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PACIFIC SCIENCE, Vol. XIX, April 1965 
specimen had its base in a depression: "Thus 
the presence of small depressions or cracks where 
it was least likely for other more rapidly growing 
organisms to obtain a foothold seemed a pre- 
requisite for fixation.” 
With A. grandis there is similar evidence 
that a texture preference does exist (Fig. 10). 
The basaltic ledges, for example, that are found 
off Molokini at depths in excess of 40 meters, 
are exceptionally smooth and do not support 
many colonies. However, where there are de- 
pressions, cracks, or other rugged features along 
these steep facades, one always finds a vigorous 
growth of black coral. 
The type of substrate is also of considerable 
importance. Few colonies were found growing 
directly on a basaltic base. On the lava flows off 
La Perouse Bay, Maui (dated 1770 zh 20 years) 
and off Kapoho, Hawaii (dated 1926), where 
several dives were made to 60 meters, not one 
colony of A. grandis was found. Off Molokini, 
where colonies did attach to a basaltic sub- 
strate, there was invariably a thin encrustation of 
CaC0 3 . This condition was not apparent unless 
the colonies were chipped off and brought to the 
surface, where they were carefully examined. 
The most favorable substrate is a fossil coral 
reef, defined as a CaC0 3 conglomerate of madre- 
FlG. 8. This branch of A. grandis was tied to a ver deal line at 12 meters and remained there for 90 days. J 
The animal tissue was completely removed by the abrasive effects of surge, after which the black skeleton was 
overgrown with filamentous green algae. 
