On Populations in Antarctic Meltwater Pools 
Charles W. Thomas 1 
ABSTRACT: In meltwater pools of the Clark Peninsula area of Antarctica fresh 
water biota spend most of the year frozen into the ice or in underlying sediments. 
In the absence of dynamic pressure (as is the case in pools), ice exerts no 
pressure on organisms. 
Survival of organisms appears to be a function of their ability to dehydrate 
or encyst. 
Brachionus and cosmopolitan forms have been introduced into Antarctica. The 
most likely agency of transport is skua gulls. 
Water samples taken from 12 meltwater 
pools on the Knox Coast, Wilkes Land, Ant- 
arctica show that the majority of them support 
myriads of animalcules. This is remarkable be- 
cause these organisms spend most of the year 
frozen into solid ice or bottom sediments and 
in the absence of light. We will discuss here 
reasons for survival, freedom from ice-crushing, 
and means by which biota may have been intro- 
duced into Antarctica. 
The collection of specimens and data for this 
study was made on Clark Peninsula and on an 
unnamed islet one mile northeast thereof, 
(66°18'S). This area on the Knox Coast of 
Wilkes Land has been described in some detail 
by Hollin and Cameron (1961). Collecting 
was done during the construction of a perma- 
nent scientific base on Clark Peninsula, Janu- 
ary 27 to February 11, 1957. 
Clark Peninsula, which is generally ice-free, 
is a headland about 5 km long and with a 
maximum width of 4 km. A snow field covers 
approximately 30% of the land area. The south 
end of the peninsula is overridden by inland 
ice which terminates in a moraine. At the time 
of pool sampling, ablation of the snow field 
had begun. 
Twelve pools were sampled at the height of 
the antarctic summer. These had probably been 
1 Museum of Comparative Zoology, Harvard Col- 
lege, Cambridge, Massachusetts. Present address: Ha- 
waii Institute of Geophysics, University of Hawaii, 
Honolulu. Manuscript received April 13, 1964. 
ice-free less than two weeks. 2 Since freezing 
began in late February the pools, in 1957, were 
ice-free less than two months. Hollin and Cam- 
eron (supra cit.) indicate that the summer of 
1957 was milder than average and that hardly 
any melting was apparent in February, 1959- 
Descriptive information concerning the pools 
is shown in Table 1. 
METHOD OF STUDY 
Samples were collected from the pools by 
immersing quart jars near the bottom and al- 
lowing them to fill. Specimens for microscopic 
examination were meted into a watch glass or 
onto slides. After about 1 cc of sampled water 
from each pool was examined, the water was 
filtered through a plankton well and the con- 
centrate preserved in 70% alcohol for further 
study and more positive identification of organ- 
isms. The water was then tested for salinity 
with a Digby and Bigg Ionic meter. 
Organisms which could be identified are 
listed in Table 2. It is difficult to establish a 
criterion by which abundance of organisms 
may be indicated in such a heterogeneous pop- 
ulation. A common numerical abundance of 
large forms might mean a paucity of small 
ones. Hence, the terms "abundant,” "common,” 
"few,” and "rare” are relative rather than 
absolute. 
2 Temperatures may be generally above freezing in 
January, but the insulating effect of snow-cover and 
sublimation delays thawing until ablation occurs. 
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