352 



THE GORGONACEtT. AS A FACTOR 



Since the foregoing statement was written, additional data upon this 

 question, secured during the summer of 1914, have shown that the above 

 estimate is far below the average over the whole reef area. 



The addition to the equipment of the laboratory of a "Dunn diving 

 hood," by the use of which the study of any bottom in less than 30 feet of 

 water is made practicable, has made it possible to secure extensive collec- 

 tions of the Alcyonarian fauna from the deeper reefs. In many instances 

 the surface of the deeper reefs is covered with a dense shrub-like growth of 

 Gorgonians of an average height of at least 3 feet. Since the surface of all 

 of the reefs is very irregular and the Gorgonian colonies are usually attached 

 to the higher points of the reef, many of them would reach above the level 

 of one's shoulders as he was walking about over the reef. In general the 

 bulk of the colonies of the most common species of Gorgonians was about 

 twice as great as that determined for the same species from specimens 

 collected on the shallow water reefs. The average weight of the colonies 

 of a number of these forms taken from a reef in 18 feet of water is given in 



table 5. 



Table 5. — Weight of Gorgonian colonies from deep water. 



The proportion of spicules in the tissues of those forms for which spicule 

 determinations were made of specimens from the deeper reefs did not differ 

 materially from that determined for specimens from the shallow reefs, so 

 that the estimate of 5.38 tons to the acre as the amount of spicules held in 

 the tissues of living Gorgonian colonies on the reefs about Tortugas would 

 be, for those reefs in more than 15 feet of water, only about half the amount 

 actually present. 



DISINTEGRATION OF GORGONIAN COLONIES AND ADDITION OF 

 THE SPICULES TO THE REEF-BUILDING MATERIALS. 



The securing of accurate data bearing upon this phase of the problem 

 has been the most difficult part of the investigation, since there is no readily 

 available method by which the actual destruction of colonies over any reef 

 area can be determined when the observations on the reef are limited to 

 a comparatively short time each year; but observations bearing directly 

 upon this point have been accumulated in the course of studies extending 

 over a period of five years upon the growth-rate and ecology of the Gorgon- 

 ians in this region, and some investigations on the time necessary for the 

 disintegration of the coenenchyma of Gorgonians were carried out in the 

 summer of 1914. 



