Reconnaissance by Submarine — Brock and Chamberlain 
389 
Subsequently, a bed which had an extent of 
more than 1500 meters was photographed dur- 
ing a submarine camera transect in an area 
between Maui and Lanai at a depth of 70 to 
80 meters. As is characteristic for this genus, 
the clams were buried deeply in the substrate 
with the lip of the shell protruding. Individual 
clams were close together, appearing to be al- 
most in contact. 
The Neritic Community 
Observations of the biota thus far have con- 
cerned benthic organisms, and suggest that dis- 
tributions of fish are related to bottom topog- 
raphy. Very few fish were observed high above 
the bottom. However, concentrations of plank- 
ton and particulate matter, possibly organic, 
were observed from the "Asherah” well above 
the bottom and also near it, at depths of 70 to 
100 meters. It was assumed that these concen- 
trations, causing a substantially reduced visual 
range, were located at the bottom of the mixed 
layer, at the thermocline. Temperature measure- 
ments were not taken to confirm this assumption. 
Discussion 
The ecological observations from the " As- 
herah” together with the data obtained by 
echo sounding, submarine photography with 
automatic cameras, and trawling and dredging 
suggest the existence of two major biotopes — 
the terraces, and the rocky outcrops and escarp- 
ments — and that each of these contains two 
recognizable subdivisions. For the terrace bio- 
tope these are: (1) the sand-covered flats, and 
(2) the extensive beds of Pinna muricata, which 
could be better characterized as a biocoenosis. 
Its investigation would likely be rewarding. 
The biotope of rocky outcrops and escarpment 
includes two subdivisions — the outcrops of reef 
rock characterized by Chromis verater and the 
less abundant Caesioperca thompsoni , and the 
escarpments characterized by large aggregations 
of Chaetodon miliaris and small schools of 
Etelis carbunculus, as well as other species. The 
observed patterns of distribution are difficult to 
understand in detail, but two general hypoth- 
eses are proposed, in part to provide a basis 
for future investigations of these matters. One 
hypothesis concerns the bathymetric distribution 
of Pinna muricata, and the other, the aggrega- 
tions of Chaetodon miliaris and associated 
species. 
Occasional specimens of Pinna muricata are 
found in quite shallow water, essentially just 
below the low tide level. The shallowest beds 
observed from the "Asherah” were about 38 
meters deep, and scuba divers have reported 
beds as shallow as 25 meters. The deepest beds 
observed from the "Asherah” off western Oahu 
were at about 100 meters. This may not, of 
course, represent the downward extension of the 
range of this species. As shown in Table 1 the 
average temperature to and including depths of 
100 meters is from 24.6° to 22.3°C, with a low 
temperature of 20.0°C at 100 meters. At 200 
meters the average temperature is 16.7°C with a 
range of plus or minus 4.7 °C. This is the 
maximum range for the water column. The 
temperature variation is less in either shallower 
or deeper water, becoming markedly less for 
depths in excess of 500 meters. There may be 
an association between the depths of abundant 
occurrence of Pinna muricata and the lower part 
of the mixed layer. Pinna is a filter feeder, and 
the lower part of the mixed layer may have a 
higher concentration of organic particulate 
material since such material, unless mobile, 
tends to settle. The sinking rate would decrease 
at the bottom of the mixed layer because of an 
increase in density of the water. As mentioned 
earlier a marked reduction in visual range was 
sometimes noted at depths between 70 and 100 
meters. Upon going deeper the transparency of 
the water increased abruptly, with a change in 
visual range from 10-15 meters to 40 meters 
or more. If the lowest portion of the mixed 
layer did have a higher concentration of particu- 
late food, the bathymetric range through which 
it passed may be the bathymetric range of the 
clam beds, with a possible additional qualifica- 
tion that the decrease in temperature with depth 
may establish an independent lower limit to the 
distribution of the clam. 
The striking aggregations of Chaetodon 
miliaris observed over certain topographic fea- 
tures of the deep escarpment must relate to 
some essential advantage that this behavior 
provides in this locality. Chaetodon miliaris is 
the commonest butterfly fish in Hawaiian waters 
and was considered to be a coral reef fish. Its 
abundant occurrence in depths of 120 meters 
