252 
PACIFIC SCIENCE, Vol. XIX, April 1965 
Percent Surface Light 
0 10 20 30 40 50 60 70 80 90 100 
Fig. 7. Percent surface light is plotted against 
depth. The triangles represent the position of the 
first colonies of A. grandis (shallowest) observed in 
areas where a shallow bottom rapidly dropped off into 
deep water. 
the entire branch at 24 meters was healthy. After 
90 days only 5 % of the former branch was alive, 
while the latter was still completely healthy. The 
living tissue on the branch in shallow water had 
been removed by the action of the surge and the 
denuded skeleton was overgrown with filamen- 
tous green algae. 
During the 90-day period surge reached ex- 
cessive magnitudes on three occasions, twice dur- 
ing wind storms with gusts over 70 miles per 
hour, and once during a 2-day period of 15- 
foot ground swells. Very turbid water accom- 
panied these extreme conditions. 
Transplant 18, which had been fixed on the 
bottom in 18 meters of water, was 80% alive 
after the same 90-day period. Along the bot- 
tom, of course, there is more particulate material 
suspended in the water, hence tissue abrasion 
would be considerably greater than in the case 
of the branches tied to a buoyed line where the 
branches were above the bottom. 
These results indicate that the limiting effect 
of surge is operational to a depth of approxi- 
mately 20 to 24 meters. Below this level surge I 
will very rarely reach limiting magnitudes. The 
only specimens of A. grandis found in water 
shallower than 24 meters during this research 
were in relatively protected areas, where surge 
was not excessive. 
Turbidity 
A. grandis is normally found in extremely 
clear water. Transplanted colonics, however, sur- 
vived well under varied turbidity conditions. In 
Kaneohe Bay, for example, where fluctuations of 
turbidity were quite pronounced, transplanted 
branches survived for 6 months, after which the 
experiments were terminated. It does not ap- 
pear, then, that turbidity per se limits the growth 
of this animal. If a heavy current or surge, how- 
ever, is coincidental with very turbid conditions, 
then the suspended particulate material may be- 
come limiting by abrading the tissues of the 
black coral. 
Oxygen , Salinity , and Temperature 
In contrast to inshore areas and surface waters, \ 
where fluctuations in oxygen concentration, sa- | 
Unity, and temperature are quite common, the 
deeper off-shore waters are relatively stable with 
respect to these factors. At all stations - during 
the period from December through May, the 
maximum differences in oxygen concentration, 
salinity, and temperature between the surface 
and the bottom (60 meters) were only on the 
order of 2 ml oxygen/liter, 1 %o salinity, and 2° 
Celsius, respectively. The magnitude of these 
differences is very small, and hence it is not 
likely that any of these factors is operative in 
limiting A, grandis to its exclusive habitat in 
deep water. 
Substrate 
A . grandis requires a firm substrate on which | 
to grow. The type and texture of the substrate 
is also important in limiting the distribution of j 
this animal. Cary (1914), in his studies on the 
ecology of gorgonians, observed that distribu- 
tion was related to the texture of the substratum. 
He found that, in every case, a one-year-old 
