Ecology of Black Coral — Grigg 
247 
strate will take the form of a flat elipse so that 
the water is practically oscillating back and 
forth in a horizontal plane. This type of surge 
was found to be of particular importance in this 
research. 
Currents are often superimposed upon surge. 
For example, if the current is running in the 
same direction as the swell, it will reinforce 
surge in one direction and inhibit it in another. 
If the current is strong enough, the latter direc- 
tion can be nullified altogether so that motion is 
uni-directional, speeding up and slowing down 
depending upon whether current and surge are 
in or out of phase. 
Surge was estimated by watching suspended 
particles in the water. A back-and-forth move- 
ment of water with a horizontal displacement of 
less than 1 foot was considered slight, of 1-3 
feet moderate, and more than 3 feet heavy. 
DEPTH: Depth was recorded in two ways. A 
fathometer or continuous depth recorder was 
used to outline bottom profiles, and a depth gage 
worn by a diver made in silu measurements 
possible. 
TRANSPLANTS: Transplanting fixtures had to 
be made so that broken branches of black coral 
could be anchored firmly to the bottom. Cement 
blocks were made with a pipe placed in the 
center (Fig. 3). A hole near the end of the pipe 
was threaded so that a bolt could be tightened 
down on an inserted branch. Metal contact 
caused the animal to die within 1 cm of the bolt 
but did not appear to affect the remainder of the 
branch. The fixtures weighed between 10 and 
15 pounds. 
In another experiment, a half-inch line was 
anchored to a projecting piece of fossil coral on 
the bottom at 43 meters. The end of the line was 
buoyed up with three metallic floats which at 
no time were visible from the surface (Fig. 4). 
Branches of A. grandis were tied to this line 
using a ring-stand clamp and string at 12, 18, 
24, and 30 meters. 
POPULATION DENSITY: Counts of the num- 
ber of colonies on the bottom were made, using 
a 10-meter marked line placed on the substrate 
so that the area could be estimated. Correlation 
of the population density with the inclination 
and configuration of the bottom was attempted. 
EPIFLORA AND EPIFAUNA: Collection of as- 
sociated organisms was made both at the bottom 
and on the surface after the colony had been 
brought up (Fig. 5). 
FEEDING: Observations on the feeding habits 
and on the type of food ingested were carried 
out. In addition a plankton tow was made at 50 
meters to determine roughly the type of food 
present in the natural environment. 
DISCUSSION AND RESULTS 
Light 
Since colonies of A. grandis are found only in 
deeper waters, where the amount of light is con- 
siderably reduced, it seems probable that strong 
light intensity is important as a limiting factor. 
Indeed, when colonies of black coral are found 
in shallow water, their bases are always situated 
in dimly lit areas such as overhangs and caves. 
Peres (1949) has found a similar condition in 
the underwater "grottos” off Marseilles, where 
certain deeper sea species were found at much 
higher levels in submarine caves. 
The shallowest depth at which the author has 
observed A. grandis was at 7 meters off Hanauma 
Bay, where a colony about 30 cm high, was 
found growing from the ceiling of a very dimly 
lit cave. Off east Lanai and Hana, Maui, small 
stunted colonies, which frequently anastamose, 
are fairly common in caves at about 20 meters. 
The Kekaha coast of Kauai (off Port Allen) has 
extensive areas at 30 meters where colonies up 
to 2 meters high have been taken. It is in- 
teresting to note that in all of these regions the 
water is at times quite turbid because of run-off 
during heavy rains. Off Lahaina, Maui, where 
the shallowest colonies are generally found at 
approximately 40 meters, the water is extremely 
clear the year round. This area is 5 miles off- 
shore and thus is not contaminated by run-off 
water. Light penetration, of course, is affected by 
depth as well as by the amount of suspended 
material in the water (Poole, 1938). 
These observations suggest that A. grandis 
will settle in water shallower than 40 meters, but 
only in areas where the light penetration is 
periodically reduced by the presence of turbid 
water or by topographical features of the bottom 
which cut off direct rays of sunlight. 
