Ecology of Black Coral- — Grigg 
259 
Feeding 
Edmondson (1929) working on the inshore 
reef at Waikiki, and Motoda (1939) working in 
Iwayama Bay, Palau, found a considerable varia- 
tion in plankton density from day to day. Gard- 
ner (1931) found, on the other hand, a small 
fluctuation in plankton density in his work on 
atolls in the Pacific. 
Wells (1957) states that the food require- 
ments of madreporian corals are low. If this 
condition holds for the antipatharian corals, then 
plankton density may not be a limiting factor. 
This statement is not based on a quantitative 
study, and is purely speculative. 
Plankton-rich water from Kaneohe Bay was 
introduced into a finger bowl in which living 
branches of A. grandis were observed through a 
binocular microscope. Ingested plankton, under 
these conditions, included amphipods, copepods, 
and chaetognaths ( Sagitta ). 
A plankton tow off Moku Manu Islands in 45 
meters of water revealed a large amount of 
detritus, many amphipods, copepods, and for- 
aminifera and, in lesser amounts, radiolaria, 
dinoflagellates, and ostracods. No chaetognaths 
were found, hence Sagitta may not be a natural 
food. 
Unlike most stony corals, the polyps of A. 
grandis have been observed to be expanded dur- 
ing the day; therefore feeding probably is not 
restricted to certain hours. 
SUMMARY AND CONCLUSIONS 
Ecological factors which limit the distribution 
of A. grandis were studied in an attempt to 
understand the biology of this species. Research 
methods are described and ecological and bio- 
logical information is presented. 
The results indicate that: 
1. Adult colonies can withstand light intensi- 
ties up to 60% of the surface incident light. 
2. Adults can tolerate ranges in depth (and 
consequently in pressure) from 1 to 146 meters, 
indicating that pressure is not likely to be a 
limiting factor, at least within the littoral zone. 
3. Oxygen concentration, salinity, and tem- 
perature are relatively stable in the natural en- 
vironment, and do not appear to. be of limiting 
importance. 
4. Adult colonies are limited by the abrasive 
effects of surge and cannot tolerate this factor in 
waters shallower than 24 meters where surge is 
heavy. In protected areas, however, colonies may 
survive in very shallow water. 
5. Since colonies are commonly found only 
below 35 meters in most areas in Hawaii, it is 
postulated that the larval stage reacts negatively 
to strong light intensities. The lack of marked 
variations in other environmental gradients sup- 
ports this view. Evidently the larvae will not 
settle or survive unless the light penetration is 
less than 25% of the surface light. In the clear- 
est water around Hawaii this value would corre- 
spond to about 35 meters in depth. Only in 
turbid water or in shaded areas are colonies 
found any shallower. 
6. There is evidence that a CaC0 3 substrate 
is more favorable than a basaltic substrate for 
the growth of A. grandis. Also, a rough or un- 
even substrate will support a larger, population 
than will a smooth substrate. And, finally, within 
the zone of observation (0 to 75 meters), a ver- 
tical and undercut substrate is able to support a 
denser population than is an otherwise equiva- 
lent horizontal substrate. This last phenomenon 
may be due to the fact that less light is present 
in such environments. 
7. The most favorable range of current for 
the growth of A. grandis is between 0.5 and 2 
knots. Presence of suspended sand particles or 
other particulate material intensifies the abra- 
sive effects of the current, and therefore reduces 
the range under which the coral can grow. 
8. Only animal material was observed to be 
ingested. 
ACKNOWLEDGMENTS 
This study would not have been possible with- 
out assistance in the field from Mr. Harold Hall, 
Jr., Mr. Jim Daugherty, Mr. Ben Oostdam, Mr. 
Paul Gebauer, Mr. Robert Johannes, and Mr. 
Tom Lee. 
The author extends special thanks to Dr. Sid- 
ney Townsley and Dr. Taivo Laevastu for their 
many helpful suggestions during the course of 
the investigation. 
The author is also indebted to Mr. David Au 
for identifying epiphytic algae, Mr. Lou Eldredge 
for identifying epizoic ascidians, and to Mr. Li- 
onel Medeiros for preparing the printed figures. 
