Ecology of Black Coral — Grigg 
257 
Hawaiian waters, with generally one major peak 
and another lower peak during a lunar day. Tidal 
elevations vary little from location to location 
around the islands, and the maximum elevation 
is only about 3 feet above mean lower low water. 
Measurements made during this study illus- 
trate several interesting features of the current. 
First of all, the surface current and bottom cur- 
rent do not necessarily coincide. They may, in 
fact, be in opposition during certain tidal mo- 
ments and wind conditions. The surface cur- 
rents, of course, are affected by the wind, whereas 
bottom currents are mainly influenced by tidal 
conditions and bottom topography. 
It was found that the surface currents were 
swifter than those close to the bottom. This 
was especially true in areas where the bottom 
topography was extremely irregular. 
Second, along coastal borders and in channel 
areas, it is known that tidal currents assume the 
form of a long elipse (Neumann, I960). In all 
cases, except at Kaena Point, Oahu, the currents 
followed this general pattern, being multi- 
directional depending upon the tide. It is quite 
likely that, for this reason, the colonies of A. 
grandis do not orient themselves in one direction 
with respect to the current. 
Off Kaena Point, however, where currents very 
commonly exceed 2 knots and are in general uni- 
directional, a definite orientation of the fern type 
black coral (Genus Antip at hello) in a fashion 
perpendicular to the current has been observed. 
It is significant that specimens of A. grandis are 
absent or extremely rare in this environment. 
Kaena Point is subject to heavy wave activity in 
winter months, during which the water is very 
turbid. This fact, coupled with the intense cur- 
rent, could well be producing an extreme abra- 
sive effect which has been found to be limiting 
to A. grandis (as with the abrasive effects of 
surge on transplanted colonies off Moku Manu 
Islands). Evidently the fern type is more tolerant 
of these conditions. 
Third, the current measurements in this study, 
in all cases except at Kaena Point, ranged be- 
tween 0 and 2 knots. In shallow water close to 
shore the currents during any 24-hour cycle re- 
main at zero for very short periods, during 
which time the tide peaks and the current 
changes direction. Offshore currents are rotary 
and at no time are completely slack. 
Colonies of A. grandis do well under these 
conditions and in fact can tolerate regular cur- 
rents as high as 2 knots. In those locations where 
a dense population of A. grandis is found (Sta- 
tions 3, 7, 8, 9), it is significant that the water is 
free of suspended abrasive particles. For this 
reason, it is postulated that excessive currents 
(over 2 knots) may only become inhibiting to 
the growth of A. grandis when the water mass 
contains a high amount of abrasional fragments 
such as sand or other particulate inorganic 
material. 
Finally, transplanted colonies in Kaneohe Bay 
survived very well in areas off Coconut Island 
where currents rarely exceed 0.5 knot (Avery, 
Cox, and Laevastu, 1963). These colonies were 
observed to feed and actually to grow through 
asexual reproductive processes. It is not known 
whether sexual reproduction is possible under 
these conditions, but even if it were the planulae 
would probably not be able to find a suitable 
site for fixation. 
On the basis of the evidence, then, it does not 
seem that strong currents are necessary to sup- 
port the growth of this animal. And since aver- 
age currents are generally in excess of 0.5 knot 
in almost all exposed offshore localities in Ha- 
waii, it does not appear that lack of current re- 
stricts the growth of A. grandis. On the other 
hand, currents higher than 0.5 knot are neces- 
sary to sweep the bottom clean of accumulated 
sediments. The inclination of the bottom is im- 
portant, of course, in this respect also. Since 
colonies of A. grandis are found only in cleanly 
swept areas, it is reasonable to assume that the 
planulae cannot settle on a substrate covered 
with an accumulation of sediment. 
In summary, then, the most favorable range of 
average current approximates values between 0.5 
and 2 knots. The presence of inorganic particu- 
late material magnifies the abrasive effect of cur- 
rent and therefore lessens the range under which 
the animal can survive. 
