Bathymetric Distribution of Chaetognatha, Siphonophorae, Medusae, 
and Ctenophorae off San Diego, California 1 * 
Angeles Alvarino 
The samples studied were obtained at various 
depths with the bongo or bmoc open-closing 
paired zooplankton net (McGowan and Brown, 
1966), at 30°30'N, 120°00'W, from 27 Au- 
gust to 8 September 1965. 
These collections were taken during night 
hours (27 August to 8 September 1965), and 
daylight hours (30 August to 5 September 
1965) . Quantitative data for each of the spe- 
cies were determined for each of the nets 
(left and right) for collections at the various 
strata surveyed; and variations in the number 
of specimens and in the species were observed 
at times in the same haul for the samples from 
the left and right nets. Diagrams were made 
showing the qualitative and quantitative dis- 
tribution of the species in the two nets for 
each of the stratified hauls. However, in the 
final diagrams the medians for both left and 
right samples were plotted for each of the 
stratified hauls. 
The data from the collections made at differ- 
ent times and depths during the same half day 
(dark or daylight) were plotted together. Since 
the hauls for the same half of the day were 
made on different dates (there was a lapse of 
time from one haul to the other), it is ob- 
vious that changes might take place at times, 
either in the depth at which the various spe- 
cies were found or in the quantity of individuals 
obtained. 
In the case of the siphonophores, the necto- 
phores of a physonectes appeared in either 
the right or left net and in the other net the 
1 These studies were conducted under the Marine 
Life Research Program, the Scripps Institution’s com- 
ponent of the California Cooperative Oceanic Fish- 
eries Investigations, and with support from the Na- 
tional Science Foundation (NSF GB-2861), and AEC 
Contract AT(ll-l)-34, Project 127. Contribution 
from Scripps Institution of Oceanography, University 
of California, San Diego, California. Manuscript re- 
ceived July 21, 1966. 
pneumatophores with the nectosoma and 
siphosoma attached. Similarly, in other cases, 
one of the paired nets contained the bract or 
the superior nectophore and the other net the 
gonophores or the inferior nectophore of the 
eudoxid or paragastric forms of the Diphyidae. 
The quantitative distribution of Chaetognatha 
and Medusae are noted in the diagrams; but 
in the case of the Siphonophorae, although 
data on the number of superior and inferior 
nectophores, gonophores, bracts, pneumato- 
phores, etc. were obtained, because of the 
peculiar anatomical structure of these orga- 
nisms it was not convenient to attempt a 
quantitative representation. In the case of the 
Monophyidae and Diphyidae, for instance, it 
will be easy to establish the number of indi- 
viduals present from the part obtained in the 
sample, but this is not so for the Physophorae 
and Hippopodiidae. Therefore, only the quali- 
tative distribution of the siphonophores was 
considered in preparing the final diagrams. 
During each tow about 10,000 m 3 of water 
were filtered through the net; thus the sam- 
ples were directly and quantitatively compar- 
able. 
Collections were made at the following 
depths (in meters) : 
NIGHT 
DAYLIGHT 
100-10 
110-0 
100-20 
350-250 
300-235 
460-0 
460-410 
525-401 
500-420 
1720-1340 
620-530 
2300-1880 
775-685 
2630-2210 
840-690 
3040-2620 
1030-860 
1040-890 
1242-1090 
1710-1450 
2020-1800 
2170-1950 
2320-2100 
2460-2100 
474 
