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PACIFIC SCIENCE, Vol. XII, April, 1958 
The chief salp component by volume in the 
central Pacific varies irregularly at the different 
stations. As volume is difficult to determine 
precisely, especially when there are few speci- 
mens of small species, volumes were deter- 
mined to the nearest cubic centimeter and the 
chief component species was estimated by 
visual inspection. In some samples no one 
species predominated but usually one species 
predominated volumetrically; the same spe- 
cies or a different one might predominate 
numerically. The chief component species by 
volume may be a single specimen of a large 
species or a few specimens of a medium sized 
species, which may predominate over even 
large numbers of smaller species such as T. 
democratica. Inasmuch as specimens larger 
than 5 cm. were removed from the samples 
before the present study, the volumetric data 
may be incorrect for some stations, although, 
as King and Demond stated, these larger 
specimens were infrequent. 
Comparison of Salp Abundance with Total 
Plankton Abundance 
King and Demond (1953) have reported 
on the total plankton of cruises 5 and 8 by 
volume and numbers per cubic meter of water 
strained. The original numerical estimates and 
volume determinations were made available 
through the courtesy of Mr. King and the 
salp percentages discussed here were calcu- 
lated from them. 
Salps comprised more than 50 per cent of 
total plankton by volume at only one station 
(50) of cruise 5 (54 per cent); the highest 
percentage by number made up by salps was 
9.1 per cent, at station 48 of cruise 5. On 
cruise 8, salps amounted to more than 50 per 
cent of the total volume at stations 9 (58 
per cent) and 101 (65 per cent); the highest 
percentage by number was 4.1, at station 9- 
These results, combined with the numerical 
percentage estimates of tunicates as com- 
pared with other zooplankters by King and 
Demond, show that tunicates in general play 
a relatively small numerical role in the central 
Pacific plankton, but that salps in particular 
may attain a substantial volume as compared 
with other plankters. Ordinarily, however, 
salps play a rather minor role both volumetric- 
ally and numerically. Thompson (1942) stated, 
in reference to southeastern Australian waters, 
"Tunicates . . . comprise, next to Crustacea, 
the chief portion of the zooplankton,” and, 
"Tunicates (chiefly salps) are the only other 
group which frequently predominates . . .,” 
with a monthly average percentage of 25.4 as 
compared to 62.5 per cent for Crustacea. Thus, 
although the methods of capture are not 
strictly comparable, there is evidently a rather 
pronounced difference in the composition of 
the plankton between the central Pacific and 
southeastern Australian waters. 
By using the methods described in Snede- 
cor (1946, chap. 7), correlation coefficients 
were calculated to determine the relationship 
between salp numbers and zooplankton num- 
bers (less salps) and salp volume and zoo- 
plankton volume (less salps) for cruises 5 and 
8. In order to make use of salp volumes that 
measured less than 1 cc., such volumes were 
given an assumed measure of 0.5 cc. in the 
calculations. Neither correlation coefficient 
was significant for numbers or volumes of 
these cruises. From the evidence based on 
these cruises, then, there is no significant 
mutual relationship between salp and zoo- 
plankton numbers or volumes. 
Comparison of Salp Abundance in the Central 
Pacific with Other Regions of the Pacific 
It is impossible to make accurate quantita- 
tive comparisons between the plankton of 
different regions unless equipment and meth- 
ods of capture are standardized. Unfortu- 
nately such optimal conditions have never 
been met. Nevertheless, as salps are relatively 
large animals and thus are taken by the com- 
monly used nets, an attempt is made here to 
compare the salps of the central Pacific to 
those of the Great Barrier Reef lagoon as 
reported upon by Russell and Colman (1931, 
1935), the only Pacific investigators who have 
