud- 
ies. In the context of the T-S-P diagram 
(Fig. 2), however, their occurrences may assist 
in the interpretation of conditions; conversely, 
the conditions in which they occur may assist 
in interpreting other features concerning the 
species, e.g., see a later discussion of Para- 
themisto spp. 
The cold-water species Hyperia spinigera is 
demonstrated as being captured in water of 
subantarctic origin (Station 210, Figs. 2, 5g) — 
water in which the species is normally resi- 
dent. Hyperoche medusarum Kroyer, another 
cold-water species, occurs at Station 79 (Figs. 
2, ^a). This might be regarded as a stray 
specimen, but the presence of small numbers 
of other species of the Subantarctic groups, 
e.g., Copepoda, suggests an intrusion of wa- 
ter of subantarctic origin towards this station. 
Two species present at Station 79 are of sub- 
tropical origin, namely Platyscelus ovoides 
(Claus) and Paralycaea gracilis Claus. These, 
and probably also Hyperia hengalensis, are re- 
garded as entering, along with water of sub- 
tropical origin, into Foveaux Strait from the 
west. As would be expected, undoubted cos- 
