Species of Zooplankton as a Means of Identifying Different Surface 
Waters and Demonstrating Their Movements and Mixing 
B. M. Bary^ 
"In an area where several water bodies mix 
. . . the plankton animals alone can give the 
clue as to the water’s origin unless the salinity 
differences are marked.” Russell (1935) makes 
this statement during discussion of the indi- 
cator species Sagitta elegans Verril and S. setosa 
J. Muller from the English Channel and 
southern Irish Sea, and he has shown that 
when the two species occurred together, they 
were indicative of mixed waters. The remark 
suggests the possibility that more general use 
could be made of zooplankton organisms to 
indicate the origins of the waters in an area 
of mixing. 
Russell’s investigations concerned an area 
already comparatively well known faunistic- 
ally and hydrologically, which is not true of 
the waters about New Zealand. A means has 
been needed whereby indicator species can be 
selected and utilized to demonstrate the 
sources, movements, and mixing of the wa- 
ters for such little known areas. Two recent 
developments have assisted the realization of 
this. First, Miller (1950) used the temperature- 
salinity (T-S) diagram to show the origins 
and interrelationships of the several waters 
contributing to a mixture over an area of the 
continental shelf near Cape Cod. Second, 
Pickford (1946, 1952) has shown that the 
occurrences of the squid Vampyroteuthis in- 
fernalis Chun, when related (in the conven- 
tional T-S diagram) to the temperature and 
salinity at its points of capture, are confined 
in certain water masses. Similarly Haffner 
(1952) and David (1955) demonstrate en- 
vironmental control over the distributions re- 
^ Formerly N.Z. Defence Scientific Corps, Navy 
Office, Wellington, N.Z. Manuscript received October 
23, 1956. 
Present address: Oceanographic Laboratory, 78 
Craighall Road, Edinburg 6, Scotland. 
spectively, of several species of the bathypela- 
gic hsh Chauliodus, and of the chaetognath 
Sagitta gazellae Ritter-Zahony. An important 
corollary of this latter method is that repre- 
sentatives of the fauna of a water mass may be 
selected as indicators of the water through the 
relationships demonstrated to temperature 
and salinity. 
The investigation by Miller concerned wa- 
ters entering near-coastal areas; that of Pick- 
ford, and others, has been concerned with 
relating occurrences of species to particular 
oceanic water masses. By combining relevant 
procedures from the two techniques it would 
be reasonable to expect that the occurrences 
of zooplankton organisms could be viewed in 
relation to the waters entering, and in, a 
coastal area. Data from collections of plank- 
ton, temperatures, and salinities could then 
be evaluated in three general and related ways. 
From the combined diagrams it should be 
possible to identify a water body entering a 
particular locality, to select species which are 
representative of the fauna inhabiting that 
water, and to pursue the subsequent history 
of that water both from its own distribution 
and from the distributions of the selected 
species. 
These several possibilities are investigated 
in the following account from data collected 
in oceanic and coastal waters, and their mix- 
tures, about southern and eastern South Is- 
land, New Zealand. The collections are typ- 
ical of those of many small scale surveys, but 
they were not intended for the present pur- 
pose and, therefore, are not ideal in certain 
respects. However, they do in fact demon- 
strate that the several possibilities may be 
realised. 
The combined temperature-salinity and 
plankton (T-S-P) diagram is believed to con- 
14 
