Zooplankton — Bary 
19 
TABLE 2 
General Properties of Waters in the Subantarctic, and off Eastern and Southern New Zealand* 
WATER BODY 
salinity, °/oo 
TEMPERATURE, °C. 
Of Subantarctic Origin 
i. cold subantarctic 
34.0 to 34.3 
8.2 to 10.9 
ii. warmed subantarctic 
34.3 to 34.7 
11 to 13.0 
Of Subtropical Origin 
35.0 to 35.5 
13 to 17.5 plus 
Coastal 
— up to 35 
13 to 16 plus 
* The values listed are derived from the present sampling, but they approximate those given by Deacon ( 1937) for 
waters of subantarctic and subtropical origins. 
strated that for the particular local conditions, 
each is largely confined within certain ranges 
of salinity and temperature (except possibly 
where mixing is taking place), and that each 
occurs in conjunction with species which can 
be stated as undoubtedly resident in the water 
characterised by those properties. They are 
thus useful indicator species under the local 
conditions. 
To cover the conditions which may occur 
in mixed waters it is necessary that indicator 
species are selected as far as possible to in- 
clude a range of adaptabilities. To this end 
more than one species is desirable from each 
water body. Further, several species may pro- 
vide additional information through their 
variable reactions. For example, an adaptable 
species may maintain an association with a 
mixture of particular waters whereas a less 
adaptable one would not. 
Frequent short plankton tows, with cor- 
responding numbers of hydrographic sam- 
ples, might well provide a better index to the 
overall surface conditions in an area than 
fewer hydrographic samples and fewer, but 
longer, tows. The latter may increase the 
quantity of a catch, but may decrease the 
relative accuracy with which the biologic 
sample can be related to the physico-chemical 
conditions. This would apply especially where 
steep gradients may exist, as for example in 
mixing waters. The geographic distributions 
of indicator species selected from the three- 
minute tows of this survey are found to 
closely coincide with the geographic distri- 
butions of their respective waters. This gen- 
eral accord suggests that, although surface 
tows may vary quantitatively and qualitatively 
between one time and place and another, the 
present procedures have largely met the re- 
quirements for this type of study. 
Collections were made as opportunity per- 
mitted. As a consequence two features pos- 
sibly affect the distribution of species in the 
T-S-P diagrams, namely, diurnal migration 
of species and the asynoptic nature of the 
collections. 
The effects of diurnal migration have been 
analysed in some detail. (Times of stations 
are given in Table 4. In this table, and in 
Fig. 3, stations are divided into those occu- 
pied during daylight, at night, and between 
dawn and sunrise, and between sunset and 
dark.) As would be expected, the numbers of 
species and of specimens captured increased 
at night (Table 4) . It was thought that varia- 
tions of this nature might render the T-S-P 
diagram of less value in the selection of indi- 
cator species, and, more especially, for reliably 
correlating their distributions with hydro- 
logical conditions. The fact that several spe- 
cies form an indicator group has some 
bearing. Thus, if the suspected adverse effects 
of diurnal migration on distribution were to 
be realised, all species of a group would have 
to react similarly at the one time. Occasions 
will arise when all species of a group could, 
for example, be absent from the surface at the 
same time. These occasions appear to affect 
group-distribution patterns in the diagrams 
