126 
PACIFIC SCIENCE, Vol. XII, April, 1958 
Relationship of Salps to Oceanic Currents 
Comparison of the species at each station 
of cruises 5 and 8 (at the latitudes of Figs. 1 
and 2, exactly listed by King and Demond, 
1953), with the current system of the central 
Pacific (Cromwell, 1954) showed that there 
were only three species of salps found in but 
one current on these cruises. On cruise 5, 
172° W., for example, Cyclosalpa hakeri and 
I hie a punctata were found only in the South 
Equatorial Current. Examination of the dis- 
tribution of these species on other longitudes 
and cruises, however, shows that they were 
found at some station in all other currents as 
well. This is true also of most other species, 
as they occurred in one longitude or another 
or on one cruise or another in all of the 
principal currents. Only three species were 
restricted in the central Pacific, Cyclosalpa 
afflnis, C. floridana , and Metcalfina hexagona , 
the first and last of which occurred in only 
one current; C. floridana occurred in only two 
currents. C. affinis occurred at no other station 
of the two cruises and only three specimens 
were captured. It is thus an uncommon spe- 
cies in the POFI collections studied, and 
probably cannot be considered as an indicator 
of this current. M. hexagona was also captured 
at only one station on only one cruise, but 
occurred in fair numbers (43 specimens). On 
other cruises, however, it is not an extremely 
rare species, since in the collections of animals 
larger than 5 cm. from all POFI cruises, it 
occurs in at least five samples. It cannot be 
considered an indicator species, then, on the 
basis of only one record on one cruise, par- 
ticularly since only 32 stations of cruise 8 
were examined. C. floridana was also a rela- 
tively uncommon species on these cruises and 
thus cannot be regarded as an indicator 
species. 
Ihlea magalhanica , a species not found in 
the POFI collections, has been considered a 
probable indicator species of colder water 
advancing northerly in the Australian area 
(Thompson, 1948). Thompson stated that 
Ih. magalhanica "is one of the salp species 
which has a low tolerance of warm water 
conditions,’’ and that it "will therefore prob- 
ably be useful as an indicator of any northern 
extension of the colder type of water condi- 
tions which may from time to time occur.” 
In the same report, however, he stated, "there 
is ... no evidence of a genuine cold water 
influence, even in Tasmanian waters, although 
in the latter region species which are character- 
istic of warm-temperature waters as well as of 
circumtropical waters are those most usually 
found (e.g., Ihlea magalhanica , Iasis zonaria 
and Thetys vagina)." Ih. magalhanica was ear- 
lier reported by Apstein (1894, 1906) in the 
Antarctic, westerly and southwesterly of the 
southern point of Africa, and in the Straits of 
Magellan, in water with a temperature range 
from 0° to 12.3° C. Thompson (1948), 
however, reported the temperature range of 
this species as between 11.6° and 22.25° C. 
This species, therefore, should perhaps be 
regarded as a eurythermal, rather than a sten- 
othermal, cool water form and its usefulness 
as an indicator of cold water currents per- 
haps is much less than was thought previous- 
ly. Its presence in water with a temperature of 
22.25° C. may be exceptional, i.e., it may have 
been transported into such water but may 
not be long viable there, or the animal(s) may 
have been actually in a deep cool layer of 
water at this station. Thompson did not ex- 
plain the situation, however. 
Therefore, it can be stated that all salps 
captured on cruises 5 and 8 can be expected 
to occur in all currents in warm latitudes and 
that they are not satisfactory indicator species 
for these latitudes. Three uncommon species 
might possibly be true indicator species, but 
this is doubtful. 
ECOLOGICAL NICHE OF SALPS 
When one contemplates niches in the mar- 
ine plankton community, it becomes clear 
that there are relatively fewer niches in the 
plankton than there are in the benthos or in 
land communities ("The 'niche’ of an animal 
means its place in the biotic environment, its 
