Central Pacific Salpidae YOUNT 
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relations to food and enemies Elton, 1927: 64). 
For example, in the warm water epipelagic 
zone, the species are remarkably similar the 
world over (this is true of salps and it is 
undoubtedly true of other plankters as well) ; 
but even an oceanic island, such as Oahu for 
example, doubtlessly possesses many times 
more species of organisms than the plankton 
of the whole, vast epipelagic zone in the warm 
water belt of the world. This observation, I 
think, reflects the general paucity of niches 
and habitats in the pelagic oceanic environ- 
ment, due most likely to the remarkable uni- 
formity of the physical conditions and to the 
lack of shelter there. 
The Salpidae is one of the many groups of 
planktonic filter feeders; salps feed by strain- 
ing the water which passes through their body 
cavities by means of mucus strings secreted 
chiefly from the endostyle (see Ihle, 1935, 
1937-39). Notwithstanding differences in 
structural and physiological mechanisms asso- 
ciated with filter feeders, they catch and con- 
sume, in general, the same organisms as other 
pelagic tunicates (pyrosomids, doliolids, and 
to some extent appendicularians), some ptero- 
pods, some copepods, and perhaps other 
constituents of the plankton, since the food 
of all these organisms is captured by simply 
filtering the water. It has long been known 
that salps are not selective feeders and that 
methods and mechanisms for feeding are 
similar in all species thus far studied (see 
Ihle, 1935, 1937-39). 
In order, then, to attempt a segregation of 
the niches of the various species of salps, an 
analysis of the gut contents of all species 
reported here was undertaken, and observa- 
tions were made as to their probable preda- 
tors. Various salp species were chosen from 
different latitudes, longitudes, and cruises in 
order to have a respresentative sample. This 
resulted in the following observations: the 
food of all specimens and species of salps is 
remarkably similar throughout the area stud- 
ied; and the food of all salp species within 
any one plankton sample is the same. 
SUMMARY OF THE RESULTS OF THE 
GUT CONTENT ANALYSES 
very common food . . unidentified matter 
diatoms 
dinoflagellates 
common food silicoflagellates 
radiolarians 
coccolithophores 
foraminiferans 
rare food .......... small crustaceans 
(chiefly copepods) 
gastropod larvae 
pteropods 
annelids 
fish eggs 
Enemies of salps under natural conditions 
are unknown. Observations that may provide 
a clue on this situation, however, have been 
made in the plankton samples. There is a 
certain amount of conjecture in such deduc- 
tions because carnivorous animals can be ex- 
pected to bite whatever is near them during 
the death struggle after formalin is added to 
a plankton sample. Nevertheless, animals that 
contain salps in their digestive tracts or that 
hold to salps in the preservative may be their 
enemies in nature. Obviously, a chaetognath 
could be predaceous on Thalia democratica 
but not on Thetys vagina except in its young 
stage. The following animal types have been 
observed holding onto salps in preserved 
plankton tows: chaetognaths, heteropods, 
coelenterates, and Crustacea (chiefly copepods 
and hyperiid amphipods). No planktonic ani- 
mals have been observed to contain salps in 
their guts, but special study was not performed 
with this object in mind. Thompson (1948: 
160) reported Salpa fusiformis from stomachs 
of blue cod from New Zealand, and Reintjes 
and King (1953) reported Pyrosoma sp., un- 
identified salps, and unidentified tunicates 
other than these in the gut contents of yellow- 
fin tuna (Neothunnus macropterus) . Fraser (1949) 
reported I. asymmetrica (= I. punctata) and 
Dolioletta gegenbauri from a herring stomach, 
and that salps were reported as part of the 
