356 THE GORGONACE^ AS A FACTOR 



reefs after the first breeding season following the cataclysm. At the end of 

 the second year most of these colonies would have attained nearly the normal 

 size and would have brought the amount of lime held as spicules up to the 

 average amount. 



ILLUSTRATIONS. 



Plates 101 to 105 are from photographs of dried specimens of the twelve 

 species of Gorgonians which were found to constitute the major part of the 

 alcyonarian fauna on the reefs about Tortugas. All the figures, except 

 Nos. 9 and 10, are of specimens rather smaller than the average size. 



CONCLUSIONS NEW TO SCIENCE. 



The results of this study show that over large reef areas, in the region 

 about Tortugas at least, the Gorgonian fauna is by far the most important 

 element contributing to the formation of reef limestones. On the basis of 

 the data recorded in tables 2 and 3 the amount of spicules in the tissues of 

 Gorgonian colonies would average at least 5.28 tons to the acre for all of the 

 reefs in the Tortugas group. ^ In many restricted areas the amount is very 

 much greater, as is shown by the bulk of the Gorgonian colonies growing in 

 these localities, or in some instances by the amount of spicules actually set 

 free on the reefs. 



The figures given above represent only a potential contribution to reef 

 formation but a study of the normal cycle of changes in the Gorgonian fauna 

 of this region has shown that at least a fifth of this amount of calcium car- 

 bonate, as spicules, will be added to the reef limestones annually. There are 

 wide fluctuations in the extent to which destruction of the Gorgonian colonies 

 takes place in any single year, but the above estimate is well within the limits 

 found by averaging the results obtained over a period of several years. 



In many regions where representatives of the family Alcyonaceae make 

 up the greater portion of the Alcyonarian fauna the contribution to the reef 

 limestone would be unquestionably greater than about the Tortugas where 

 the family Gorgonida" is alone represented by numerous specimens. 



SUMMARY. 



1. The Alcyonarian fauna of the FIorida-Antillean region is composed 

 almost entirely of representatives of the order Ciorgonaces, in which the 

 entire lime-bearing skeletal elements are spicules formed in the coenenchyma. 

 The Gorgonians are, however, very numerous on most of the shallow reefs, 

 and the presence of their spicules in practically all bottom samples indicates 

 that they are an important element in reef limestone formation. 



2. When analyzed for percentage of spicule content of the 12 species 

 occurring most abundantly about Tortugas, it is found that from 19.75 per 



'See table 5. 



